AstroSat view of MAXI J1535-571: broadband spectro-temporal features

Abstract

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 Hz 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 ~ 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 broadband 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 between 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${}_{\odot }$. The physical model based on the two-component accretion flow gives disc accretion rates as high as ~ 1 ${\dot{m}}_{Edd}$ and halo rate ~ 0.2 ${\dot{m}}_{Edd}$ 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 to 7.83 M${}_{\odot }$.

15 pages, 9 figures, MNRAS (Accepted on 2019 May 10)

References in corpus (9)

• X-ray Properties of Black-Hole Binaries
• No Time for Dead Time: Timing analysis of bright black hole binaries with NuSTAR
• Evolution of the quasi-periodic oscillation frequency in GRO J1655-40 -- Implications for accretion disk dynamics
• AstroSat/LAXPC reveals the high energy variability of GRS 1915+105 in the chi class
• Reflection Spectra of the Black Hole Binary Candidate MAXI J1535-571 in the Hard State Observed by NuSTAR
• Determination of mass of IGR J17091-3624 from "Spectro-Temporal" variations during onset-phase of the 2011 outburst
• Periodic massloss from viscous accretion flows around black holes
• Insight-HXMT observations of the first binary neutron star merger GW170817
• AstroSat/LAXPC observation of Cygnus X-1 in the hard state

Cited by in corpus (2)

• Spectro-timing analysis of MAXI J1535-571 using AstroSat
• Shocks in relativistic viscous accretion flows around Kerr black holes