Spectropolarimetric study of 4U 1630$-$47 in Steep Power law state with IXPE and NICER

Abstract

We probe the spectropolarimetric properties of the black-hole binary source 4U 1630$-$47 in the steep power law state. We detect a significant polarization fraction of $\sim$7 % at a polarization angle of $\sim$21 ${}^{\circ }$. The $2-12$ keV NICER spectrum can be fitted with a combination of a thermal and a Comptonization component, the latter characterized by a spectral index, $\Gamma \sim$2.1, along with a reflection feature at $\sim$7.0 keV. In the $2-8$ keV band, the degree of polarization of 4U 1630$-$47 in the steep power law state is 4.4 $\sigma$ different from the value previously measured in the high soft state. In the steep power law state, the polarization fraction increases as a function of energy but exhibits an overall drop in each energy band compared to that of the high soft state. We propose that the decrease in the polarization fraction in the steep power law state could be attributed to the presence of a corona. The observed polarization properties in both states can be explained by the self-irradiation of the disk around a Kerr black hole, likely influenced by the frame-dragging effect.

arXiv comment6 pages, 7 figures, 3 tables, accepted for publication in MNRAS

References in corpus (24)

• On the Absorption of X-rays in the Interstellar Medium
• X-ray Properties of Black-Hole Binaries
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• The evolution of the timing properties of the black-hole transient GX 339-4 during its 2002/2003 outburst
• An Empirical Background Model for the NICER X-ray Timing Instrument
• ixpeobssim: a Simulation and Analysis Framework for the Imaging X-ray Polarimetry Explorer
• Analyzing the Data from X-ray Polarimeters with Stokes Parameters
• X-ray emission from black-hole binaries
• Design, Construction, and Test of the Gas Pixel Detectors for the IXPE Mission
• Discovery of two simultaneous non-harmonically related Quasi-Periodic Oscillations in the 2005 outburst of the black-hole binary GRO J1655-40
• Absorption dips in the light curves of GRO J1655-40 and 4U 1630-47 during outburst
• The Disk Wind in the Rapidly Spinning Stellar-Mass Black Hole 4U 1630-472 Observed with NuSTAR
• Suzaku discovery of iron absorption lines in outburst spectra of the X-ray transient 4U 1630-472
• IXPE and NICER view of Black hole X-ray binary 4U 1630-47: First significant detection of polarized emission in thermal state
• Chandra high-resolution spectra of 4U~1630-47: the disappearance of the wind
• Missing hard states and regular outbursts: the puzzling case of the black hole candidate 4U 1630-472
• AstroSat and Chandra view of the high soft state of 4U 1630-47 (4U 1630-472): evidence of the disk wind and a rapidly spinning black hole
• Suzaku Observation of the Black Hole Binary 4U 1630--47 in the Very High State
• The spins of the Galactic black holes in MAXI J1535-571 and 4U 1630-472 from Insight-HXMT
• Detection of X-ray polarized emission and accretion-disk winds with IXPE and NICER in the black-hole X-ray binary 4U 1630-47
• The XMM Newton spectra of the 2012 outburst of the black-hole candidate 4U 1630-47 revisited
• Disk emission and atmospheric absorption lines in black hole candidate 4U 1630-472
• The First X-ray Polarization Observation of the Black Hole X-ray Binary 4U 1630-47 in the Steep Power Law State
• The first X-ray polarimetric observation of the black hole binary LMC X-1

Cited by in corpus (2)

• X-ray polarisation properties of thermal-radiative disc winds in binary systems
• The peculiar disk evolution of 4U 1630--472 observed by Insight-HXMT during the 2022 and 2023 outbursts