Spectroscopic Studies of an Ultraluminous Supersoft X-Ray Source in M81
Abstract
Ultraluminous supersoft X-ray sources (ULSs) exhibit supersoft X-ray spectra with blackbody temperatures below 0.1 keV and bolometric luminosities above 1039 ergs s-1. In this Letter, we report the first optical spectroscopic observations of a ULS in M81 using the LRIS spectrograph on the Keck I telescope. The detected Balmer emission lines show a mean intrinsic velocity dispersion of 400 ± 80 km s-1, which is consistent with that from an accretion disk. The spectral index of the continuum on the blue side is also consistent with the multi-color disk model. The Hα emission line exhibits a velocity of ∼180 km s-1 relative to the local stellar environment, suggesting that this ULS may be a halo system in M81 belonging to an old population. No significant shift is found for the Hα emission line between two observations separated by four nights.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 2015
- DOI:
- 10.1088/2041-8205/802/2/L27
- arXiv:
- arXiv:1508.07651
- Bibcode:
- 2015ApJ...802L..27B
- Keywords:
-
- galaxies: individual: M81;
- X-rays: binaries;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 2015ApJ...802L..27B