X-ray outburst of 4U 0115+634 and ROTSE observations of its optical counterpart V635 Cas

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Baykal A., Kiziloglu U., Kiziloglu N., Balman S., Inam S.

ASTRONOMY & ASTROPHYSICS, vol.439, no.3, pp.1131-1134, 2005 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 439 Issue: 3
  • Publication Date: 2005
  • Doi Number: 10.1051/0004-6361:20052968
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.1131-1134
  • Middle East Technical University Affiliated: Yes


ROTSE IIId ( The Robotic Optical Transient Experiment) observations of the X-ray binary system 4U 0115+634/V635 Cas obtained during 2004 June and 2005 January make it possible, for the first time, to study the correlation between optical and type II X-ray outbursts. The X-ray outburst sharply enhanced after periastron passage where the optical brightness was reduced by 0.3 mag for a few days. We interpret the sharp reduction of optical brightness as a sign of mass ejection from the outer parts of the disc of the Be star. After this sharp decrease, the optical brightness rose again and reached the pre-X-ray outburst level. Afterwards, a gradual decrease of the optical brightness followed until a minimum then a gradual increase started again. Qualitatively, the change of the optical lightcurve suggests a precession of the Be star disc of around a few hundred days. We also investigate the periodic signatures from the archival RXTE-ASM (Rossi X-ray Timing Explorer - All Sky Monitor) light curve covering a time span of similar to 9 years. We find significant orbital modulation in the ASM light curve during the type I X-ray outburst.