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

Abstract

Context. Multiwavelength observations of gamma-ray burst prompt and afterglow emission are a key tool to separate the various possible emission processes and scenarios proposed to interpret the complex gamma-ray burst phenomenology. Aims. We collected a large dataset on GRB 060908 in order to carry out a comprehensive analysis of the prompt emission as well as the early and late afterglow. Methods. Data from Swift-BAT, -XRT and -UVOT together with data from a number of different ground-based optical/near-infrared and millimeter telescopes allowed us to follow the afterglow evolution after about a minute from the high-energy event down to the host galaxy limit. We discuss the physical parameters required to model these emissions. Results. The prompt emission of GRB 060908 was characterised by two main periods of activity, spaced by a few seconds of low intensity, with a tight correlation between activity and spectral hardness. Observations of the afterglow began less than one minute after the high-energy event, when it was already in a decaying phase, and it was characterised by a rather flat optical/near-infrared spectrum which can be interpreted as due to a hard energy-distribution of the emitting electrons. On the other hand, the X-ray spectrum of the afterglow could be fit by a rather soft electron distribution. Conclusions. GRB 060908 is a good example of a gamma-ray burst with a rich multi-wavelength set of observations. The availability of this dataset, built thanks to the joint efforts of many different teams, allowed us to carry out stringent tests for various interpretative scenarios, showing that a satisfactorily modelling of this event is challenging. In the future, similar efforts will enable us to obtain optical/near-infrared coverage comparable in quality and quantity to the X-ray data for more events, therefore opening new avenues to progress gamma-ray burst research.

Long-term X-ray emission from Swift J1644+57

“…The origin of the hard electron distribution (p < 2) is not yet clear. The observations also confirmed the evidence for hard electron distribution in some GRBs (Dai & Cheng 2001;Huang et al 2006;Covino et al 2010). Simulations of the Fermi process in relativistic shocks including large angle scattering have resulted in hard electron energy spectra (Stecker, Baring & Summerlin 2007).…”

GRB 091127/SN 2009nz and the VLT/X-shooter spectroscopy of its host galaxy: probing the faint end of the mass-metallicity relation

“…This is not unprecedented behaviour, as very blue optical spectra have been previously reported (e.g. for GRB 060908, Covino et al 2010). The optical spectral slope and rest-frame extinction show a high degree of degeneracy.…”

Lowly Polarized Light from a Highly Magnetized Jet of GRB 190114C

“…Several GRBs exhibit a similar light curve flattening from α opt,1 ∼ 1.3 − 1.6 to α opt,2 ∼ 0.8 − 1.1 in the optical at early times; see Table 4: GRB 021211 (Fox et al 2003), GRB 050525A (Shao & Dai 2005), GRB 050904 (Haislip et al 2006;Wei et al 2006), GRB 060908 (Covino et al 2010), GRB 061126 (Gomboc et al 2008;Perley et al 2008), GRB 090102 (Steele et al 2009;Gendre et al 2010), GRB 090424 (Jin et al 2013) and GRB 090902B (Pandey et al 2010). Additionally, most of them bear similar spectral and temporal properties to GRB 190114C in both optical and X-rays regimes.…”