Concepts for Future High-Energy Astrophysics Missions

In July 2015, the High-Energy Large- and Medium-Class Space Missions in the 2020s Workshop was held in Chicago to provide input to NASA via its Program Assessment Groups (PAGs) regarding high-energy large mission concepts and probe class missions. The meeting included invited talks covering HEA-related large and medium-class mission concepts along with overviews of HEA science goals for the 2020s. The presentations at this workshop are available here, and included a number of these mission concepts (the notation '2015ChiWS' in the list below links to the pdf or ppt version of the presentation given at the workshop).

US-led (often with international partners) AdEPT: Advanced Energetic Pair Telescope, a concept for a pair production telescope for medium-energy gamma-ray polarimetry designed to achieve angular resolution within a factor of two of the pair production kinematics limit (~0.6 degrees at 70 MeV), continuum sensitivity comparable with the Fermi-LAT front detector, and minimum detectable polarization less than 10% for a 10 mCrab source in 1 Ms. AEGIS: Astrophysics Experiment for Grating and Imaging Spectroscopy, a concept for a high-throughput, high-resolution, moderate cost, soft X-ray spectrometer. APT: Advanced Pair Telescope [2015ChiWS]: a mission concept having 10 times the Fermi LAT geometry factor, with the primary science being to characterize dark matter by providing measurements of annihilation spectra and angular distributions of gamma-ray emission in the 3 - 500 GeV band. Arcus, a concept for an X-ray grating spectrometer mission to be placed into a high earth orbit, with a spectral resolution of > 2500 and an effective area of ~ 550 sq. cm at the critical O VII wavelength near 21 A, with an overall bandpass from 12 - 50 A (0.25 - 1.0 keV), enabling a wide range of science objectives, including determining the composition of minute interstellar dust grains, studying feedback from supermassive black holes, and exploring structure formation in galaxy clusters. This mission was selected for a MidEx Phase A concept study in August 2017. ASCOT: Advanced Scintillator Compton Telescope [2015ChiWS], a concept for a medium-energy gamma-ray mission covering the energy range from approximately 0.4 - 20 MeV to follow the success of the COMPTEL instrument on CGRO. AXIS: Advanced X-ray Imaging Satellite, a NASA Probe Mission Concept to be the premier high (less than 0.3 arcseconds) angular resolution X-ray mission of the mid-2020s, with a large effective area (4,000 sq cm at 1 keV and 1,000 sq cm at 6 keV) and CCD spectral resolution (150 eV at 6 keV). AXSIO: Advanced X-ray Spectroscopic Imaging Observatory, a concept for a broad-bandpass, high-sensitivity, high-resolution X-ray imaging spectroscopy mission. AXTAR: Advanced X-Ray Timing Array, a concept for a large collecting area X-ray timing mission to study black holes and neutron stars. BEST: Black Hole Evolution an Space-Time Observatory, a mission concept for deep hard X-ray imaging (5 - 70 keV) and broad-band X-ray polarimetry (2 - 70 keV). Black Hole Finder, a possible component of NASA's Physics of the Cosmos program, with 2 possible proposed implementations: CASTER: Coded Aperture Survey Telescope for Energetic Radiation. EXIST: Energetic X-Ray Imaging Survey Telescope. BHI: Black Hole Imager: an X-ray mission which will directly resolve the event horizons of black holes. EPE: Extreme Physics Explorer: a concept for a timing/spectroscopy mission that would use micro-channel plate optics (MCPO) to provide 4 m2 effective area focused to ~1 arc-min onto an X-ray calorimeter. EREXS: Epoch of Reionization Energetic X-ray Survey, a mission concept to study the birth and growth of the first black holes, as well as to perform a multiwavelength time domain astrophysics survey of a wide range of objects. EXIST: Energetic X-ray Imaging Survey Telescope, a hard X-ray (5-600 keV) imaging all-sky deep survey mission that will use a coded-mask high-energy telescope (HET) with imaging CZT detectors to image sources such as AGN, black hole transients, etc., in a 70 by 90 degree field of view with 2 arcminute resolution; an accompanying optical/IR telescope (OIT) will enable multiwavelength studies and prompt follow-up of gamma-ray bursts. Gen-X: The Generation X-Ray Mission, a large effective area (50 square meters at 1 keV, or 500 x Chandra) X-ray telescope to study the new frontier of astrophysics: the birth and evolution of the first stars, galaxies, and black holes in the early Universe. HEX-P: High-Energy X-ray Probe, a concept for a probe-class next-generation high-energy X-ray mission with broadband (0.1-200 keV) response and ~40 times the sensitivity of previous missions above 10 keV. IXPE: Imaging X-ray Polarimetry Explorer: a concept for a highly sensitive x-ray polarimeter with imaging capability sensitive enough to measure X-ray (linear) polarization for a broad range of cosmic sources, primarily those involving neutron stars, stellar black holes, and supermassive black holes (AGN). IXPE was one of 3 missions selected for a SMEX Phase A study in July 2015, and selected for launch in 2020 by NASA on January 3rd, 2017. ISS-Lobster: a concept for a low-cost, wide-field X-ray transient mission on the International Space Station, with 30 x higher sensitivity compared to BAT, ASM, MAXI, and designed for transient study of black holes, neutron Stars, GRBs, etc. ISS-TAO, the Transient Astrophysics Observer on the ISS, a proposed Explorer Mission of Opportunity (MoO) for a wide-field X-ray transient detector that would observe numerous transient events every year due to compact objects, e.g., gravitational wave counterparts, X-ray bursts, gamma-ray bursts, etc., that was approved by NASA in August 2017 for a concept study. The Lynx Space Telescope: a mission concept with a large gain in collecting area over Chandra and XMM-Newton, an angular resolution of half an arcsecond, and high-throughput spectroscopy over a large field of view (FOV). The Lynx mission concept study is being performed under the leadership of a community-selected Science and Technology Definition Team (STDT). It is anticipated that the 2020 Astrophysics Decadal Survey Committee will use this and other studies in formulating their recommendation for the priorities for large strategic missions of the future. Pharos: a concept for a rapid response mission to study the warm-hot intergalactic medium using GRBs as its probes, as well as to study the host galaxies of GRBs and the phyics of GRBs. PRAXyS: Polarimetry of Relativistic X-ray Sources, an X-ray polarimeter instrument optimized for observations of faint persistent sources using a time projection chamber approach to achieve the required high sensitivity, with a combination of high analyzing power and good quantum efficiency. PRAXyS was selected for a SMEX Phase A study in July 2015, but did not get selected for Phase B. SAHARA: Spectral Analysis with High Angular Resolution Astronomy, a mission concept for a soft X-ray optic with high spatial and spectral resolution over a wide field of view. SMART-X: Square Meter, Arcsecond Resolution X-ray Telescope, a mission concept for a 2.3 m2 effective area, 0.5 arcsecs angular resolution X-ray telescope, with a 5 arcmins FOV, 1 arcsec pixel size microcalorimeter, 22 arcmins FOV imager, and high-throughput gratings. STROBE-X, the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays mission, a concept for a NASA probe class (<$1B) observatory designed for X-ray timing and spectroscopy in the 0.2-30 keV band with a huge collecting area and good spectral resolution that builds on the heritage of NICER. TAP: Transient Astrophysics Probe, selected by NASA for an Astrophysics Probe Mission Concept Study in 2017, is a multi-instrument (wide-field X-ray and gamma-ray monitors, high-resolution sensitive X-ray telescope and a wide-field infrared telescope) platform sensitive to a broad variety of astrophysical phenomena across the entire sky, with rapid transient follow up with high sensitivity over a broad energy range. WhimEx: Warm-Hot Inter-Galactic Medium Explorer, a concept for a high-resolution (relection grating) spectrometer to study the WHIM, AGN outflows and many other classes of X-ray sources. WFXIS, the Wide-Field X-ray Imaging Spectrometer, a proposed mission to provide wide-field X-ray imaging spectroscopy with both high energy resolution (~ 5 eV) and high angular resolution (~ 10 arcsecs). WFXT: Wide-Field X-ray Telescope [ 2015ChiWS], a proposed mission with an effective area 15 times Chandra's at 1 keV which will perform surveys of the sky in the soft X-ray band (0.4-7 keV). Xenia: a Probe of Cosmic Chemical Evolution, a concept for a medium-size cosmology mission (with international collaborators) which will use gamma-ray bursts to probe the cosmic 'web', dark energy, dark matter, and clusters of galaxies. X-Ray Surveyor [2015ChiWS]: a mission concept with a large effective area and high angular resolution: i.e., compared to Chandra, 1-2 orders of magnitude gain in sensitivity and field of view (with sub-arcsecond imaging), and high-resolution spectroscopy for both point-like and extended sources, in the 0.2-10 keV band.

Multinational and International (often with US partners) A-STAR: All-Sky Transient Astrophysics Explorer, a mission concept to detect and locate X-ray transients (XRT's), likely including gravitational wave sources, TDE's, gamma-ray bursts, etc., using a wide-FOV coded mask instrument (Owl) to detect XRT's and a sensitive wide-field focussing soft X-ray instrument (Lobster) to obtain arcminute or better positions [Europe]. Athena, an X-ray observatory proposed as a concept for a large effective area mission for the ESA science program, incorporating a single telescope with a fixed focal length (12 m) and two interchangeable instruments in the focal plane, a wide-field imager (WFI) and an X-ray integral field unit (X-IFU), i.e., an X-ray calorimeter. On Nov 28th, 2013, ESA selected the science theme "The Hot and Energetic Universe" for its next large satellite mission (L2), and on Jun 27th, 2014, it selected Athena as the mission for this theme, with a target launch date of 2028 [ESA with possible NASA participation]. EDGE: Explorer of Diffuse emission and Gamma ray burst Explosions, a mission with a high (< 3 eV) spectral resolution wide field spectrometer (WFS), together with a wide (1.4-degree diameter) field imager (WFI), a very wide (1/4 of the sky) field monitor (WFM) and a gamma-ray burst detector (GRBD) [Europe]. eXTP, the enhanced X-ray Timing and Polarimetry mission, a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism by making simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond) with a suite of instruments [China, Europe: circa 2025]. FORCE: Focusing On Relativistic universe and Cosmic Evolution, a hard X-ray telescope with improvements over the previous NuSTAR and Hitomi telescopes [JAXA, mid-2020's]. GRAVITAS: General Relativistic Astrophysics Via Timing and Spectroscopy, a large (1.5 m2) effective area, moderate (125 eV) spectral resolution, high (100 µs) temporal resolution broad (0.1 - 10 keV) band X-ray mission targetted at studies of the Fe K line region at 6.4 keV in compact objects [Europe]. LISA: Laser Interferometer Space Antenna gravitational-wave observatory, a trio of satellites separated by 2.5 million km designed to detect and accurately measure low-frequency (10-4 - 10-1 Hz) gravitational waves as are expected to be produced by binary stars within our galaxy, binary supermassive black holes (SMBHs) in other galaxies, and extreme-mass-ratio inspirals and bursts produced by a stellar-mass compact object orbiting a SMBH. [ESA with possible NASA participation with a target launch date of 2034] LOFT: Large Observatory For X-ray Timing ( [2015ChiWS]), a mission intended to answer fundamental questions about the motion of matter orbiting close to the event horizon of a black hole, and the state of matter in neutron stars, using a highly capable 10 sq. meter broad-band (1 - 80 keV) X-ray telescope with 10 μs timing resolution [Europe]. MIRAX: Monitor e Imageador de Raios X, an X-ray transient mission.[Brazil] NHXM: New Hard X-ray Mission, a mission to do soft and hard (0.2-80 keV) X-ray imaging and polarimetry [Italy]. PheniX, a very-broad-band (1-200 keV) high spectral-resolution (<~ 0.5 keV) focussing X-ray telescope able to do Compton polarimetry for E > 50 keV, and a coded-mask all-sky monitor [Multi-national]. THESEUS: the Transient High Energy Sources and Early Universe Surveyor, a mission concept proposed in response to the ESA call for medium-size mission (M5) within the Cosmic Vision Programme, will have 1) wide and deep sky monitoring in a broad energy band (0.3 keV - 20 MeV); 2) focusing capabilities in the soft X-ray band providing large grasp and high angular resolution; and 3) on board near-IR capabilities for immediate transient identification and redshift determination. [ESA]. Tsubame, a micro-satellite designed to perform X-ray polarimetry on gamma-ray bursts [Japan]. XRISM, X-ray Imaging and Spectroscopy Mission, an approved mission with a target launch date in 2021 that will "recover" the science that was mostly not possible due to the early demise of Hitomi (Astro-H), and that will have a moderate-resolution large-FOV soft X-ray imager (SXT-I) and a high-resolution small-FOV microcalorimeter array (SXT-S) [JAXA, NASA. ESA]. XIPE: the X-ray Imaging Polarimetry Explorer, a mission to do cosmic polarimetry in the 2-10 keV band, as well as solar flare polarimetry in the 15-35 keV band and solar coronal spectroscopy in the 1.2-15 keV band. XIPE was selected by ESA in June 2015 to undergo a 2 years-long assessment phase in the context of the Cosmic Vision M4 competition [ESA].