NICER observes a decay of the U Sco X-ray flux
ATel #15513; Marina Orio, INAF-Padova and U Wisconsin and Keith Gendreau, NASA-Goddard
on 13 Jul 2022; 20:29 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Marina Orio (orio@astro.wisc.edu)
Subjects: Cataclysmic Variable, Transient
Following its recent outburst, the recurrent nova
U Scorpii (ATel #15508, #15502, #15499, #15465,
#15451, #15499, #15428, #15436, #15435, #15423, #15422, #15420, #15417)
is being monitored with NICER. Daily
monitoring started on 2022 June 24 at UT 15:36:08 (see ATel #15508)
and the count rate in the 0.2-12 keV range
was observed to increase from 9.220±0.85
counts s-1
to a peak average value 64.760±0.32 counts s-1 measured during a plateau with
occasional fluctuations that occurred between 2022 July 4 and July 7. On 2022 July 7
until 2022 July 12 a constant decrease in count rate has been observed,
with a last measured value 18.620±0.10 cts s-1 in
the 0.2-12 keV range of NICER,
(however like like before, see ATel #15508, with no counts above the background at energy higher than
2.5 keV). In the last exposures, the spectrum appears "harder" (albeit still
very soft), and still complex, with several components as described in
ATel #15508. The flux has decreased from a peak around
5.3 x 10-11 erg/cm2/s to approximately 1.5 x 10-11 erg/cm2/s.
NICER is a 0.2-12 keV X-ray detector operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.
