Fermi-LAT detection of Fermi J1623-1752 and its possible association with recurrent nova U Scorpii
ATel #14939; B. Rani (Korea Astronomy and Space Science Institute), G. La Mura (LIP), C. C. Cheung (NRL), on behalf of the Fermi Large Area Telescope Collaboration
on 28 Sep 2021; 19:31 UT
Credential Certification: Teddy Cheung (Teddy.Cheung@nrl.navy.mil)
Subjects: Gamma Ray, >GeV, Nova, Transient
The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has detected a new transient gamma-ray source, Fermi J1623-1752. From data obtained on 2021 Sep 28 (00:00-06:00 UTC), preliminary analysis indicates a detection of greater than 5-sigma significance with a (E >100 MeV) flux of (7.2 +/- 5.2) x 10^-7 photons cm^-2 s^-1 and a relatively hard spectrum (single power-law photon index = 1.8 +/- 0.4); statistical uncertainties only. The best-fit position is RA, Dec (J2000) = 245.82 deg, -17.88 deg, with a 95% (99%) confidence error radius of 0.16 deg (0.20 deg).
A possible counterpart to the LAT transient is the recurrent nova U Scorpii with position offset by 0.18 deg from the LAT position, thus just outside the 95% confidence error circle, but within the 99% confidence error circle. U Sco has a known recurrence interval of 10.3 years (Schaefer 2010, ApJS, 187, 275) prior to its outburst in January 2010, thus a new outburst from U Sco could be anticipated. The last observation of U Sco in the AAVSO lightcurve database was on 2021 Sep 19.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multi-wavelength observations, particularly optical follow-up of U Sco. For this source the Fermi LAT contacts are B. Rani (binduphysics@gmail.com) and C.C. Cheung (Teddy.Cheung@nrl.navy.mil).
The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
