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17-05-2010
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A dwarf nova in outburst

Submitter: Valeriu Tudose
Description: SS Cyg is a binary system in which a white dwarf accretes matter from a companion star. Once in a while the system switches into an active state, its "brightness" increasing significantly over a broad range of the electromagnetic spectrum.

Mid-April, amateur astronomers observing SS Cyg from their backyards with commercially available optical instruments, announced the American Association of Variable Stars Observers (AAVSO) that the object is entering an outburst phase. This set in motion the JACPOT Team who started a monitoring campaign at radio, optical/infra-red and X-ray bands using various facilities around the world. This is likely the best multi-wavelength coverage of an outburst from SS Cyg (and perhaps of any dwarf nova). One of the scientific goals is to understand the behaviour of dwarf novae as compared to that of their closely related objects, the X-ray binary systems, which harbour a neutron star or a black hole as the accreting object. Evidence for the presence of jets in the system, i.e. ejections of matter, is another thing the team is after, given the fact that until now only indirect evidence has been found for matter being ejected during a dwarf nova event.

The image above shows two radio maps of the SS Cyg region, taken a few days apart by the Westerbork Synthesis Radio Telescope (WSRT) and the Very Large Array (VLA). Note the flux variation of SS Cyg between the two observational epochs. Light curves are also presented, with optical (AAVSO, black points), X-ray (Swift satellite) and radio (VLA) data. The black triangles show the dates of the Very Long Baseline Array (VLBA) observations. Plots of hardness (the ratio between the fluxes of two different X-ray bands) and radio spectral index (between 5 and 8 GHz) are as well represented. These are partial results. The monitoring campaign is under way.
Copyright: JACPOT Team
 
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