2004/09/16 by R. Fiorito, Ralph Fiorito, L. Titarchuk +1 · 3 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/425736
published as Astrophys.J. 614 (2004) L113-L116 · 7 pages and 3 figures. Accepted for publication in ApJ Letters, v.614, 2004, October 20
arxiv created 2004/09/16 · openalex publication_date 2004/09/17 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
Ultraluminous X-ray sources (ULXs) with apparent luminosities up to hundreds of times the Eddington luminosity for a neutron star have been discovered in external galaxies. The existence of intermediate-mass black holes has been proposed to explain these sources. We present evidence for an intermediate-mass black hole in the ULX M82 X-1 based on the spectral features and timing (quasi-periodic oscillation [QPO]) properties of the X-radiation from this source. We revisited XMM-Newton and Rossi X-Ray Timing Explorer ( RXTE ) data for M82 X-1 obtained in 2001 and 1997 for XMM and RXTE , respectively. We show for these observations that the source is either in transition or in a high/soft state with photon spectral indices 2.1 and 2.7, respectively. We confirm the early determination of the QPO frequency ν ≈ 55 mHz in this source by Strohmayer & Mushotzky and identify this as the low-frequency QPO for the source. We apply a new method to determine the black hole mass of M82 X-1. The method uses the index-QPO low-frequency correlation that has been recently established in Galactic black hole candidates GRS 1915+105, XTE J1550-564, 4U 1630-47, and others. Using scaling arguments and the correlation derived from the consideration of Galactic black holes, we conclude that M82 X-1 is an intermediate black hole with a mass of the order of 1000 M ☉ .