2005/10/06 by M. R. Goad, T. P. Roberts, J. N. Reeves +1 · 1 citation
Engineering · Physics and Astronomy · #Accretion (finance) #Amplitude #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Black hole (networking) #Compact star #Galaxy #Luminosity #Mechanics and Biomechanics Studies #Neutron star #Physics #Pulsars and Gravitational Waves Research #Stars #X-ray binary #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2005.09702.x
published as Mon.Not.Roy.Astron.Soc. 365 (2006) 191-198 · 8 pages, 6 figures, accepted for publication in MNRAS
arxiv created 2005/10/06 · openalex publication_date 2005/12/13 · arxiv updated 2015/06/24 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present results from a 112-ks long look by XMM-Newton at the ultraluminous X-ray source (ULX) Holmberg II X-1 (Ho II X-1), long thought to be the one of best candidates for the missing class of intermediate-mass black holes (IMBHs). Our data comprises the first high-quality XMM-Newton/RGS (reflection grating spectrometer) spectrum of an ULX, and an XMM-Newton/EPIC (European Photo Imaging Camera) spectrum with unprecedented signal-to-noise ratio. A detailed timing analysis shows that any variability on time-scales of minutes to hours is very weak (less than a few per cent fractional rms), though larger amplitude variations on much shorter time-scales could be hidden by photon counting statistics. This result suggests that if Ho II X-1 harbours an IMBH, then we are observing this source in a highly unusual and atypical state when compared with the known variability behaviour of other accreting systems of large mass. Moreover, unlike galactic X-ray binaries, our spectral analysis indicates the possible presence of an optically thick low-temperature corona. Taken together our timing and spectral analysis suggests that the compact companion is most likely a high-luminosity analogue of black hole binary systems similar to GRS 1915+105, the galactic microquasar, harbouring a compact object of mass no greater than 100 M⊙.