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arXiv:astro-ph/0011232 (astro-ph)
[Submitted on 12 Nov 2000]

Title:Discovery of Spectral Transitions from Two Ultra-Luminous Compact X-Ray Sources in Ic342

Authors:Aya Kubota (1), Tsunefumi Mizuno (2), Kazuo Makishima (1), Yasushi Fukazawa (2), Jun'ichi Kotoku (1), Tomohisa Ohnishi (1), Makoto Tashiro (3) ((1) University of Tokyo, (2) Hiroshima University (3) Saitama University)
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Abstract: Two {\it ASCA} observations were made of two ultra-luminous compact X-ray sources (ULXs), Source 1 and Source 2, in the spiral galaxy IC 342. In the 1993 observation, Source 2 showed a 0.5--10 keV luminosity of $6 \times 10^{39}$ ergs s$^{-1}$ (assuming a distance of 4.0 Mpc), and a hard power-law spectrum of photon index $\sim 1.4$. As already reported, Source 1 was $\sim 3$ times brighter on that occasion, and exhibited a soft spectrum represented by a multi-color disk model of inner-disk temperature $ \sim 1.8$ keV. The second observation made in February 2000 revealed that Source 1 had made a transition into a hard spectral state, while Source 2 into a soft spectral state. The ULXs are therefore inferred to exhibit two distinct spectral states, and sometimes make transitions between them. These results significantly reinforce the scenario which describes ULXs as mass-accreting black holes.
Comments: 11 pages, 3 figures; acceoted for ApJL
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:astro-ph/0011232
  (or arXiv:astro-ph/0011232v1 for this version)
  https://doi.org/10.48550/arXiv.astro-ph/0011232
Related DOI: https://doi.org/10.1086/318903

Submission history

From: Aya Kubota [view email]
[v1] Sun, 12 Nov 2000 12:53:50 UTC (274 KB)
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