摘要:

Orbital period changes are an important diagnostic for understanding low mass X‐ray binary (LMXB) accretion‐induced angular momentum exchange and overall system evolution. We present our most recent results for the eclipse timing of the LMXB EXO0748‐676. Since its discovery in 1985 it has apparently undergone three distinct orbital period “epochs”, each characterized by a different orbital period than the previous epoch. We outline the orbital period behavior for EXO0748‐676 over the past 18 years and discuss the implications of this behavior in light of current theoretical ideas for LMXB evolution. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781061

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Timing capabilities of the current and future X‐ray astronomy satellites in Japan are reviewed. Stresses are put on the two programs, Astro‐E2 and NeXT, and some other programs are also mentioned. Astro‐E2 is developed under the Japan‐US collaboration, and is scheduled to be launched in February, 2005. Astro‐E2 is basically a spectroscopic mission, and its timing capability of the focal‐plane detectors is rather limited. However, the non‐imaging, hard X‐ray detector can provide a good time resolution. Astro‐E2 will be followed by the NeXT satellite, which we plan to launch around 2010. NeXT is characterized by the direct imaging capability up to ∼80 keV. Its timing capability is also limited, but may be good for some kind of timing observations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781062

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The Rossi X‐ray Timing Explorer (RXTE) has demonstrated that the dynamical variation of the X‐ray emission from accreting neutron stars and stellar mass black holes is a powerful probe of their strong gravitational fields. At the same time, the X‐ray burst oscillations at the neutron star spin frequency have been used to set important constraints on the mass and radius of neutron stars, hence on the equation of state of their high density cores. The X‐ray Evolving Universe Spectroscopy mission (XEUS), the potential follow‐on mission to XMM‐Newton, will have a mirror aperture more than ten times larger than the effective area of the RXTE proportional counter array (PCA). Combined with a small dedicated fast X‐ray timing detector in the focal plane (XTRA: XEUS Timing for Relativistic Astrophysics), this collecting area will provide a leap in timing sensitivity by more than one order of magnitude over the PCA for bright sources, and will open a brand new window on faint X‐ray sources, owing to the negligible detector background. The use of advanced Silicon drift chambers will further improve the energy resolution by a factor of ∼ 6 over the PCA, so that spectroscopic diagnostics of the strong field region, such as the relativistically broadened Iron line, will become exploitable. By combining fast X‐ray timing and spectroscopy, XTRA will thus provide the first real opportunity to test general relativity in the strong gravity field regime and to constrain with unprecedented accuracy the equation of state of matter at supranuclear density. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781063

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The Energetic X‐ray Timing Survey Telescope (EXIST) mission concept is under study as the Black Hole Finder Probe (BHFP), one of the three Einstein Probe missions in the Beyond Einstein Program in the current NASA Strategic Plan. EXIST would conduct an all‐sky imaging hard X‐ray (∼10–600 keV) survey with unprecedented sensitivity: about 5 × 10−13cgs over any factor of 2 bandwidth, or comparable to that achieved at soft X‐rays in the ROSAT survey. The proposed angular resolution of 5arcmin, temporal resolution of 10microsec, energy resolution of 1–4 keV over the broad band, and duty cycle of 0.2–0.5 for continuous coverage of any source provide an unprecedented phase space for timing and spectral studies of black holes —from stellar to supermassive, as well as neutron stars and accreting white dwarfs. The large sky coverage allows intrinsically rare events to be studied. One particularly exciting example is the possible detection of tidal disruption of stars near quiescent AGN. Super flares from SGRs could be detected out to the Virgo cluster. The large duty cycle and all sky monitor nature of the mission will enable QPOs from luminous AGN and BH X‐ray binaries to be studied on timescales not possible before. I provide an overview of the mission concept and Reference Design, the X‐ray timing science prospects for EXIST, and how these might be further optimized in the current Study for EXIST as the BHFP so that EXIST might include many of the desirable features of a next‐generation timing mission. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781064

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The great success of the Rossi X‐Ray Timing Explorer (RXTE) has shown that X‐ray timing is an excellent tool for study of the physics of strong gravitational fields and for measurement of fundamental physical properties of black holes and neutron stars. In order to provide a qualitative advance in X‐ray timing capabilities, the next generation X‐ray timing mission will require an effective area near 10 square meters with sensitivity extending into the hard X‐ray band an order of magnitude increase in effective area over RXTE. Achieving such a large effective area at reasonable cost will require advances in detector technology. Silicon‐based detectors have a long heritage in space applications and can be fabricated in the large numbers needed for a large area detector by industry with existing facilities and at reasonable cost. I describe current work on the development of silicon‐based detectors suitable for a next generation X‐ray timing mission. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781065

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The next generation X‐ray timing observatory will be a more powerful and versatile facility if it is based upon focusing optics rather than large area detectors. With X‐ray CCDs or active pixel detectors (or possibly even microcalorimeters) in the focal plane(s) the spectral resolution will be significantly superior to the RXTE PCA making it possible to study the dynamics of the gravitationally redshifted Fe line in great detail. With orders of magnitude reduction of background the ability to study temporal variations of fainter sources in external galaxies will be much greater than with large area counters of the same collecting area. Furthermore, source confusion will not be an issue as it may be when large area detectors observe sources near the galactic center or in other galaxies. Focusing detectors do require larger open apertures than counters and their bandwidth is smaller. However, they are not necessarily heavier and in fact one candidate optic would be much lighter. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781066

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We report on progress in developing thick silicon detectors for X‐ray and gamma‐ray astronomy. Silicon detectors offer good spectroscopy at reasonably low cost and with low internal background in the energy range between 5–50 keV. This technology offers a smooth energy response and a very fast timing response for high rate applications. We are testing large area, double‐sided 2mm thick detectors for applications requiring large quantities of silicon. Our current laboratory prototypes are 63 × 63 mm in area, and we will soon have detectors that are 95×95 mm in area and with thicknesses up to 3 mm. As part of our prototyping efforts, we are developing double‐sided strip detectors, pixel detectors, as well as hybrid pixel/strip detectors. We present our latest laboratory results in terms of imaging and spectroscopy, as well as our progress in developing and integrating custom readout ASICs. These detectors and electronics, while not a perfect match for a next generation X‐ray timing mission, form a good basis for the design of dedicated large area detectors in the 5–50 keV energy range. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781067

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Very lightweight X‐ray optics are being developed by ESA and its industrial partners, for a number of X‐ray astronomy and planetary missions. These developments could significantly improve the performance of future X‐ray timing instrumentation. Based on Micro‐Channel Plates (MCPs), the novel optics effectively reduce the mirror thickness by almost two orders of magnitude, and therefore also the mass of the telescope optics. Very large collecting areas become feasible for space implementation, especially as required for X‐ray timing observations. Furthermore this technology leads to much reduced detector sizes due to the use of imaging X‐ray optics. This dramatically improves the detected signal‐to‐noise ratios, as well as introducing photon collection areas sufficiently large as to study temporal phenomona on the millisecond time scale. This is particularly important to improve the studies of compact X‐ray sources, both for improving the signal:noise ratios in temporal bins so that spectral or fluctuation analyses are improved, and for extending the range of measurements to fainter classes of objects.We present a brief overview of the MCP optics technology, and some basic design rules relevant to such systems. The performance of such optics and some possible mission implementations will be discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781068

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

“QVD” detectors are based on thermoelectric heat‐to‐voltage (Q→V) conversion and digital (V→D) readout. For spectroscopic applications, the theoretical performance limits are competitive with superconducting tunnel junction (STJ) detectors and transition edge sensor (TES) devices. We discuss theoretical and demonstrated timing performance of QVD detectors with different design architectures. Detectors with lanthanum‐cerium hexaboride sensors can be very fast, up to 100 MHz/pixel counting rates. They can serve as focal plane detectors for X‐ray timing, in situations where very large apertures are used to gather X‐ray photons at high event rates. Practical implementation of thermoelectric (QVD) detectors requires cryogenic thermoelectric sensors with high figures of merit. There can be different solutions: thin films, bulk materials and “whiskers.” We are exploring all three design options and summarize progress in each area. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781069

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The next generation of X‐ray monitoring missions should include detectors sensitive to X‐rays with energies below 2 keV. This capability will allow us to explore the physics associated with soft sources, including hot white dwarfs, intermediate‐mass black holes, soft active galactic nuclei, soft emission in &ggr;‐ray burst afterglows, and many X‐ray active stars. I also show, usingChandradata from 4 galaxies, that more than half of the photons from even so‐called “canonical” X‐ray sources (with strong emission signatures above 2 keV) have energies below 2 keV. This suggests that soft‐X‐ray monitoring can open new doors to our understanding of even well‐studied sources. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1781070

出版商:AIP    

年代:1904

数据来源: AIP