SWIFT STUDY OF THE FIRST SOFT γ-RAY REPEATER LIKE BURST FROM AXP 1E 1841-045 IN SNR Kes 73

We report the study of the short (32 ms) and first soft gamma-ray repeater like burst observed from the anomalous X-ray pulsar (AXP) 1E 1841-045 associated with the supernova remnant Kes 73, discovered on 2010 May 6 by the Burst Alert Telescope on board the Swift gamma-ray observatory. The 15-100 keV time-averaged burst spectrum is modeled by a single power law (PL) with a photon index G = 3.2(-1.0)(+1.8) and has a fluence of 1.1(-0.6)(+0.4) x 10(-8) erg cm(-2), a luminosity of 2.9(-1.6)(+1.1) x 10(39) erg s(-1), and an energy of 7.2(-0.6)(+0.4) x 10(36) erg. The prompt after-burst 0.5-10 keV quiescent spectrum obtained with the Swift X-ray Telescope (XRT) is best fit by an absorbed PL model with Gamma = 2.6 +/- 0.2 and an unabsorbed flux of 9.1(-1.4)(+1.2) x 10(-11) erg cm(-2) s(-1). To investigate the pre-burst 0.5-10 keV persistent emission, we analyzed the archival XMM-Newton observations, and the spectra are well fitted by a two-component blackbody plus PL model with a temperature kT = 0.45 +/- 0.03 keV, Gamma = 1.9 +/- 0.2, and an unabsorbed flux of 4.3(-1.2)(+0.9) x 10(-11) erg cm(-2) s(-1). Comparing the Swift-XRT spectrum with the XMM-Newton spectrum, spectral softening post-burst is evident with a 2.1 times increase in the unabsorbed flux. We discuss the burst activity and the persistent emission properties of AXP 1E 1841-045 in comparison with other magnetars and in the context of the magnetar model.