2008/02/21 by Jifeng Liu, Ji‐Feng Liu · 16 citations
Physics and Astronomy · #Accretion (finance) #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Black-body radiation #Eclipse #Galaxies: Formation, Evolution, Phenomena #Galaxy #Light curve #Solar mass #Supernova #White dwarf #astro-ph
paper · pdf · doi:10.1086/587551
published in The Astrophysical Journal Supplement Series 177(1), 181-188 (Institute of Physics) · 19 pages, 7 figures, 1 table, to appear in ApJS
arxiv created 2008/02/21 · openalex publication_date 2008/06/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Luminous supersoft X-ray sources found in the Milky Way and Magellanic Clouds are likely white dwarfs that steadily or cyclically burn accreted matter on their surface, which are promising type Ia supernova progenitors. Observations of distant galaxies with Chandra and XMM-Newton have revealed supersoft sources that are generally hotter and more luminous, including some ultraluminous supersoft sources (ULSs) that are possibly intermediate mass black holes of a few thousand solar masses. In this paper we report our X-ray spectral and timing analysis for M81-ULS1, an ultraluminous supersoft source in the nearby spiral galaxy M81. M81-ULS1 has been persistently supersoft in 17 Chandra ACIS observations spanning six years, and its spectrum can be described by either a kTbb≈70 eV blackbody for a ∼1.2M_\odot white dwarf, or a kTin ≈ 80 eV multicolor accretion disk for a \gtrsim103M_\odot intermediate mass black hole. In two observations, the light curves exhibited dramatic flux drop/rise on time scales of 103 seconds, reminiscent of eclipse ingress/egress in eclipsing X-ray binaries. However, the exhaustive search for periodicity in the reasonable range of 50 ksec to 50 days failed to reveal an orbital period. The failure to reveal any periodicity is consistent with the long period (≥30 yrs) predicted for this system given the optical identification of the secondary with an asymptotic giant star. Also, the eclipse-like dramatic flux changes in hours are hard to explain under the white dwarf model, but can in principle be explained by disk temperature changes induced by accretion rate variations under the intermediate mass black hole model.