Volume 436, Number 2, June III 2005
|Page(s)||647 - 652|
|Section||Stellar structure and evolution|
|Published online||30 May 2005|
INTEGRAL spectroscopy of the accreting millisecond pulsar XTE J1807-294 in outburst
CEA Saclay, DSM/DAPNIA/Service d'Astrophysique (CNRS FRE 2591), 91191 Gif-sur-Yvette, France e-mail: email@example.com
2 Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
3 Dipartimento di Fisica, Università di Ferrara, via Paradiso 12, 44100 Ferrara, Italy
4 Observatoire Astronomique, 11 rue de l'Université, 67000 Strasbourg, France
5 Laboratory for Particle Astrophysics, Institute of High Energy Physics, CAS, Beijing 100039, PR China
6 SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
Accepted: 7 March 2005
The transient X-ray accreting millisecond pulsar XTE J1807-294 was observed during its February/March 2003 outburst by INTEGRAL, partly simultaneously with the XMM-Newton and RXTE satellites. We present here the first study of the 0.5-200 keV broad-band spectra of the source. On February 28, the source spectrum was consistent with thermal Comptonization by electrons of temperature ~40 keV, considerably higher than the value (~10 keV) previously derived from the low energy XMM-Newton data alone. The source is detected by INTEGRAL up to 200 keV with a luminosity in the energy band (0.1-200) keV of erg s-1 (assuming a distance of 8 kpc). 22 days later the luminosity dropped to erg s-1. A re-analysis of XMM-Newton data yields the orbital Doppler variations of the pulse period and refines the previous ephemeris. For this source, with shortest orbital period of any known binary radio or X-ray millisecond pulsar, we constrain the companion mass , assuming minimum mass transfer driven by gravitational radiation. Only evolved dwarfs with a C/O composition are consistent with the Roche lobe and gravitational radiation constraints, while He dwarfs require an unlikely low inclination.
Key words: accretion, accretion disks / X-rays: binaries / stars: individual: XTE J1807-294 / stars: neutron
© ESO, 2005
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