Fermi LAT detection of a new bright gamma-ray transient: Fermi J1710-0323
ATel #14743; Stefano Ciprini (INFN Roma Tor Vergata, & ASI Space Science Data Center, Rome, Italy), on behalf of the the Fermi Large Area Telescope Collaboration
on 29 Jun 2021; 20:37 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)
Subjects: Gamma Ray, >GeV, Request for Observations, Transient
On June 24, 2021, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed gamma-ray emission from a new transient source, Fermi J1710-0323. Preliminary analysis indicates a daily-interval signal with TS = 44 (corresponding to more than 5 sigma formal significance), a flux (E >100 MeV) of (1.3+/-0.4)x10^-6 ph cm^-2 s^-1, and a spectral photon index of 2.5+/-0.3.
The best-fit location on this daily interval of this bright gamma-ray transient source (R.A.=257.65 deg, Dec.=-3.39 deg; J2000) has a 95% containment radius of 0.21 deg (13 arcmin, errors are statistical only). This source, which we designate Fermi J1710-0323, is located at 20.5 degrees above the Galactic plane and next to the Galactic Bulge, and, preliminarily is not in agreement, spatially, with the localization of 4FGL J1709.4-0328, a nearby unassociated gamma-ray source included in the fourth Fermi-LAT source catalog data release 2 (4FGL-DR2; Ballet et al., arXiv:2005.11208), and has not been detected by AGILE or EGRET in the past. On the other hand, Fermi J1710-0323 is spatially in agreement with the position of 2FGL J1710.0-0323, an unassociated gamma-ray source included in the second Fermi-LAT source catalog (Nolan et al. 2012, ApJS, 199, 31).
No promising candidate counterparts are apparent at lower energies: for example anonymous radio sources TXS 1707-033 and TXS 1707-034, an X-ray source 1RXS J171100.5-031456, a passive galaxy NVSS J171021-031334 and anonymous field stars are within the 95% containment circle. Outside of this positional error circle, for example at 20 arcmin and 33 arcmin distance from the Fermi J1710-0323 position, we find, respectively, the flat spectrum radio source PMN J1711-0306 (a.k.a. CRATES J1711-0306), and the BL Lac object PKS 1707-038 (z=1.923).
The transient source Fermi J1710-0323 was not detected on June 23, or on the follows days of June 25, 26, and 27. Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is S. Ciprini (stefano.ciprini at ssdc.asi.it).
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.
