A spectral study of the black hole X-ray binary MAXI J1820+070 with AstroSat and NuSTAR. Issue 4 (7th September 2020)

• Record Type: Journal Article
• Authors: Chakraborty, Sudip; Navale, Nilam; Ratheesh, Ajay; Bhattacharyya, Sudip
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 498:Issue 4(2020)
• Page Start: 5873
• Page End: 5884
• Publication Date: 2020-09-07
• Subjects: accretion, accretion discs -- methods: data analysis -- X-rays: binaries -- X-rays: individual: MAXI J1820+070; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa2711
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: MAXI J1820+070 is a newly discovered transient black hole X-ray binary, which showed several spectral and temporal features. In this work, we analyse the broad-band X-ray spectra from all three simultaneously observing X-ray instruments onboard AstroSat, as well as contemporaneous X-ray spectra from NuSTAR, observed during the hard state of MAXI J1820+070 in 2018 March. Implementing a combination of multicolour disc model, relativistic blurred reflection model relxilllpcp, and a distant reflection in the form of xillvercp, we achieve reasonable and consistent fits for AstroSat and NuSTAR spectra. The best-fitting model suggests a low temperature disc ( kT in ∼ 0.3 keV), iron overabundance ( A Fe ∼ 4–5 solar), a short lamp-post corona height ( h ≲ 8 R g ), and a high corona temperature ( kT e ∼ 115–150 keV). Addition of a second Comptonization component leads to a significantly better fit, with the kT e of the second Comptonization component being ∼14–18 keV. Our results from independent observations with two different satellites in a similar source state indicate an inhomogeneous corona, with decreasing temperature attributed to increasing height. Besides, utilizing the broader energy coverage of AstroSat, we estimate the black hole mass to be 6.7–13.9 M⊙, consistent with independent measurements reported in the literature.