X-RAY SPECTRAL AND OPTICAL PROPERTIES OF A ULX IN NGC 4258 (M106)
Journal Article
·
· Astrophysical Journal
- Department of Physics, Cukurova University, 01330 Adana (Turkey)
- Department of Physics, Middle East Technical University, 06800 Ankara (Turkey)
- Space Sciences and Solar Energy Research and Application Center (UZAYMER), Cukurova University, 01330 Adana (Turkey)
We study the X-ray and optical properties of the ultraluminous X-ray source (ULX) X-6 in the nearby galaxy NGC 4258 (M106) based on the archival XMM-Newton , Chandra , Swift , and Hubble Space Telescope (HST) observations. The source has a peak luminosity of L {sub X} ∼ 2 × 10{sup 39} erg s{sup −1} in the XMM-Newton observation of 2004 June. Consideration of the hardness ratios and the spectral model parameters shows that the source seems to exhibit possible spectral variations throughout the X-ray observations. In the images from the HST /Advanced Camera for Surveys, three optical sources have been identified as counterpart candidates within the 1 σ error radius of 0.″3. The brightest one has an absolute magnitude of M {sub V} ≈ −7.0 and shows extended structure. The remaining two sources have absolute magnitudes of M {sub V} ≈ −5.8 and −5.3. The possible spectral types of the candidates from brightest to dimmest were determined as B6–A5, B0–A7, and B2–A3. The counterparts of the X-ray source possibly belong to a young star cluster. Neither the standard disk model nor the slim disk model provides firm evidence to determine the spectral characteristics of ULX X-6. We argue that the mass of the compact object lies in the range 10–15 M {sub ☉}, indicating that the compact source is most likely a stellar-mass black hole.
- OSTI ID:
- 22667438
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 828; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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