Discovery of orbital dips and superhumps in the optical counterpart of the X-ray transient GRO J0422+32

Details Discovery of orbital dips and superhumps in the optical counterpart of the X-ray transient GRO J0422+32 Discovery of orbital dips and superhumps in the optical counterpart of the X-ray transient GRO J0422+32

Feb 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995pasj...47...31k&link_type=abstract

PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 47, no. 1, p. 31-39

Astronomy and Astrophysics

Astronomy

36

Accretion Disks, Black Holes (Astronomy), Orbit Calculation, Orbital Elements, Periodic Variations, X Ray Astronomy, X Ray Binaries, Cataclysmic Variables, Light Curve, Mass Ratios, Stability

Scientific paper

We report on the first detection of a period of 0.21211 +/- 0.00002 d (= 5.0906 +/- 0.0005 hr) during decline, and a significantly different period of 0.2157 +/- 0.0010 d (= 5.18 +/- 0.02 hr) during outburst in a newly discovered ultrasoft X-ray transient GRO J0422+32. We interpret these as being the orbital and superhump periods; using the relation between the mass ratio of the binary and the superhump period excess, we succeeded for the first time to estimate the mass ratio of the underlying binary of GRO J0422+32 as being between 5.4 and 20.5, which corresponds to the mass of a compact object between 3.0 and 11.5 solar mass with the assumption of a Roche lobe-filling main-sequence secondary. This fact strongly supports the idea that all ultrasoft X-ray transients contain black holes. The new findings that superhumps appeared only in the X-ray minimum (approximately 100 days after the peak) suggests that it takes a longer time before superhumps appear in X-ray transients than in cataclysmic variables (a few days after the peak). A possible scenario to produce peculiar optical and X-ray light curves of ultrasoft X-ray transients is briefly discussed in connection to the tidal instability of the accretion disk.

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