A unifying view of Gamma Ray Burst Afterglows
arXiv:0811.1038 · doi:10.1111/j.1365-2966.2008.14214.x
Abstract
We selected a sample of 33 Gamma Ray Bursts (GRBs) detected by Swift, with known redshift and optical extinction at the host frame. For these, we constructed the de-absorbed and K-corrected X-ray and optical rest frame light curves. These are modelled as the sum of two components: emission from the forward shock due to the interaction of a fireball with the circum-burst medium and an additional component, treated in a completely phenomenological way. The latter can be identified, among other possibilities, as "late prompt" emission produced by a long lived central engine with mechanisms similar to those responsible for the production of the "standard" early prompt radiation. Apart from flares or re-brightenings, that we do not model, we find a good agreement with the data, despite of their complexity and diversity. Although based in part on a phenomenological model with a relatively large number of free parameters, we believe that our findings are a first step towards the construction of a more physical scenario. Our approach allows us to interpret the behaviour of the optical and X-ray afterglows in a coherent way, by a relatively simple scenario. Within this context it is possible to explain why sometimes no jet break is observed; why, even if a jet break is observed, it is often chromatic; why the steepening after the jet break time is often shallower than predicted. Finally, the decay slope of the late prompt emission after the shallow phase is found to be remarkably similar to the time profile expected by the accretion rate of fall-back material (i.e. proportional to t^{-5/3}), suggesting that this can be the reason why the central engine can be active for a long time.
20 pages, 17 figures, Accepted for publication in MNRAS
References in corpus (38)
- An online repository of Swift/XRT light curves of GRBs
- No supernovae associated with two long-duration gamma ray bursts
- An enigmatic long-lasting gamma-ray burst not accompanied by a bright supernova
- The First Survey of X-ray Flares from Gamma Ray Bursts Observed by Swift: Temporal Properties and Morphology
- REM observations of GRB 060418 and GRB 060607A: the onset of the afterglow and the initial fireball Lorentz factor determination
- Fallback and Black Hole Production in Massive Stars
- A time - luminosity correlation for Gamma Ray Bursts in the X - rays
- On the Mechanism of Gamma-Ray Burst Afterglows
- Can the early X-ray afterglow of GRBs be explained by a contribution from the reverse shock?
- "Late prompt" emission in Gamma Ray Bursts?
- Swift observations of GRB 060614: an anomalous burst with a well behaved afterglow
- X-ray flares and the duration of engine activity in gamma-ray bursts
- Precursors in Swift Gamma Ray Bursts with redshift
- The Remarkable Afterglow of GRB 061007: Implications for Optical Flashes and GRB Fireballs
- Confirming the gamma-ray burst spectral-energy correlations in the era of multiple time breaks
- Multiwavelength analysis of the intriguing GRB 061126: the reverse shock scenario and magnetization
- GRB 071003: Broadband Follow-up Observations of a Very Bright Gamma-Ray Burst in a Galactic Halo
- Detection of GRB 060927 at z = 5.47: Implications for the Use of Gamma-Ray Bursts as Probes of the End of the Dark Ages
- The complex light-curve of the afterglow of GRB071010A
- Optical and X-Ray Observations of GRB 060526: A Complex Afterglow Consistent with An Achromatic Jet Break
- The nature of the X-Ray Flash of August 24 2005
- Swift GRB Afterglows and the Forward-Shock Model
- Three intervening galaxy absorbers towards GRB060418: faint and dusty?
- Multi-wavelength afterglow observations of the high redshift GRB 050730
- X-ray flares, plateaus, and chromatic breaks of GRB afterglows from up-scattered forward-shock emission
- Multi-color Shallow Decay and Chromatic Breaks in the GRB 050319 Optical Afterglow
- The Two-Component Afterglow of Swift GRB 050802
- The prompt to late-time multiwavelength analysis of GRB 060210
- Extensive multiband study of the X-ray rich GRB 050408. A likely off-axis event with an intense energy injection
- X-ray flares, neutrino cooled disks, and the dynamics of late accretion in GRB engines
- Early emission of rising optical afterglows: The case of GRB 060904B and GRB 070420
- GRB 060206 and the quandary of achromatic breaks in afterglow light curves
- Gamma-ray burst afterglows
- Observations of the Optical Afterglow of GRB 050319 : Wind to ISM transition in view
- Optical afterglow luminosities in the Swift epoch: confirming clustering and bimodality
- The circumburst environment of a FRED GRB: study of the prompt emission and X-ray/optical afterglow of GRB 051111
- The exceptionally extended flaring activity in the X-ray afterglow of GRB 050730 observed with Swift and XMM-Newton
- Optical observations of GRB 060124 afterglow: A case for an injection break