REM observations of GRB 060418 and GRB 060607A: the onset  of the afterglow and the initial fireball  Lorentz factor determination

Molinari, E.; Vergani, S. D.; Malesani, D.; Covino, S.; D’Avanzo, P.; Chincarini, G.; Zerbi, F. M.; Antonelli, L. A.; Conconi, P.; Testa, V.; Tosti, G.; Vitali, F.; D’Alessio, F.; Malaspina, G.; Nicastro, L.; Palazzi, E.; Guetta, Dafne; Campana, S.; Goldoni, P.; Masetti, N.; Meurs, E. J. A.; Monfardini, A.; Norci, L.; Pian, E.; Piranomonte, S.; Rizzuto, Debora; Stefanon, Mauro; Stella, L.; Tagliaferri, G.; Ward, Paul A. S.; Ihle, G.; González, L.; Pizarro, Alonso; Sinclaire, P.; Valenzuela, J.

doi:10.1051/0004-6361:20077388

Cited by 228 publications

(150 citation statements)

References 40 publications

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“…For an ISM-like environment the median value is 225, with most values being above 100, in agreement with measurements in the literature (e.g. [5], [9], [10], [11]). On the other hand, if we assume a wind-like environment the median value of the initial Lorentz factor is only 93, and is below 50 for several bursts; this is close to the limit imposed by the compactness problem and may suggest that these GRBs cannot have occurred in a wind-like environment.…”

Section: Resultssupporting

confidence: 90%

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Spectral evolution and the onset of the X-ray GRB afterglow

Evans¹,

Osborne²,

Willingale³

et al. 2011

AIP Conference Proceedings

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Abstract. Based on light curves from the Swift Burst Analyser, we investigate whether a 'dip' feature commonly seen in the early-time hardness ratios of Swift-XRT data could arise from the juxtaposition of the decaying prompt emission and rising afterglow. We are able to model the dip as such a feature, assuming the afterglow rises as predicted by Sari and Piran [1]. Using this model we measure the initial bulk Lorentz factor of the fireball. For a sample of 23 GRBs we find a median value of Γ 0 = 225, assuming a constant-density circumburst medium; or Γ 0 = 93 if we assume a wind-like medium.

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Section: Resultssupporting

confidence: 90%

“…From this one can determine the bulk Lorentz factor at the deceleration radius of the fireball (e.g. [1]; [5]). …”

Section: Introductionmentioning

confidence: 99%

Spectral evolution and the onset of the X-ray GRB afterglow

Evans¹,

Osborne²,

Willingale³

et al. 2011

AIP Conference Proceedings

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“…When X-ray flares are observed by XRT, it is typically the case that no flaring is seen in the optical band by the UVOT. A notable example is GRB 060418 (Molinari et al 2007), whose optical-infrared afterglow spectra is not consistent with lightcurves of Swift burst afterglows. Data for long-duration bursts with known redshifts, from GRB 050126 to GRB 070724A, have been gathered from the Swift XRT lightcurve and spectral data depository at the UK Swift Science Data Centre (Evans et al 2007;Evans et al 2008).…”

Section: Afterglow Observationsmentioning

confidence: 99%

Gamma-Ray Bursts in theSwiftEra

Gehrels

Ramírez-Ruiz

Fox

2009

Annu. Rev. Astron. Astrophys.

592

474

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With its rapid-response capability and multiwavelength complement of instruments, the Swift satellite has transformed our physical understanding of γ-ray bursts (GRBs). Providing highquality observations of hundreds of bursts, and facilitating a wide range of follow-up observations within seconds of each event, Swift has revealed an unforeseen richness in observed burst properties, shed light on the nature of short-duration bursts, and helped realize the promise of GRBs as probes of the processes and environments of star formation out to the earliest cosmic epochs. These advances have opened new perspectives on the nature and properties of burst central engines, interactions with the burst environment from microparsec to gigaparsec scales, and the possibilities for nonphotonic signatures. Our understanding of these extreme cosmic sources has thus advanced substantially; yet, more than 40 years after their discovery, GRBs continue to present major challenges on both observational and theoretical fronts.

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“…Different peak times of the afterglow for the two bursts may be explained by difference in the initial Lorentz factor According to equation 1 in [20], the rise time of the afterglow is more sensitive to the initial Lorentz factor than to the total energy release. The delayed peak time in the afterglow of GRB 080330 may point to a small initial Lorentz factor, which is consistent with this event being soft and classified as an X-ray Flash in terms of its fluence ratio in BAT high and low energy band [21,4].…”

Section: Discussionmentioning

confidence: 99%

Prompt optical observations of GRB 080330 and GRB 080413A

Yuan

Rykoff

Schaefer

et al. 2008

AIP Conference Proceedings

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Abstract. We report on the results of rapid responses to GRB 080330 and GRB 080413A by the ROTSE-IIIb and ROTSEIIIc telecopes. In both cases, optical follow-up started during the prompt emission phase and recorded optical flares peaking at similar times as the last hard X-ray pulses detected by the Swift BAT. For both events, the XRT observations started at the end of the prompt BAT detection and displayed an evolution in time opposite to the optical lightcurve. These very early observations provide us an opportunity to probe the onset of afterglow for these two events.

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REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination

Cited by 228 publications

References 40 publications

Spectral evolution and the onset of the X-ray GRB afterglow

Spectral evolution and the onset of the X-ray GRB afterglow

Gamma-Ray Bursts in theSwiftEra

Prompt optical observations of GRB 080330 and GRB 080413A

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