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 7 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${}_{-0.5}^{+0.9}$ hr, we deduce that the source is accreting almost pure helium ($X\le 0.1$) fuel. Two bursts occurred just 18 minutes 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 $30\pm 10$ degrees, we estimate the distance to be $14\pm 2$ kpc, where we report the statistical uncertainty but note that there could be up to $20\%$ variation in the distance due to systematic effects discussed in the paper. The corresponding maximum accretion rate is $0.30\pm 0.05$ 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.

10 pages, 6 figures, 2 tables. Accepted for publication in MNRAS

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Cited by in corpus (7)

• Low-Mass X-ray Binaries
• UltraCompCAT: a comprehensive Catalogue of Ultra-Compact and Short Orbital Period X-ray Binaries
• The Galactic LMXB Population and the Galactic Centre Region
• Catalog of outbursts of neutron star LMXBs
• A Machine Learning Approach For Classifying Low-mass X-ray Binaries Based On Their Compact Object Nature
• Robust inference of neutron-star parameters from thermonuclear burst observations
• SRG/ART-XC all-sky X-ray survey: Catalog of sources detected during the first year