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

**Authors:** Sreehari H., Ravishankar B. T., Nirmal Iyer, V. K. Agrawal, Tilak B. Katoch, Samir Mandal, Anuj Nandi  
**arXiv:** [1905.04656](https://arxiv.org/abs/1905.04656)  
**Date:** 2019-05-12  
**Summary page:** https://www.summarizepaper.com/en/paper/1905.04656v1/

## Key points

- The study presents results of Target of Opportunity (ToO) observations made with AstroSat of the black hole binary MAXI J1535-571.
- Prominent C-type Quasi-periodic Oscillations (QPOs) were detected, with frequencies varying from 1.85 Hz to 2.88 Hz, along with distinct harmonics in all the AstroSat observations.
- The fundamental QPO is seen in the 3 - 50 keV energy band, while the harmonic is not significant above ~35 keV.
- The AstroSat observations were made in the hard intermediate state.
- 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; seed photon temperature is within 0.19 to 0.29 keV.
- High flux in the 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$_{\odot}$.
- Physical model based on two-component accretion flow gives disc accretion rates as high as ~1 $\dot{m}_{Edd}$ and halo rate ~0.2 $\dot{m}_{Edd}$ respectively; these near Eddington accretion rates seem responsible for unprecedentedly high flux observed from this source, which is estimated to have a black hole mass between 5.14 to 783 M$_{\odot}$.

## Summary

In a recent study, Sreehari H. and colleagues present the results of Target of Opportunity (ToO) observations made with AstroSat of the newly discovered black hole binary MAXI J1535-571. The team detected 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. They noted 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. The team attempted 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 the 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; these near Eddington accretion rates seem to be responsible for the unprecedentedly high flux observed from this source, which is estimated to have a black hole mass between 5.14 to 783 M$_{\odot}$.