XMMU J181227.8-181234: a new ultracompact X-ray binary candidate. (arXiv:1904.10970v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Goodwin_A/0/1/0/all/0/1">A. J. Goodwin</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Galloway_D/0/1/0/all/0/1">D. K. Galloway</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Zand_J/0/1/0/all/0/1">J. J. M. in 't Zand</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Kuulkers_E/0/1/0/all/0/1">E. Kuulkers</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Bilous_A/0/1/0/all/0/1">A. Bilous</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Keek_L/0/1/0/all/0/1">L. Keek</a> (5) ((1) School of Physics and Astronomy, Monash University, (2) SRON Netherlands Institute for Space Research, (3) ESA/ESTEC, (4) Anton Pannekoek Institute for Astronomy, University of Amsterdam, (5) Department of Astronomy, University of Maryland)
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$^{+0.9}_{-0.5}$
hr, we deduce that the source is accreting almost pure helium ($X leq 0.1$)
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 $30pm{10}$ degrees, we estimate the distance to be
$14pm{2}$ 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
$0.30pm0.05$ 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.
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$^{+0.9}_{-0.5}$
hr, we deduce that the source is accreting almost pure helium ($X leq 0.1$)
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 $30pm{10}$ degrees, we estimate the distance to be
$14pm{2}$ 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
$0.30pm0.05$ 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.
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