Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...20925407s&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #254.07; Bulletin of the American Astronomical Society,
Astronomy and Astrophysics
Astronomy
Scientific paper
We continue the photometric monitoring of Cygnus X-1 (P = 5.6-d (O9I + BH)) in UBV and Hα (wide and narrow) filters began in 2000 using the 0.8-m Four College APT. We search for variations in the long term X-ray emissions and correlate these with contemporaneous optical photometry. We present the analysis of 10-yrs. of X-ray (soft/hard) data obtained from the RXTE long term All Sky Monitoring Archive. Cyg X-1 has been reported by many observers to undergo many short and long-term variations. The largest optical variations in our U-band data are of the order of ΔU 0.08 mag over a period of 7 years. The low amplitude (0.04-0.05 mag) quasi-sinusoidal 5.6-d light variations commonly seen are primarily orbital and arise from the motions of the tidally distorted (and X-ray heated) O9 supergiant. These are superimposed on long-term variations with time scales of months to years. The X-ray data exhibit variations (albeit small but significant) reflecting the 5.6-d orbital period. The X-rays undergo transitions between two distinct X-ray spectral states. A hard (5.0 - 12.0 keV) state and a soft (1.3 - 3.0 keV) state. In both, the X-ray spectrum is characterized by power laws of different indices. Typically the system spends most of its time in the soft state and the hard-soft transitions are faster than the soft-hard. Here we discuss our study of the system’s X-ray activity and probe possible correlations between the X-ray high/low states and the UBV light curves. We believe the X-ray variations, i.e. the transition between the states, reflect the intrinsic activity of the supergiant component via variation in its stellar winds and dynamics. We present some of the correlations which exist between the optical and X-ray data. This work was supported by NSF/RUI grants NSF-0507542 and AST-0507536 grant.
Guinan Edward
McCook George
Siah Javad
Tammaro E.
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