A multi-wavelength study of the hard and soft states of MAXI J1820+070 during its 2018 outburst

Abstract

We present a comprehensive multi-wavelength spectral analysis of the black hole X-ray binary MAXI J1820+070 during its 2018 outburst, utilizing AstroSat far UV, soft and hard X-ray data, along with (quasi-)simultaneous optical and X-ray data from Las Cumbres Observatory and NICER, respectively. In the soft state, we detect soft X-ray and UV/optical excess components over and above the intrinsic accretion disk emission ($k{T}_{\mathrm{in}}\sim 0.58$ keV) and a steep X-ray power-law component. The soft X-ray excess is consistent with a high-temperature blackbody ($kT\sim 0.79$ keV), while the UV/optical excess is described by UV emission lines and two low-temperature blackbody components ($kT\sim 3.87$ eV and $\sim 0.75$ eV). Employing continuum spectral fitting, we determine the black hole spin parameter ($a=0.77\pm 0.21$), using the jet inclination angle of $64^{\circ }\pm 5^{\circ }$ and a mass spanning $5-10M_{\odot }$. In the hard state, we observe a significantly enhanced optical/UV excess component, indicating a stronger reprocessed emission in the outer disk. Broad-band X-ray spectroscopy in the hard state reveals a two-component corona, each associated with its reflection component, in addition to the disk emission ($k{T}_{\mathrm{in}}\sim 0.19$ keV). The softer coronal component dominates the bolometric X-ray luminosity and produces broader relativistic reflection features, while the harder component gets reflected far from the inner disk, yielding narrow reflection features. Furthermore, our analysis in the hard state suggests a substantial truncation of the inner disk ($\gtrsim 51$ gravitational radii) and a high disk density ($\sim 10^{20}\mathrm{c}{\mathrm{m}}^{-3}$).

29 pages, 19 figures, 8 Tables, Accepted for publication in The Astrophysical Journal

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Cited by in corpus (5)

• Radiative plasma simulations of black hole accretion flow coronae in the hard and soft states
• Investigating the consistency of the shape and flux of X-ray reflection spectra in the hard state with an accretion disk reaching close to the black hole
• Tracking optical variability and outflows across the accretion states of the black hole transient MAXI J1820+070
• Interaction between disk and extended corona in a general relativistic framework
• Ultraviolet spectroscopy of the black hole X-ray binary MAXI J1820+070 across a state transition