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

Abstract

Extragalactic black hole X-ray binaries LMC X-1 and LMC X-3 are the persistent sources, usually found in soft spectral state. We present the results from spectral and timing study of these sources using MAXI, NICER, NuSTAR and AstroSat observations carried out during 2014-2020. Study of long-term MAXI lightcurve shows that the fractional variability of flux in 2-10keV is moderate ($\sim$20%) in LMCX-1 and high ($\sim$50%) in LMCX-3. The energy spectra of both sources are characterized by a disc blackbody and a Comptonization component with LMCX-1 having an additional Fe-line emission feature. NICER (0.3-10keV), NuSTAR (3.0-40keV) and AstroSat (0.5-20keV) spectral analysis collectively show that LMC X-1 remained in the soft state (disc flux contribution $f_{disc}>80$%, photon index$\Gamma \sim 2.06-4.08$) throughout 2014-2020. Mass accretion rate, $\dot{M}$ of LMC X-1 calculated from bolometric luminosity (0.1-50keV) is found to be within $0.07-0.24{\dot{M}}_{Edd}$ (Eddington mass accretion rate). Although LMC X-3 remained in the soft state ($f_{disc}>95\%,\Gamma \sim 2.3$) during most of the time, it exhibits transition into intermediate ($f_{disc}=47-73\%,\Gamma \sim 2.02-2.36$) and hard state ($f_{disc}\sim 26\%,\Gamma \sim 1.6$). $\dot{M}$ of LMC X-3 through different spectral states varies within $0.01-0.42{\dot{M}}_{Edd}$. Temporal study show that the Power Density Spectra (PDS) in 0.3-10keV follow a red-noise with rms of 2% for LMC X-1 and in case of LMC X-3, it is 0.08-2.35% during the soft state, but relatively high in the intermediate(3.05-4.91%) and hard state($\sim$17.06%). From continuum-fitting method we constrain spin of LMC X-1 and LMC X-3 to be within 0.85-0.94 and 0.16-0.33 respectively and from Fe-line fitting method, spin of LMC X-1 is found to be 0.93-0.94. Finally, we discuss the implication of our findings in the context of accretion disc dynamics around the vicinity of the BHs.

16 pages, 9 figures, accepted for publication in ASR

References in corpus (13)

• X-ray Properties of Black-Hole Binaries
• A Determination of the Spin of the Black Hole Primary in LMC X-1
• AstroSat view of MAXI J1535-571: broadband spectro-temporal features
• AstroSat and MAXI view of the Black Hole binary 4U 1630-472 during 2016 and 2018 Outbursts
• A review of rapid X-ray variability in X-ray binaries
• Hysteresis of spectral evolution in the soft state of black-hole binary LMC X-3
• Estimation of the black hole spin in LMC X-1 using AstroSat
• X-ray Spectral and Timing evolution of MAXI J1727-203 with NICER
• Broadband 'spectro-temporal' features of extragalactic black hole binaries LMC X-1 and LMC X-3: An AstroSat perspective
• AstroSat and MAXI view of Cygnus X-1: Signature of an `extreme' soft nature
• AstroSat view of IGR J17091-3624 and GRS 1915+105: decoding the 'pulse' in the 'Heartbeat State'
• NuSTAR and Swift Observations of the Extragalactic Black Hole X-ray Binaries
• Suzaku Observation of X-ray Variability in Soft State LMC X-1