Scaling of the photon index vs mass accretion rate correlation and estimate of black hole mass in M101 ULX-1

Abstract

We report the results of Swift and Chandra observations of an ultra-luminous X-ray source, ULX-1 in M101. We show strong observational evidence that M101 ULX-1 undergoes spectral transitions from the low/hard state to the high/soft state during these observations. The spectra of M101 ULX-1 are well fitted by the so-called bulk motion Comptonization (BMC) model for all spectral states. We have established the photon index (Γ) saturation level, Γ_{sat}=2.8 +/- 0.1, in the Γvs. mass accretion rate (\dot M) correlation. This Γ-\dot M correlation allows us to evaluate black hole (BH) mass in M101 ULX-1 to be M_{BH}~(3.2 - 4.3)x10^4 solar masses assuming the spread in distance to M101 (from 6.4+/- 0.5 Mpc to 7.4+/-0.6 Mpc). For this BH mass estimate we use the scaling method taking Galactic BHs XTE~J1550-564, H~1743-322 and 4U~1630-472 as reference sources. The Gamma vs. \dot M correlation revealed in M101~ULX-1 is similar to that in a number of Galactic BHs and exhibits clearly the correlation along with the strong Γsaturation at ~2.8. This is robust observational evidence for the presence of a BH in M101 ULX-1. We also find that the seed (disk) photon temperatures are quite low, of order of 40-100 eV which is consistent with high BH mass in M101~ULX-1. Thus, we suggest that the central object in M101 ULX-1 has intermediate BH mass of order 10^{4} solar masses

12 pages, 9 figures, accepted by Astronomy & Astrophysics

References in corpus (7)

• Physical Properties of Wolf-Rayet Stars
• An online repository of Swift/XRT light curves of GRBs
• Black hole-like hysteresis and accretion states in neutron star low mass X-ray binaries
• The 2003 Outburst of the X-ray Transient H 1743-322: Comparisons with the Black Hole Microquasar XTE J1550-564
• Comprehensive Analysis of RXTE Data from Cyg X-1: Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations
• Black hole mass determination in the X-ray binary 4U 1630--47: Scaling of spectral and variability characteristics
• Hardness Ratio Estimation in Low Counting X-ray Photometry

Cited by in corpus (14)

• Estimation of Mass of Compact Object in H 1743-322 from 2010 and 2011 Outbursts using TCAF Solution and Spectral Index - QPO Frequency Correlation
• Anatomy of the AGN in NGC 5548: VII. Swift study of obscuration and broadband continuum variability
• BL Lacertae: X-ray spectral evolution and a black-hole mass estimate
• ESO 243-49 HLX-1: scaling of X-ray spectral properties and black hole mass determination
• NGC 4051: Black hole mass and photon index-mass accretion rate correlation
• Scaling of X-ray spectral properties of a black hole in the Seyfert 1 galaxy NGC~7469
• Investigation of X-ray timing and spectral properties of ESO 243-49 HLX-1 with long-term Swift Monitoring
• Swift J164449.3+573451 and Swift J2058.4+0516: Black hole mass estimates for tidal disruption event sources
• Spectral index-mass accretion rate correlation and evaluation of black hole masses in AGNs 3C~454.3 and M87
• MAXI~J1348--630: Estimating the black hole mass and binary inclination using a scaling technique
• Measuring the black hole mass in Ultraluminous X-ray Sources with the X-ray Scaling Method
• Estimating black hole masses in obscured AGN using X-rays
• OJ~287: a new BH mass estimate of the secondary
• Emission Line Diagnostics for IMBHs in Dwarf Galaxies: Accounting for BH Seeding and ULX Excitation