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The X-ray bursts within the 2010 outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021

  • Ziwei Wu
  • Guoqiang Ding
  • Zhibing Li
  • Yupeng Chen
  • Jinlu Qu
Original Article

Abstract

With the observations from Rossi X-ray Timing Explorer, we search and study the X-ray bursts of accreting millisecond X-ray pulsar SAX J1748.9-2021 during its 2010 outburst. We find 13 X-ray bursts, including 12 standard type-I X-ray bursts and an irregular X-ray burst which lacks cooling tail. During the outburst, the persistent emission occurred at \(\sim (1\mbox{--}5)\%{\dot{\mathrm{M}}_{\mathrm{Edd}}}\). We use a combination model of a blackbody (BB), a powerlaw, and a line component to fit the persistent emission spectra. Another BB is added into the combination model to account for the emission of the X-ray bursts due to the thermonuclear burning on the surface of the neutron star. Finally, we modify the combination model with a multiplicative factor \(f_{\mathrm{a}}\), plus a BB to fit the spectra during the X-ray bursts. It is found that the \(f_{\mathrm{a}}\) is inversely correlated with the burst flux in some cases. Our analysis suggests that the ignition depth of the irregular X-ray burst is obviously smaller than those of the type-I X-ray bursts. We argue that the detected type-I X-ray bursts originate from helium-rich or pure-helium environment, while the irregular X-ray burst originates from the thermonuclear flash in a shallow ocean.

Keywords

Stars: neutron X-rays: bursts Individual (SAX J1748.9-2021) 

Notes

Acknowledgements

We thank the anonymous referee for her or his constructive comments and suggestions, which helped us to improve the presentation of this paper. This research has made use of the data obtained through the High Energy Astrophysics Science Archive Research Center (HEASARC) On-line Service, provided by NASA/Goddard Space Flight Center (GSFC). This work is supported by the National Program on Key Research and Development Project (Grant Nos. 2016YFA0400804, 2016YFA0400803), the Natural Science Foundation of China (Grant Nos. 11673023, 11733009), and the 2014 Project of Xinjiang Uygur Autonomous Region of China for Flexibly Fetching in Upscale Talents.

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Copyright information

© Springer Nature B.V. 2018

Authors and Affiliations

  • Ziwei Wu
    • 1
    • 2
  • Guoqiang Ding
    • 1
  • Zhibing Li
    • 1
  • Yupeng Chen
    • 3
  • Jinlu Qu
    • 3
  1. 1.Xinjiang Astronomical ObservatoryChinese Academy of SciencesUrumqiChina
  2. 2.University of Chinese Academy of SciencesBeijingChina
  3. 3.Key Laboratory for Particle Astrophysics, Institute of High Energy PhysicsChinese Academy of SciencesBeijingChina

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