ATEL Fermi-LAT Detection of enhanced gamma-ray activity from the SSRQ/CSS 3C 380
ATel #13999; I. Mereu (INFN Perugia), R. Angioni (SSDC/INFN), E. Torresi (INAF OAS Bologna), on behalf of the Fermi Large Area Telescope Collaboration
on 8 Sep 2020; 18:53 UT
Credential Certification: Isabella Mereu (mereuisabella@gmail.com)
Subjects: Gamma Ray, Request for Observations, AGN
Referred to by ATel #: 14012
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray flaring activity from a source positionally consistent with the steep spectrum radio quasar 3C 380, also known as 4FGL J1829.5+4845 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 277.3824204 deg, Decl. = 48.7461556 deg (J2000; Petrov et al. 2006, AJ, 131,1872), and redshift z=0.692 (Lawrence et al. 1996, ApJS,107,541). 3C 380 is a well-known compact steep spectrum (CSS) quasar (Fanti et al. 1990, A&A, 231, 333).
Preliminary analysis indicates that 3C 380 was in an elevated gamma-ray emission state on 5 September 2020, with a daily averaged gamma-ray flux (E>100MeV) of (5.4+/-1.1) X 10^-7 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 14 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.14+/-0.15, and is smaller than the 4FGL value of 2.43 +/- 0.03, indicating a spectral hardening accompanying the flux increase. The source continues to be detected in the following two days (6-7 September), with flux (3.3+/-0.8) X 10^-7 photons cm^-2 s^-1 and (2.8+/-1.1) X 10^-7 photons cm^-2 s^-1, respectively, and photon index 2.2+/-0.2 and 2.4+/-0.3, respectively. The values of fluxes and indexes reported here are the results of a dedicated follow up analysis.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We have requested and obtained Target of Opportunity observations with the Neil Gehrels Swift Observatory. We encourage further multifrequency observations of this source. For this source, the Fermi-LAT contact person is Isabella Mereu (mereuisabella@gmail.com).
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.
