THE DIVERSE BROADBAND LIGHT CURVES OFSWIFTGAMMA-RAY BURSTS REPRODUCED WITH THE CANNONBALL MODEL

Abstract

Two radiation mechanisms, inverse Compton scattering (ICS) and synchrotron radiation (SR), suffice within the Cannonball (CB) model of long gamma-ray bursts (LGRBs) and X-ray flashes (XRFs) to provide a very simple and accurate description of their observed prompt emission and afterglows (AGs). Simple as they are, the two mechanisms and the burst environment generate the rich structure of the light curves at all frequencies and times. This is demonstrated for 33 selected Swift LGRBs and XRFs, which are well sampled from early until late time and faithfully represent the entire diversity of the broadband light curves of Swift LGRBs and XRFs. Their prompt gamma-ray and X-ray emission is dominated by ICS of "glory" light. During their fast decline phase, ICS is taken over by SR, which dominates their broadband AG. The pulse shape and spectral evolution of the gamma-ray peaks and the early-time X-ray flares, and even the delayed optical "humps" in XRFs, are correctly predicted. The "canonical" and noncanonical X-ray light curves and the chromatic behavior of the broadband AGs are well reproduced. In particular, in canonical X-ray light curves, the initial fast decline and rapid softening of the prompt emission, the transition to the plateau phase, the subsequent gradual steepening of the plateau to an asymptotic power-law decay, and the transition from chromatic to achromatic behavior of the light curves agree well with those predicted by the CB model. The Swift earlytime data on XRF 060218 are inconsistent with a blackbody emission from a shock breakout through a stellar envelope. Instead, they are well described by ICS of glory light by a jet breaking out from SN2006aj.

Challenging gamma-ray burst models through the broadband dataset of GRB 060908

“…A comparable emission due to the reverse and forward shock was also proposed for GRB 070802 (Krühler et al 2008). Partly motivated by the increasing difficulties of the so-called "standard model" in interpreting the rich multiwavelength datasets now available, there is a rising interest in alternative scenarios, such as the "cannonball" model (Dado & Dar 2009b;Dado et al 2009a). This scenario has shown remarkable fitting capabilities (e.g.…”

“…The afterglow is instead due to synchrotron radiation from the cannonballs, which are sweeping up the ionised circumburst medium (see Dado & Dar 2009b;Dado et al 2009a, and references therein for a comprehensive review).…”

“…Adopting the terminology in Dado et al (2002) and in Dado et al (2009a), the spectral behaviour of an afterglow depends on the location of the so-called bend frequency ν b (t), i.e. the typical frequency radiated by electrons that enter a cannonball at a given time (see e.g.…”

The origin of the prompt optical emission in GRB 060111B

“…We have attempted to test the CB model for the optical light curve of GRB 060111B. Following Dado et al (2009Dado et al ( , 2010, we interpreted the observed optical emission as early synchrotron radiation produced by the ionized external matter entering in the CB and interacting with internal magnetic field. Describing the external matter density profile as n ∝ e −a/(r−rw)/(r−rw) 2 for r > r w (and n = 0 for r < r w ), the flux is F ν ∝ e −a/(t−t i ) R 2 (t − t i ) (1−β) ν −β where a is the wind opacity time scale, t i is the time at which the CB enters into the wind (i.e.…”

“…Alternatively, the Cannonball model is also providing good match with the observations (e.g. Dado et al 2009). …”