Search

With the Swift detection of GRB090423 at z = 8.2, it was confirmed that GRBs are now detectable at (significantly) larger redshifts than AGN, and so can indeed be used as probes of the Early Universe. The Energetic X-ray Imaging Survey Telescope (EXIST) mission has been designed to detect and promptly measure redshifts and both soft X-ray (0.1-10 keV) and simultaneous nUV-nIR (0.3-2.3 microns) imaging and spectra for GRBs out to redshifts z∼18, which encompasses (or even exceeds) current estimates for Pop III stars that are expected to be massive and possibly GRB sources. Scaling from Swift for the ∼10X greater sensitivity of EXIST, more than 100 GRBs at z>= 8 may be detected and would provide direct constraints on the formation and evolution of the first stars and galaxies. For GRBs at redshifts z>= 8, with Lyman breaks at greater than 1.12 microns, spectra at resolution R = 30 or R = 3000 for afterglows with AB magnitudes brighter than 24 or 20 (respectively) within ∼3000 sec of trigger will directly probe the Epoch of Reionization, formation of galaxies, and cosmic star formation rate. The proposed EXIST mission can probe these questions, and many others, given its unparalleled combination of sensitivity and spatial-spectral-temporal coverage and resolution. Here we provide an overview of the key science objectives for GRBs as probes of the early Universe and of extreme physics, and the mission plan and technical readiness to bring this to EXIST. [ABSTRACT FROM AUTHOR]

The Energetic X-ray Imaging Survey Telescope (EXIST) mission concept was selected for further study under the Astrophysics Strategic Mission Concept Study (ASMCS) program. The mission design is optimized for study of high-z GRBs as probes of the early Universe. With a 4.5 m2 imaging 5–600 keV (CZT) detector imaging a 90°×70° (>10% coding fraction) field of view with 2’ resolution and <20” (90% conf.) positions for >5σ sources, EXIST will perform rapid (<200 sec) slews onto GRBs and obtain prompt images and spectra with a co-aligned soft X-ray telescope 0.1–10 keV) and with a 1.1 m optical-IR telescope (IRT) simultaneously in 4 bands (0.3–0.52 μm, 0.52–0.9 μm, 0.9–1.38 μm, and 1.38–2.3 μm) for prompt identification (by dropouts or variability) of the GRB within a 3.75×4.25’ FoV. An autonomous spacecraft re-point (<2’) will then (at ∼300 sec after GRB trigger) put the GRB on a 0.2×10” slit for either R = 3000 (for AB <21) or R = 30 (for AB ∼21–25) prompt spectra over the 0.3–0.9 μm and 0.9–2.3 μm bands. This will provide onboard redshifts within ∼500–2000 sec for most GRBs, reaching z ∼20 (for Lyman-α breaks) if such GRBs exist, and spectra for studies of the host galaxy and local re-ionization bubble as well as intervening cosmic structure. With ∼600 GRBs/yr expected, EXIST will open a new era in studies of the early Universe as well as carry out a rich program of AGN and transient-source science. An overview of the GRB science objectives and a brief discussion of the overall mission design and operations is given, and example high-z GRB spectra are shown. EXIST is being proposed to the Astro2010 Decadal Survey as a Medium Class mission that could be launched as early as 2017. [ABSTRACT FROM AUTHOR]

In recent years, X-ray observations with Chandra and XMM-Newton have significantly increased our understanding of rotation-powered (radio) millisecond pulsars (MSPs). Deep Chandra studies of several globular clusters have detected X-ray counterparts to a host of MSPs, including 19 in 47 Tuc alone. These surveys have revealed that most MSPs exhibit thermal emission from their heated magnetic polar caps. Realistic models of this thermal X-ray emission have provided important insight into the basic physics of pulsars and neutron stars. In addition, intrabinary shock X-ray radiation observed in “black-widow” and peculiar globular cluster “exchanged” binary MSPs give interesting insight into MSP winds and relativistic shock. Thus, the X-ray band contains valuable information regarding the basic properties of MSPs that are not accesible by radio timing observations. [ABSTRACT FROM AUTHOR]

Dwarf novae (DNe) are a subclass of Cataclysmic Variables (CVs) with outbursts powered by a disk instability leading to a sudden increase in the accretion rate. The Digital Access to a Sky Century at Harvard (DASCH) Collaboration is preparing to digitize over 500,000 Harvard plates from the 1880s to the 1980s with limiting magnitudes ranging from B∼14–19. As a demonstration project, we have scanned more than 500 plates in the fields centered on the galactic open cluster M44. There are 21 CVs in the fields within 10 degrees of M44 covered by the scans. Here we present the preliminary results of DN outbursts of the known CVs to derive long-term DN outburst duty cycles. In addition, a 100y lightcurve for a XMM–Newton source is also presented to demonstrate DASCH capabilities. [ABSTRACT FROM AUTHOR]

The synergy of GLAST and the proposed EXIST mission as the Black Hole Finder Probe in the Beyond Einstein Program is remarkable. With its full-sky per orbit hard X-ray imaging (3–600 keV) and “nuFnu” sensitivity comparable to GLAST, EXIST could measure variability and spectra of Blazars in the hard X-ray synchrotron component simultaneous with GLAST (∼10–100GeV) measures of the inverse Compton component, thereby uniquely constraining intrinsic source spectra and allowing measured high energy spectral breaks to measure the cosmic diffuse extra-galactic background light (EBL) by determining the intervening diffuse IR photon field required to yield the observed break from photon-photon absorption. Such studies also constrain the physics of jets (and parameters and indeed the validity of SSC models) and the origin of the >100 MeV gamma-ray diffuse background likely arising from Blazars and jet-dominated sources. An overview of the EXIST mission, which could fly in the GLAST ere, is given together with a synopsis of other key synergies of GLAST-EXIST science. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The exhilerating results from Swift in its first year of operations have opened a new era of exploration of the high energy universe. The surge to higher redshifts of the Gamma-ray bursts now imaged with increased sensitivity establishes them as viable cosmic probes of the early universe. Wide-field coded aperture imaging with solid-state pixel detectors (Cd-Zn-Te) has been also established as the optimum approach for GRB discovery and location as well as to conduct sensitive full-sky hard X-ray sky surveys. I outline the current and future major science questions likely to dominate the post-Swift era for GRBs and several related disciplines and the mission requirements to tackle these. The EXIST mission, under study for NASA’s Black Hole Finder Probe (BHFP) in the Beyond Einstein Program, could achieve these objectives as the Next Generation GRB Mission with ‘ultimate’ sensitivity and wide-field survey capability. Analysis tools for processing Swift/BAT slew data are under development at CfA and will both test EXIST scanning imaging and provide new data on GRBs and transients. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Our deep Chandra exposures of 47Tuc and moderate exposures of NGC 6397 reveal a wealth of new phenomena for interacting X-ray binaries (IXBs) in globular clusters. In this (late) Review, updated since the conference, I summarize recent and ongoing analysis of the millisecond pulsars, the compact binaries containing white dwarfs and neutron stars, and the chromospherically active binaries in both globular clusters. Spectral variability analysis enables new insights into source properties and evolutionary history. These binary populations, now so “easily” visible, are large enough that their properties and spatial distributions reveal new hints of compact object formation and binary interactions with their parent cluster. Neutron stars appear overabundant, relative to white dwarfs, in 47Tuc vs. NGC 6397. The IXBs containing neutron stars (i.e., MSPs and qLMXBs), as the most massive and ancient compact binary sample, may trace the protocluster disk in 47Tuc, whereas compact binaries may have been ejected preferentially along the cluster rotation equator during the recent core collapse in NGC 6397. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

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 × 10-13 cgs 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 [ABSTRACT FROM AUTHOR]

We have been conducting the Chandra Multi-wavelength Plane Survey (ChaMPlane) for the last decade. ChaMPlane is designed to survey the point X-ray sources discovered by the Chandra X-ray Observatory in the galactic plane in order to constrain the X-ray binary population in the Galaxy. This survey includes the data from the Chandra achieve, and the optical and infrared images and spectroscopes we obtained. So far we have observed 74 ChaMPlane fields which cover about 25 square degrees and 295 ACIS observations in the galactic plane (AO1-10). This paper reports our findings towards the Galactic Center. [ABSTRACT FROM AUTHOR]