A Low-mass Main-sequence Star and Accretion Disk in the Very Faint X-Ray Transient M15 X-3
Abstract
We present near-simultaneous {\text{}}{Chandra}/Hubble Space Telescope ({\text{}}{HST}) observations of the very faint (Lx < 1036 erg s-1) X-ray transient source M15 X-3, as well as unpublished archival {\text{}}{Chandra} observations of M15 X-3. The {\text{}}{Chandra} observations constrain the luminosity of M15 X-3 to be <1034 erg s-1 in all observed epochs. The X-ray spectrum shows evidence of curvature, and prefers a fit to a broken power law with break energy {E}{break}={2.7}-0.6+0.4 keV, and power-law indices of {{{Γ }}}1={1.3}-0.2+0.1 and {{{Γ }}}2={1.9}-0.2+0.2 over a single power law. We fit our new F438W (B), F606W (broad V), and F814W (I) HST data on the blue optical counterpart with a model for an accretion disk and a metal-poor main-sequence star. From this fit, we determine the companion to be consistent with a main-sequence star of mass {0.440}-0.060+0.035 M⊙ in a ∼4 hr orbit. X-ray irradiation of the companion is likely to be a factor in the optical emission from the system, which permits the companion to be smaller than calculated above, but larger than 0.15 M⊙ at the 3σ confidence level. M15 X-3 seems to be inconsistent with all suggested hypotheses explaining very faint transient behavior, except for magnetospherically inhibited accretion.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 2015
- DOI:
- 10.1088/0004-637X/807/1/52
- arXiv:
- arXiv:1505.07117
- Bibcode:
- 2015ApJ...807...52A
- Keywords:
-
- accretion;
- accretion disks;
- galaxies: clusters: individual: M15;
- stars: neutron;
- techniques: photometric;
- X-rays: binaries;
- X-rays: individual: M15 X-3;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, 5 figures, accepted for publication in ApJ on May 22, 2015