The radio afterglow from the giant flare of SGR 1900+14: the same mechanism as afterglows from classic gamma-ray bursts?

Abstract

A radio afterglow was detected following the 1998 August 27 giant flare from the soft gamma repeater (SGR) 1900+14. Its short-lived behavior is quite different from the radio nebula of SGR 1806-20, but very similar to radio afterglows from classic gamma-ray bursts (GRBs). Motivated by this, we attempt to explain it with the external shock model as invoked in the standard theory of GRB afterglows. We find that the light curve of this radio afterglow is not consistent with the forward shock emission of an ultra-relativistic outflow, which is suggested to be responsible for the initial hard spike of the giant flare. Nevertheless, shock emission from a mildly or sub-relativistic outflow expanding into the interstellar medium could fit the observations. The possible origin for this kind of outflow is discussed, based on the magnetar model for SGRs. Furthermore, we suggest that the presence of an ultra-relativistic fireball from SGR giant flares could be tested by rapid radio to optical follow-up observations in the future.

Accepted for publication in ApJ Letters, expanded version with one extra figure

References in corpus (3)

• The Giant Flare of 1998 August 27 from SGR 1900+14: II. Radiative Mechanism and Physical Constraints on the Source
• Waiting for the Big One: A New Class of SGR Outbursts?
• External shock model for the large-scale, relativistic X-ray jets from the microquasar XTE J1550-564

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• Constraining the bulk Lorentz factor from the photosphere emission
• A Two-Component Explosion Model for the Giant Flare and Radio Afterglow from SGR1806-20
• High Energy Afterglow Emission from Giant Flares of Soft Gamma-Ray Repeaters: The Case of the 2004 December 27 Event from SGR 1806-20
• AT2020hur: A Possible Optical Counterpart of FRB 180916B