The Reappearance of the Transient Low Mass X-ray Binary X1658−298
نویسنده
چکیده
In April 1999 the transient low mass X-ray binary X1658−298 resumed its strong and persistent X-ray emission after a 21-year interval of quiescence. We present RXTE data obtained soon after the reappearance, including four eclipses with a mean duration of 901.9±0.8 sec and ingress/egress times of 6–13 sec. Our updated ephemeris for the source indicates that the 7.1-hr orbital period of the system is decreasing with a timescale of 10 yr. Contemporaneous optical observations provide the first-ever lightcurve of V2134 Oph, the optical counterpart of X1658−298. The optical modulation is highly variable from night to night and exhibits a distinct, narrow eclipse feature of about 0.2 mag superposed on a gradual brightness variation with ∼ 0.7 − 0.8 mag amplitude. Our data indicate that there is no significant offset between the time of mid-eclipse in the X-ray and optical and that the narrow optical eclipse feature is of the same duration as the X-ray eclipse. This implies an accretion disk structure characterized by enhanced optical emission coincident with the central X-ray emitting area. Subject headings: accretion, accretion disks — binaries: close — binaries: eclipsing — stars: individual (V2134 Oph) — stars: neutron — stars: variables: other — X-rays: stars
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