Identifying young gamma-ray burst fossils.pdfVIP

a r X i v : a s t r o - p h / 0 4 0 3 0 3 9 v 2 7 M a y 2 0 0 4 Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 2 February 2008 (MN LATEX style file v2.2) Identifying young gamma-ray burst fossils Enrico Ramirez-Ruiz 1,2 1 School of Natural Sciences, Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA. 2 Chandra Fellow. ABSTRACT The recent reports of temporal and spectral peculiarities in the early stages of some after- glows suggest that we may be wrong in postulating a central engine which becomes dormant after the burst itself. A continually decreasing postburst relativistic outflow, such as put out by a decaying magnetar, may continue to be emitted for periods of days or longer, and we argue that it can be efficiently reprocessed by the ambient soft photon field radiation. Photons produced either by the postexplosion expansion of the progenitor stellar envelope or by a bi- nary companion provide ample targets for the relativistic outflow to interact and produce high energy γ-rays. The resultant signal may yield luminosities high enough to be detected with the recently launched Integral and the Glast experiment now under construction. Its detec- tion will surely offer important clues for identifying the nature of the progenitor and possibly constraining whether some route other than single star evolution is involved in producing a rapidly rotating helium core which in turn, at collapse, triggers a burst. Key words: radiation mechanisms:non-thermal; hydrodynamics; gamma-rays: bursts; stars: neutron 1 INTRODUCTION The typical GRB model assumes that the energy input episode is brief, typically tgrb ≤ 1 ? 10 2 s (see Me?sza?ros 2002 for a recent review). However, peculiarities in the early stages of some afterglows, e.g. GRB 021004, have served as motivation for considering a more extended input period in which the energy injection continues well beyond tgrb (Fox et al. 2003). The enduring activity could in principle emanate from the slu