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AstroSat view of MAXI J1535-571: broad-band spectro-temporal features

Sreehari, H and Ravishankar, BT and Iyer, Nirmal and Agrawal, V K and Katoch, Tilak B and Mandal, Samir and Nandi, Anuj (2019) AstroSat view of MAXI J1535-571: broad-band spectro-temporal features. In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 487 (1). pp. 928-941.

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Official URL: https://doi.org/10.1093/mnras/stz1327


We present the results of Target of Opportunity (ToO) observations made with AstroSat of the newly discovered black hole binary MAXI J1535-571. We detect prominent C-type quasi-periodic oscillations (QPOs) of frequencies varying from 1.85 to 2.88 Hz, along with distinct harmonics in all the AstroSat observations. We note that while the fundamental QPO is seen in the 3-50 keV energy band, the harmonic is not significant above similar to 35 keV. The AstroSat observations were made in the hard intermediate state, as seen from state transitions observed by MAXI and Swift. We attempt spectral modelling of the broad-band data (0.7-80 keV) provided by AstroSat using phenomenological and physical models. The spectral modelling using nthComp gives a photon index in the range 2.18-2.37 and electron temperature ranging from 21 to 63 keV. The seed photon temperature is within 0.19 to 0.29 keV. The high flux in 0.3-80 keV band corresponds to a luminosity varying from 0.7 to 1.07 L-Edd assuming the source to be at a distance of 8 kpc and hosting a black hole with a mass of 6 M-circle dot. The physical model based on the two-component accretion flow gives disc accretion rates as high as similar to 1 (m) over dot(Edd) and halo rate similar to 0.2 (m) over dot(Edd), respectively. The near-Eddington accretion rate seems to be the main reason for the unprecedented high flux observed from this source. The two-component spectral fitting of AstroSat data also provides an estimate of a black hole mass between 5.14 and 7.83 M-circle dot.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to OXFORD UNIV PRESS
Keywords: accretion; black hole physics; stars: individual: MAXI J1535-571; X-rays: binaries
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 24 Dec 2019 05:52
Last Modified: 24 Dec 2019 05:52
URI: http://eprints.iisc.ac.in/id/eprint/63309

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