Contamination of short GRBs by giant magnetar flares: Significance of downward revision in distance to SGR 1806-20

摘要

We highlight how the downward revision in the distance to the star cluster associated with SGR 1806-20 by Bibby et al. (2008) reconciles the apparent low contamination of BATSE short GRBs by intense flares from extragalactic magnetars without recourse to modifying the frequency of one such flare per 30 years per Milky Way galaxy. We also discuss the variety in progenitor initial masses of magnetars based upon cluster ages, ranging from ～50 M_⊕ for SGR 1806-20 and AXP CXOU J164710.2-455216 in Westerlund 1 to ～17 M_⊕ for SGR 1900+14 according to Davies et al. (2009) and presumably also IE 1841-045 if it originated from one of the massive RSG clusters #2 or #3.