Astrophys. J., 875, 68-68 (2019/April-2)
Optical counterparts of ULXs and their host environments in NGC 4490/4485.
AVDAN S., AKYUZ A., VINOKUROV A., AKSAKER N., AVDAN H., FABRIKA S., VALEEV A., AKKAYA-ORALHAN I. and BALMAN S.
Abstract (from CDS):
We report the identification of the possible optical counterparts of five out of seven ultraluminous X-ray sources (ULXs) in the galaxy pair NGC 4490/4485. Using archival Hubble Space Telescope (HST) imaging data, we identified a single optical candidate for two ULXs (X-4 and X-7) and multiple optical candidates for the other three (X-2, X-3, and X-6) within ∼0.''2 error radius at the 90% confidence level. 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 NGC 4490. Absolute magnitudes (MV) of the optical candidates lie between -5.7 and -3.8. Color-magnitude diagrams have been used to investigate the properties of the counterparts and their environments. The locations of the counterparts of X-2, X-4, and X-6 suggest possible association with a nearby group of stars, while the others have no association with a star cluster or group of stars. For comparison purposes, we analyzed three previously unused archival XMM-Newton observations. The long-term X-ray light curves of the sources (except transient X-7) show variability by a factor of three on a timescale of more than a decade. The use of a disk blackbody model for the mass of the compact objects indicates that these objects most likely have masses in the range 10-15 M☉.
© 2019. The American Astronomical Society. All rights reserved.
galaxies: individual: (NGC 4490,4485) - X-rays: general
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