TY - JOUR
T1 - Spectropolarimetric study of 4U 1630-47 in steep power-law state with IXPE and NICER
AU - Rawat, Divya
AU - Garg, Akash
AU - Mendez, Mariano
N1 - Funding Information:
We extend our gratitude to an anonymous reviewer for their valuable insights, which greatly contributed to enhancing the manuscript's quality. This research has used data from the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center. DR acknowledges Tomaso M. Belloni for providing the ghats package used in this work for timing analysis. MM acknowledges support from the research program Athena with project number 184.034.002, which is (partly) financed by the Dutch Research Council (NWO).
Publisher Copyright:
© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2023/10
Y1 - 2023/10
N2 - 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 ∼7 per cent at a polarization angle of ∼21°. 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, Γ ∼2.1, along with a reflection feature at ∼7.0 keV. In the 2-8 keV band, the degree of polarization of 4U 1630-47 in the steep power-law state is 4.4σ 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 disc around a Kerr black hole, likely influenced by the frame dragging effect.
AB - 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 ∼7 per cent at a polarization angle of ∼21°. 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, Γ ∼2.1, along with a reflection feature at ∼7.0 keV. In the 2-8 keV band, the degree of polarization of 4U 1630-47 in the steep power-law state is 4.4σ 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 disc around a Kerr black hole, likely influenced by the frame dragging effect.
KW - accretion: accretion discs
KW - polarization
KW - software: data analysis
KW - techniques: polarimetric
KW - X-rays: binaries
KW - X-rays: individual: 4U 1630-47
UR - http://www.scopus.com/inward/record.url?scp=85168684387&partnerID=8YFLogxK
U2 - 10.1093/mnras/stad2327
DO - 10.1093/mnras/stad2327
M3 - Article
AN - SCOPUS:85168684387
SN - 0035-8711
VL - 525
SP - 661
EP - 666
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -