scispace - formally typeset
Search or ask a question
Author

C. Markwardt

Bio: C. Markwardt is an academic researcher. The author has contributed to research in topics: Gamma-ray burst & X-ray transient. The author has an hindex of 3, co-authored 27 publications receiving 64 citations.

Papers
More filters
01 Oct 2006
TL;DR: The Swift/Burst Alert Telescope (BAT) provides near real-time coverage of the X-ray sky in the energy range 15-50 keV with a detection sensitivity of 5.3 mCrab for a full-day observation and a time resolution as fine as 64 s as discussed by the authors.
Abstract: 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 For the new sources that are previously unpublished, we present basic data analysis and interpretations.

16 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: In this article, the authors presented a 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.
Abstract: 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

339 citations

Journal ArticleDOI
TL;DR: In this article, the afterglows and host galaxies of three short-duration gamma-ray bursts (GRBs): 100625A, 101219A, and 110112A were observed.
Abstract: 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.

204 citations

Journal ArticleDOI
TL;DR: In this article, the authors present observations of the afterglows and host galaxies of three short-duration gamma-ray bursts (GRBs): 100625A, 101219A and 110112A. The bursts have inferred circumburst densities of ~1e-4-1 cm^-3, and isotropic-equivalent gamma energy and kinetic energies of 1e50-1e51 erg.
Abstract: 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.

190 citations

Journal ArticleDOI
TL;DR: In this paper, the authors performed a monitoring campaign with Swift of four supergiant fast X-ray transients (SFXTs) (IGR J16479-4514, XTE J1739-302, IGR J17544-2619, and AX J1841).
Abstract: Supergiant fast X-ray transients (SFXTs) are a new class of high-mass X-ray binaries (HMXBs) discovered thanks to the monitoring of the Galactic plane performed with the INTEGRAL satellite in the last 5 years. These sources display short outbursts (significantly shorter than typical Be/X-ray binaries) with a peak luminosity of a few 1036 erg s−1. The quiescent level, measured only in a few sources, is around 1032 erg s−1. The X-ray spectral properties are reminiscent of those of accreting pulsars; thus, it is likely that all the members of the new class are indeed HMXBs hosting a neutron star, although only two SFXTs have a measured pulse period, IGR J11215–5952 (~187 s) and IGR J18410–0535 (~4.7 s). Several competing mechanisms have been proposed to explain the shortness of these outbursts, mostly involving the structure of the wind from the supergiant companion. To characterize the properties of these sources on timescales of months (e.g., the quiescent level and the outburst recurrence), we are performing a monitoring campaign with Swift of four SFXTs (IGR J16479–4514, XTE J1739–302, IGR J17544–2619, and AX J1841.0–0536/IGR J18410–0535). We report on the first 4 months of Swift observations, which started on 2007 October 26. We detect low-level X-ray activity in all four SFXTs, which demonstrates that these transient sources accrete matter even outside their outbursts. This fainter X-ray activity is composed of many flares with a large flux variability, on timescales of thousands of seconds. The light-curve variability is also evident on larger timescales of days, weeks, and months, with a dynamic range of more than 1 order of magnitude in all four SFXTs. The X-ray spectra are typically hard, with an average 2-10 keV luminosity during this monitoring of about 1033-1034 erg s−1. We detected pulsations from the pulsar AX J1841.0–0536/IGR J18410–0535, with a period of 4.7008 ± 0.0004 s. This monitoring demonstrates that these transients spend most of the time accreting matter, although at a much lower level (~100-1000 times lower) than during the bright outbursts, and that the "true quiescence," characterized by a soft spectrum and a luminosity of a few 1032 erg s−1, observed in the past in only a couple of members of this class, is probably a very rare state.

108 citations

Journal ArticleDOI
TL;DR: No emission lines are visible directly under the burst position, implying little ongoing star formation at the burst location, and Spectroscopy of the galaxy provides a redshift of z = 0.1218, the lowest redshift yet observed for a short GRB.
Abstract: 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.

107 citations