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SUMMARY:Variability of X-ray polarization of Cyg X-1
DTSTART:20260420T103000Z
DTEND:20260420T110000Z
DTSTAMP:20260530T234900Z
UID:indico-event-15@events.gw.iucaa.in
DESCRIPTION:Speakers: Sudeb Ranjan Datta (IUCAA)\n\nArXiv Link: https://ar
 xiv.org/abs/2505.03942\n \nWe present the results of a three-year X-ray\,
  optical\, and radio polarimetric monitoring campaign of the prototypical 
 black hole X-ray binary Cyg X-1\, conducted from 2022 to 2024. The X-ray p
 olarization of Cyg X-1 was measured 13 times with the Imaging X-ray Polari
 metry Explorer (IXPE)\, covering both hard and soft spectral states. The X
 -ray polarization degree (PD) in the hard state was found to be ≈4.0%\, 
 roughly twice as high as in the soft state\, where it was around 2.2%. In 
 both states\, a statistically significant increase of PD with the energy w
 as found. Moreover\, a linear relation between PD and spectral hardness su
 ggests a gradual and continuous evolution of the polarization properties\,
  rather than an abrupt change of polarization production mechanism between
  states. The polarization angle (PA) was independent of the spectral state
  and showed no trend with the photon energy. The X-ray PA is well aligned 
 with the orientation of the radio jet\, as well as the optical and radio P
 As. We find significant orbital changes of PA in the hard state\, which we
  attribute to scattering of X-ray emission at intrabinary structure. No si
 gnificant superorbital variability in PD or PA was found at the period Pso
  = 294 d. We also find no correlation between the X-ray and optical polari
 zation\; if any\, there is a long-term anti-correlation between the X-ray 
 PD and the radio PD.\n \n\nhttps://events.gw.iucaa.in/event/15/
LOCATION:Lecture Hall/Bhaskara-1 (IUCAA\, Pune\, India)
URL:https://events.gw.iucaa.in/event/15/
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