We report on the spectral cross-calibration results of the Konus-Wind, the Suzaku/WAM, and the Swift/BAT instruments using simultaneously observed gamma-ray bursts (GRBs). This is the first attempt ...to use simultaneously observed GRBs as a spectral calibration source to understand systematic problems among the instruments. Based on these joint spectral fits, we find that (1) although a constant factor (a normalization factor) agrees within 20% among the instruments, the BAT constant factor shows a systematically smaller value by 10%–20% compared to that of Konus-Wind, (2) there is a systematic trend that the low-energy photon index becomes steeper by 0.1–0.2 and
$E_{\rm peak}$
becomes systematically higher by 10%–20% when including the BAT data in the joint fits, and (3) the high-energy photon index agrees within 0.2 among the instruments. Our results show that cross-calibration based on joint spectral analysis is an important step to understanding the instrumental effects that could be affecting the scientific results from the GRB prompt emission data.
We present the discovery and monitoring of the optical transient (OT) associated with GRB 020410. The fading OT was found by Hubble Space Telescope (HST) observations taken 28 and 65 days after burst ...at a position consistent with the X-ray afterglow, making this the first time that the optical afterglow of a gamma-ray burst (GRB) has been discovered by an orbiting observatory. Subsequent reexamination of early ground-based observations revealed that a faint OT was present 6 hr after burst, confirming the source association with GRB 020410. A deep nondetection after one week requires that the OT rebrightened between day 7 and day 28, and further late-time HST data taken approximately 100 days after burst imply that it is very red (F sub( upsilon ) proportional to upsilon super(-2.7)). We compare both the flux and color of the excess with supernova models and show that the data are best explained by the presence of a Type Ib/c supernova at a redshift z approximately 0.5, which occurred roughly coincident with the day of the GRB.
We report the simultaneous observations of the prompt emission in the gamma-ray and hard X-ray bands by the Swift BAT and the Konus-Wind instruments of the short-hard burst, GRB 060313. The ...observations reveal multiple peaks in both the gamma-ray and hard X-ray bands suggesting a highly variable outflow from the central explosion. We also describe the early-time observations of the X-ray and UV/optical afterglows by the Swift XRT and UVOT instruments. The combination of the X-ray and UV/optical observations provides the most comprehensive light curves to date of a short-hard burst at such an early epoch. The afterglows exhibit complex structure with different decay indices and flaring. This behavior can be explained by the combination of a structured jet, radiative loss of energy, and decreasing microphysics parameters occurring in a circumburst medium with densities varying by a factor of approximately two on a length scale of 10 super(17) cm. These density variations are normally associated with the environment of a massive star and inhomogeneities in its windy medium. However, the mean density of the observed medium (n610 super(4) cm super(3)) is much less than that expected for a massive star. Although the collapse of a massive star as the origin of GRB 060313 is unlikely, the merger of a compact binary also poses problems for explaining the behavior of this burst. Two possible suggestions for explaining this scenario are that some short bursts may arise from a mechanism that does not invoke the conventional compact binary model, or that soft late-time central engine activity is producing UV/optical but no X-ray flaring.
The double burst, GRB 110709B, triggered the Swift/Burst Alert Telescope (BAT) twice at 21:32:39 UT and 21:43:45 UT, respectively, on 2011 July 9. This is the first time we observed a gamma-ray burst ...(GRB) with two BAT triggers. In this paper, we present simultaneous Swift and Konus-WIND observations of this unusual GRB and its afterglow. If the two events originated from the same physical progenitor, their different time-dependent spectral evolution suggests they must belong to different episodes of the central engine, which may be a magnetar-to-BH accretion system.
Extended Tails from SGR 1806-20 Bursts Göǧüş, Ersin; Woods, Peter M; Kouveliotou, Chryssa ...
The Astrophysical journal,
10/2011, Volume:
740, Issue:
2
Journal Article
Peer reviewed
Open access
In 2004, SGR 1806-20 underwent a period of intense and long-lasting burst activity that included the giant flare of 2004 December 27--the most intense extra-solar transient event ever detected at ...Earth. During this active episode, we routinely monitored the source with Rossi X-ray Timing Explorer and occasionally with Chandra. During the course of these observations, we identified two relatively bright bursts observed with Konus-Wind in hard X-rays that were followed by extended X-ray tails or afterglows lasting hundreds to thousands of seconds. Here, we present detailed spectral and temporal analysis of these events observed about 6 and 1.5 months prior to the 2004 December 27 giant flare. We find that both X-ray tails are consistent with a cooling blackbody of constant radius. These spectral results are qualitatively similar to those of the burst afterglows recorded from SGR 1900+14 and recently from SGR 1550--5418. However, the latter two sources exhibit significant increase in their pulsed X-ray intensity following the burst, while we did not detect any significant changes in the rms pulsed amplitude during the SGR 1806-20 events. Moreover, we find that the fraction of energy partitioned to the burst (prompt energy release) and the tail (afterglow) differs by an order of magnitude between SGR 1900+14 and SGR 1806-20. We suggest that such differences can be attributed to differences in the crustal heating mechanism of these neutron stars combined with the geometry of the emitting areas.
EXTENDED TAILS FROM SGR 1806-20 BURSTS Goegues, Ersin; Kaneko, Yuki; Woods, Peter M. ...
The Astrophysical journal,
10/2011, Volume:
740, Issue:
2
Journal Article
Peer reviewed
In 2004, SGR 1806-20 underwent a period of intense and long-lasting burst activity that included the giant flare of 2004 December 27-the most intense extra-solar transient event ever detected at ...Earth. During this active episode, we routinely monitored the source with Rossi X-ray Timing Explorer and occasionally with Chandra. During the course of these observations, we identified two relatively bright bursts observed with Konus-Wind in hard X-rays that were followed by extended X-ray tails or afterglows lasting hundreds to thousands of seconds. Here, we present detailed spectral and temporal analysis of these events observed about 6 and 1.5 months prior to the 2004 December 27 giant flare. We find that both X-ray tails are consistent with a cooling blackbody of constant radius. These spectral results are qualitatively similar to those of the burst afterglows recorded from SGR 1900+14 and recently from SGR 1550-5418. However, the latter two sources exhibit significant increase in their pulsed X-ray intensity following the burst, while we did not detect any significant changes in the rms pulsed amplitude during the SGR 1806-20 events. Moreover, we find that the fraction of energy partitioned to the burst (prompt energy release) and the tail (afterglow) differs by an order of magnitude between SGR 1900+14 and SGR 1806-20. We suggest that such differences can be attributed to differences in the crustal heating mechanism of these neutron stars combined with the geometry of the emitting areas.
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