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Search for the GeV counterparts of two gamma ray bursts: Swift 317662 and Fermi bn081017474

C. R. A. Augusto, C. E. Navia, M. B. Robba, and K. H. Tsui

Instituto de Física, Universidade Federal Fluminense, 24210-346, Niterói, RJ, Brazil

Phys. Rev. D 78, 122001 – Published 3 December, 2008

DOI: https://doi.org/10.1103/PhysRevD.78.122001

Abstract

We examine the possibility of the ground observation of the GeV counterparts of two gamma ray bursts, the Swift GRB-080723 ( $Trigger = 317662$ ) and the Fermi GRB081017474 ( $trigger = bn 081017474$ ). The data come from two small directional muon telescopes at sea level inside the South Atlantic Anomaly region. This characteristic offers the muon telescopes a low rigidity of response to primary and secondary charged particles ( $\geq 0.4 GV$ ). In both cases, the GRB trigger coordinates are within the effective field of view of the vertical Tupi muon telescopes. There is a ground level enhancement (GLE) on the muon counting rate background, with a statistical significance above $4 σ$ , 38.22 minutes after the Swift trigger occurrence, and there are at least two GLEs, with a significance above $4 σ$ , at 7.2 minutes and 19.2 minutes after the Fermi trigger, respectively. We argue that the GeV counterpart of a keV GRB could be similar to the highest GRBs, observed by EGRET within BATSE’s field of view, where the high-energy emission arrives at the detector in fragments, and they are delayed and/or anticipated with respect to the keV-MeV burst. This behavior is observed in both cases. In short, the analysis suggests that they may be physically associated. Details and some implications of this possible association are reported in this work.

Article Text

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