Jonker, P. G., Steeghs, D., Chakrabarty, Deepto and Juett, Adrienne M. (2007) The cold neutron star in the soft X-ray transient 1H-1905+000. Astrophysical Journal, Vol.665 (No.2). L147-L150. doi:10.1086/521079 ISSN 0004-637X.

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Abstract

We report on our analysis of 300 ks of Chandra observations of the neutron star soft X-ray transient 1H 1905+000 in quiescence. We do not detect the source down to a 95% confidence unabsorbed flux upper limit of 2 x 10(-16) ergs cm(-2) s(-1) in the 0.5-10 keV energy range for an assumed Gamma = 2 power-law spectral model. A limit of 1.4 x 10(-16) ergs cm(-2) s(-1) is derived if we assume that the spectrum of 1H 1905+000 in quiescence is described well with a blackbody of temperature of 0.2 keV. For the upper limit to the source distance of 10 kpc this yields a 0.5-10 keV luminosity limit of 2.4 x 10(30) ergs s(-1)/1.7 x 10(30) ergs s(-1) for the abovementioned power law or blackbody spectrum, respectively. This luminosity limit is lower than the luminosity of A0620-00, the weakest black hole soft X-ray transient in quiescence reported so far. Together with the uncertainties in relating the mass transfer and mass accretion rates we come to the conclusion that the claim that there is evidence for the presence of a black hole event horizon on the basis of a lower quiescent luminosity for black holes than for neutron stars is unproven. We also briefly discuss the implications of the low quiescent luminosity of 1H 1905+000 for the neutron star equation of state. Using deep Magellan images of the field of 1H 1905+000 obtained at excellent observing conditions, we do not detect the quiescent counterpart of 1H 1905+000 at the position of the outburst optical counterpart down to a magnitude limit of i' > 25.3. This can be converted to a limit on the absolute magnitude of the counterpart of I >9.6, which implies that the counterpart can only be a brown or a white dwarf.

Item Type:	Journal Article
Subjects:	Q Science > QB Astronomy
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Library of Congress Subject Headings (LCSH):	X-ray binaries, Neutron stars, Black holes (Astronomy)
Journal or Publication Title:	Astrophysical Journal
Publisher:	IOP Publishing
ISSN:	0004-637X
Official Date:	20 August 2007
Dates:	Date Event 20 August 2007 Published
Volume:	Vol.665
Number:	No.2
Number of Pages:	4
Page Range:	L147-L150
DOI:	10.1086/521079
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Date of first compliant deposit:	14 December 2015
Date of first compliant Open Access:	14 December 2015
Funder:	United States. National Aeronautics and Space Administration (NASA), Nederlandse Organisatie voor Wetenschappelijk Onderzoek [Netherlands Organisation for Scientific Research] (NWO), Particle Physics and Astronomy Research Council (Great Britain) (PPARC), Science and Technology Facilities Council (Great Britain) (STFC)
Grant number:	G06-7032X (NASA)

Data sourced from Thomson Reuters' Web of Knowledge

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