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 γ-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 γ-ray observatory. The 15-100 keV time-averaged burst spectrum is modeled by a single power law (PL) with a photon index Γ = 3.2^+1.8 _-1.0 and has a fluence of 1.1^+0.4 _-0.6 × 10^-8 erg cm^-2, a luminosity of 2.9^+1.1 _-1.6 × 10³⁹ erg s^-1, and an energy of 7.2^+0.4 _-0.6 × 10³⁶ 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 Γ = 2.6 ± 0.2 and an unabsorbed flux of 9.1^+1.2 _-1.4 × 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, Γ = 1.9 ± 0.2, and an unabsorbed flux of 4.3^+0.9 _-1.2 × 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.