XMM-NEWTON GUEST OBSERVER PROGRAM MISSION DESCRIPTION
1. OVERVIEWXMM-Newton, the X-ray Multi-mirror Mission, is the second cornerstone of the Horizon 2000 program of the European Space Agency (ESA). It was launched by ESA on 10 December 1999 on an Ariane 5 rocket from Kourou, French Guiana. The observatory consists of three coaligned high-throughput 7.5m focal length telescopes with 6" FWHM (15" HPD) angular resolution. XMM-Newton provides images over a 30 arc minute field of view with moderate spectral resolution using the European Photon Imaging Camera (EPIC), which consists of one p-n CCD and two MOS CCD arrays. High-resolution spectral data (E/dE~300) are provided by the Reflection Grating Spectrometer (RGS) that deflects half of the beam on two of the X-ray telescopes (those with the MOS CCDs). The observatory also has a coaligned 30cm optical/UV telescope called the Optical Monitor (OM). More detailed information on the instruments can be found in the XMM-Newton Users' Handbook (GSFC or SOC sites).
Participation by U.S. astronomers in the XMM-Newton Guest-Observer (GO) program is welcomed, and is supported by a Guest Observer Facility (GOF) at the NASA/Goddard Space Flight Center (GSFC). The GOF will provide a clearing house for project-generated technical information and analysis software, as well as user and proposal support on the US side of the Atlantic.
XMM-Newton is designed specifically to investigate in detail the X-ray emission characteristics, i.e., the angular variation, spectra, and temporal variability of cosmic sources down to a limiting flux of order 1E-16 erg/(s cm2). With its high throughput and moderate angular resolution, XMM-Newton is extremely sensitive to low surface brightness X-ray emission. Some astronomical sources are prominent X-ray emitters, but are faint or even invisible in other parts of the electromagnetic spectrum. Therefore, high-quality X-ray observations of these objects are very important and cannot be replaced by data obtained through other observing techniques. Instead, X-ray observations supplement data from other wavebands, leading to a more complete picture of the universe. Other objects are bright not only in the X-ray, but also in other parts of the spectrum, e.g., the optical or UV. Due to internal reprocessing, some sources emit both X-rays and photons of other energies, but the optical or UV emission sometimes lags the X-ray light. Therefore, to further broaden the scope of the investigations, the Optical Monitor (OM) onboard XMM-Newton offers the possibility to simultaneously study the optical/UV properties of the observed X-ray sources. The basic characteristics of XMM-Newton's X-ray telescopes are a 6" (FWHM) point-spread function, a 30 arc minute field of view, spectroscopic resolution (E/dE) in the range from a few ten to several hundred, and a large effective area of 4650 cm2 (before detector efficiencies are considered).
2. Science PayloadX-ray observations can be conducted in different ways, depending on the scientific goals of the investigator. XMM-Newton has different science instruments, each of which has various operational modes so that the observations can be tuned the scientific need. The basic observing techniques are: imaging, spectroscopy, and photometry. In addition, with its Optical Monitor (an optical/UV telescope mounted parallel to the three X-ray telescopes), XMM-Newton performs another basic task: simultaneous optical observation.
2.1. ImagingXMM-Newton carries telescopes with CCD cameras in their focal surfaces which image the X-ray sky with very high sensitivity and good angular resolution. The EPIC CCDs are designed to exploit the full design range of the X-ray mirrors, 0.1-15 keV. They provide energy resolution at 6.5 keV of E/dE~50, and their positional resolution is sufficient to resolve the mirror performance of 6" FWHM (15" HEW). A variety of data collection modes are provided which trade imaging performance against timing resolution and maximum count rate. A selection of filters mounted on a wheel in front of each camera allows the rejection of long wavelength optical and UV radiation in such a way as to optimize the low energy response of the instrument.
Two of the EPIC instruments on XMM-Newton consist of Metal-Oxide-Silicon (MOS) technology, X-ray-sensitive CCD arrays. The third EPIC detector is a fully depleted p-n CCD. The combination of these detectors exploits the full design energy range of the X-ray mirrors with moderate energy resolution.
The MOS CCDs are front-illuminated 1024x768 pixel devices from EEV. The physical size of each pixel is 27pm, corresponding to 0.74 arc seconds on the sky. The CCDs are offset from one another to match the curvature of the focal plane.
The p-n camera consists of X-ray CCDs, with 6x2 chips on a single wafer. Thus, they are produced as one array and not assembled later, as in the case of the MOS camera. With 64x200 pixels per chip, the p-n camera offers a square field of view with a size similar to that of the 7 MOS chips. The chip array itself is embedded in an electronics board carrying the camera electronics.
2.2. X-ray SpectroscopyThe same X-ray CCD cameras that are used for imaging also register the energy of incoming X-ray photons. Therefore, radiation can also be analyzed with respect to its spectral characteristics within the XMM-Newton passband (from 0.1 to 15 keV energy). The spectral resolution of the CCDs is only moderate, and does not reveal the full complexity of many X-ray spectra. Therefore, XMM-Newton carries a different type of spectrometer, with much higher spectral resolution for very detailed studies in the 0.35 to 2.5 keV energy range, the so-called "Reflection Grating Spectrometer" (RGS).
Reflection Grating Spectrometers are included on two of the three XMM-Newton X-ray telescopes. These consist of Reflection Grating Assemblies (RGAs) and RGS Focal Cameras (RFCs). The RGS provides high spectral resolution (E/delta E from 200 to 800) X-ray spectroscopy over the energy range 0.35-2.5 keV (5-35 Å). The RGAs intercept about 50% of the X-rays passing through the mirrors. The reflected X-rays are directed onto linear arrays of 9 MOS chips forming the RFC.
The high throughput of the XMM-Newton telescopes allows the RGS to perform detailed measurements of emission and absorption features in a large variety of stellar, interstellar and extragalactic hot, ionized plasmas. Compared to previous missions, this greatly enhances the use of line diagnostics in understanding cosmic X-ray sources, and leads to the determination of chemical composition, ion and elemental abundances, and the electron temperature and density distributions.
2.3. TimingThe time of each photon's detection within the X-ray detector, in addition to the direction and energy, is registered. This allows observers to perform studies of the homogeneity or variability of X-ray sources over time by counting how many events were registered over short time intervals. Both the MOS and p-n EPIC detectors can be operated in a variety of modes to "tune" the instruments to the timing aspects of the sources (e.g, expected count rates and the period of temporal variation). Operating the OM in its fast mode, the arrival times of individual optical or UV photons can be registered in the same fashion, thus allowing for comparative timing studies.
2.4. Simultaneous Optical ObservationIt is a general goal of X-ray missions to detect and identify X-ray sources on the sky. XMM-Newton has the Optical Monitor (OM) onboard for contemporaneous X-ray and optical/UV observations. Both the X-ray telescopes and the OM are very sensitive and capable of detecting faint sources. However, since the pointing of satellites is not always perfectly accurate, it is sometimes difficult to determine unambiguously which X-ray emitting objects that might be visible on optical images of the sky have actually been observed. XMM-Newton has good X-ray imaging capabilities, with a width of the point-spread function's core of only 6". Together with good pointing reliability, this ensures that the X-ray and optical images are well-aligned, making it easy to identify sources in the field of view by comparing the images from the different instruments. The OM offers a variety of filters and includes two grisms for higher-resolution spectroscopy work.
3. OPERATIONThe XMM-Newton satellite is three-axis stabilized, and has only a modest requirement for absolute pointing accuracy (± 1 arc minutes). It was launched by an Ariane 5 and placed in a highly elliptical orbit (47.8 hour synchronous period, 7400 km perigee, 114000 km apogee) for a combination of scientific and operational reasons. The perigee is constrained by the requirement that the spacecraft shall not pass through the Earth's proton belt. (Such radiation will cause significant degradation to the CCD cameras, mainly by decreasing the CCD charge-transfer efficiency.) The length of the orbit allows for long, continuous exposures unaffected by Earth blockage. The orbit inclination (40 degrees) and azimuth allows for nearly continuous coverage from ground stations at Perth, Australia, and Kourou, French Guiana. Control of the XMM-Newton observatory will be through the Mission Operation Center (MOC) in Darmstadt, Germany.
3.1. Phases of OperationOriginally, the total available XMM-Newton time was subdivided into several categories, described below. At this point, Guest Observer Observing Time dominates the observing schedule, though some ToOs and calibration observations are included.
Commissioning: The commissioning phase, including outgassing of payload and spacecraft, in-orbit switch-on, and check-out is expected to last for about four weeks. During this period basic engineering checks on the system will also be performed.
Calibration and Performance Verification (Cal/PV): This time is allocated to a first characterization of the telescope and instruments, to determine sensitivities, etc. It is expected to last about 11-12 weeks.
Full Guaranteed Observing Time: During this phase 80% of the observatory time is set aside for the Principal Investigators (PIs), Telescope Scientist (TS), Project Scientist (PS) and Survey Scientist (SS) and the Observatory Team. The remaining 20% of the time are Mission Scientist (MS) and Observatory Time (10% each). This phase will last for three months and terminate approximately six months after launch.
Mixed Observing Time: During the second six month period of the first year in orbit, open time proposals will be interleaved with the guaranteed time observations such that, on the average, the time is split 50/50, with a linear run of the Guaranteed Time from 80% at the beginning to 20% at the end of the period. Observations as part of the XMM-Newton Guest Observer (GO) program will commence approximately six months after launch. Starting at that time, the GO share of the total observatory time will increase to 75%, at which it will stay for the remainder of the first 27 months in orbit. 5% of the available time is allocated as Observatory Time.
Full Guest Observer Observing Time: By early 2003 all Guaranteed Time observations will be completed. GO observations will then dominate the observing schedule with some ToOs and calibration observations included.
3.2. General OperationAlthough the approved implementation of the XMM-Newton mission was only for a duration of 27 months, and the expected lifetime was ca. 10 years, XMM-Newton has been operational for over 20 years.
4. PROPOSAL PREPARATION AND SUBMISSIONThe XMM-Newton proposal procedure for US Guest Observers is a two-step process. The first step is a science proposal submitted to ESA to request observing time. This entire process is handled completely by ESA. NASA, through the GSFC XMM-Newton GOF, provides only technical support and information for prospective GOs employed by US institutions. The second step (Stage II) is a funding proposal submitted to NASA by successful XMM-Newton GOs who are employed by US institutions.
4.1. Scientific ProposalsThe XMM-Newton Project Scientist will issue calls for proposals in "Announcements of Opportunity" (AOs) in regular intervals. AOs are for periods of approximately one year.
Policies concerning, e.g., duplication avoidance, proposal categories (GO, ToO), and target categories (stars, galaxies, AGNs etc.) are described in the AO documentation and the XRPS Users' Manual.
4.2. Budget ProposalsAfter the completion of the scientific review process by ESA and the announcement of the results, NASA will issue a call for budgets from the successful GOs who are employed by US institutions. This includes only Principal Investigators (PIs) with Category A or B targets. Only one budget proposal will be allowed for each accepted scientific proposal meeting the criteria. Communications concerning the budgets and budget proposals will only be with PIs. PIs with C targets which are observed may be eligible for funding; in these cases, the GOF will notify the PIs with further instructions.
A Peer Review panel selected by NASA in conjunction with the XMM-Newton GOF will be responsible for evaluating the budget proposals.
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