NICER detection of a 83 s periodicity in the super-soft source emission from V3890 Sgr
ATel #13086; A. P. Beardmore, K. L. Page (U. Leicester), C. B. Markwardt, K. C. Gendreau, Z. Arzoumanian (NASA/GSFC), J. S. Pope (KBRwyle/NASA/GSFC)
on 7 Sep 2019; 01:24 UT
Credential Certification: Andy Beardmore (apb@star.le.ac.uk)
Following the detection of super-soft source (SSS) emission from the recurrent nova V3890 Sgr by the Swift-XRT (Page et al., ATel#13084), we initiated a real-time target of opportunity observation of the source with NICER. 737 s of data were obtained on 2019-Sep-06 from 19:00 to 19:14 UTC (i.e., starting 9.923 days after the optical discovery of the nova outburst). NICER measures a counting rate of 215 count/s over 0.3-10 keV and confirms the SSS emission. The observed rate is over a factor of three times higher than that estimated from the Swift-XRT data taken 19 hours earlier.
Closer examination of the data reveal a clear oscillation in the NICER light curve, on a timescale of 83 s. The modulation, confined to the SSS spectral component (i.e., below 0.7 keV), has a sinusoidal profile when folded, with an amplitude of 6 per cent.
Prior to this observation, five other nova undergoing SSS emission have revealed short period oscillations in their soft X-ray light curves (i.e., below 1 keV), with timescales ranging from 33 to 70 s. These include RS Oph (35 s: ATel#770, Osborne et al. 2011, ApJ, 727, 124, Ness et al. 2007, ApJ 665, 1334), KT Eri (35 s: Beardmore et al. ATel#2423), V339 Del (54 s: Beardmore et al. ATel#5573, Ness et al. ATel#5626) and Nova LMC 2009a (33 s: Ness et al ATel#6147). A similar timescale modulation was also seen in the persistent SSS Cal 83 (67 s: Odendaal et al. 2014, MNRAS, 437, 2948). The origin of these short-period modulations is not certain and is possibly related to either the spin of the white dwarf, or nonradial g-mode pulsations driven by an instability in the nuclear burning rate of the hot white dwarf.
Further observations with NICER are planned.
NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.
