Properties of X-ray rich gamma ray bursts and X-ray flashes detected with BeppoSAX and Hete-2

Free access article

Issue		A&A Volume 460, Number 3, December IV 2006


Page(s)		653 - 664
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20054501

A&A 460, 653-664 (2006)
DOI: 10.1051/0004-6361:20054501

Properties of X-ray rich gamma ray bursts and X-ray flashes detected with BeppoSAX and Hete-2

V. D'Alessio¹, L. Piro¹, and E. M. Rossi^{2, 3}

¹ INAF - Sezione di Roma, via del Fosso del Cavaliere, 100, 00113 Roma, Italy
e-mail: valeria.dalessio@rm.iasf.cnr.it
² Max Planck Institute for Astrophysics, Garching Karl-Schwarzschild-Str. 1, Postfach 1317, 85741 Garching, Germany
³ JILA, University of Colorado, 440 UCB Boulder, CO 80309-0440, USA

(Received 9 November 2005 / Accepted 16 June 2006)

Abstract
We study the spectrum of the prompt emission and the X-ray and optical afterglow fluxes of 54 X-Ray Rich Gamma Ray Burst (XRRs) and X-Ray Flashes (XRFs), observed by BeppoSAX and HETE-2. A comparison is then performed with classical Gamma Ray Bursts (GRBs). The goal of this paper is to investigate the nature of XRRs/XRFs, as high redshift GRBs or off-axis GRBs, analyzing both their prompt and afterglow properties. We find that the XRR/XRF spectral indexes of the Band function are similar to those of classical GRBs, whereas the peak energy is lower by a factor of 4. We study the optical and X-Ray afterglow properties of the XRRs/XRFs; in particular we analyze the XRR 011030 afterglow. We find that the X-ray and optical flux distributions and the lightcurves of the XRRs/XRFs sample are consistent with those of classical GRBs; in particular, they show evidence of a break and no rising temporal slope. We compare these results with the afterglow predictions of the high redshift scenario, where XRFs are GRBs at higher redshift and of the off-axis scenario, where the observed differences are due to viewing angle effects. In this last framework, we consider jets with a homogeneous, a -2 power-law shaped and a Gaussian luminosity angular distribution. We find that the high redshift scenario can explain some events but not the total sample of XRRs/XRFs. The off-axis model may be consistent with our findings when a homogeneous jet is considered. However, given the uncertainties on the selection effects in our sample, a Gaussian jet viewed at small angles from the Gaussian core and a power-law shaped cannot be ruled out.

Key words: X-rays: general -- gamma rays: bursts

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.