NICER / ISS Science Nugget
for May 14, 2020

NICER observes a compact binary in outburst

This week, NICER received a Target of Opportunity (TOO) request to observe the cataclysmic variable (CV) star system "SS Cygnus". SS Cygnus is a compact binary system consisting of a red dwarf and a white dwarf separated by only about 100,000 miles in an orbit that is only 6.5 hours long. At about 400 light years away, it is a relatively nearby CV system and is one of the most observed variable stars in the sky.

The TOO was triggered because SS Cygnus appears to be in an optical outburst that occurs as matter from the red dwarf suddenly accretes onto the white dwarf. NICER has begun observations of SS Cygnus that will span nearly two weeks to track the X-ray evolution of the outburst. The figure shows the X-ray spectrum that NICER measured in the first few days.

The X-ray spectrum of SS Cygnus as it brightens in the optical band

Figure: The X-ray spectrum captured by NICER of SS Cygnus from May 11 to May 14, 2020 is shown in red compared to the estimate of the background spectrum shown in green. A clear iron emission line complex is seen around 6.5 keV.

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