Open AccessSpectral, polarization and time‐lag properties of GRS 1915+105 radio oscillations
Author(s) -
Fender R.P.,
Rayner D.,
Trushkin S.A.,
O'Brien K.,
Sault R.J.,
Pooley G.G.,
Norris R.P.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05072.x
Subject(s) - physics , polarization (electrochemistry) , spectral index , spectral line , astrophysics , radio spectrum , radio frequency , spectral shape analysis , lag , flare , computational physics , astronomy , telecommunications , chemistry , computer science , computer network
We report high‐sensitivity dual‐frequency observations of radio oscillations from GRS 1915+105 following the decay of a major flare event in 2000 July. The oscillations are clearly observed at both frequencies, and the time‐resolved spectral index traces the events between optically thin and thick states. While previously anticipated from sparse observations and simple theory, this is the first time a quasi‐periodic signal has been seen in the radio spectrum, and is a clear demonstration that flat radio spectra can arise from the combination of emission from optically thick and thin regions. In addition, we measure the linear polarization of the oscillations, at both frequencies, at a level of about 1–2 per cent, with a flat spectrum. Cross‐correlating the two light curves we find a mean delay, in the sense that the emission at 8640 MHz leads that at 4800 MHz, of around 600 s. Comparison with frequency‐dependent time‐delays reported in the literature reveals that this delay is variable between epochs. We briefly discuss possible origins for a varying time‐delay, and suggest possible consequences.