Astronomy and Astrophysics Seminars
Nature of the long X-ray periods from ultraluminous X-ray sources: Orbital or super-orbital ?
by Mr. Dheeraj Reddy (University of Maryland, USA)
Tuesday, August 14, 2012
from
to
(Asia/Kolkata)
at Colaba Campus ( A269 )
at Colaba Campus ( A269 )
TIFR
Description |
Ultraluminous X-ray sources are bright, pointlike, off-nuclear, extragalactic X-ray sources with apparent X-ray (0.3-10.0 keV) luminosities in the range of 10^39-10^41 ergs/sec. They remain mysterious in the sense that their high luminosities imply either sub-Eddington accretion onto the long-sought intermediate-mass black holes (a few 100-1000 solar masses) or super-Eddington accretion onto stellar-mass black holes (3-30 solar masses). A certain sub-sample of these sources exhibit long-term X-ray modulations: M82 with a period of 62 days and NGC 5408 X-1 with periods of 115 & 243 days. It is currently not clear whether these modulations are due to the orbital motion of the binary or if they represent a super-orbital modulation of the system (e.g., a precessing warped accretion disk). Identifying the source of these X-ray periods can help us better understand the nature of accretion processes operating within these systems. I will discuss various properties of these modulations including their coherence, energy dependence, phase-resolved spectroscopy, time-resolved periodograms that will resolve some of the degeneracies between the various models. |