AstroSat Unveils Mysteries of Black Hole X-ray Binary MAXI J1820+070

Space New ,India :- AstroSat's advanced multi-wavelength capabilities have empowered an international team of scientists to unravel the enigmatic nature of the X-ray binary system MAXI J1820+070, which hosts a black hole. The extensive study, titled "A Multi-Wavelength Spectral Study of MAXI J1820+070 in the Soft and Hard States," has been accepted for publication in The Astrophysical Journal. This research provides unique insights into the behavior of the transient black hole X-ray binary during its 2018 outburst, led by researchers from IUCAA, Pune, along with contributors from India, the United Kingdom, Abu Dhabi, and Poland.

Positioned approximately 9800 light-years away from Earth, MAXI J1820+070 is a transient black hole X-ray binary that gained significant attention within the astronomy community when first detected during its 2018 outburst using the MAXI instrument aboard the International Space Station (ISS). Due to its proximity to Earth and remarkable brightness, ranking as the second brightest object in the X-ray sky, MAXI J1820+070 sparked numerous observing campaigns across various electromagnetic bands.

Equipped with three X-ray payloads and a UV telescope, AstroSat captured soft and hard X-ray emissions as well as far ultraviolet radiation, creating a detailed portrait of the regions surrounding the black hole in MAXI J1820+070. By collaborating with optical data from Las Cumbres Observatory and soft X-ray data from NASA's NICER mission, the research team gained a comprehensive understanding of the system's dynamics.

The study divulges intriguing findings about the accretion states of MAXI J1820+070. Black hole X-ray binaries, including MAXI J1820+070, often exhibit multiple accretion states throughout an outburst. The study reveals distinctions between the hard and soft states, characterized by the emission of predominantly higher-energy X-rays from the corona surrounding the black hole in the hard state, and softer X-rays emitted by the accretion disk itself in the soft state. The research, utilizing advanced techniques, also unveiled the black hole's spin, providing insights into its fundamental properties.

Additionally, the study establishes a compelling connection between X-ray emission from the inner regions near the black hole and optical/UV emission from the outer region of the accretion disk. Reprocessed radiation in the outer accretion disk emerges as a primary mechanism for generating optical/UV photons, with a notably higher proportion observed during the hard state.

This research extends beyond the specific case of MAXI J1820+070, emphasizing the crucial role of AstroSat in advancing the understanding of transient black hole X-ray binaries. With its unique multi-wavelength capabilities, AstroSat paves the way for further exploration of diverse astrophysical phenomena, laying the groundwork for future endeavors in the field.

The significance of this study is underscored by its highlighting of the importance of acquiring multi-wavelength spectroscopic data for X-ray binaries, providing novel insights into the intricate workings of these cosmic phenomena.

The accompanying schematic diagram illustrates the geometries associated with the hard state (upper panel) and soft state (lower panel) of MAXI J1820+070, as deduced in this study. Various physical processes contributing to X-ray emissions are denoted by blue-colored arrows, while those responsible for optical/UV emissions are represented by red-colored arrows.