The Optical Counterpart of the Accreting Millisecond Pulsar SAX J1808.4-3658 in Outburst: Constraints on the Binary Inclination

Wang, Zhongxiang; Chakrabarty, Deepto; Roche, Paul; Charles, Philip A.; Kuulkers, Erik; Shahbaz, Tariq; Simpson, Chris; Forbes, Duncan A.; Helsdon, Stephen F.
Referencia bibliográfica

The Astrophysical Journal, Volume 563, Issue 1, pp. L61-L64.

Fecha de publicación:
12
2001
Número de autores
9
Número de autores del IAC
1
Número de citas
53
Número de citas referidas
42
Descripción
We present multiband optical/IR photometry of V4580 Sgr, the optical counterpart of the accretion-powered millisecond pulsar SAX J1808.4-3658, taken during the 1998 X-ray outburst of the system. The optical flux is consistent with emission from an X-ray-heated accretion disk. Self-consistent modeling of the X-ray and optical emission during the outburst yields a best-fit extinction of AV=0.68+0.37-0.15 and an inclination of cosi=0.65+0.23-0.33 (90% confidence), assuming a distance of 2.5 kpc. This inclination range requires that the stellar companion of the pulsar has extremely low mass, Mc=0.05-0.10 Msolar. Some of the IR observations are inconsistent with disk emission and are too bright to be from either the disk or the companion, even in the presence of X-ray heating.