No orbital polarization modulation at P_orb or P_orb/2 is detected in combined IXPE data for Cygnus X-1, with 99% upper limits of 0.54-2.13% on P_orb/2 amplitude across 2-8 keV bands, consistent with sensitivity limits.
An Improved Orbital Ephemeris for Cygnus X-1
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abstract
By accumulating all available radial velocity data and combining it with our own spectroscopy we present a new and improved ephemeris for Cygnus X-1 (V1357 Cygni/HDE226868). We initially calculate an orbital period of 5.599847+/-0.000018.days and then, by including the more recent radial velocities of LaSala et al. (1998) and Sowers et al.(1998) we refine this to 5.599829+/-0.000016 days. Using 27 years' worth of photometry, we also calculate a photometric period of 5.599836+/-0.000024 - remarkably similar to the spectroscopic one.
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Energy-Resolved Limits on Orbital X-ray Polarization Modulation in Cygnus X-1
No orbital polarization modulation at P_orb or P_orb/2 is detected in combined IXPE data for Cygnus X-1, with 99% upper limits of 0.54-2.13% on P_orb/2 amplitude across 2-8 keV bands, consistent with sensitivity limits.