The Remarkable Afterglow of GRB 061007: Implications for Optical Flashes and GRB Fireballs

Mundell, C. G.; Melandri, A.; Guidorzi, C.; Kobayashi, S.; Steele, I. A.; Malesani, D.; Amati, L.; D’Avanzo, P.; Bersier, D.; Gomboc, A.; Rol, E.; Bode, M. F.; Carter, D.; Mottram, C. J.; Monfardini, A.; Smith, R. J.; Malhotra, Sangeeta; Wang, J.; Bannister, N.; O’Brien, P. T.; Tanvir, N. R.

doi:10.1086/512605

Cited by 90 publications

(105 citation statements)

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“…[See the electronic edition of the Journal for a color version of this figure. ] to event and that all events should exhibit an X-ray plateau. However, there are few bursts-<10% of the 30 or so afterglow observations that began early and measured with high signal-tonoise ratio the tail of the prompt emission-that do not show early HR variation and do appear to show an afterglow-like component decaying as a power law after the prompt emission at t k100 s. The best example GRBs, namely, GRB 050717 (see also Krimm et al 2006), GRB 060105 (see also Tashiro et al 2007), and GRB 061007 (see also Mundell et al 2007;Schady et al 2007), are shown in Figure 7. These have especially bright and hard prompt emission with E peak k 500 keV (suggestive of high À) and hard X-ray emission detected beginning after t % 90 s with energy index % 1.…”

Section: Events With No Hardness Variationmentioning

confidence: 98%

X‐Ray Hardness Variations as an Internal/External Shock Diagnostic

Butler

Kocevski

2007

ApJ

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The early, highly time-variable X-ray emission immediately following gamma-ray bursts (GRBs) exhibits strong spectral variations that are unlike the temporally smoother emission that dominates after t $ 10 3 s. The ratio of hardchannel (1.3Y10.0 keV ) to soft-channel (0.3Y1.3 keV ) counts in the Swift X-ray telescope provides a new measure delineating the end time of this emission. We define T H as the time at which this transition takes place and measure for 59 events a range of transition times that spans 10 2 to 10 4 s, on average 5 times longer than the prompt T 90 duration observed in the gamma-ray band. It is very likely that the mysterious light-curve plateau phase and the later powerlaw temporal evolution, both of which typically occur at times greater than T H and hence exhibit very little hardness ratio evolution, are both produced by external shocking of the surrounding medium and not by the internal shocks thought responsible for the earlier emission. We use the apparent lack of spectral evolution to discriminate among proposed models for the plateau phase emission. We favor energy injection scenarios with a roughly linearly increasing input energy versus time for six well-sampled events with nearly flat light curves at t % 10 3 Y10 4 s. Also, using the transition time T H as the delineation between the GRB and afterglow emission, we calculate that the kinetic energy in the afterglow shock is typically a factor of 10 lower than that released in the GRB. Three very bright events suggest that this presents a missing X-ray flux problem rather than an efficiency problem for the conversion of kinetic energy into the GRB. Lack of hardness variations in these three events may be due to a very highly relativistic outflow or due to a very dense circumburst medium. There are a handful of rare cases of very late time t > 10 4 s hardness evolution, which may point to residual central engine activity at very late time.

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Section: Events With No Hardness Variationmentioning

confidence: 98%

X‐Ray Hardness Variations as an Internal/External Shock Diagnostic

Butler

Kocevski

2007

ApJ

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“…On the other hand, the color evolution of the afterglow of GRB 061126 (Perley et al 2008c) goes from redder to bluer, similar to the case of the very well sampled early afterglow of GRB 080319B Racusin et al 2008;Woźniak et al 2009). Several other afterglows show no early color changes at all, e.g., those of GRB 060418 and GRB 060607A (Molinari et al 2007;Nysewander et al 2009b) and GRB 061007 (Mundell et al 2007b;Schady et al 2007b).…”

Section: The Luminosity Distribution At Early Times: Diversity and CLmentioning

confidence: 99%

“…Finally, the derived very high extinction for GRB 060210 is unsure (see Appendix B.3 for more details), implying that the afterglow, which seems to show a standard (not rapid, like GRB 050904 and GRB 080319B) decay after a short plateau and peak, may be much less luminous. Excluding these special events, the early afterglow of GRB 061007 (Mundell et al 2007b;Schady et al 2007b) is the most luminous in the sample, although it decays rapidly. 68 Between 0.01 and 0.5 days, the afterglow of GRB 090313 is the most luminous, though we caution that so far, we have only an extensive GCN data set.…”

Section: Does An Upper Limit On the Forward Shock Luminosity Exist?mentioning

confidence: 99%

“…Eight afterglows (GRBs 080319B, 050904, 061007, 060210, 080810, 080721, 990123, and 080413B) are brighter than this cluster (albeit significantly, in some cases). Most of these are probably dominated by additional emission components at early times (see below), although the unbroken decay from very early times on in the case of GRB 061007 may speak against an additional component (Mundell et al 2007b;Schady et al 2007b). GRB 080721 is a similar case (Starling et al 2009).…”

Section: The Luminosity Distribution At Early Times: Diversity and CLmentioning

confidence: 99%

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THE AFTERGLOWS OFSWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFTANDSWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS

Канн

Klose

Zhang

et al. 2010

ApJ

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15131514 KANN ET AL.Vol. 720 ABSTRACT We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical highluminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.

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“…We finally note that there are several sources that exhibit optical light curves analogous to GRB 061121, that is, GRB 021004 (Uemura et al 2002), GRB 050525A (Klotz et al 2005;Blustin et al 2006), GRB 060117 (Jelínek et al 2006), GRB 060526 (Dai et al 2007), and GRB 061007 (Mundell et al 2007). For all of them, an early decay phase was terminated by a flattening or a hump at 10 2−4 s, which was followed by a steeper decay phase.…”

Section: Implication To the Synchrotron-shock Modelmentioning

confidence: 83%

Optical behavior of GRB 061121 around its X-Ray shallow decay phase

Uehara

Uemura

Arai

et al. 2011

A&A

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Aims. We report on a detailed study of the optical afterglow of GRB 061121 with our original time-series photometric data. Along with our optical observations and public X-ray data, we discuss the origin of its optical and X-ray afterglows. Methods. We observed the optical afterglow of Swift burst GRB 061121 with the Kanata 1.5-m telescope at Higashi-Hiroshima Observatory. Our observation covers a period just after an X-ray plateau phase. We also performed deep imaging with the Subaru telescope in 2010 in order to estimate the contamination by the host galaxy. Results. In the light curve, we find that the optical afterglow also exhibited a break as in the X-ray afterglow. However, our observation suggests a possible hump structure or a flattening period before the optical break in the light curve. There is no sign of such a hump in the X-ray light curve. Conclusions. This implies that the optical emitting region was distinct from the X-ray one. The hump in the optical light curve was possibly caused by a passage with the typical frequency of synchrotron emission from another forward shock distinct from the early afterglow. The observed decay and spectral indices are inconsistent with the standard synchrotron-shock model. As a results, the observation requires a change in microphysical parameters in the shock region or prior activity by the central engine. Alternatively, the emission during the shallow decay phase may be a composition of two forward shock emissions, as indicated by the hump structure in the light curve.

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The Remarkable Afterglow of GRB 061007: Implications for Optical Flashes and GRB Fireballs

Cited by 90 publications

References 50 publications

X‐Ray Hardness Variations as an Internal/External Shock Diagnostic

X‐Ray Hardness Variations as an Internal/External Shock Diagnostic

THE AFTERGLOWS OFSWIFT-ERA GAMMA-RAY BURSTS. I. COMPARING PRE-SWIFTANDSWIFT-ERA LONG/SOFT (TYPE II) GRB OPTICAL AFTERGLOWS

Optical behavior of GRB 061121 around its X-Ray shallow decay phase

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