Open AccessDiscovery of Spectral Transitions from Two Ultraluminous Compact X-Ray Sources in IC 342
Author(s) -
Aya Kubota,
Tsunefumi Mizuno,
Kazuo Makishima,
Yasushi Fukazawa,
J. Kotoku,
T. Ohnishi,
M. Tashiro
Publication year - 2001
Publication title -
the astrophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.376
H-Index - 489
eISSN - 1538-4357
pISSN - 0004-637X
DOI - 10.1086/318903
Subject(s) - physics , astrophysics , spiral galaxy , luminosity , galaxy , accretion (finance) , spiral (railway) , black hole (networking) , accretion disc , spectral shape analysis , photon , spectral line , spectral index , optics , astronomy , mathematical analysis , computer network , routing protocol , routing (electronic design automation) , mathematics , computer science , link state routing protocol
Two {\it ASCA} observations were made of two ultra-luminous compact X-raysources (ULXs), Source 1 and Source 2, in the spiral galaxy IC 342. In the 1993observation, 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 spectrumof photon index $\sim 1.4$. As already reported, Source 1 was $\sim 3$ timesbrighter on that occasion, and exhibited a soft spectrum represented by amulti-color disk model of inner-disk temperature $ \sim 1.8$ keV. The secondobservation made in February 2000 revealed that Source 1 had made a transitioninto a hard spectral state, while Source 2 into a soft spectral state. The ULXsare therefore inferred to exhibit two distinct spectral states, and sometimesmake transitions between them. These results significantly reinforce thescenario which describes ULXs as mass-accreting black holes.Comment: 11 pages, 3 figures; acceoted for ApJ
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