PI Name: PHILIP KAARET Title: PARTICLE ACCELERATION IN A TEV BINARY Abstract: Understanding particle acceleration in relativistic shocks occurs is a key goal in high energy astrophysics. We propose to observe a binary star system, containing a pulsar and a massive star, that is known to emit TeV gamma-rays indicating acceleration of particles to high energies. The NuSTAR observations will provide information on the spectrum of electrons accelerated in the pulsar wind/stellar outflow interaction which is complementary to information on the magnetic fields near the acceleration regions that will be obtained from IXPE observations. The observations will provide unique information for a novel class, TeV binaries, and have the potential to provide new insights into relativistic shock acceleration and the propagation of high energy particles away from the shock.
Proposal Number: 10016 PI Name: SHUO ZHANG Title: CAPTURE PEAK X-RAY LUMINOSITY OF GALACTIC CENTER MOLECULAR CLOUD THE BRIDGE: STORYTELLER OF A PAST SGR A* OUTBURST Abstract: After two decades of X-ray brightening, the Bridge has become the brightest giant molecular cloud in the Galactic center due to X-ray reflection of a past Sgr A* outburst that happened about 200 years ago. It is the only molecular cloud that will allow us to investigate the full profile of a Sgr A* illumination event. The Bridge will reach its peak X-ray luminosity in spring 2024. Its peak luminosity and duration are essential information to characterize the past Sgr A* outburst. A 100 ks simultaneous NuSTAR and XMM-Newton observation will most efficiently measure the peak X-ray luminosity of the Bridge. Characterizing past Sgr A* outbursts is a necessary step towards understanding the physical mechanisms that triggered major outbursts from a quiescent supermassive black hole.
Proposal Number: 10022 PI Name: SHUO ZHANG Title: JOINT NUSTAR AND EHT PROBE OF SGR A*: FLARES, BLACK HOLE SHADOWS AND A NEW HARD X-RAY SOURCE Abstract: Following successful joint NuSTAR/Chandra/EHT observation campaigns during 2017-2018 and 2021-2023, we propose a 100 ks NuSTAR exposure to overlap with the EHT observation window in spring 2025 during NuSTAR AO Cycle 10. Our primary science goals include: 1) Detect bright X-ray flares, determine flare start/stop time and X-ray variability during a flare to feed to the EHT analysis; 2) Enlarge the existing NuSTAR Sgr A* flare sample by detecting and characterizing new flares and test the trend that brighter X-ray flares have harder spectra than fainter flares. A secondary science goal is to monitor a new hard X-ray source newly revealed by archival NuSTAR data, which is located only 1 pc from Sgr A*.
Proposal Number: 10024 PI Name: CHUN-CHE(LUPIN) LIN Title: SEARCHING FOR CYCLOTRON ABSORPTION FEATURE OF PSR J1849-0001 Abstract: MeV pulsar is a peculiar type of young pulsar, in which the non-thermal spectrum has a peaking at around 1 MeV. This peaking energy is about three orders of magnitude smaller than that of Fermi-LAT GeV pulsar. We request a 60ks NuSTAR observation of PSR J1849-0001 and search for a cyclotron absorption feature in the spectrum. The previous NuSTASR data reports marginal evidence of the absorption line feature, and more data is necessary to investigate the absorption feature. If the line feature is real, the emission region of the MeV pulsar is located near the stellar surface. A confirmation of the absorption-line feature advances the understanding for the non-thermal emissions of the MeV pulsars and the difference bet which is different from the outer magnetosphere of the Fermi-LAT pulsar.
Proposal Number: 10034 PI Name: FAN ZOU Title: X-RAYING A LOW-MASS GALAXY WITH A POWERFUL, CANDIDATE COMPTON-THICK AGN Abstract: We propose a 100 ks exposure of a low-mass galaxy hosting a candidate Compton-thick (CT), powerful AGN. Our target has a notably high [Ne v]3426 emission-line equivalent width that indicates CT-level obscuration, as also supported by its multi-wavelength SED decomposition. Our proposed NuSTAR observation can examine the CT nature of our target. If confirmed, our target will be the second confirmed low-mass CT AGN and can thus help us understand the obscuration properties of AGNs in low-mass galaxies.
Proposal Number: 10040 PI Name: RYOTA TOMARU Title: THE PRECISE TEST OF THE WIND DRIVING MECHANISMS FOR LOW-MASS X-RAY BINARIES Abstract: The understanding of accretion disc winds in low-mass X-ray binaries (LMXBs) gives us a rich physical insight into the accretion process, leading us to investigate the physical origin of AGN feedback. These winds are typically observed as blue-shifted absorption lines but could be observed as emission lines when the direct X-ray from the central source is blocked. The accretion disc corona (ADC) source shows those emission lines since the highly inclined disc blocks the direct photons. Those emission lines in the V395 Car are well described by the wind, which is driven by radiative heating and acceleration. Here, we propose a simultaneous NuSTAR observation with XRISM and NICER-IXPE for this object to conduct the most precise critical test of this wind-driving mechanism.
Proposal Number: 10042 PI Name: MARIA CHERNYAKOVA Title: HARD X-RAY VIEW OF 2024 PERIASTRON PASSAGE OF PSR B1259-63 Abstract: PSR B1259-63 is a millisecond radio pulsar. Interaction of the pulsar wind with the Be star outflow generates a broadband emission from radio up to TeV with a unique GeV flare shortly after the periastron. To study the peculiarities of this system INTEGRAL has approved a 750 ks observation. Interpretation of INTEGRAL data are complicated by the presence of nearby X-ray pulsar 2RXP J130159.6-635806. Within current proposal we ask for 30 ksec observations of 2RXP J130159.6-635806 (Priority 1) accompanied with 30 ksec observations of PSR B1259-63 (Priority 2). These observations will allow us: (i) recover the spectral parameters of 2RXP J130159.6-635806 and use them for the accurate INTEGRAL/ISGRI data analysis; (ii) study the possible short-timescale variations of PSR B1259-63 flux.
Proposal Number: 10047 PI Name: SIBASISH LAHA Title: NUSTAR MONITORING OF A CHANGING-LOOK AGN WITH A NEWLY-LAUNCHED RADIO JET Abstract: 1ES 1927+654 is one of the most enigmatic changing-look AGN which exhibited a major TDE-like outburst in the optical/UV in Dec 2017 followed by a vanishing X-ray corona. Since late 2022 the source has shown a considerable variability in the X-ray flux, along with an exponential rise (~35 times) in the core radio flux. Very recently the source has shown the emergence of a nascent jet. Here we propose to monitor this interesting source with NuSTAR for the next 1 year at bi-monthly cadence, with 40 ks exposure per snapshot (total of 6 snapshots =240 ks) to track the long-term changes in the coronal properties and reflection features (at E>10 kev), along with the evolving jet. This unique campaign will help us understand if AGN coronal properties evolve during a jet formation, in real-time.
Proposal Number: 10049 PI Name: SANTIAGO DEL PALACIO Title: TESTING THE CONNECTION BETWEEN NEUTRINO AND HARD X-RAY EMISSION IN AGNS Abstract: Active galactic nuclei (AGN) are galactic centers with a supermassive black hole that radiates due to accretion. There is growing evidence of a significant correlation between the neutrino and hard X-ray emission from these systems, but the sample is still very scarce (four sources). We aim to significantly increase the sample size and reduce potential selection effects by conducting high-sensitivity hard X-ray observations of the two AGNs with the most significant neutrino signal. Confirming and understanding the reason of the hard X-ray -- neutrino correlation would be a breakthrough in multi-messenger astrophysics. For this we request 60 ks of observing time with NuSTAR.
Proposal Number: 10066 PI Name: JENNIFER SOKOLOSKI Title: A HARD X-RAY VIEW OF THE BRIGHTEST NOVA THIS CENTURY Abstract: The goal of this ToO proposal is to use high S/N hard X-ray spectra from NuSTAR and NICER during a nova eruption of the symbiotic recurrent nova T CrB to test two models for the GeV and TeV emission from such events. We will determine whether novae in symbiotic binaries lead to multiple gamma-ray shocks that traverse and probe different portions of the ejecta and circumbinary medium. The strength of non-thermal X-ray emission will also constrain the origin of gamma-rays. T CrB, which may experience a nova during Cycle 10, is ideal for this test, the results of which have implications for the physics of particle acceleration in shocks, high-energy emission from eruptive transients, and mass transfer in wide binaries. A project with this objective was approved but not triggered in Cycle 9.
Proposal Number: 10072 PI Name: ROBIN CORBET Title: THE SHARP ORBITAL FLARES OF THE HMXB XTE J1829-098 AND THE QUEST FOR THE LUMINOSITY GAP Abstract: XTE J1829-098 is a member of the rare group of HMXBs that exhibit very sharp periodic outbursts, and it is the only member of that group in our Galaxy. Previous TOO observations show that NuSTAR and NICER can provide high-quality data on the source. However, they did not cover a full outburst and were not obtained simultaneously. We can probe much deeper into the nature of this source by carrying out pre-planned systematic simultaneous observations, supported by ground-based IR observations. We will study the timing properties, the CRSF in the spectrum, and search for the start of the onset of the propeller regime.
Proposal Number: 10081 PI Name: FRANCESCO URSINI Title: X-RAY SPECTROPOLARIMETRY OF BRIGHT ATOLL SOURCES Abstract: X-ray spectropolarimetry is providing significant new insights on accretion in non-magnetic neutron stars. Atoll sources are an especially interesting class, given the puzzling nature of their X-ray polarization, which is now measured in an increasing number of sources with IXPE. We ask to observe with NuSTAR four bright atolls that were chosen as targets for IXPE Cycle 1. Simultaneous NuSTAR data will allow us to accurately model their broad-band X-ray spectrum, in particular to constrain the reflection component and the hard X-ray tail if present. This is essential to interpret the polarimetric signal and build a coherent physical scenario. We request a total of 150 ks NuSTAR time.
Proposal Number: 10084 PI Name: PABLO SAZ PARKINSON Title: NUSTAR OBSERVATIONS OF TWO ENERGETIC GAMMA-RAY PULSARS POWERING SUPERNOVA REMNANTS MSH 11--62 AND CTB 37A Abstract: Supernova remnants MSH 11-62 (G291.1-0.9) and CTB 37A (G348.5+0.1) share key properties. Discovered in radio decades ago, and extensively studied in soft X-rays (e.g. Chandra), both host strong pulsar wind nebulae (PWNe) and appear as bright GeV gamma-ray sources in Fermi-LAT. Despite this, the overall nature of their high-energy emission remains unclear. The recent discovery of two energetic pulsars within these SNRs sheds light on this mystery. Utilizing NuSTAR's broad coverage of the unexplored hard X-ray spectrum and its precise timing resolution, we aim to detect hard X-ray pulsations from these pulsars, which combined with a broadband spectral analysis will help disentangle the PWN and pulsar (PSR) emissions, refining our understanding of these systems' high-energy properties.
Proposal Number: 10087 PI Name: GAURAVA KUMAR JAISAWAL Title: THERMONUCLEAR X-RAY BURSTS FROM 4U 1820-30 Abstract: We propose to observe thermonuclear X-ray bursts from 4U 1820-30 in its low-hard state using NuSTAR and NICER. The goal of this study is to understand the nature of the so-called persistent emission and how it responds to X-ray bursts. We aim to investigate the timing and spectral properties of the bursts, including their recurrence time. Using various spectral models, our study will be crucial in examining how photospheric radius expansion bursts affect the geometry of the accretion flow, such as the inner disk and corona.
Proposal Number: 10090 PI Name: KAYA MORI Title: NUSTAR TOO OBSERVATIONS OF X-RAY TRANSIENTS IN THE GALACTIC CENTER Abstract: We propose NuSTAR ToO observations of new X-ray transients and recurrent outbursts from the known very faint X-ray transients (VFXTs) through daily Swift-XRT monitoring of the Galactic Center. Broad-band X-ray spectral and timing data obtained by NuSTAR will provide useful diagnostic tools for identifying X-ray transients in the Galactic Center. NuSTAR will play a crucial role in investigating the nature of X-ray transients in the central parsec, as demonstrated by the discovery of a transient magnetar, the black hole spin measurements from two new transients, and characterizing VFXT's broadband X-ray properties. Identifying new X-ray transients, combined with investigating quiescent X-ray binaries, will explore the unique population and formation of X-ray binaries near Sgr A*.
Proposal Number: 10097 PI Name: RAFFAELLA MARGUTTI Title: PROMPT BROAD-BAND FOLLOW-UP OF THE MOST NEARBY STRONGLY-INTERACTING SNE WITH NUSTAR+XRT Abstract: Contrary to expectations from current stellar evolutionary models, recent observations uncovered the ejection of shells of material by massive stars in the years before the supernova (SN) explosion. The physical mechanism behind the impulsive mass ejection synchronized with the stellar core-collapse is unclear. Building on the recent success with SN2023ixf, here we propose a coordinated NuSTAR-XRT effort to map the evolution of the broad-band X-ray spectrum of 1 young nearby (d< 20 Mpc) or X-ray bright (Fx>5 x 10^-14 erg/s/cm2) strongly interacting SN and enable progress. Our program has the immediate goal to characterize the medium around strongly interacting SNe, which originate from stellar progenitors with the most extreme mass loss before explosion.
Proposal Number: 10100 PI Name: RAFFAELLA MARGUTTI Title: A SYSTEMATIC SEARCH FOR HARD X-RAYS FROM COMPACT-OBJECT MERGERS Abstract: We propose NuSTAR observations of the high-energy afterglows of GW sources discovered during Cycle 10 (which overlaps with the second half of LIGO/Virgo/KAGRA Observing Run 4) to constrain the nature and structure of their relativistic outflows. These observations will provide new insight into the current debate about the nature of the relativistic ejecta of compact-object mergers and their (now questioned) capability to successfully launch ultra-relativistic jets in their environment. This proposal opens a new window of investigation on GW sources.
Proposal Number: 10103 PI Name: YUHAN YAO Title: PROBING BLACK HOLE SUPER-EDDINGTON ACCRETION IN TIDAL DISRUPTION EVENTS Abstract: Tidal disruption events (TDEs) offer great opportunities to study the physics of black hole accretion in the super-Eddington regime. A growing number of X-ray bright TDEs are being discovered by current and upcoming time domain surveys. We propose two epochs of 50ks NuSTAR + 15ks Swift ToO observations on TDEs with bright hard X-ray emission. For jetted TDEs, this program will shed light on the location, composition and radiation mechanism of relativistic jets launched from super-Eddington accreting black holes. For non-jetted TDEs with non-thermal X-ray emission, this program will provide a broadband X-ray spectrum with relativistic reflection features that allows us to measure key physical quantities of the accretion flow (e.g., disk ionization state, BH spin, inclination).
Proposal Number: 10112 PI Name: QI FENG Title: SEARCHING FOR NEUTRINO-EMITTING BLAZARS IN HARD X-RAY BAND Abstract: We propose NuSTAR target-of-opportunity (ToO) observations of a candidate neutrino-emitting blazar, triggered by the combination of an IceCube neutrino alert and detections of a spatially coincident blazar by Fermi-LAT and Swift-XRT. We request 40 ks of initial NuSTAR observation within 24 hours, on a best-effort basis, after the trigger. If the hard-X-ray flux from the initial observation is > 1.5 x 10^-12 erg cm^-2 s^-1, we request another 40 ks of follow-up NuSTAR observations to characterize the low-flux state.
Proposal Number: 10118 PI Name: PRAGATI PRADHAN Title: PROBING THE HARD X-RAY PROPERTIES OF MS 1603.6+2600 WITH NICER AND NUSTAR Abstract: We propose a 50 ks observation of the Accretion Disk Corona (ADC) candidate MS 1603.6+2600 with NuSTAR and 10 ks with NICER. With the broadband spectra, we will accurately model the X-ray continuum, which is suspected to either originating via reflection off the accretion disk or through inverse Compton scattering in the accretion column. We will also measure the energy dependent eclipse depths in MS 1603.6+2600 to map the origin of hard and soft X-rays. In addition, we will search for pulsations in the NuSTAR lightcurves as well as explore for the presence of quasi-periodic oscillations (QPOs) or cyclotron line attributed to the neutron star in MS 1603.6+2600.
Proposal Number: 10119 PI Name: DANIEL WILKINS Title: FOLLOWING THE DISK-JET-CORONA CONNECTION IN THE UNIQUE RADIO GALAXY 3C120 Abstract: 3C120 is a unique broad-line radio galaxy. Alongside the vast jets launched by the supermassive black hole in its nucleus, 3C120 possesses a compact X-ray emitting corona that irradiates the inner disk. This provides a unique view of the inner regions around the black hole in which the jet is launched and the corona is formed. We propose four, monthly, 160ks observations of 3C120 with NuSTAR to be coordinated with ongoing monthly VLBA observations of the jet. Two of these are to be simultaneous with 210ks XMM-Newton observations. These observations will map the accretion geometry and trace the connection between the accretion disk, corona and jet. This comprehensive program will give us important new insight into how jets are launched by black holes.
Proposal Number: 10120 PI Name: CAMILLE DIEZ Title: ON THE ONSET OF THE ACCRETION WAKE IN THE HIGH-MASS X-RAY BINARY 4U1538-52 Abstract: We propose a 50 ks NuSTAR observation, with complementary 50 ks using XMM-Newton, of the High-Mass X-ray Binary (HMXB) 4U1538-52 at orbital phase 0.35-0.65 where the accretion structure (or 'wake') crosses and obscures our line of sight. By monitoring the source before and during the passage of the wake using NuSTAR's high energy coverage, we can distinguish changes in the continuum caused by the wake from changes caused by the neutron star's intrinsic variability down to the pulse period (526.69 s). We will also determine the geometry of the accretion columns by measuring the variability of the cyclotron lines, located at 22 keV and 47 keV. Complementary XMM-Newton data will reveal a plethora of emission lines below 3 keV, particularly with RGS, to assess the wind's ionisation state.
Proposal Number: 10121 PI Name: QI FENG Title: NUSTAR OBSERVATIONS OF 1LHAASO J1219+2915/NGC 4278 Abstract: In this proposal, we request 80 ks of NuSTAR observations in the region of the new TeV source 1LHAASO J1219+2915. The source is detected above 1 TeV and spatially coincident with NGC 4278, a nearby low-ionization nuclear emission-line region (LINER) and low-luminosity active galactic nucleus (LLAGN), a source class that has not been previously detected at TeV energies. The proposed NuSTAR observations will be the first hard X-ray measurements of this source, crucial to the characterization of the peak of its broadband spectral energy distribution (SED) and the investigation of its emission mechanism in the X-ray and gamma-ray bands.
Proposal Number: 10126 PI Name: VAIDEHI PALIYA Title: X-RAYING THE MOST DISTANT GAMMA-RAY DETECTED FR II RADIO GALAXY Abstract: We propose to observe the radio source TXS 1433+205, which was recently identified as the most distant gamma-ray emitting FR II radio galaxy, jointly with NuSTAR (70 ksec) and XMM Newton (35 ksec). This source has no sensitive X-ray spectral measurements. The NuSTAR+XMM observations will allow us to fully characterize the proposed source's X-ray spectral behavior, enabling us to accurately determine the associated jet power and the particle population responsible for the observed emission. We will also compare the derived results with other gamma-ray emitting FR I and II radio galaxies.
Proposal Number: 10127 PI Name: LORENZO DUCCI Title: UNVEILING THE PROPERTIES OF THE SUPERGIANT X-RAY BINARY IGR J00370+6122 WITH NUSTAR Abstract: IGR J00370+6122 is an enigmatic and poorly studied supergiant X-ray binary. It has one of the most eccentric orbits of its class and it shows fast X-ray flares and a strong orbital modulation. The donor star shows anomalous abundances and high rotational velocity, suggesting a non-standard evolutionary channel. Although IGR J00370+6122 is unconventional and of particular interest for evolutionary studies and for understanding the accretion mechanism that causes its X-ray behaviour, it was scarcely observed above 10 keV. Therefore, we propose the first NuSTAR observation of IGR J00370+6122 to perform the most sensitive spectral and timing study to measure fundamental parameters such as the spin period and magnetic field strength, with the ultimate goal of understanding its nature.
Proposal Number: 10134 PI Name: RICCARDO MIDDEI Title: NUSTAR AND MULTI-ENERGY SPECTRAL AND POLARIMETRIC OBSERVATIONS OF A FLARING HSP BLAZAR Abstract: We propose a ToO observation with NuSTAR (40 ks) of a high synchrotron peaked (HSP) blazar during a TeV flare. The requested ToO observation lies in the context of an already approved IXPE ToO that is complemented by multiwavelength observations in radio, optical, TeV-gamma-rays. Precise estimates of the photon index alpha and the broadband spectral curvature beta are key ingredients of a robust spectropolarimetric analysis in the X-ray band. Nustar, thanks to its unrivaled bandpass in best suited to accurate model the curved spectrum of an HSP and to track the spectral variability down to few ks timescale. The proposed ToO will provide insight into the acceleration and cooling processes experienced by the particles during the flare.
Proposal Number: 10141 PI Name: ALESSIO MARINO Title: FOLLOWING THE DISC-JET BEHAVIOUR OF GX 340+0 ALONG THE Z-TRACK Abstract: Z-sources are a group of persistent bright neutron star (NS) low-mass X-ray binaries. Their signature behaviour is the continuous Z-shaped track that these sources draw on a Hardness Intensity Diagram. Along this track, these systems display marked variability in both the X-rays (disc) and radio (jet) emission. We propose a 100 ks NuSTAR campaign to investigate the X-rays spectral and timing changes in the Z-source GX 340+0 as it completes a Z-track. This observing campaign will be part of a larger multi-band (from radio to soft X-rays) campaign. The proposed observations will allow us to follow in detail how both the accretion flow and the jet evolve in tandem, giving us unprecedented insights into disc-jet coupling in Z-sources and X-ray binaries in general.
Proposal Number: 10142 PI Name: VITTORIA GIANOLLI Title: ADVANCEMENTS IN THE X-RAY POLARIZATION STUDIES OF THE CORONAL ENVIRONMENT: THE SECRETS OF NGC4151 Abstract: We propose to observe the Seyfert galaxy NGC4151 simultaneously with NuSTAR (for 100 ks) and XMM-Newton (for 50 ks) during a 750ks IXPE pointing. NGC4151 is the first radio-quiet Active Galactic Nucleus with an X-ray polarization measure for the corona and offers the unique opportunity to investigate possible changes in the polarization properties of the system, due to its extreme variability and high luminosity. The synergy between NuSTAR, XMM-Newton and IXPE will allow us to measure the physical properties of the hot corona and assess the different spectral component contributions. NGC4151 is also a target for XRISM program, offering the chance for contemporaneous observations.
Proposal Number: 10143 PI Name: MATTEO BACHETTI Title: TRACKING THE ORBITAL DECAY OF THE FIRST ULTRALUMINOUS PULSAR M82 X-2 Abstract: Ultraluminous x-ray sources (ULXs) are X-ray binaries radiating above the Eddington luminosity. An increasing sample of ULXs are known to be powered by accreting pulsars (PULXs), and it is currently unclear if their observed emission is amplified by strong radiation beaming or it denotes a genuine super-Eddington mass accretion rate. Following the publication of a orbital period decay in the first discovered PULX, M82 X-2, that would imply a mass transfer rate even more extreme than previously thought, we will use pulsar timing to track the orbital evolution of this pulsar, and verify whether the orbital period evolution is indeed compatible with the claimed mass transfer.
Proposal Number: 10144 PI Name: CHRISTIAN MALACARIA Title: THE IDEAL TARGET FOR UNDERSTANDING LOW ACCRETION REGIME PHYSICS IN X-RAY PULSARS: MAXI J0655-013 Abstract: MAXI J0655-013 is a recently discovered accreting X-ray pulsar that has been characterized only in a limited accretion domain. Recently, this class of sources has been shown to transition to a special double-hump spectral shape when its accretion rate reaches its lowest possible value (before propeller even prevents accretion). However, due to the intrinsic low flux at such stages, only a few of them have been caught in this special regime with Nustar, which is the only suitable observatory for studying the broadband spectrum. Here we propose for a joint Nustar + XMM observation of MAXI J0655. Because of its vicinity, slow rotation, low interstellar absorption and a tentative magnetic field measured strength, this source ranks amongst the most convenient targets for low-luminosity studies.
Proposal Number: 10145 PI Name: TANUMAN GHOSH Title: BROADBAND X-RAY PROBE OF THE CANDIDATE NEUTRON STAR ULX NGC 5474 X-1 Abstract: We propose to coordinate a deep simultaneous NuSTAR (150 ks) and XMM (80 ks) observation of a nearby hard ULX, NGC 5474 X-1, to study its broadband spectral properties for the first time, confirm the potential cyclotron line and search for pulsating nature of the host compact object with high S/N data. The source exhibits one of the hardest spectra among ULXs; however, it has received very little observational attention so far. Analysis of archival Chandra data indicates the presence of CRSF near ~7 keV; however, with low statistical confidence. In addition, the hard spectral index suggests the source may host a pulsar at the core. CRSF and pulsation in ULXs are rare, and if new broadband data detect these features, NGC 5474 X-1 will be among the rare neutron star ULXs.
Proposal Number: 10147 PI Name: GIORGIO LANZUISI Title: A NUSTAR WISSHFUL PROGRAM: X-RAY CORONA AND WINDS IN QUASARS AT COSMIC NOON Abstract: We propose to observe with NuSTAR, for 750ks in total, 7 luminous QSOs at Cosmic Noon (z=2-4). We request coordination with already approved long XMM observations from the multi-year Heritage program WISSHFUL, aimed at searching for Ultra Fast Outflows (UFOs) in these targets. By leveraging the unprecedented XMM time allocation, this NuSTAR program will allow for the first systematic study of the coronal properties of luminous QSOs shining at Cosmic Noon. In turn, the availability of NuSTAR data will maximize the outcome of the XMM Program by allowing an accurate determination of the continuum above the Fe K band, boosting the reliability of the UFO detections.
Proposal Number: 10148 PI Name: KAYA MORI Title: WHAT IS THE ORIGIN OF HIGH-ENERGY EMISSION FROM THE GLOBULAR CLUSTER TERZAN 5? Abstract: Terzan 5 hosts the largest number of millisecond pulsars (MSPs) and stands out as the only globular cluster detected in the TeV band, indicating a population of relativistic electrons extending beyond the cluster. Chandra observations found diffuse non-thermal X-ray emission with a flat spectrum outside the core where all known MSPs exist. The elusive origin of this diffuse X-ray emission holds the key to understanding the GeV emission mechanism. We aim to (1) determine the nature of the diffuse X-ray emission with NuSTAR, (2) characterize the spatial and energy distribution of electrons around the cluster, and (3) test the two competing GeV emission models: curvature radiation from pulsar magnetospheres or inverse Compton scattering of CMB and stellar photons by relativistic electrons.
Proposal Number: 10154 PI Name: JAEGEUN PARK Title: PROBING THE LEPTONIC CONTRIBUTION TO CTB 87 S TEV EMISSION Abstract: In our analysis of archival X-ray observations of CTB 87, we found a spectral curvature and potential pulsations in the source. The serendipitous NuSTAR observation at a 5' off-axis angle played the central role, but part of the source emission fell outside the detector, prohibiting a comprehensive and accurate characterization. Therefore, we request a 60-ks NuSTAR observation of CTB 87 to accurately measure the spectral curvature and confirm the pulsations. These results will tightly constrain the parameters of multi-zone models and help accurately estimate electron contribution to the TeV emission from the source. Our investigation will provide insights into the acceleration of particles and their flow within energetic PWNe, holding the potential to shed light on leptonic PeVatrons.
Proposal Number: 10158 PI Name: CHANHO KIM Title: UNRAVELING THE INTERACTION DYNAMICS BETWEEN THE TAZ PWN AND THE LYNDS 227 CLOUD Abstract: The enigmatic X-ray emission from the Taz pulsar wind nebula (PWN), possibly exhibiting dramatically different spectra between two adjacent regions, holds the potential to reveal the intimate interaction between the PWN and a cloud. The results from archival XMM data, although highly suggestive, were inconclusive since the spectral difference could not be confirmed with high significance. Moreover, the underlying process for the difference, nonthermal bremsstrahlung emission or particle re-acceleration within the interaction region, could not be explored due to the limited passband of XMM. We request a 60 ks NuSTAR observation to extend the data to >10 keV, which are crucial to overcome the aforementioned difficulties, allowing a detailed investigation of the PWN-cloud interaction.
Proposal Number: 10160 PI Name: JESSIE DUNCAN Title: INVESTIGATING SOLAR ACTIVE REGION HEATING WITH NUSTAR AND THE MAGIXS-2 SOUNDING ROCKET Abstract: The elevated temperature of the solar corona with respect to the photosphere is one of the largest outstanding questions in solar physics. MaGIXS-2 is an upcoming solar sounding rocket that seeks to investigate this question, via spectrally and spatially resolved soft x-ray observation of the corona. Various theorized coronal heating mechanisms can be distinguished via their effects on the distribution of hot plasma present in the corona, which are measurable by MaGIXS. NuSTAR, too, is sensitive to emission from hot coronal plasma providing excellent synergy between these two instruments. We propose to perform coordinated observations between NuSTAR and MaGIXS-2 during its upcoming flight, in order to take advantage of an invaluable opportunity for coordinated solar science.
Proposal Number: 10161 PI Name: ANDREA MARINUCCI Title: HOT CORONAE IN LUMINOUS RADIO-QUIET QUASARS Abstract: We propose to observe the two luminous quasars RBS229 and PG1407+265 at z=0.334 and z=0.940, for 230 ks of net exposure time each. Thanks to their brightness, they offer the unique opportunity to probe the extreme radio-quiet AGN luminosity regimes with NuSTAR. We will study the yet poorly investigated emission of these objects in the hard X-rays in order to explore the properties of their hot coronal environment. Archival XMM-Newton observations show featureless continua, lacking any contribution from neutral Compton reflection or absorption which may contaminate the primary power law. Our proposed targets will provide unique spectral templates to properly infer fluxes and luminosities as well as assess the detectability of z>6 quasars with present-day and future X-ray facilities.
Proposal Number: 10167 PI Name: LUCIA BALLO Title: OBSERVATION OF TWO IXPE EXTREME BLAZARS: PROBING THE MECHANISMS BEHIND HIGHLY EFFICIENT PARTICLE ACCELERATION IN JETS Abstract: Multiwavalength polarization, and in particular X-ray polarization, is an important probe of the magnetic field geometry, acceleration physics, and high-energy emission processes in blazar jets. IXPE is opening a new window to probe the Universe through high-energy polarization. Here, we propose contemporaneous NuSTAR observations of two IXPE-approved EHBL targets. The proposed observations will supplement the planned multiwavelength campaign in radio, optical, and gamma-rays. Simultaneous polarimetry at optical and mm wavelengths will complement the campaign, the first so complete ever tried on sources of this particular class apart from the archetypal 1ES 0229+200.
Proposal Number: 10168 PI Name: TOLGA GUVER Title: BROADBAND OBSERVATIONS OF X-RAY BURSTS FROM 4U 1323-62 Abstract: We propose to observe 4U 1323-62 using NuSTAR and XMM for 120ks, a prominent dipping X-ray binary with clocked bursts. Recent hard X-ray observations enable us to investigate the interaction between bursts and the surrounding corona. Soft X-ray photons from bursts induce cooling, leading to a temporary decrease in hard X-ray flux. Simulations indicate that the deficit in the 8-24keV flux vary depending on corona optical depth and aspect ratio. Proposed observation involves monitoring the orbital phase with XMM, and probing burst effects on the corona with NuSTAR data. We expect 10 X-ray bursts during the observation and use the orbital inclination and phase to detect time-dependent changes in the hard X-ray deficit. This will enable us to constrain the size and location of the corona.
Proposal Number: 10170 PI Name: ENRICO BOZZO Title: HUNTING FOR CYCLOTRON LINES IN THE SYMBIOTIC X-RAY BINARY 3XMM J181923.7-170616 WITH NUSTAR Abstract: Symbiotic X-ray binaries (SyXBs) are rare low mass X-ray binaries hosting a Gyr-old red giant and a neutron star (NS) accreting from the slow wind of its companion. The NS in these systems is suspected to be strongly magnetized and thus only Myr-old. The puzzling question about SyXBs is how is it possible to have a young strongly magnetized NS coupled with a Gyr-old companion. So far, only in two cases a cyclotron line could be observed to confirm the young age of the NS due to the lack of data on other sources. We aim at searching for cyclotron lines in the last observable source of the class with NuSTAR, i.e. 3XMM J181923.7-170616, using a 80 ks-long NuSTAR observation.
Proposal Number: 10171 PI Name: JIACHEN JIANG Title: A NUSTAR AND NICER VIEW OF THE GALACTIC ULTRALUMINOUS X-RAY PULSAR SWIFT J0243.6+6124 Abstract: The detections of pulsations in ultraluminous pulsars suggest that the accreting objects are neutron stars. This puts a robust upper limit on the mass of the compact objects and indicates luminosities that far exceed the Eddington. We request three NuSTAR ToO observations with 20 ks exposure to observe the next outburst of the only Galactic ultraluminous X-ray pulsar Swift J0243.6+6124. Each observation will be implemented by one 3 ks NICER observation to cover the soft X-ray band. These observations will enable us to study the geometry of the innermost accretion region and the magnetic field's strength in this pulsar. In particular, we will consider a super-Eddington disk reflection spectral model based on GRMHD simulations.
Proposal Number: 10177 PI Name: SCOTT JOFFRE Title: UNCOVERING THE MOST POWERFUL JETS THROUGH COSMIC TIME Abstract: From the 4LAC catalog, we have chosen four high-latitude blazars with redshifts in the range 2.5
Proposal Number: 10179 PI Name: VALENTINA BRAITO Title: MONITORING THE UNPRECEDENTED DISK WIND IN MCG-03-58-007 Abstract: We propose to supplement an awarded XMM large program monitoring MCG-03-58-007, for which only half of the observations have a simultaneous NuSTAR pointing. Here we seek to fully cover that program with additional 3x40 ksec NuSTAR exposures. MCG-03-58-007 has a powerful and extremely variable disk wind, where a dramatic and fast variability of the wind velocity was revealed, decreasing from v/c~ -0.2 to v/c~-0.074 in 16 days. Such variability is at odds with other disk winds and challenging for current models. A complete coverage with NuSTAR will ensure that for each observation the primary continuum and energetics of the wind will be accurately measured. We also seek a Swift monitoring (20x3 ksec) to follow its variability every 2 days to investigate the wind response to the X-ray flux.
Proposal Number: 10180 PI Name: JOSEPH NEILSEN Title: X-RAY JETS & BH SHADOWS: NUSTAR, EHT, CHANDRA, AND SWIFT ON M87 Abstract: With a large, well-studied jet and the second largest event horizon on the sky, the radio galaxy M87 is one of the primary targets for the Event Horizon Telescope. In light of the great success of recent EHT campaigns, we are eagerly planning for observations in 2025. To this end, we request 100 ks of NuSTAR time and 10x1 ks with Swift on M87 to be coordinated with Chandra. In addition to the potential tests of GR, coordinated X-ray/EHT observations offer an incredible opportunity: a chance to observe structures near the event horizon while tracking their high-energy variability. NuSTAR spectra of M87 (in synergy with Swift, Chandra, and multiwavelength SEDs) will place tight constraints on the energetics and acceleration of particles near the event horizon of this supermassive black hole.
Proposal Number: 10182 PI Name: DHEERAJ PASHAM Title: NUSTAR AND NICER OBSERVATIONS TO IDENTIFY AND STUDY COSMOLOGICAL BLACK HOLES AS THEY TURN ON A RELATIVISTIC JET Abstract: Following NICER+NuSTAR's recent success in capturing the spectro-timing variability of the farthest stellar tidal disruption event (TDE) to-date we propose ToO monitoring observations of a future relativistic TDE, i.e., a system with a newborn relativistic jet pointed directly along our line of sight. Our main goals are 1) to establish the relativistic nature of the future transient by measuring its luminosity and variability, and 2) combine NICER+NuSTAR data with our approved multi-frequency radio data to perform multi-epoch spectral energy distribution modelings to shed light on the underlying jet physics. Our scientific goals require high-cadence monitoring for weeks and hard X-ray coverage making NICER + NuSTAR ideal facilities for the proposed study.
Proposal Number: 10183 PI Name: FELIX FUERST Title: CONTINUED SPIN-TRACKING OF THE NEUTRON STAR ULX NGC7793 P13 WITH NUSTAR Abstract: NGC 7793 P13 is one of the best targets among the ultra-luminous X-ray pulsars (ULXPs) to study how mass transfer and accretion works in the super-Eddington regime. It shows long-term flux variability, monitored over the last ~10 years, but at the same a rather stable spin-up. Recently it entered a historic bright state, after an off- and dim-state in the last few years. The new bright state now affords us with the ideal opportunity to check for spectral and geometric changes in the source, which would shed new light on accretion physics beyond the Eddington limit, as well as continue monitoring the pulse period. We will build on a very successful monitoring campaign and propose to observe NGC 7793 for 2 50 ks.
Proposal Number: 10185 PI Name: KIRILL SOKOLOVSKY Title: TRACING SHOCK DEVELOPMENT IN A NOVA Abstract: We propose 3x50ks observations of a new bright (V<7.5) nova likely to be detected in gamma-rays. The observations will trace the development of shocks within the nova ejecta, constrain the non-thermal particle acceleration and gamma-ray production mechanisms. We'll put an upper limit on the particle acceleration efficiency by comparing thermal X-ray and optical to GeV luminosity and search for predicted non-thermal X-rays. Understanding nova shocks is relevant for other shock-powered transients: interacting supernovae, tidal disruption events, stellar mergers. NuSTAR is the only instrument capable of detecting hard X-rays from novae simultaneously with the GeV emission. The observations should be conducted now to take advantage of the simultaneous operations with Fermi, Swift and XMM.
Proposal Number: 10191 PI Name: MIRKO KRUMPE Title: TRACKING THE X-RAY EVOLUTION OF AN ONGOING SDSS-V CHANGING-LOOK AGN Abstract: SDSS-V, now in full operation, is obtaining repeated optical spectroscopy for thousands of AGN. This will allow for the optical identification of extremely rare, currently transitioning changing-look AGN. We request 2 ToOs (each consisting of a 150 ks observation) to track the X-ray spectral evolution of an ongoing optical transition with a cadence of two months. The combined X-ray and optical datasets will explore how the X-ray corona, accretion disc, and broad-emission line region in AGN interact with each other. It will deliver valuable insights into how accretion flows evolve during AGN ignitions and depletions. We will compare our results with the outcomes of a program on X-ray-selected changing-look AGN.
Proposal Number: 10193 PI Name: SOPHIA WADDELL Title: CONSTRAINING THE AGN TORUS GEOMETRY WITH EROSITA HARD SOURCES Abstract: eROSITA has recently detected an interesting new class of obscured AGN, detected only in its hardest (2.3-5keV) bandpass. These AGN are viewed through the cold, dusty torus, which obscures the X-ray spectrum. While obscured AGN are more difficult to detect in soft X-ray surveys, it is believed that a large fraction of AGN in the local Universe are obscured and that a large fraction of the total accretion energy density of the Universe is contained therein, so it is of key importance to characterise the torus geometry and structure. We propose to follow-up on a sub-sample of 5 eRASS1 hard X-ray selected AGN with spec-z. These will allow us to verify that the eROSITA hard-only sample selects extreme (likely uniform and spherical) torus geometries, and compare face-on and edge-on galaxies.
Proposal Number: 10198 PI Name: ANDREA GOKUS Title: UNCOVERING THE HIGH-ENERGY PROPERTIES OF HIGH REDSHIFT BLAZARS Abstract: We propose a 100ks ToO observation of a high-redshift (z>=3) blazar during a gamma-ray flare detected with Fermi/LAT. Gamma-ray emission has only been detected for 12 high-z blazars so far, mostly while these sources were in outburst. In order to expand the elusive and small sample of gamma-detected MeV blazars, we want to gain simultaneous multi-wavelength data during a flare, that is, when the gamma-ray spectrum can be constrained well for accurate SED modelling. NuSTAR plays a crucial role in our campaign as the hard X-ray data is needed to constrain the high-energy hump of the SED. Our multiwavelength data set will yield insights into the processes of accreting super massive black holes in the early Universe, which are also key targets for future MeV telescopes.
Proposal Number: 10204 PI Name: NURIA TORRES-ALBA Title: PROBING AGN OBSCURATION VARIABILITY WITH NUSTAR Abstract: Active galactic nuclei (AGN) are powered by accreting supermassive black holes, surrounded by a torus of obscuring material. Recent observations have detected variability in the line of sight column density, giving rise to the 'patchy torus' hypothesis. Other observations, however, fail to find the variability expected from a patchy torus in Sy2 galaxies. Here, we propose to monitor a Sy2 galaxy, with confirmed yearly column density variability, but that lacks short-term monitoring. We need additional observations on timescales of weeks-to-months to properly constrain the obscurer properties. The number of sources for which a monitoring campaign (i.e. > two observations) has shown variability is only a handful, making the addition of every possible source vital.
Proposal Number: 10206 PI Name: XIN LIU Title: ARE INTRINSICALLY X-RAY LUMINOUS AGNS TRULY PREVALENT IN LATE STAGE GALAXY MERGERS? Abstract: While it has been demonstrated by numerical simulations over the past decade, the causality between galaxy mergers and AGN triggering remains an open question. And a consensus of the AGN occupation rate in mergers is still absent, which is tied to the challenge of detecting heavily obscured and/or intrinsic low-luminosity AGNs. Thanks to the unprecedented sensitivity of NuSTAR at energy band above 10 keV, it stands out as the only instrument with the capability to recover the intrinsic AGN luminosity and the level of obscuration. We propose to carry out observations of seven dual AGN systems with separations < 5 kpc, which signifies the late stage of mergers and are perfect targets to test the merger-induced AGN scenario and study the essential physics of SMBH feeding and feedback.
Proposal Number: 10209 PI Name: ISAIAH COX Title: UNVEILING NEW COMPTON-THICK AGN IN THE LOCAL UNIVERSE Abstract: Compton-thick AGN are believed to represent a significant fraction of the cosmic X-ray background, especially around 30 keV. However, there is a discrepancy in the fraction obtained from population synthesis models and the observed fraction, mainly due to the bias against detecting heavily obscured AGN. To address this, we have developed a volume-limited sample of AGN detected by BAT. We select three sources that have soft X-ray data indicative of a Compton-thick scenario. We propose to jointly observe the three sources with NuSTAR and XMM-Newton to confirm their Compton-thick nature and constrain torus properties with physically motivated torus models. Doing so will allow us to accurately measure the Compton-thick AGN fraction in the local Universe after accounting for selection effects.
Proposal Number: 10210 PI Name: HANNAH EARNSHAW Title: THE BROADBAND VARIABILITY OF NGC 4190 ULX-1 Abstract: We propose to observe a bright nearby ULX, NGC 4190 ULX-1, using two quasisimultaneous NuSTAR and XMM-Newton exposures of 50ks and 35ks per observation respectively. Its persistently high flux (>10^-12 erg/s/cm^2) and variable spectral behaviour at high X-ray energies make NGC 4190 ULX-1 a particularly accessible and interesting object of study. While pulsations have not previously been detected, the narrow profile of its hot thermal component and its luminosity-temperature relation suggest the presence of a super-Eddington disk truncated by a strong magnetic field. Multiple broadband observations are required to populate its luminosity-temperature relation, estimate a magnetic field strength, and search for pulsations which would be the smoking gun' indicating a neutron star accretor.
Proposal Number: 10212 PI Name: PETER BOORMAN Title: PROBING THE DENSE ENVIRONMENT SURROUNDING A GROWING IMBH Abstract: Approximately half of all supermassive black holes (SMBHs) are expected to undergo growth phases behind Compton-thick veils of obscuring gas. However despite being responsible for the seeding of SMBHs, there are currently no examples known of a Compton-thick accreting intermediate mass black hole (IMBH). We propose a 220 ks NuSTAR observation of the only known AGN with (1) an accurate and precise intermediate black hole mass measurement and (2) an Fe emission line equivalent width > 2 keV that can only be explained with a Compton-thick line-of-sight column density. Given the importance of the IMBH occupation fraction for seeding models of SMBHs, the proposed observation will additionally provide invaluable insights into the effect circum-nuclear obscuration has on the selection of IMBHs.
Proposal Number: 10213 PI Name: RAHUL SHARMA Title: A BROADBAND X-RAY STUDY OF LMXB XTE J1710 281 Abstract: We propose 60 ks NuSTAR observation of NS LMXB XTE J1710 281 jointly with 4 ks NICER observation, aiming for broadband spectroscopy of this eclipsing binary in 0.2-78 keV. This will enable us to decode emission geometry, by modelling thermal emission from NS surface and accretion disc, Comptonized emission and their source of seed photons. This is ideal for studying reprocessed X-rays during eclipse when primary X-rays are blocked by the donor star. Broadband spectroscopy during the dipping phases will be used to probe the accretion disc atmosphere and the outer disc structure. XTE J1710 281 is known to show sudden orbital period glitches. A 60 ks observation will cover 5 full eclipses and timing their occurrence will be used to refine constraints on its orbital ephemeris.
Proposal Number: 10214 PI Name: MITSURU KOKUBO Title: A SEARCH FOR AN INTERMEDIATE-MASS ACTIVE BLACK HOLE IN THE BLUE COMPACT GALAXY SBS 0335-052E WITH NUSTAR Abstract: SBS0335-052E is one of the lowest mass galaxies (~10^7 M_sun) in the local Universe. Based on the multi-wavelength SED analysis and IR variability detection in 3-4 micron bands, SBS0335-052E is supposed to be hosting a highly-accreting obscured AGN whose black hole mass is in the intermediate-mass BH (IMBH) mass range (<10^5 M_sun). The stringent upper limit on the soft X-ray luminosity by Chandra indicates that the AGN is Compton-thick. Here we propose a NuSTAR hard X-ray observation to confirm the presence of the Compton-thick IMBH AGN in SBS0335-052E. The proposed observation will for the first time reveal the hitherto unexplored population of Compton-thick highly-active IMBHs in the local Universe, which will have profound implications for the SMBH seed formation/evolution scenarios.
Proposal Number: 10216 PI Name: JAVIER GARCIA Title: A HARD LOOK OR HARDLY LOOKING? A MONITORING CAMPAIGN FOR BRIGHT BLACK HOLE BINARIES Abstract: Transient black hole binaries (BHB) undergo X-ray outbursts that display a plethora of physical phenomena on human timescales, typically lasting several months. This includes rapid changes in both the spectral and timing data of these systems. We request a total of 500 ks of NuSTAR time to monitor any known or new BHB system that goes into an outburst during Cycle 10, triggering ~18 observations to sample all accretion states. We also request 50 ks of quasi-simultaneous NICER time to support this campaign by covering the soft energy band and providing fast timing observations. The key goal is to provide a comprehensive view of the properties of accreting BHs, including robust measurements of their mass and spin via spectral-timing modeling of the X-ray data.
Proposal Number: 10218 PI Name: SHIFRA MANDEL Title: DECIPHERING THE NATURE OF A NEWLY DISCOVERED POPULATION OF PERIODIC X-RAY SOURCES Abstract: We propose a pilot observing program of a new population of periodic X-ray sources serendipitously identified near the Galactic center (GC) in order to decipher their nature using NuSTAR's unique broadband energy capabilities. These sources may belong to one of several classes of exotic compact objects, and their study will provide a rare window into the tens of thousands of unidentified GC X-ray sources. We demonstrate that our requested observations will allow us to determine the source types by differentiating between different cases and study the source characteristics.
Proposal Number: 10220 PI Name: MEGUMI SHIDATSU Title: UNDERSTANDING DISK WINDS IN PREVIOUSLY UNCOVERED STATES OF BLACK HOLE X-RAY BINARIES Abstract: We propose NuSTAR observations of transient BHXBs simultaneously with the XRISM ToO observations, to study the properties of disk winds in the low/hard state and in low inclination angle sources, which are not well understood. The new satellite XRISM is expected to revolutionize these studies, with unprecedented weak lines detection and resolution capabilities. Simultaneous NuSTAR observations enable us to determine the shape of the hard X-ray continuum spectrum, which is crucial to determine wind properties from the XRISM high resolution spectrum. Moreover, NuSTAR can provide the reflection features. Combining them with the information of narrow absorption lines obtained with XRISM, we can reveal the underlying wind mechanisms and the accretion disk structure in the low/hard state.
Proposal Number: 10226 PI Name: NURIA TORRES-ALBA Title: NUSTAR'S FIRST GAMMA-RAY PROTOSTELLAR JET Abstract: Protostellar jets have been proposed over the past decade as possible accelerators of non-thermal particles, and therefore high-energy (hard X-rays to gamma-ray) sources. Radio observations have found signatures of non-thermal (synchrotron) emission in some jets, but soft X-ray observations have only detected thermal emission. We have compiled a sample of likely gamma-ray-emitting protostellar jets from the Fermi-LAT catalog. Our sample's gamma-ray properties mark them as a likely new and distinct source class. Here, we propose to observe with NuSTAR the most promising target, which shows hard (5-7 keV) X-ray emission (powerlaw) in the Chandra range. This will be the first-ever NuSTAR observation of a protostellar jet, and confirm protostellar jets as a new high-energy source class.
Proposal Number: 10229 PI Name: SARA SAEEDI Title: FOLLOW-UP OF NEW TRANSIENT LOW-MASS X-RAY BINARY SRGT J071522.1-191609 Abstract: We request for a 50 ks follow-up observation of a new transient low mass X-ray binary\,(LMXB) SRGt J071522.1-191609, which is probably a member of CMa dwarf spheroidal galaxy (dSph) and is thus the first candidate for an LMXB in old populations of dSphs. The sources is discovered by eROSITA in 2020 and have a follow-up XMM-Newton observation(2021). XMM-Newton spectrum is well fitted with an absorbed (black-body+power law) model and it shows a hard and bright X-ray emission of the order of 10^-11 erg/s/cm^2 (0.8-12 keV), making it a good candidate for NuSTAR observation to further investigate the nature of SRGt J071522.1-191609 system.
Proposal Number: 10231 PI Name: AKOS BOGDAN Title: UNLOCKING PANDORA'S SECRETS: PROBING THE THERMODYNAMICS OF ABELL 2744 Abstract: Abell 2744, known as Pandora's Cluster, is a prime example of merging clusters in the low-redshift universe. As one of the Hubble Frontier Field clusters, it has extensive data across the electromagnetic spectrum. Deep Chandra X-ray observations reveal its highly complex morphology and mergers among multiple sub-clusters and demonstrate its extremely high luminosity and ICM temperature. Radio studies of Abell 2744 have identified multiple relics that are typically associated with merger shocks. In this proposal, we aim to enhance this rich data set with NuSTAR observations, which will allow us to map the thermodynamics of Abell 2744, study shocks in this massive cluster, test electron heating theories, and search for inverse Compton scattering.
Proposal Number: 10233 PI Name: CHANDREYEE MAITRA Title: INVESTIGATING THE NATURE OF THE HOTTEST SPECTRAL COMPONENT OF SN 1987A THROUGH THE HARD X-RAY EYES OF NUSTAR Abstract: We request a 350 ks observation to perform a broad-band spectral study of SN 1987A. Monitoring in the hard X-ray band of this unique object is especially crucial at an epoch where the flux > 3 keV dominates the emission, as the blast waves have propagated beyond the dense equatorial ring. The NuSTAR observation will be instrumental in solving the long-standing question whether the hard emission originates from the PWN of the putative NS or has its origin in the shocked plasma itself (DSA or reflected shocks). Coverage beyond 10 keV is the only way to disentangle the scenarios mentioned above. The observation will further shed light on the origin of the Fe K emission in SN1987A.
Proposal Number: 10241 PI Name: MARINA ORIO Title: V407 LUP: A MAGNETIC NOVA Abstract: Nova V407 Lup had a spectacular outburst in 2016, exhibiting flux modulation with a period of 565 s, attributed to the rotation of a strongly magnetized white dwarf. This modulation continued in quiescence, implying that this binary appears to belong to a recently discovered group of "intermediate-polar-novae", in which the accretion disk is disrupted and accretion occurs directly to the pole. XMM-Newton X-ray spectra of V407 Lup are complex, with several components; one component is very hard and may be non-thermal in origin. V407 Lup may thus be also a new "white dwarf pulsar" in which the white dwarf accelerates electrons in the atmosphere of the companion star.
Proposal Number: 10243 PI Name: PRAGATI PRADHAN Title: TWO ACCRETION MODES, PROPELLER EFFECT AND CLUMPY WINDS: A RECIPE FOR EXTREME VARIABILITY IN GX 1+4 Abstract: We request 180 ks NuSTAR observations of GX 1+4 (20 ks per month over 9 months) with 2 ks simultaneous NICER data to unravel long-term X-ray variability in this unique neutron star hosting symbiotic X-ray binary, GX 1+4. The X-ray variability is hypothesized to be caused by onset of two accretion modes: quasi-spherical (small flares) and free-fall (large flares). Increased absorption during dips suggests clumps, while low luminosity phases hint at the propeller regime. Previous NICER/Chandra monitoring could not constrain the source's spin period. NuSTAR's large photon collecting area over broadband energies is vital for interpreting the physics of this enigmatic source that has puzzled the X-ray binary community since discovery.
Proposal Number: 10244 PI Name: NICOLE FORD Title: NUSTAR/NICER/EVENT HORIZON TELESCOPE STUDIES OF LOW LUMINOSITY AGNS: JETS AND ACCRETION Abstract: In the past four years, the Event Horizon Telescope (EHT) has assembled the first images of supermassive black holes (SMBHs) buried in the centers of galaxies. The successful radio and multi-wavelength (MW) imaging of M87 and SgrA* has paved the way for a new sample of active galactic nuclei (AGNs) targets. NGC 4594 (Sombrero galaxy/M104), IC 1459, NGC 3998, and NGC 4261 are among the very few AGNs that can be imaged at < 50 gravitational radii resolution. For this reason, these AGNs are all prime targets for EHT observations in 2025. We propose to observe up to two of these four systems with NuSTAR and NICER to complement EHT s 2025 campaign and investigate these AGNs' accretion, emission, and jet launching processes.
Proposal Number: 10245 PI Name: GUGLIELMO MASTROSERIO Title: SPECTRAL-POLARIMETRIC ANALYSIS DURING THE OUTBURST OF GX 339-4 Abstract: X-ray polarization has proven to be effective in constraining the orientation of the innermost regions of black hole binaries (BHBs). However, the IXPE telescope covers a very small energy range of 2-8 keV which does not allow us to properly distinguish among the different spectral components. It is crucial to combine the new polarimetric diagnostics with a proper separation of the different spectral components to relate each component with its polarisation measurements. NuSTAR observations are critical to perform this task. Thus, we propose to observe GX 339-4 with NuSTAR during the 3 IXPE exposures already scheduled for the hard, intermediate, and soft states. We request the minimum NuSTAR exposure 20~ks for each observation for a total of 60~ks which has already proven to be effective.
Proposal Number: 10246 PI Name: DANIEL LAWTHER Title: MAPPING OUT THE X-RAY SOURCE IN A CHANGING-LOOK AGN Abstract: After a decade of quiescence, the changing-look AGN Mrk 590 has been in a repeat flaring state since 2017. Its strong, coherent and delayed UV response to X-rays is inconsistent with standard models of the AGN central engine. Here, we propose deep NuSTAR and XMM-Newton observations to capture Mrk 590 during the peak of an X-ray flare. These observations will test whether hitherto undetected signatures of a thin accretion disk appear as the flares reach their highest luminosities. They also provide timing information with which we will measure the distances between the primary X-ray continuum (hot corona), soft X-ray excess, and reflection component. This will probe whether the primary X-ray continuum is emitted co-spatially with the warm Comptonization and UV-emitting regions.
Proposal Number: 10247 PI Name: SUDIP CHAKRABORTY Title: DECIPHERING THE COMPTONIZATION PROPERTIES OF NGC 2110 THROUGH SIMULTANEOUS X-RAY SPECTRO-POLARIMETRY Abstract: Through their place in the universality of Comptonization processes of accreting black hole systems, LLAGN signifies a crucial piece in the puzzle of non-thermal processes in the vicinity of SMBHs. However, to decipher the exact nature of the Comptonization processes, the mechanism behind the power-law spectral component and the geometry of the corona has to be understood well beyond the limitations of pure spectral/timing techniques. To shed light beyond the existing degeneracies in the $\tau$-$kT_{\rm e}$ space, we propose to look at spectro-polarimetric signatures in the X-ray band for the LLAGN NGC 2110. While the IXPE GO-cycle observation will shed light on the coronal geometry, our proposed simultaneous 50 ks NuSTAR observation will help constrain the Comptonization parameters.
Proposal Number: 10249 PI Name: SEAN PIKE Title: RAPID FOLLOW-UP OF UNKNOWN MAXI SOURCES NEAR THE SUN WITH NUSTAR Abstract: We propose rapid follow-up observations of up to 3 unknown MAXI X-ray transients which lie between 10 and 47 degrees of the Sun using NuSTAR in order to tile the corresponding MAXI error region, localize the source, and perform spectral analyses for the purpose of source classification. Sources near the Sun often go unobserved due to the limitations of many X-ray observatories. The ToO program we propose will ensure that observations are carried out for sources that would be unobservable to observatories other than NuSTAR. As demonstrated by a number of recent NuSTAR observations at low Sun angle, observations like this have the potential to help answer important astrophysical questions regarding the evolution of accretion disks throughout outbursts, the onset of jet formation, and more.
Proposal Number: 10251 PI Name: PETER KOSEC Title: PROBING THE RESPONSE OF AN ACCRETION DISK WIND TO X-RAY PULSATIONS Abstract: Her X-1 is a pulsar with a period of 1.24 s and an ionized accretion disk wind. We will leverage the ionization response of the wind to the X-ray pulsation to constrain the wind number density, in turn constraining its launching mechanism. We will combine the high-resolution Chandra gratings (50 ks exposure already approved in the previous proposal cycle, to be carried out in 2024) with the broad 3-79 keV spectral coverage of NuSTAR. NuSTAR is crucial to accurately track the time-variable broadband spectral energy distribution of Her X-1, allowing us to measure the wind ionizing balance at all times and thus its ionization state. We request two 20-ks NuSTAR observations to be carried out simultaneously with our Chandra exposure (likely to be split into two ~25-ks observations).
Proposal Number: 10254 PI Name: RANDALL ROJAS Title: EXPLORING THE TRAIN WRECK WITH NUSTAR: AN ANALYSIS OF ABELL 520 Abstract: Since the Big Bang, the most energetic events in the Universe are the merging of several galaxy clusters. These mergers drive shock fronts and turbulence that heat the gas and accelerate electrons, which result in X-ray and radio features. Shock fronts are often distinguishable because of features like surface brightness (SB) edges in the X-ray and radio relics. In rare cases, SB edges are associated with radio halos, like in Abell 520. NuSTAR's ability to probe hard X-ray energies can provide insights into the properties of these rare regions. NuSTAR's precision when measuring temperatures will allow for a precise measurement of the shock and it's ability to probe the high energy non-thermal regime will provide constraints on inverse Compton scattering that may be associated with it.
Proposal Number: 10256 PI Name: REED MASEK Title: PERFORMING MULTI-MESSENGER MEASUREMENTS OF MICROFLARE-ACCELERATED PARTICLES AND ASSOCIATED PHENOMENA Abstract: We will investigate how weakly energetic solar flares, known as microflares, accelerate particles, how the particles propagate away from the flare site, and how the particles interact with the rest of the heliosphere. Microflares are the least energetic flares currently observable in hard X-rays, and NuSTAR's high sensitivity makes it uniquely capable of directly observing emission from accelerated particles at the microflare site. Recently, Parker Solar Probe perihelia have provided excellent opportunities for the heliophysics community to coordinate with various radio, extreme ultraviolet, and X-ray instruments to co-observe the same region on the Sun.
Proposal Number: 10257 PI Name: AMRUTA JAODAND Title: CHASING THE X-RAY AFTERGLOWS OF GRAVITATIONAL-WAVE EVENTS Abstract: Many astrophysical questions regarding NS mergers still remain open. What fraction of them have central engines and how long do they operate? What is the maximum mass for a stable NS remnant? How much energy do mergers release? Do all mergers produce successful relativistic jets and short GRBs? Broadband X-ray observations (Using soft and hard X-ray observations) of diverse NS merger events (especially in conjunction with radio observations) will be able to answer many of these questions. In LIGO O4 we expect about 2--7 GW events with electromagnetic counterparts, and therefore arc-second localizations. NuSTAR's broadband coverage and ability to look close-to/at the Sun will crucial for following-up these neutron star gravitational wave mergers.
Proposal Number: 10259 PI Name: ANDREA GOKUS Title: INVESTIGATING THE BROADBAND X-RAY EMISSION OF NEW MEV BLAZAR CANDIDATES IDENTIFIED WITH EROSITA Abstract: Observations of high-redshift (z>3) blazars offer glimpses into the first ~1 billion years of our Universe and enable us to study black hole growth and its connection to galaxy evolution. Blazars make up the most powerful class of AGN and their high luminosities enable us to study them across cosmic distances. So far, not many sources have been studied since they generally appear faint and high quality data, especially at X-ray energies, requires large resources in the form of long observations. Using its all-sky survey capabilities, the X-ray instrument eROSITA has identified three new MeV blazar candidates (3
Proposal Number: 10260 PI Name: JAMES STEINER Title: SLIM-DISK SPECTRO-POLARIMETRY WITH LMC X-3 Abstract: We propose monitoring of LMC X-3 to accompany upcoming IXPE observations of this persistent soft black hole X-ray binary which ranges from a few percent Eddington to near its Eddington limit. Spectro-polarimetric data over this luminosity range allows assessment of slim-disk effects on the inner-disk geometry. At low luminosities, the thermal state of black holes in X-ray binaries is simple and stable, with a fixed inner-disk radius and low power-spectral rms variability. At high luminosities >~30% of the Eddington limit, slim-disk effects manifest as the disk scale-height grows. NuSTAR's sensitive high-energy coverage is critical in using spectro-polarimetry to map the inner-disk geometry vs. luminosity, and identify changes associated with a thickened disk profile.
Proposal Number: 10265 PI Name: GEORGE YOUNES Title: POST-OUTBURST X-RAY PROPERTIES OF THE MAGNETAR SGR 1935+2154 Abstract: SGR 1935+2154 is one of the most prolific burster within the magnetar family, as proven in the last few years when it emitted several burst storms during which hundreds of brusts are detected in the span of hours to days. The source also emitted several bright radio bursts during the active periods, one of which reminiscent of extragalactic FRBs, a remarkable discovery that has the potential to further our understanding of both phenomena. Here, we propose simultaneous 3x40ks NuSTAR and 3x20ks XMM-Newton monitoring campaign of SGR 1935+2154 to establish its current temporal and spectral properties post-outburst, during a seemingly quiet period, and how that compares to the quiescent state of the source established in 2014.
Proposal Number: 10267 PI Name: JON MILLER Title: TRIGGERED NUSTAR OBSERVATIONS OF SEYFERTS IN FAST OUTFLOW STATES Abstract: The combination of NuSTAR and XRISM has the potential to open new windows on ultra-fast outflows and feedback in AGN. NuSTAR is uniquely able to define the hard continuum that ionizes the Fe XXV and Fe XXVI lines that define most UFOs, while XRISM can reveal their velocity structure, driving mechanisms, and kinetic power. However, UFOs are known to be variable, and it is vital to observe the right sources at the right times. We propose to use hardness-intensity monitoring to trigger NuSTAR and XRISM observations of PG 1211+143 and Mrk 817. These sources optimize a combination of source flux and UFO strength, and may launch UFOs via distinct mechanisms. We request an 80 ks observation of PG 1211+143 and 100 ks observation of Mrk 817 during NuSTAR Cycle 10.
Proposal Number: 10268 PI Name: BENJAMIN COUGHENOUR Title: SPIN AND REFLECTION IN A BLACK HOLE TRANSIENT Abstract: We propose a joint 50 ks NuSTAR and 5 ks NICER ToO observation of a transient black hole (BH) X-ray binary during outburst. Using up to an additional 5 ks with NICER to monitor the source state, we will trigger the primary joint NuSTAR/NICER observation when the source transitions from the hard state to its intermediate state. The BH spin will be measured by modeling reflection signatures in the source spectrum, which will also constrain properties of the innermost accretion environment. Targets include sources that have not yet been observed by NuSTAR during outburst, whether that means an entirely new transient BH candidate or a previously known BH X-ray binary that has been in quiescence since the launch of NuSTAR (GRO J1655-40 or XTE J1550-564, e.g.).
Proposal Number: 10272 PI Name: EKATERINA SOKOLOVA-LAPA Title: MEASURING SURFACE MAGNETIC FIELDS OF NEUTRON STARS IN BE X-RAY BINARIES:\\ THE HIGH-ENERGY QUIESCENT EMISSION Abstract: X-ray observations of Be X-ray binaries in quiescence provide a unique opportunity to measure the surface magnetic field strength of accreting neutron stars directly from the X-ray spectra. The most recent advances in emission modeling and observations of sources with known fields indicated that the magnetic fields can be measured by describing the high-energy emission within 10% accuracy. We propose observations of three carefully selected galactic Be X-ray binaries with unknown magnetic fields, long spin periods, and poorly studied hard X-ray emission in quiescence. Our targets promise to noticeably extend the list of galactic BeXRBs with known magnetic fields,covering a broad range of spin periods and provide new insights into physics of accretion onto magnetized neutron stars.
Proposal Number: 10275 PI Name: GAYATHRI RAMAN Title: CHARCTERIZING THE PECULIAR FLARING BEHAVIOR IN 1A 0538-66 Abstract: We request a total of 60 ks (3x20 ks) near-periastron NuSTAR observations of 1A 0538-66. This pulsar, located in the LMC, belongs to a subset of Be X-ray pulsars that exhibit peculiar flares, characterized by short time scales (2 50 s) and complex spectral behavior. Despite being observed by several instruments during its outburst and quiescent phases, 1A 0538-66 has never been characterized beyond 10 keV. We, therefore, propose to carry out NuSTAR observations near the periastron with the following objectives: 1) To study the peculiar flaring behavior and monitor the variability properties, 2) to characterize the soft and hard spectral components of the flares 3) search for cyclotron absorption lines, and 4) confirm the presence of a 69 ms pulsation.
Proposal Number: 10279 PI Name: FRANCESCA CIVANO Title: THE NUSTAR VIEW OF THE X-RAY ABSORBER IN NGC 4945: A DECADE LATER Abstract: The nearby, bright Seyfert 2 galaxy NGC4945 has been studied by NuSTAR in 2013 with three 50 ks observations. The analysis of 2013 data showed that the nuclear hard X-ray emission is highly variable on timescales as short as 20 ks, and pierces through a Compton-thick absorbing medium with a column density of 2-4 x 10^24 cm^-2. We propose a 100 ks observation that will provide a new view into this source to study absorption variability on timescales as short as about 15 ks and up to 10 years. The analysis of the variability of the reflected component over long time scales and any variations in the density column of the absorbing medium will allow us to constrain the distance of the reflector/absorbing medium from the nucleus.
Proposal Number: 10281 PI Name: AAFIA ANSAR MOHIDEEN Title: FOLLOW-UP OF EROSITA HIGH MASS X-RAY BINARY CANDIDATES Abstract: We propose independent 60ks observations of three HMXB candidates discovered in the Spectrum-Roentgen-Gamma/eROSITA all-sky survey. Two candidates are persistent with a near-constant flux above 10^-12 erg/s, while the third shows variability consistent with HMXBs. The proposed observations are imperative in order to conduct detailed spectral and timing analysis of the candidates. The goal of this analysis would be to confirm their characterisation as X-ray binaries and to determine the nature of the compact object. This will increase the number of known low luminosity HMXBs and help subsequently probe their behaviour at low luminosities. We expect between 5000-10000 counts in the total exposure time proposed for, sufficient to conduct detailed studies to achieve the above.
Proposal Number: 10284 PI Name: JENNIFER SOKOLOSKI Title: DIRECT MASS MEASUREMENT OF THE NEAR-CHANDRASEKHAR WHITE DWARF IN SYMBIOTIC BINARY RT CRU Abstract: The X-ray emission from the accretion shock in RT Crucis (hereafter RT Cru) is harder than in any other symbiotic binary star, indicating that this system harbors one of the most massive white dwarfs (WDs). However, estimating the WD mass from the temperature of the X-ray emitting plasma is subject to systematic errors. The recently launched X-ray observatory, XRISM, with its microcalorimeter instrument, Resolve, has the potential to allow a direct measurement of the gravitational redshift on the WD surface, and hence the WD mass. Here we propose a coordinated NuSTAR observation to support such a direct measurement by providing an accurate characterization of the broad-band X-ray spectrum of RT Cru, and by providing a direct comparison with an X-ray continuum-based estimate of the WD mass.
Proposal Number: 10289 PI Name: DAVID TURNER Title: PRE-MERGING GALAXY CLUSTERS A399 & A401: USING 2D LENSING MASS MAPS, SZ, AND X-RAYS TO SEARCH FOR NON-THERMAL EMISSION Abstract: Galaxy clusters are powerful probes of astrophysics and cosmology. We have produced a set of individual 2D weak-lensing mass maps to probe the scatter of individual clusters from scaling relations. NuSTAR will search for non-thermal hard X-ray emission from a pair of massive interacting galaxy clusters, A401 and A399. Constraints will be placed on the Inverse-Compton flux, and we will develop a multi-wavelength method to use mass maps, SZ, and X-ray data to ascertain the hydrostatic bias and link it to the non-thermal emission. We will measure spatially resolved temperatures with NuSTAR, searching for temperature enhancement with its significant energy range, and compare to XMM maps. An XMM-NuSTAR Tx calibration will be measured using archival data, and our analyses will be open source.
Proposal Number: 10291 PI Name: JOOYUN WOO Title: A NEW HARD X-RAY VIEW OF TYCHO SUPERNOVA REMNANT AFTER 10 YEARS Abstract: The lack of emission above 10 TeV questions the young supernova remnants as PeV cosmic ray accelerators. However, Tycho SNR may develop local PeVatrons in the decelerating outer rim interacting with a dense environment. Multi-epoch Chandra observations unveiled year-scale variabilities of non-thermal X-ray filaments coincident with hard X-ray knots detected by NuSTAR in 2014. The proposed NuSTAR observations will yield a detailed hard X-ray variability map of Tycho for the first time and identify the most energetic CR acceleration sites. Spatially-resolved broadband X-ray spectra will allow us to trace the evolution of the hard X-ray knots over a decade and measure the maximum particle energies through synchrotron emission modeling and the latest diffusive shock acceleration theory.
Proposal Number: 10296 PI Name: CICELY POTTER Title: THE TEMPERATURE AND MASS OF ABELL 2204 AND 2142: COMPARING CHANDRA, XMM-NEWTON AND NUSTAR Abstract: Relaxed galaxy clusters can be assumed to be in Hydrostatic Equilibrium (HSE), meaning the mass can be calculated with the hydrostatic mass equation; this requires both the temperature and density profiles. X-ray telescopes are ideal for measuring the temperature of the Intracluster Medium, but different X-ray telescopes measure different temperatures for the same clusters; XMM-Newton temperatures are systematically lower than Chandra temperatures and this difference increases with cluster temperature. NuSTAR, being less susceptible to calibration issues and having a higher effective area at higher energies, is ideal for exploring this presumed calibration issue.
Proposal Number: 10302 PI Name: SARA BUSON Title: CONSTRAINING THE HADRONIC COMPONENT IN CANDIDATE NEUTRINO-EMITTER BLAZARS Abstract: We propose a pilot study to observe with NuSTAR and XMM-Newton a sample of blazars proposed as promising IceCube neutrino emitters. If these blazars originate neutrinos, they are powered by hadronic processes. The emission in the X-ray band has been shown to be the key to constraining the hadronic contribution to the spectral energy distribution (SED) in these sources. The NuSTAR spectra, along with XMM-Newton simultaneous observations, are the crucial missing information to model the broadband, simultaneous multi-wavelength SEDs of these blazars and compare the results with theoretical expectations in terms of neutrino production.
Proposal Number: 10303 PI Name: DANIEL WIK Title: EXTREME EMISSION IN ABELL 2219: HOT GAS AND INVERSE COMPTON CONSTRAINTS Abstract: The abundance of galaxy clusters is an important cosmological probe; however, hydrostatic masses are significantly below what's expected, hindering their usefulness for cosmology. We propose to observe the massive galaxy cluster Abell 2219 to investigate the heating mechanism at its NW shock front, which may shed light on a lack of thermalization of the gas, and to search for inverse Compton emission associated with its radio halo, which will constrain the magnetic field and inform possible non-thermal pressure support leading to underestimates of cluster mass. Conflicting ICM measurements of this cluster from Chandra and XMM derived maps will also be investigated in light of the broader cross-calibration temperature discrepancy between these observatories.
Proposal Number: 10306 PI Name: ROSS SILVER Title: DISCOVERING COMPTON-THICK AGN WITH A.I. Abstract: The X-ray spectral analysis of new Compton thick (CT-) active galactic nuclei (AGN) represents a fundamental step to understand the physics of the obscuring material surrounding accreting super-massive black holes. However, at the present day, CT-AGN remain extremely hard to detect. Implementing a previously successful machine learning algorithm, we propose to target 5 low-redshift candidate CT-AGN from the BAT 150-Month catalog for 20-35 ks of NuSTAR and 15-30 ks of XMM-Newton time each. This analysis will help determine the true intrinsic fraction of CT-AGN in the local universe and their contribution to the Cosmic X-ray Background (CXB).
Proposal Number: 10309 PI Name: OLUWASHINA ADEGOKE Title: PROBING OBSCURATION, DISK WINDS AND THEIR RELATIONSHIP WITH ACCRETION STATES IN BLACKHOLE X-RAY BINARIES Abstract: A few blackhole X-ray binaries (BHXRBs) show recurrent intensity dips in their light curves during outburst. These systems also always show indication of disk winds. The dips are believed to be caused by clumps of obscuring material passing along the line of sight to the X-ray source. Our knowledge of the origin of such obscurer, its composition and any relation with disk winds as well as spectral state is limited. Because soft X-ray photons are mostly absorbed by the obscuring material, NuSTAR's high energy capabilities make it the instrument of choice to study the nature of dips and obscuration in BHXRBs. NICER s high S/N also allows to probe the evolution of these features. We Therefore propose target of Opportunity observations with NuSTAR jointly with NICER to study these features.
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