First Detection of X-ray Polarization and Its Short-term Increase Pre- and Post-Eclipse in HMXB 4U 1700-377

Abstract

We report the first statistically significant detection of X-ray polarization from the high-mass X-ray binary (HMXB) 4U 1700-377, observed using the Imaging X-ray Polarimetry Explorer (IXPE). A polarization degree exceeding 10% was detected above 5 keV, placing it among the highest polarization observed in HMXBs to date. The observation was conducted over a full orbital period of the binary system, during which several sporadic and instantaneous flares were detected. We identify a clear correlation between the polarization degree and orbital phase, with the highest polarization occurring just before and after the eclipse, reaching over 20% for a few tens of ks. These results suggest that the scattering medium responsible for the observed polarization is spatially localized between the compact object and the O-type companion star, likely created by large-scale inhomogeneities in the stellar wind and its interaction with the compact star's emission. We also explore the roles of disk winds and orbital reflection in the observed polarization variability. While both mechanisms contribute to the polarization, the substantial increase in polarization before and after the eclipse cannot be fully explained by these models alone, suggesting that the involvement of additional factors. The properties of the X-ray polarization observed by IXPE provide new insights into the accretion processes, X-ray emission, and wind structure in 4U 1700-377, advancing our understanding of their complex environments and the nature of the compact objects within.

References in corpus (13)

• Analyzing the Data from X-ray Polarimeters with Stokes Parameters
• Design, Construction, and Test of the Gas Pixel Detectors for the IXPE Mission
• Handling Background in IXPE polarimetric data
• Thermal disc emission from a rotating black hole: X-ray polarization signatures
• A weighted analysis to improve the X-ray polarization sensitivity of IXPE
• The stellar and wind parameters of six prototypical HMXBs and their evolutionary status
• IXPE observations of the quintessential wind-accreting X-ray pulsar Vela X-1
• X-ray polarisation properties of thermal-radiative disc winds in binary systems
• The IXPE Instrument Calibration Equipment
• X-ray polarization from accretion disk winds
• Ultrasoft state of microquasar Cygnus X-3: X-ray polarimetry reveals the geometry of astronomical puzzle
• Evidence of Compton cooling during an X-ray flare supports a neutron star nature of the compact object in 4U1700-37
• Polarized X-rays Correlated with Short--Timescale Variability of Cygnus X-1