The First Survey of X‐Ray Flares from Gamma‐Ray Bursts Observed by<i>Swift</i>: Spectral Properties and Energetics

Falcone, A.; Morris, D.; Racusin, J. L.; Chincarini, G.; Moretti, A.; Romano, P.; Burrows, D. N.; Pagani, C.; Stroh, M. C.; Grupe, D.; Campana, S.; Covino, S.; Tagliaferri, G.; Willingale, R.; Gehrels, N.

doi:10.1086/523296

Cited by 197 publications

(263 citation statements)

References 55 publications

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“…These X-ray flares are unexpected in the framework of the standard external shock model because it predicts a monotonous decay of the X-ray afterglow with a power-law form (Burrows et al 2005). The X-ray flare is observed in a half of GRB afterglows (Falcone et al 2007). The afterglow emission from the external shock could exhibit short-term modulations when a shell passes a high-density region of the interstellar medium (Wang & Loeb 2000), or slow shells catch up with the main shell (Rees & Meszaros 1998).…”

Section: Introductionmentioning

confidence: 94%

Infrared/optical – X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506

Uehara¹,

Uemura

Kawabata

et al. 2010

A&A

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Aims. We investigate the origin of short X-ray flares which are occasionally observed in early stages of afterglows of gamma-ray bursts (GRBs). Methods. We observed two Swift events, GRB 071112C and GRB 080506, before the start of X-ray flares in the optical and nearinfrared (NIR) bands with the 1.5-m Kanata telescope. In conjunction with published X-ray and optical data, we analyzed densely sampled light curves of the early afterglows and spectral energy distributions (SEDs) in the NIR-X-ray ranges. Results. We found that the SEDs had a break between the optical and X-ray bands in the normal decay phases of both GRBs regardless of the model for the correction of the interstellar extinction in host galaxies of GRBs. In the X-ray flares, X-ray flux increased by 3 and 15 times in the case of GRB 071112C and 080506, respectively, and the X-ray spectra became harder than those in the normal decay phases. No significant variation in the optical-NIR range was detected together with the X-ray flares. Conclusions. These results suggest that the X-ray flares were associated with either late internal shocks or external shocks from two-component jets.

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Section: Introductionmentioning

confidence: 94%

Infrared/optical – X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506

Uehara¹,

Uemura

Kawabata

et al. 2010

A&A

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“…All XRT data were in photon counting (PC) mode and were reduced 3 By default xspec uses the abundances from Anders & Grevesse (1989), which are consistent with those of Asplund et al (2009) with the xrtpipeline tool (v0.12.4). Spectra were extracted following the method described in Evans et al (2009), avoiding time intervals that showed evidence of spectral evolution, such as during the early-time steep decay phase of the X-ray light curve (Nousek et al 2006), during flares (Falcone et al 2007). Both UVOT and GROND data were reduced following the standard procedures described in Poole et al (2008) and Küpcü-Yoldaş et al (2008), respectively.…”

Section: Sed Analysismentioning

confidence: 99%

The missing gas problem in GRB host galaxies: evidence for a highly ionised component

Schady¹,

Savaglio²,

Kruehler³

et al. 2010

A&A

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There is considerable discrepancy between the amount of X-ray absorption and what is inferred from optical (rest frame UV) as measured along gamma-ray burst (GRB) sight lines, with the former typically an order of magnitude higher than what would be expected from the measurement of neutral element species via optical absorption line spectroscopy. We explored this "missing gas problem" in a sample of 29 GRBs with redshifts in the range 0.7-6.3 by studying the X-ray and optical spectra, as well as the afterglow broadband spectral energy distributions. The low ionisation species detected in the UV are associated with the neutral interstellar medium in the GRB host galaxy, while soft X-ray absorption, which is weakly dependent on the ionisation state of the gas, provides a probe of the total column of gas along the sight line. After careful consideration of any systematic effects, we find that the neutral gas consists of 10% of the total gas, and this limit decreases the more ionised the X-ray absorbing gas is, which in our spectral fits is assumed to be neutral. Only a very small fraction of this ionised gas, however, is detected in UV absorption lines with ionisation potentials up to ∼200 eV (i.e. Si iv, C iv, N v, O vi), which leaves us to postulate that the X-ray excess comes from ultra-highly-ionised, dense gas in the GRB vicinity.

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“…Finally, at later times it sometimes further steepens as a result of a jet break. Flares with short rise and decay times can be superimposed on this global evolution (Chincarini et al 2007;Falcone et al 2007). These different components are not always present.…”

Section: Introductionmentioning

confidence: 99%

Was the “naked burst” GRB 050421 really naked?

Hascoët

Uhm

Mochkovitch

et al. 2011

A&A

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Context. A few long gamma-ray bursts such as GRB 050421 show no afterglow emission beyond the usual initial steep decay phase. It has been suggested that these events correspond to "naked" bursts that occur in a very low density environment. We reconsider this possibility in the context of various scenarios for the origin of the afterglow. Aims. In the standard model where the afterglow results from the forward shock as well as in the alternative model where the afterglow comes from the reverse shock, we aim to obtain constraints on the density of the environment, the microphysics parameters, or the Lorentz factor of the ejecta, which are imposed by the absence of a detected afterglow. Methods. For the two models we compute the afterglow evolution for different values of the external density (uniform or wind medium) and various burst parameters. We then compare our results to the Swift data of GRB 050421, which is the best example of a long burst without afterglow. Results. In the standard model we show that consistency with the data imposes that the external density does not exceed 10 −5 cm −3 or that the microphysics parameters are very small with e < ∼ 10 −2 and B < ∼ 10 −4 . If the afterglow is caused by the reverse shock, we find that its contribution can be strongly reduced if the central source has mainly emitted fast-moving material (with less than 10-30% of the kinetic energy at Γ < 100) and was located in a dense environment. Conclusions. The two considered scenarios therefore lead to opposite constraints on the circumburst medium. The high-density environment, favored by the reverse shock model, better corresponds to what is expected if the burst progenitor was a massive star.

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The First Survey of X‐Ray Flares from Gamma‐Ray Bursts Observed bySwift: Spectral Properties and Energetics

Cited by 197 publications

References 55 publications

Infrared/optical – X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506

Infrared/optical – X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506

The missing gas problem in GRB host galaxies: evidence for a highly ionised component

Was the “naked burst” GRB 050421 really naked?

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