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21st of April 2020
How does a nova brighten?
by Aydi et al.
An international team of astronomers have used a combination of satellites and ground-based telescopes to follow the aftermath of a nova explosion in V906 Car, an object in the southern constellation of Carina. This study found a series of flares appearing simultaneously in gamma-rays and at optical wavelengths. The team conclude that as the nova fades, much of its brightness comes from shocks as a wind from the binary star system piles into slower-moving material expelled earlier. Observations over the following 18 months at radio wavelengths with the Australia Telescope Compact Array revealed that long after the nova had faded from view at other wavelengths, more shocks were still being generated by an even faster wind moving at close to 2,500 kilometres per second.

The image above shows the radio light curve of V906 Car over the first 533 days of outburst, superimposed with a model of thermal ejecta expanding at 2500 km/s. The measurements are represented by solid dots (with 1-sigma error bars) or arrows marking 3-sigma upper limits for nondetections. Measurements at the same frequency are connected by solid lines. The model light curves are plotted as dotted lines. There is a clear indication of excess radio emission between days 50 and 100, above the expectation for the optically-thick expanding blackbody. The leading explanation for this excess is synchrotron emission produced by relativistic electrons accelerated in nova shocks More details are given in the article published in Nature Astronomy. (Text credit: Stuart Ryder)

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