Multi-mission views of extragalactic black hole x-ray binaries: Constraining spin and mass of LMC X-1 and LMC X-3
Abstract
LMC X-1 and LMC X-3 are the extragalactic Black Hole X-ray Binaries (BH-XRBs) located in the Large Magellanic Cloud (LMC) galaxy. Low hydrogen column density along the line of sight of LMC along with the availability of excellent data from present space based X-ray observatories makes LMC X-1 and LMC X-3 the ideal laboratories to study extreme physics of BH-XRBs. In this work, we have carried out a comprehensive spectral and timing analysis of both sources using the data observed by AstroSat, MAXI,NICER and NuSTAR during the period of 2016-2020. We have studied the long-term ($2016-2020$) lightcurve variability using MAXI lightcurve data in $2-10$ keV energy band which shows that fractional variance of LMC X-1 and LMC X-3 are $\sim$25% and $\sim$53% respectively. Broadband spectral analysis using AstroSat ($0.5-20$ keV), NICER ($0.5-10$ keV) and NuSTAR ($3-20$ keV) data during different observations show that the energy spectra of LMC X-1 is characterised by thermal disc blackbody component ($kT_{in} \sim$1 keV) along with a steep power-law ($\Gamma \sim$ 2.8). Dominant disc contribution to the source flux, low rms percentage and absence of Quasi Periodic Oscillations (QPOs) in power spectra show that the source was in soft state (SS) during the entire period of $2016-2020$. Meanwhile, we found LMC X-3 to be in its SS during most of the observations whereas some of the energy spectra are characterized by disk component ($kT_{in}$ $\sim$0.8 keV) and relatively stronger power-law ($\Gamma$ $\sim$1.8), indicating the hard state (HS) of the source. The availability of large number of broadband observations ($0.5-20$ keV) of both sources motivated us to examine the physical parameters of these BH-XRBs via continuum-fitting method. Modelling with relativistic accretion disc model, we could constrain the mass accretion rate, spin and mass values which points that LMC X-1 is a maximally rotating (a $=0.86-0.93$) with BH mass of $M_{BH}=9.49-10.79$(M_\odot), whereas LMC X-3 is a weakly rotating (a = $0.29-0.41$) black hole with mass of $M_{BH}=5.5-6.6$(M_\odot). We discuss the implications of our findings in the context of dynamics of accretion around the vicinity of BH-XRBs.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1588B