Abstract Extragalactic black hole X-ray binaries LMC X-1 and LMC X-3 are the persistent sources which are usually found in a soft spectral state. In this study, we consider multi-mission (MAXI, NICER, NuSTAR and AstroSat) X-ray observations of both these sources carried out during 2014–2020 to perform a detailed spectral and temporal analysis. Study of long term MAXI lightcurve shows that the flux variability of LMC X-1 is moderate (fractional variability, F var 20 % ) whereas that of LMC X-3 is high ( F var 50 % ) in 2–10 keV which is associated with the change in spectral state. The energy spectra of LMC X-1 and LMC X-3 are characterized by a multi-color disc blackbody and a Comptonization component, with LMC X-1 having an additional Fe-line emission feature. NICER ( 0.3 - 10 keV), NuSTAR ( 3.0 - 40 keV) and AstroSat ( 0.5 - 20 keV) spectral analysis collectively shows that LMC X-1 has remained in the soft state (disc flux contribution in 0.3–40 keV, f disc > 80 % , photon index Γ 2.06 - 4.08 ) throughout the period of 2014–2020. Mass accretion rate ( M ̇ ) of LMC X-1 during this period, calculated from bolometric luminosity ( 0.1 - 50 keV) is found to be within 0.07 - 0.24 M ̇ Edd (Eddington mass accretion rate). Although LMC X-3 remained in the soft state during most of the observations ( f disc > 95 % , Γ 2.3 ), it exhibits a transition into hard state ( f disc 26 % , Γ 1.6 ) and intermediate state ( f disc = 47 - 73 % , Γ 2.02 - 2.36 ). M ̇ of LMC X-3 through different spectral states varies in the range 0.01 - 0.42 M ̇ Edd . Temporal studies carried out for these observations show that the Power Density Spectra (PDS) in 0.3 - 10 keV follow a red-noise with fractional rms of 2 % for LMC X-1 and in case of LMC X-3, rms is less during the soft state ( 0.08 - 2.35 % ), but relatively high in the intermediate ( 3.05 - 4.91 % ) and hard states ( 17.06 % ). From spectral modeling of the soft X-ray continuum of NICER and NuSTAR energy spectra with relativistic accretion disc and reflection models, we constrain the spin and accretion rate ( M ̇ ) of the BHs. In case of LMC X-1, spin is estimated to be within 0.85 - 0.94 by continuum-fitting method and 0.93 - 0.94 by Fe-line fitting method and in case of LMC X-3 continuum-fitting yields its value is in the range 0.16 - 0.33 . Finally, we discuss the implications of our findings in the context of accretion disc dynamics around the vicinity of the BHs.


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    Title :

    Multi-mission view of extragalactic black hole X-ray binaries LMC X-1 and LMC X-3: Evolution of broadband spectral features


    Contributors:
    Bhuvana, G.R (author) / Radhika, D. (author) / Nandi, Anuj (author)

    Published in:

    Advances in Space Research ; 69 , 1 ; 483-498


    Publication date :

    2021-09-29


    Size :

    16 pages




    Type of media :

    Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English




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