6,631 research outputs found
Class Transitions and Two Component Accretion Flow in GRS 1915+105
The light curve of the galactic micro-quasar GRS 1915+105 changes in at least
thirteen different ways which are called classes. We present examples of the
transitions from one class to another as observed by the IXAE instrument aboard
the Indian Satellite IRS-P3. We find that the transitions are associated with
changes in photon counts over a time-scale of only a few hours and they take
place through unknown classes. Assuming that the transitions are caused by
variation of the accretion rates, this implies that a significant fraction of
the matter must be nearly freely falling in order to have such dramatic changes
in such a short time.Comment: 9 pages, 6 figures, Astronomy and Astrophys. (in press
Evidence of Class Transitions in GRS 1915+105 from IXAE Data
GRS 1915+105 shows at least twelve distinct classes of light curves. By
analysing the data obtained from Indian X-ray Astronomy Experiment (IXAE)
instrument aboard IRS-P3 satellite, we show that in at least two days,
transitions between one class to another were observed. In these days the
so-called class went to class and class went to
class. In the frequency-time plane such transitions exhibited change in
quasi-periodic oscillation (QPO) frequency. We could detect that low-frequency
QPOs can occur in anticipation of a class transition several hundred minutes
before the actual transitionComment: 14 pages, 3 figures, Astrophysical Journa
Spectral Signatures of Winds from Accretion Disks Around Black Holes
We show that with the wind/jet activity, the spectral index of hard X-ray is
changed in galactic microquasars. When mass loss takes place, the spectrum
becomes softer and when mass gain takes place, the spectrum becomes harder. We
present examples of such changes in GRS1915+105.Comment: 4 pages, 2 figures To be published in the Proceedings of 10th Marcel
Grossman Meeting, Ed. R. Ruffini et al. (World Scientific: Singapore
Ionospheric effects in active retrodirective array and mitigating system design
The operation of an active retrodirective array (ARA) in an ionospheric environment (that is either stationary or slowly-varying) was examined. The restrictions imposed on the pilot signal structure as a result of such operation were analyzed. A 3 tone pilot beam system was defined which first estimates the total electron content along paths of interest and then utilizes this information to aid the phase conjugator so that correct beam pointing can be achieved
Brans-Dicke Wormhole Revisited
A basic constraint to be satisfied by Brans class I solution for being a
traversible wormhole is derived. It is argued that the solution could be a
wormhole analogue of the Horowitz-Ross naked black hole. It is further
demonstrated that the wormhole is traversible only "in principle", but not in
practice. Using a recently proposed measure of total gravitational energy
inside a static wormhole configuration, it is shown that the wormhole contains
repulsive gravity required for the defocussing of orbits at the throat.Comment: 13 pages, 6 figures, accepted for publication in Class. Quant. Gra
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