The optical counterparts of Accreting Millisecond X-Ray Pulsars during quiescence

Дата и время публикации : 2009-11-13T00:20:35Z

Авторы публикации и институты :
P. D’Avanzo
S. Campana
J. Casares
S. Covino
G. L. Israel
L. Stella

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: Accepted for publication by A&A; 12 pages, 12 figures
Первичная категория: astro-ph.SR

Все категории : astro-ph.SR

Краткий обзор статьи: Eight Accreting Millisecond X-ray Pulsars (AMXPs) are known to date. Optical and NIR observations carried out during quiescence give a unique opportunity to constrain the nature of the donor star and to investigate the origin of the observed quiescent luminosity at long wavelengths. Using data obtained with the ESO-Very Large Telescope, we performed a deep optical and NIR photometric study of the fields of XTE J1814-338 and of the ultracompact systems XTE J0929-314 and XTE J1807-294 during quiescence in order to look for the presence of a variable counterpart. If suitable candidates were found, we also carried out optical spectroscopy. We present here the first multi-band (VR) detection of the optical counterpart of XTE J1814-338 in quiescence together with its optical spectrum. The optical light curve shows variability in both bands consistent with a sinusoidal modulation at the known 4.3 hr orbital period and presents a puzzling decrease of the V-band flux around superior conjunction that may be interpreted as a partial eclipse. The marginal detection of the very faint counterpart of XTE J0929-314 and deep upper limits for the optical/NIR counterpart of XTE J1807-294 are also reported. We also briefly discuss the results reported in the literature for the optical/NIR counterpart of XTE J1751-305. Our findings are consistent with AMXPs being systems containing an old, weakly magnetized neutron star, reactivated as a millisecond radio pulsar during quiescence which irradiates the low-mass companion star. The absence of type I X-ray bursts and of hydrogen and helium lines in outburst spectra of ultracompact (P_orb < 1 hr) AMXPs suggests that the companion stars are likely evolved dwarf stars.

Category: Physics