X-RAY SPECTRAL AND OPTICAL PROPERTIES OF A ULX IN NGC 4258 (M106)

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Avdan H., Avdan S., AKYÜZ A., Balman S., AKSAKER N., AKKAYA ORALHAN I.

ASTROPHYSICAL JOURNAL, cilt.828, sa.2, 2016 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 828 Sayı: 2
  • Basım Tarihi: 2016
  • Doi Numarası: 10.3847/0004-637x/828/2/105
  • Dergi Adı: ASTROPHYSICAL JOURNAL
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Anahtar Kelimeler: galaxies: individual (NGC 4258), X-rays: binaries, X-rays: general, MASS BLACK-HOLES, MEDIUM-SENSITIVITY SURVEY, XMM-NEWTON OBSERVATIONS, ACCRETION DISKS, STATE TRANSITIONS, BINARY-SYSTEMS, 1313 X-1, EMISSION, GALAXY, COUNTERPARTS
  • Orta Doğu Teknik Üniversitesi Adresli: Evet

Özet

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-X similar to 2 x 10(39) erg s(-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 sigma error radius of 0 ''.3. The brightest one has an absolute magnitude of M-V approximate to -7.0 and shows extended structure. The remaining two sources have absolute magnitudes of M-V approximate to -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 10-15M(circle dot), indicating that the compact source is most likely a stellar-mass black hole.