XMMU J181227.8-181234: a new ultracompact X-ray binary candidate
Abstract
We report the discovery of Type I (thermonuclear) X-ray bursts from the transient source XMMU J181227.8-181234 = XTE J1812-182. We found seven X-ray bursts in Rossi X-ray Timing Explorer observations during the 2008 outburst, confirming the source as a neutron star low-mass X-ray binary. Based on the measured burst fluence and the average recurrence time of 1.4^{+0.9}_{-0.5} h, we deduce that the source is accreting almost pure helium (X ≤ 0.1) fuel. Two bursts occurred just 18 min apart; the first short waiting time bursts observed in a source accreting hydrogen-poor fuel. Taking into consideration the effects on the burst and persistent flux due to the inferred system inclination of 30 ± 10°, we estimate the distance to be 14 ± 2 kpc, where we report the statistical uncertainty but note that there could be up to 20{{ per cent}} variation in the distance due to systematic effects discussed in the paper. The corresponding maximum accretion rate is 0.30 ± 0.05 times the Eddington limit. Based on the low hydrogen content of the accreted fuel and the short average recurrence time, we classify the source as a transient ultracompact low-mass X-ray binary.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2019
- DOI:
- 10.1093/mnras/stz1094
- arXiv:
- arXiv:1904.10970
- Bibcode:
- 2019MNRAS.486.4149G
- Keywords:
-
- stars: neutron;
- X-rays: binaries;
- X-rays: bursts;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, 6 figures, 2 tables. Accepted for publication in MNRAS