Journal Article

Spectral comparison of weak short bursts to the persistent X-rays from the magnetar 1E 1547.0–5408 in its 2009 outburst

T. Enoto, Y. E. Nakagawa, T. Sakamoto and K. Makishima

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 427, issue 4, pages 2824-2840
Published in print December 2012 | ISSN: 0035-8711
Published online December 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.22086.x
Spectral comparison of weak short bursts to the persistent X-rays from the magnetar 1E 1547.0–5408 in its 2009 outburst

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Abstract

In 2009 January, the 2.1-s anomalous X-ray pulsar 1E 1547.0−5408 evoked intense burst activity. A follow-up Suzaku observation on January 28 recorded enhanced persistent emission in both soft and hard X-rays. Through a reanalysis of the same Suzaku data, 18 short bursts were identified in the X-ray events recorded by the Hard X-ray Detector (HXD) and the X-ray Imaging Spectrometer (XIS). Their spectral peaks appear in the HXD–PIN band, and their 10–70 keV X-ray fluences range from ∼2 × 10−9 to 10−7 erg cm−2. Thus, the 18 events define a significantly weaker burst sample than has ever been obtained previously, ∼10−8–10−4 erg cm−2. In the ∼0.8 to ∼300 keV band, the spectra of the three brightest bursts can be represented successfully by a two-blackbody model, or a few alternative models. A spectrum that is constructed by stacking 13 weaker short bursts with fluences in the range (0.2–2) × 10−8 erg s−1 is less curved, and its ratio to the persistent emission spectrum becomes constant at ∼170 above ∼8 keV. As a result, the two-blackbody model was able to reproduce the stacked weaker-burst spectrum only after adding a power-law model, for which the photon index is fixed at 1.54 as measured by the persistent spectrum. These results imply that there is a possibility that the spectrum composition that employs an optically thick component and a hard power-law component can describe the wide-band spectra of both the persistent and weak-burst emissions, despite the fact that their fluxes differ by two orders of magnitude. Based on the spectral similarity, we discuss a possible connection between the unresolved short bursts and the persistent emission.

Keywords: stars: magnetars; pulsars: individual: 1E 1547.0-5408; pulsars: individual: SGR J1550-5418; pulsars: individual: PSR J1550-5418; pulsars: individual: G327.24-013; ISM: supernova remnant

Journal Article.  10161 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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