The Swift Gamma-Ray Burst Explorer performed its first autonomous, X-ray follow-up to a newly detected GRB on 2005 January 17, within 193 s of the burst trigger by the Swift Burst Alert Telescope. ...While the burst was still in progress, the X-Ray Telescope (XRT) obtained a position and an image for an uncataloged X-ray source simultaneously with the gamma-ray observation. The XRT observed flux during the prompt emission was 1.1 x 10 super(-8) ergs cm super(-2) s super(-1) in the 0.5-10 keV energy band. The emission in the X-ray band decreased by 3 orders of magnitude within 700 s, following the prompt emission. This is found to be consistent with the gamma-ray decay when extrapolated into the XRT energy band. During the following 6.3 hr, the XRT observed the afterglow in an automated sequence for an additional 947 s, until the burst became fully obscured by the Earth limb. A faint, extremely slowly decaying afterglow, a = -0.21, was detected. Finally, a break in the light curve occurred and the flux decayed with a < -1.2. The X-ray position triggered many follow-up observations: no optical afterglow could be confirmed, although a candidate was identified 3" from the XRT position.
The long gamma-ray burst (GRB) rate is essential for revealing the connection between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at high redshift provides a strong probe of ...star formation history in the early universe. While hundreds of GRBs are observed by Swift, it remains difficult to determine the intrinsic GRB rate due to the complex trigger algorithm of Swift. Current studies usually approximate the Swift trigger algorithm by a single detection threshold. However, unlike the previously flown GRB instruments, Swift has over 500 trigger criteria based on photon count rate and additional image threshold for localization. To investigate possible systematic biases and explore the intrinsic GRB properties, we developed a program that is capable of simulating all the rate trigger criteria and mimicking the image trigger threshold. We use this program to search for the intrinsic GRB rate. Our simulations show that adopting the complex trigger algorithm of Swift increases the detection rate of dim bursts. As a result, we find that either the GRB rate is much higher than previously expected at large redshift, or the luminosity evolution is non-negligible. We will discuss the best results of the GRB rate in our search, and their impact on the star-formation history.
Rapid searches for counterparts of GRB 930131 Schaefer, Bradley E.; Barthelmy, Scott D.; Palmer, David M. ...
Astrophysical journal/The Astrophysical journal,
02/1994, Volume:
422, Issue:
2
Journal Article
Peer reviewed
Open access
A fading counterpart to a gamma-ray burst (GRB) would appear as a point source inside a GRB error region soon after the burst which dims on a timescale from minutes to days. The favorable ...circumstances of the burst GRB 930131 allowed for an international campaign to search for fading counterparts starting 6.8 hr after the burst. We report observations from many optical sites, two radio telescopes, and archival ROSAT data, including deep Schmidt exposures 35, 44, and 64 hr after the burst. No fading counterparts were detected with our observations.
To date, the Burst Alert Telescope (BAT) onboard Swift has detected ~ 1000 gamma-ray bursts (GRBs), of which ~ 360 GRBs have redshift measurements, ranging from z = 0.03 to z = 9.38. We present the ...analyses of the BAT-detected GRBs for the past ~ 11 years up through GRB151027B. We report summaries of both the temporal and spectral analyses of the GRB characteristics using event data (i.e., data for each photon within approximately 250 s before and 950 s after the BAT trigger time), and discuss the instrumental sensitivity and selection effects of GRB detections. We also explore the GRB properties with redshift when possible. The result summaries and data products are available at http://swift.gsfc.nasa.gov/results/batgrbcat/index.html . In addition, we perform searches for GRB emissions before or after the event data using the BAT survey data. We estimate the false detection rate to be only one false detection in this sample. There are 15 ultra-long GRBs (~ 2% of the BAT GRBs) in this search with confirmed emission beyond ~ 1000 s of event data, and only two GRBs (GRB100316D and GRB101024A) with detections in the survey data prior to the starting of event data. (Some figures shown here are in lower resolution due to the size limit on arXiv. The full resolution version can be found at http://swift.gsfc.nasa.gov/results/batgrbcat/3rdBATcatalog.pdf )
The unique capability of the Swift satellite to perform a prompt and autonomous slew to a newly detected gamma-ray burst (GRB) has yielded the discovery of interesting new properties of GRB X-ray ...afterglows, such as the steep early light-curve decay and the frequent presence of flares detected up to a few hours after the GRB trigger. We present observations of GRB 050607, the fourth case of a GRB discovered by Swift with flares superimposed on the overall fading X-ray afterglow. The flares of GRB 050607 were not symmetric as in previously reported cases, showing a very steep rise and a shallower decay, similar to the fast rise, exponential decay that are frequently observed in the gamma-ray prompt emission. The brighter flare had a flux increase by a factor of 625, peaking for 30 s at a count rate of approximately 30 counts s super(-1), and it presented hints of additional short-timescale activity during the decay phase. There is evidence of spectral evolution during the flares. In particular, at the onset of the flares the observed emission was harder, with a gradual softening as each flare decayed. The very short timescale and the spectral variability during the flaring activity are indicators of possible extended periods of energy emission by the GRB central engine. The flares were followed by a phase of shallow decay, during which the forward shock was being refreshed by a long-lived central engine or by shells of lower Lorentz factors, and by a steepening after approximately 12 ks to a decay slope considered typical of X-ray afterglows.
The Burst Alert Telescope (BAT) onboard the Swift gamma-ray burst explorer has a coded aperture mask and a detector array of 32 K CdZnTe semiconductor devices. Due to the small mobility and short ...lifetime of carriers, the electron-hole pairs generated by gamma-ray irradiation cannot be fully collected. Hence the shape of the measured spectra has a broad low-energy tail. We have developed a method to model the spectral response by taking into account the charge transport properties which depend on the depth of the photon interaction . The mobility-lifetime products for detectors derived from our method vary by more than one order of magnitude among detectors. In this paper, we focus on the nonuniformity of the mobility at the millimeter scale by employing a scanning experiment for a single detector. We reveal almost an order of magnitude variance in the mobility-lifetime product of holes within a single detector, while those of electrons remains fairly uniform.
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