Discovery of Optical Pulsations in V2116 Ophiuchi ≡ GX 1+4
Open Access
- 20 June 1997
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 482 (2) , L171-L174
- https://doi.org/10.1086/310699
Abstract
We report the detection of pulsations with an approximately 124 s period in V2116 Oph, the optical counterpart of the low-mass X-ray binary GX 1+4. The pulsations are sinusoidal with modulation amplitude of up to 4% in blue light and were observed in 10 different observing sessions during 1996 April-August using a CCD photometer at the 1.6 m and 0.6 m telescopes of Laboratório Nacional de Astrofísica, in Brazil. The pulsations were also observed with the UBVRI fast photometer. With only one exception, the observed optical periods are consistent with those observed by the BATSE instrument on board the Compton Gamma Ray Observatory at the same epoch. There is a definite correlation between the observability of pulsations and the optical brightness of the system: V2116 Oph had R magnitude in the range 15.3-15.5 when the pulsed signal was detected, and R = 16.0-17.7 when no pulsations were present. The discovery makes GX 1+4 only the third of about 40 accretion-powered X-ray pulsars to be firmly detected as a pulsating source in the optical. The presence of flickering and pulsations in V2116 Oph adds strong evidence for an accretion disk scenario in this system. The absolute magnitude of the pulsed component on 1996 May 27 is estimated to be MV ~ -1.5. The implied dimensions for the emitting region are 1.1 R☉, 3.2 R☉, and 7.0 R☉, for blackbody spectral distributions with T = 105 K, 2 × 104 K, and 1 × 104 K, respectively.Keywords
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