Late flares from GRBs - Clues about the central engine

Andrew I. MacFadyen, Enrico Ramirez-Ruiz, Weiqun Zhang

    Research output: Chapter in Book/Report/Conference proceedingConference contribution


    We discuss the implications of late flares following GRBs for determining the nature of the central engine. We argue that since the flare timescales are much longer than naturally expected for a stellar mass compact object, progenitor systems containing a non-compact star are favored for short bursts displaying minute-long flares. For the case of short bursts, we argue that a minute-long flare time scale may be naturally explained if the progenitor is a binary system consisting of a neutron star and a non-compact companion, e.g. a low mass X-ray binary. In this scenario, the neutron star accretes mass and angular momentum from its companion until it undergoes accretion-induced collapse to a black hole or quark star. Due to its rapid spin when it collapses, a small torus of neutron star material forms and accretes on a viscous time. The burst itself is expected to be short, (τ ≲1s), but the relativistic flow it accelerates hits the companion producing a minute-long flare. The delay between the GRB and beginning of the flare is given by the light travel time from the collapsed neutron star to the surface of the companion, tens of seconds, while the duration is given by the time for the relativistic shock to cross the star, a few minutes. No supernova-like emission is expected in this model. The progenitor systems are expected in both old and young stellar populations, consistent with the observed locations of short bursts in elliptical and star-forming galaxies. For long bursts, late flares are naturally explained by late accretion episodes if the massive stellar progenitor is not entirely disrupted during outburst.

    Original languageEnglish (US)
    Title of host publicationGAMMA-RAY BURSTS IN THE SWIFT ERA
    Subtitle of host publicationSixteenth Maryland Astrophysics Conference
    Number of pages6
    StatePublished - May 19 2006
    EventGAMMA-RAY BURSTS IN THE SWIFT ERA: 16th Maryland Astrophysics Conference - Washington, D.C., United States
    Duration: Nov 29 2005Dec 2 2005

    Publication series

    NameAIP Conference Proceedings
    ISSN (Print)0094-243X
    ISSN (Electronic)1551-7616


    OtherGAMMA-RAY BURSTS IN THE SWIFT ERA: 16th Maryland Astrophysics Conference
    Country/TerritoryUnited States
    CityWashington, D.C.


    • Binaries: close
    • Black hole physics
    • Gamma rays: burst
    • Shock waves
    • Stars: neutron
    • X-rays: binaries

    ASJC Scopus subject areas

    • General Physics and Astronomy


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