X-ray scattered halo around IGR J17544-2619

Junjie Mao, Zhixing Ling, Shuang-Nan Zhang

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

X-ray photons coming from an X-ray point source not only arrive at the detector directly, but also can be strongly forward-scattered by the interstellar dust along the line of sight (LOS), leading to a detectable diffuse halo around the X-ray point source. The geometry of small angle X-ray scattering is straightforward, namely, the scattered photons travel longer paths and thus arrive later than the unscattered ones; thus the delay time of X-ray scattered halo photons can reveal information of the distances of the interstellar dust and the point source. Here we present a study of the X-ray scattered around IGR J17544-2619, which is one of the so-called supergiant fast X-ray transients. IGR J17544-2619 underwent a striking outburst when observed with Chandra on 2004 July 3, providing a near delta-function lightcurve. We find that the X-ray scattered halo around IGR J17544-2619 is produced by two interstellar dust clouds along the LOS. The one which is closer to the observer gives the X-ray scattered at larger observational angles; whereas the farther one, which is in the vicinity of the point source, explains the halo with a smaller angular size. By comparing the observational angle of the scattered halo photons with that predicted by different dust grain models, we are able to determine the normalized dust distance. With the delay times of the scattered halo photons, we can determine the point source distance, given a dust grain model. Alternatively we can discriminate between the dust grain models, given the point source distance.
Original languageEnglish
Pages (from-to)1-10
Number of pages10
JournalThe Astrophysical Journal
Volume785
Issue number1
DOIs
Publication statusPublished - 20 Feb 2014

Fingerprint

halos
point sources
dust
x rays
photons
line of sight
time lag
delta function
travel
detectors
geometry
scattering

Keywords

  • astro-ph.HE
  • astro-ph.SR
  • X-rays
  • X-rays: ISM
  • IGR J17544-2619

Cite this

Mao, J., Ling, Z., & Zhang, S-N. (2014). X-ray scattered halo around IGR J17544-2619. The Astrophysical Journal, 785(1), 1-10. https://doi.org/10.1088/0004-637X/785/1/23
Mao, Junjie ; Ling, Zhixing ; Zhang, Shuang-Nan. / X-ray scattered halo around IGR J17544-2619. In: The Astrophysical Journal. 2014 ; Vol. 785, No. 1. pp. 1-10.
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Mao, J, Ling, Z & Zhang, S-N 2014, 'X-ray scattered halo around IGR J17544-2619', The Astrophysical Journal, vol. 785, no. 1, pp. 1-10. https://doi.org/10.1088/0004-637X/785/1/23

X-ray scattered halo around IGR J17544-2619. / Mao, Junjie; Ling, Zhixing; Zhang, Shuang-Nan.

In: The Astrophysical Journal, Vol. 785, No. 1, 20.02.2014, p. 1-10.

Research output: Contribution to journalArticle

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AU - Zhang, Shuang-Nan

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N2 - X-ray photons coming from an X-ray point source not only arrive at the detector directly, but also can be strongly forward-scattered by the interstellar dust along the line of sight (LOS), leading to a detectable diffuse halo around the X-ray point source. The geometry of small angle X-ray scattering is straightforward, namely, the scattered photons travel longer paths and thus arrive later than the unscattered ones; thus the delay time of X-ray scattered halo photons can reveal information of the distances of the interstellar dust and the point source. Here we present a study of the X-ray scattered around IGR J17544-2619, which is one of the so-called supergiant fast X-ray transients. IGR J17544-2619 underwent a striking outburst when observed with Chandra on 2004 July 3, providing a near delta-function lightcurve. We find that the X-ray scattered halo around IGR J17544-2619 is produced by two interstellar dust clouds along the LOS. The one which is closer to the observer gives the X-ray scattered at larger observational angles; whereas the farther one, which is in the vicinity of the point source, explains the halo with a smaller angular size. By comparing the observational angle of the scattered halo photons with that predicted by different dust grain models, we are able to determine the normalized dust distance. With the delay times of the scattered halo photons, we can determine the point source distance, given a dust grain model. Alternatively we can discriminate between the dust grain models, given the point source distance.

AB - X-ray photons coming from an X-ray point source not only arrive at the detector directly, but also can be strongly forward-scattered by the interstellar dust along the line of sight (LOS), leading to a detectable diffuse halo around the X-ray point source. The geometry of small angle X-ray scattering is straightforward, namely, the scattered photons travel longer paths and thus arrive later than the unscattered ones; thus the delay time of X-ray scattered halo photons can reveal information of the distances of the interstellar dust and the point source. Here we present a study of the X-ray scattered around IGR J17544-2619, which is one of the so-called supergiant fast X-ray transients. IGR J17544-2619 underwent a striking outburst when observed with Chandra on 2004 July 3, providing a near delta-function lightcurve. We find that the X-ray scattered halo around IGR J17544-2619 is produced by two interstellar dust clouds along the LOS. The one which is closer to the observer gives the X-ray scattered at larger observational angles; whereas the farther one, which is in the vicinity of the point source, explains the halo with a smaller angular size. By comparing the observational angle of the scattered halo photons with that predicted by different dust grain models, we are able to determine the normalized dust distance. With the delay times of the scattered halo photons, we can determine the point source distance, given a dust grain model. Alternatively we can discriminate between the dust grain models, given the point source distance.

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Mao J, Ling Z, Zhang S-N. X-ray scattered halo around IGR J17544-2619. The Astrophysical Journal. 2014 Feb 20;785(1):1-10. https://doi.org/10.1088/0004-637X/785/1/23