2018MNRAS.477.3623W -
Mon. Not. R. Astron. Soc., 477, 3623-3645 (2018/July-1)
Discovery of two eclipsing X-ray binaries in M 51.
WANG S., SORIA R., URQUHART R. and LIU J.
Abstract (from CDS):
We discovered eclipses and dips in two luminous (and highly variable) X-ray sources in M 51. One (CXOM51 J132943.3+471135) is an ultraluminous supersoft source, with a thermal spectrum at a temperature of about 0.1 keV and characteristic blackbody radius of about 104 km. The other (CXOM51 J132946.1+471042) has a two-component spectrum with additional thermal-plasma emission; it approached an X-ray luminosity of 1039 erg s–1 during outbursts in 2005 and 2012. From the timing of three eclipses in a series of Chandra observations, we determine the binary period (52.75 ± 0.63 h) and eclipse fraction (22 ±0.1per cent) of CXOM51 J132946.1+471042. We also identify a blue optical counterpart in archival Hubble Space Telescope images, consistent with a massive donor star (mass of ∼20-35 M☉). By combining the X-ray light-curve parameters with the optical constraints on the donor star, we show that the mass ratio in the system must be M2/M1≳18 and therefore the compact object is most likely a neutron star (exceeding its Eddington limit in outburst). The general significance of our result is that we illustrate one method (applicable to high-inclination sources) of identifying luminous neutron star X-ray binaries, in the absence of X-ray pulsations or phase-resolved optical spectroscopy. Finally, we discuss the different X-ray spectral appearance expected from super-Eddington neutron stars and black holes at high viewing angles.
Abstract Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
stars: neutron - galaxies: individual: M51 - X-rays: binaries
Status at CDS
:
Large table(s) will be appraised for possible ingestion in VizieR.
Simbad objects:
20
Full paper
View the references in ADS
To bookmark this query, right click on this link: simbad:2018MNRAS.477.3623W and select 'bookmark this link' or equivalent in the popup menu