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Covino S.,National institute for astrophysics | Campana S.,National institute for astrophysics | Conciatore M.L.,Harvard - Smithsonian Center for Astrophysics | D'Elia V.,National institute for astrophysics | And 40 more authors.
Astronomy and Astrophysics | Year: 2010

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. © 2010 ESO.

Guidorzi C.,University of Milan Bicocca | Guidorzi C.,National institute for astrophysics | Vergani S.D.,Dunsink Observatory | Vergani S.D.,Dublin City University
Journal of the Korean Physical Society | Year: 2010

GRB 070311 was a long burst discovered by INTEGRAL. Here, we present prompt γ-ray, early near infrared (NIR)/optical, late optical, and X-ray data on this burst. We fitted the gamma-ray and the optical light curves and scaled the result to the late-time optical and X-radiation. The H-band light curve acquired by REM shows two pulses one at 80 and the other at 140 s after the peak of the γ-ray burst, with marginal evidence for a faint γ-ray tail. Notably, the late optical and X-ray afterglow experienced a rebrightening between 3 × 104 and 2 × 105 s after the burst, with energy comparable to that of the prompt emission extrapolated to the X-ray band. We describe the time profile of the late rebrightening as a combination of a time-rescaled version of the prompt γ-ray pulse and an underlying power law. This result supports a common origin for both prompt and late X-ray/optical afterglow rebrightenings of GRB 070311 within the external shock scenario.

Meurs E.J.A.,Dunsink Observatory | O'Maoileidigh C.,Dunsink Observatory | Norci L.,Dublin City University | Fennell G.,Dunsink Observatory
New Astronomy Reviews | Year: 2010

Two competing production mechanisms for runaway stars have been used for explaining their origin: dynamical ejection from dense groups and supernovae occurring in binaries. The latter route would lead to some fraction of the runaway stars being accompanied by a neutron star. Searches for compact companions to runaway stars have however mostly been unsuccessful, which is often interpreted as favouring dynamical ejection. On the other hand, the effects of natal kicks due to asymmetric supernova explosions have to be taken into account when comparing with observational data. After reviewing several search methods and summarizing new results at X-rays, we consider the feasibility of high-precision astrometric detections and extend that to X-ray binaries in general. Finally we argue that both suggested production mechanisms fit naturally into one evolutionary scenario. © 2010.

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