High Energy Afterglow Emission from Giant Flares of Soft Gamma-Ray Repeaters: The Case of the 2004 December 27 Event from SGR 1806-20

Abstract

We discuss the high enegry afterglow emission (including high energy photons, neutrinos and cosmic rays) following the 2004 December 27 Giant Flare from SGR 1806-20. If the initial outflow is relativistic with a bulk Lorentz factor Γ_0\sim {\rm tens}, the high-energy tail of the synchrotron emission from electrons in the forward shock region gives rise to a prominent sub-GeV emission, if the electron spectrum is hard enough and if the intial Lorentz factor is high enough. This signal could serve as a diagnosis of the initial Lorentz factor of the giant flare outflow. This component is potentially detectable by GLAST if a similar giant flare occurs in the GLAST era. With the available 10 MeV data, we constrain that Γ_0 < 50 if the electron distribution is a single power law. For a broken power law distribution of electrons, a higher Γ_0 is allowed. At energies higher than 1 GeV, the flux is lower because of a high energy cut off of the synchrotron emission component. The synchrotron self-Compton emission component and the inverse Compton scattering component off the photons in the giant flare oscillation tail are also considered, but they are found not significant given a moderate Γ_0 (e.g. \leq 10). The forward shock also accelerates cosmic rays to the maximum energy 10^{17}eV, and generate neutrinos with a typical energy 10^{14}eV through photomeson interaction with the X-ray tail photons. However, they are too weak to be detectable.

arXiv comment6 pages (3 figures), accepted for publication in MNRAS

References in corpus (14)

• The Dynamics and Light Curves of Beamed Gamma Ray Burst Afterglows
• An exceptionally bright flare from SGR1806-20 and the origins of short-duration gamma-ray bursts
• Gamma-Ray Observations of a Giant Flare from The Magnetar SGR 1806-20
• On The Synchrotron Self-Compton Emission from Relativistic Shocks and Its Implications for Gamma-Ray Burst Afterglows
• The Giant Flare of 1998 August 27 from SGR 1900+14: II. Radiative Mechanism and Physical Constraints on the Source
• Overall Evolution of Jetted Gamma-ray Burst Ejecta
• High Energy Spectral Components in Gamma-Ray Burst Afterglows
• An expanding radio nebula produced by a giant flare from the magnetar SGR 1806-20
• Discovery of a Radio Source following the 27 December 2004 Giant Flare from SGR 1806-20
• The Connection between W31, SGR 1806-20, & LBV 1806-20: Distance, Extinction, and Structure
• High energy neutrinos from magnetars
• An energetic blast wave from the December 27 giant flare of the soft gamma-ray repeater 1806-20
• The radio afterglow from the giant flare of SGR 1900+14: the same mechanism as afterglows from classic gamma-ray bursts?
• Fireball/Blastwave Model and Soft Gamma-ray Repeaters

Cited by in corpus (6)

• A Re-brightening of the Radio Nebula associated with the 2004 December 27 giant flare from SGR 1806--20
• GRB 200415A: A Short Gamma-Ray Burst from a Magnetar Giant Flare?
• High energy emission of GRB 130427A: evidence for inverse Compton radiation
• A Two-Component Explosion Model for the Giant Flare and Radio Afterglow from SGR1806-20
• Diffuse high energy neutrinos and cosmic rays from hyperflares of soft-gamma repeaters
• The Giant Flare from SGR 1806-20 and its Radio Afterglow