Determining interstellar dust properties with scattered X-ray halo

• Published in: Earth, planets, and space Vol. 63; no. 10; pp. 1047 - 1050
• Main Authors: Ling, Zhixing, Zhang, Shuang Nan
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.01.2011; Terra; Springer Nature B.V
• Subjects: Cosmochemistry. Extraterrestrial geology; Dust; Earth; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; Gamma ray bursts; Geology; Geophysics/Geodesy; Grains; Halos; Photons; Time lag; X-rays; Cyg X-3; dust grain; Cyg X-1; halo; Scattering; GRB; models; Galaxies; Interstellar dust; X-rays; concentration; Gamma ray burst; haloes; Earth; point sources; Dust grain; instruments; Light curve; geometry; Interstellar matter
• DOI: 10.5047/eps.2011.02.004
• ISSN: 1343-8832

X-ray photons, emitted by X-ray sources, are absorbed and scattered by dust grains when they travel through interstellar medium. The scattered photons within small angles result in a diffuse X-ray “halo”. Therefore, the scattered X-ray photons carry information about various properties of the dust. We study the light curves of the dust-scattered X-ray halo of Cyg X-1. Significant time lags are found between the light curves of the point source and its halo. This time lag increases with the angular distance. This can be caused by a dust concentration at 1.75 kpc from the Earth along the line of sight (LOS), with a width of Δ L = 33 pc. The time lag of Cyg X-3 also reveals a dust concentration between the point source and the Earth, and the distance of Cyg X-3 is estimated to be about 7.2 kpc. The origin of these dust concentrations is still not clearly known. Along with recent results on the dust halos of Gamma Ray Bursts (GRBs), we conclude that the dust distribution is quite nonuniform. We also study dust properties with an expanding X-ray ring from the observation of a distant GRB. The distribution of the halo photons can be used to determine the dust-radius model. Our preliminary results show that dust grain geometries may vary significantly across the Galaxy. We also propose to use the scattered X-ray halo to study the composition of the dust grains. The applicability of this method needs to be tested with advanced instruments in the future.