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Published in

Oxford University Press (OUP), Monthly Notices of the Royal Astronomical Society, 4(499), p. 5682-5689, 2020

DOI: 10.1093/mnras/staa3073

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Identification of a new ultraluminous X-ray source in NGC 1316

Journal article published in 2020 by S. Allak ORCID, A. Akyuz ORCID, N. Aksaker ORCID, M. Ozdogan Ela ORCID, S. Avdan ORCID, F. Soydugan ORCID
This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Data provided by SHERPA/RoMEO

Abstract

ABSTRACT In this study, we report identification of a new ultraluminous X-ray source (ULX) named as X-7 in NGC 1316, with an unabsorbed luminosity of 2.1 × 1039 erg s−1 using the two recent Chandra archival observations. The X-7 was detected in the Chandra 2001 observation and was included in the source list of the NGC 1316 as CXOUJ032240.8−371224 with a luminosity of 5.7 × 1038 erg s−1. Present luminosity implies a luminosity increase of a factor of ∼4. The best-fitting spectral model parameters indicate that X-7 has a relatively hot disc and hard spectra. If explained by a disc blackbody model, the mass of compact object is estimated as ∼8 M⊙ which is in the range of a stellar-mass black hole. The X-7 shows a relatively long-term count rate variability while no short-term variability is observed. We also identified a unique optical candidate within 0.22 arcsec error circle at 95 per cent confidence level for X-7 using the archival HST/ACS (Hubble Space Telescope/Advanced Camera for Surveys) and HST/WFC3 (The Wide Field Camera 3) data. Absolute magnitude (MV) of this candidate is −7.8 mag. Its spectral energy distribution is adequately fitted a blackbody model with a temperature of 3100 K indicating an M type supergiant, assuming the donor star dominates the optical emission. In addition, we identified a transient ULX candidate (XT-1) located 6 arcsec away from X-7 has a (high) luminosity of ∼1039 erg s−1 with no visible optical candidate.