Swift 1644+57: the longest gamma-ray burst?

Authors

  • E. Quataert,

    Corresponding author
    1. Astronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, 601 Campbell Hall, Berkeley, CA 94720, USA
    2. Department of Physics, University of California, Berkeley, Le Conte Hall, Berkeley, CA 94720, USA
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  • D. Kasen

    Corresponding author
    1. Astronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, 601 Campbell Hall, Berkeley, CA 94720, USA
    2. Department of Physics, University of California, Berkeley, Le Conte Hall, Berkeley, CA 94720, USA
    3. Nuclear Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
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E-mail: eliot@berkeley.edu (EQ); kasen@berkeley.edu (DK)

ABSTRACT

Swift recently discovered an unusual gamma-ray and X-ray transient (Swift 1644+57) that was initially identified as a long-duration gamma-ray burst (GRB). However, the ∼10 keV X-ray emission has persisted for over approximately a month with a luminosity comparable to its peak value. The astrometric coincidence of the source with the centre of its host galaxy, together with other considerations, motivated the interpretation that Swift 1644+57 was produced by an outburst from a ∼106–107 M black hole at the centre of the galaxy. Here we consider the alternate possibility that Swift 1644+57 is indeed a long-duration GRB, albeit a particularly long one! We discuss the general properties of very long-duration, low-power GRB-like transients associated with the core-collapse of a massive star. Both neutron star (magnetar) spin-down and black hole accretion can power such events. The requirements for producing low-power, very long duration GRBs by magnetar spin-down are similar to those for powering extremely luminous supernovae by magnetar spin-down, suggesting a possible connection between these two unusual types of transients. Alternatively, Swift 1644+57 could be associated with the faintest core-collapse explosions: the collapse of a rotating red supergiant in a nominally failed supernova can power accretion on to a solar-mass black hole for up to ∼100 d; the jet produced by black hole accretion inevitably unbinds the outer envelope of the progenitor, leading to a weak ∼1049 erg explosion. In both neutron-star and black hole models, a jet can burrow through the host star in a few days, with a kinetic luminosity ∼1045–1046 erg s−1, sufficient to power the observed emission of Swift 1644+57.

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