We present the catalog of sources detected in the first 22 months of data from the hard X-ray survey (14-195 keV) conducted with the Burst Alert Telescope (BAT) coded mask imager on the Swift satellite The catalog contains 461 sources detected above the 48σ level with BAT High angular resolution X-ray data for every source from Swift-XRT or archival data have allowed associations to be made with known counterparts in other wavelength bands for over 97% of the detections, including the discovery of ~30 galaxies previously unknown as active galactic nuclei and several new Galactic sources A total of 266 of the sources are associated with Seyfert galaxies (median redshift z ~ 003) or blazars, with the majority of the remaining sources associated with X-ray binaries in our Galaxy This ongoing survey is the first uniform all-sky hard X-ray survey since HEAO-1 in 1977 Since the publication of the nine-month BAT survey we have increased the number of energy channels from four to eight and have substantially increased the number of sources with accurate average spectra The BAT 22 month catalog is the product of the most sensitive all-sky survey in the hard X-ray band, with a detection sensitivity (48σ) of 22 × 10–11 erg cm–2 s–1 (1 mCrab) over most of the sky in the 14-195 keV band

/pdf/the-22-month-swift-bat-all-sky-hard-x-ray-survey-1yy76yltx9.pdf

The 22 Month Swift-BAT All-Sky Hard X-ray Survey

We present observations of the afterglows and host galaxies of three short-duration gamma-ray bursts (GRBs): 100625A, 101219A, and 110112A. We find that GRB 100625A occurred in a z = 0.452 early-type galaxy with a stellar mass of ≈4.6 × 10^9 M_☉ and a stellar population age of ≈0.7 Gyr, and GRB 101219A originated in a star-forming galaxy at z = 0.718 with a stellar mass of ≈1.4 × 10^9 M_☉, a star formation rate of ≈16 M_☉ yr^(–1), and a stellar population age of ≈50 Myr. We also report the discovery of the optical afterglow of GRB 110112A, which lacks a coincident host galaxy to i ≳ 26 mag, and we cannot conclusively identify any field galaxy as a possible host. From afterglow modeling, the bursts have inferred circumburst densities of ≈10^(–4)-1 cm^(–3) and isotropic-equivalent gamma-ray and kinetic energies of ≈10^(50)-10^(51) erg. These three events highlight the diversity of galactic environments that host short GRBs. To quantify this diversity, we use the sample of 36 Swift short GRBs with robust associations to an environment (~1/2 of 68 short bursts detected by Swift to 2012 May) and classify bursts originating from four types of environments: late-type (≈50%), early-type (≈15%), inconclusive (≈20%), and "host-less" (lacking a coincident host galaxy to limits of ≳26 mag; ≈15%). To find likely ranges for the true late- and early-type fractions, we assign each of the host-less bursts to either the late- or early-type category using probabilistic arguments and consider the scenario that all hosts in the inconclusive category are early-type galaxies to set an upper bound on the early-type fraction. We calculate most likely ranges for the late- and early-type fractions of ≈60%-80% and ≈20%-40%, respectively. We find no clear trend between gamma-ray duration and host type. We also find no change to the fractions when excluding events recently claimed as possible contaminants from the long GRB/collapsar population. Our reported demographics are consistent with a short GRB rate driven by both stellar mass and star formation.

/pdf/demographics-of-the-galaxies-hosting-short-duration-gamma-2ikkoldwcy.pdf

Demographics of the galaxies hosting short-duration gamma-ray bursts

We present observations of the afterglows and host galaxies of three short-duration gamma-ray bursts (GRBs): 100625A, 101219A and 110112A. We find that GRB 100625A occurred in a z=0.452 early-type galaxy with a stellar mass of 4.6e9 M_Sun and a stellar population age of 0.7 Gyr, and GRB 101219A originated in a star-forming galaxy at z=0.718 with a stellar mass of 1.4e9 M_Sun, a star formation rate of 16 M_Sun yr^-1, and a stellar population age of 50 Myr. We also report the discovery of the optical afterglow of GRB 110112A, which lacks a coincident host galaxy to i>26 mag and we cannot conclusively identify any field galaxy as a possible host. The bursts have inferred circumburst densities of ~1e-4-1 cm^-3, and isotropic-equivalent gamma-ray and kinetic energies of 1e50-1e51 erg. These events highlight the diversity of galaxies that host short GRBs. To quantify this diversity, we use the sample of 36 Swift short GRBs with robust associations to an environment (~1/2 of 68 short bursts detected by Swift to May 2012) and classify them as follows: late-type (50%), early-type (15%), inconclusive (20%), and host-less (lacking a coincident host galaxy to limits of >26 mag; 15%). To find likely ranges for the true late- and early-type fractions, we assign each of the host-less bursts to the late- or early-type category using probabilistic arguments, and consider the scenario that all hosts in the inconclusive category are early-type galaxies to set an upper bound on the early-type fraction. The most likely ranges for the late- and early-type fractions are ~60-80% and ~20-40%, respectively. We find no clear trend between gamma-ray duration and host type, and no change to the fractions when excluding events recently claimed as possible contaminants from the long GRB/collapsar population. Our reported demographics are consistent with a short GRB rate driven by both stellar mass and star formation.

/pdf/demographics-of-the-galaxies-hosting-short-duration-gamma-u5bp76wg1b.pdf

Demographics of the Galaxies Hosting Short-duration Gamma-Ray Bursts

We present the discovery of short GRB 080905A, its optical afterglow and host galaxy. Initially discovered by Swift, our deep optical observations enabled the identification of a faint optical afterglow, and subsequently a face-on spiral host galaxy underlying the GRB position, with a chance alignment probability of <1 per cent. There is no supernova component present in the afterglow to deep limits. Spectroscopy of the galaxy provides a redshift of z = 0.1218, the lowest redshift yet observed for a short GRB. The GRB lies offset from the host galaxy centre by similar to 18.5 kpc, in the northern spiral arm which exhibits an older stellar population than the southern arm. No emission lines are visible directly under the burst position, implying little ongoing star formation at the burst location. These properties would naturally be explained were the progenitor of GRB 080905A a compact binary merger.

/pdf/discovery-of-the-afterglow-and-host-galaxy-of-the-low-2qjdc84z84.pdf

Discovery of the afterglow and host galaxy of the low-redshift short GRB 080905A

We present the discovery of short GRB 080905A, its optical afterglow and host galaxy. Initially discovered by Swift, our deep optical observations enabled the identification of a faint optical afterglow, and subsequently a face-on spiral host galaxy underlying the GRB position, with a chance alignment probability of <1%. There is no supernova component present in the afterglow to deep limits. Spectroscopy of the galaxy provides a redshift of z=0.1218, the lowest redshift yet observed for a short GRB. The GRB lies offset from the host galaxy centre by ~18.5 kpc, in the northern spiral arm which exhibits an older stellar population than the southern arm. No emission lines are visible directly under the burst position, implying little ongoing star formation at the burst location. These properties would naturally be explained were the progenitor of GRB 080905A a compact binary merger.

Discovery of the afterglow and host galaxy of the low redshift short GRB 080905A

The Swift/Burst Alert Telescope (BAT) hard X-ray transient monitor provides near real-time coverage of the X-ray sky in the energy range 15-50 keV. The BAT observes 88% of the sky each day with a detection sensitivity of 5.3 mCrab for a full-day observation and a time resolution as fine as 64 s. The three main purposes of the monitor are (1) the discovery of new transient X-ray sources, (2) the detection of outbursts or other changes in the flux of known X-ray sources, and (3) the generation of light curves of more than 900 sources spanning over eight years. The primary interface for the BAT transient monitor is a public Web site. Between 2005 February 12 and 2013 April 30, 245 sources have been detected in the monitor, 146 of them persistent and 99 detected only in outburst. Among these sources, 17 were previously unknown and were discovered in the transient monitor. In this paper, we discuss the methodology and the data processing and filtering for the BAT transient monitor and review its sensitivity and exposure. We provide a summary of the source detections and classify them according to the variability of their light curves. Finally, we review all new BAT monitor discoveries. For the new sources that are previously unpublished, we present basic data analysis and interpretations.

Announcement of the Swift/BAT Hard X-ray Transient Monitor

GRB 060908, Swift-BAT refined analysis.

Swift-BAT refined analysis of short GRB 071227.

GRB 061201, Swift-BAT refined analysis of the SHB.

GRB 051221: refined analysis of the Swift-BAT short hard burst.

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