GRB 070201: A possible Soft Gamma Ray Repeater in M31

TL;DR

This paper investigates the possibility that GRB 070201 was an extragalactic Soft Gamma-ray Repeater in M31, analyzing multi-wavelength data and simulations to identify potential SGR/AXP signatures in nearby galaxies.

Contribution

It presents a detailed analysis of GRB 070201 as a candidate extragalactic SGR, including optical and X-ray observations, and discusses detection prospects for extragalactic SGRs/AXPs.

Findings

GRB 070201 is a strong candidate for an extragalactic SGR in M31.

No optical transient was detected in follow-up observations.

Simulations indicate a 10-50% chance of detecting periodic X-ray signals from extragalactic SGRs.

Abstract

The gamma-ray burst (GRB) 070201 was a bright short-duration hard-spectrum GRB detected by the Inter-Planetary Network (IPN). Its error quadrilateral, which has an area of 0.124 sq. deg, intersects some prominent spiral arms of the nearby M31 (Andromeda) galaxy. Given the properties of this GRB, along with the fact that LIGO data argues against a compact binary merger origin in M31, this GRB is an excellent candidate for an extragalactic Soft Gamma-ray Repeater (SGR) giant flare, with energy of 1.4x10^45 erg. Analysis of ROTSE-IIIb visible light observations of M31, taken 10.6 hours after the burst and covering 42% of the GRB error region, did not reveal any optical transient down to a limiting magnitude of 17.1. We inspected archival and proprietary XMM-Newton X-ray observations of the intersection of the GRB error quadrilateral and M31, obtained about four weeks prior to the outburst, in order to look for periodic variable X-ray sources. No SGR or Anomalous X-ray Pulsar (AXP) candidates (periods in range 1 to 20 s) were detected. We discuss the possibility of detecting extragalactic SGRs/AXPs by identifying their periodic X-ray light curves. Our simulations suggest that the probability of detecting the periodic X-ray signal of one of the known Galactic SGRs/AXPs, if placed in M31, is about 10% (50%), using 50 ks (2 Ms) XMM-Newton exposures.