A search for optical counterparts of ULX-4 in M51 galaxy


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AKYÜZ A., Avdan S., AKSAKER N., Allak S., Oralhan I.

10th Jubilee Conference of the Balkan Physical Union, BPU 2018, Sofija, Bulgaria, 26 - 30 August 2018, vol.2075 identifier identifier

  • Publication Type: Conference Paper / Full Text
  • Volume: 2075
  • Doi Number: 10.1063/1.5091220
  • City: Sofija
  • Country: Bulgaria

Abstract

We report on the identi cation of the optical counterparts of ve out of seven Ultraluminous X-ray Sources (ULXs) in NGC 4490/4485 galaxy pair. Using archival Hubble Space Telescope (HST) imaging data, we identi ed unique optical counterparts for three ULXs (X-3, X-4 and X-7) and three candidate counterparts for the other two ULXs (X-2 and X-6) within 0:0015 error radius. Of the two remaining ULXs, X-1 has no HST imaging data and photometry could not be performed due to the position of
X-5 in NGC4490. Absolute magnitudes (MV ) of the optical counterparts lie between ??6:3 and ??3:7. Color-Magnitude Diagrams (CMDs) have been used to investigate the properties of counterparts and their environments. The location of the counterparts of X-2, X-4, and X-6 suggest possible association with nearby group of stars while others have no association with a star cluster or a group of stars. For comparison purposes, we analyzed previously unused three archival XMM-Newton observations. The long-term X-ray light curve of the sources (except transient X-7) shows variability by a factor of three
in a time scale more than a decade. The use of disk blackbody (DISKBB) model for the mass of the compact objects indicates that these objects to be most likely in the range 10??15 M .