Discovery of spectral transitions from two ultraluminous compact x-ray sources in IC 342

A. Kubota, T. Mizuno, K. Makishima, Y. Fukazawa, J. Kotoku, T. Ohnishi, M. Tashiro

Research output: Contribution to journalArticlepeer-review

100 Citations (Scopus)


Two ASCA observations were made of two ultraluminous compact X-ray sources (ULXs) in the spiral galaxy IC 342. In the 1993 observation, source 2 showed a 0.5-10 keV luminosity of 6 × 1039 ergs s-1 (assuming a distance of 4.0 Mpc) and a hard power-law spectrum of photon index ∼1.4. As already reported, source 1 was ∼3 times brighter on that occasion and exhibited a soft spectrum represented by a multicolor disk model with an inner-disk temperature of ∼1.8 keV. The second observation, made in 2000 February, revealed that source 1 had made a transition into a hard spectral state, while source 2 made a transition into a soft spectral state. The ULXs are therefore inferred to exhibit two distinct spectral states, and they sometimes make transitions between them. These results significantly reinforce the scenario that describes ULXs as mass-accreting black holes.

Original languageEnglish
Pages (from-to)L119-L122
JournalAstrophysical Journal
Issue number2 PART 2
Publication statusPublished - 2001 Feb 1
Externally publishedYes


  • Black hole physics
  • Galaxies: spiral
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Discovery of spectral transitions from two ultraluminous compact x-ray sources in IC 342'. Together they form a unique fingerprint.

Cite this