Journal Article

An X-Ray Emitting Supernova Remnant Candidate, M 33 X-4

Yuu Okada, Hiromitsu Takahashi and Kazuo Makishima

in Publications of the Astronomical Society of Japan

Volume 53, issue 4, pages 663-668
Published in print August 2001 | ISSN: 0004-6264
Published online August 2001 | e-ISSN: 2053-051X | DOI:

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  • Galaxies
  • Astronomy and Astrophysics
  • Interstellar Medium


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Based on ASCA observations of the Local-Group spiral galaxy M 33, a report is made on the X-ray properties of luminous X-ray source called X-4, which is located in a giant H ii region in M 33. The 0.8-8.0keV spectrum of X-4 is described by a two-component model, consisting of a thin thermal plasma emission with a temperature of [math], and a power law emission with a photon index of [math]. The two spectral components cross over at [math]. These spectral properties are similar to those of a young supernova remnant (SNR), except that the 0.8-8.0keV luminosity of M 33 X-4, [math], is considerably higher than those of the SNRs in the Milky Way. There is also evidence of excess absorption, or an over-abundance of [math]-elements relative to iron. If this source is an SNR, the hard component is thought to be synchrotron radiation from high-energy particles, produced either by shock acceleration, like in SN 1006, or by a central neutron star, like in the Crab Nebula.

Keywords: galaxies: individual (M 33); galaxies: spiral; ISM: supernova remnants; X-rays: galaxies

Journal Article.  3523 words.  Illustrated.

Subjects: Galaxies ; Astronomy and Astrophysics ; Interstellar Medium