NICER follow-up of SRGA J181414.6-225604
ATel #14527; P. M. Bult, K. C. Gendreau (NASA/GSFC)
on 7 Apr 2021; 22:45 UT
Credential Certification: Peter Bult (p.m.bult@nasa.gov)
Subjects: X-ray, Transient
Referred to by ATel #: 14528
Following the recent report of the detection of a possible new X-ray transient with the SRG observatory (ATel #14510), we executed follow-up observations with the Neutron Star Interior Composition Explorer (NICER). We observed the direction of the reported eRosita coordinates for a total of 11 ks good time exposure, collected between April 5 16:03 UTC and April 6 14:22 UTC. We detect an X-ray source with an average count rate of 2.3 ct/s in the 0.5-10 keV band, which is above the estimated instrument background rate of 0.7 ct/s for the same energy range.
The 0.5-10 keV spectrum shows a prominent soft peak between 0.5-1.5 keV, a hard power law tail above 2 keV, and a spectral emission feature at 6.4 keV. Fitting the higher energy data with an absorbed power law plus Gaussian, we measure an absorption column density of 6.0 +/- 0.5 x1022 cm2, with a photon index of 1.5 +/- 0.2. The Gaussian has a line energy of 6.42 +/- 0.04 keV and an equivalent width of 0.15 +/- 0.07 keV. The unabsorbed 1-10 keV X-ray flux associated with the power law is about 2 x10-11 erg/s/cm2, roughly consistent with the SRG measurement (ATel #14510). The origin of the 0.5-1.5 keV flux excess is not clear at this time, although we suggest it may be due to contamination from a soft background source within NICERs 3 arcmin radius field of view.
Finally, we constructed a power density spectrum for these observations, but did not find any evidence of temporal variability. Instead, the 0.5-10 keV and 2-10 keV power spectra were consistent with Poisson noise for all frequencies above ~1/32 Hz.
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.
