Fermi-LAT detection of renewed gamma-ray activity from BL Lacertae
ATel #15688; G. La Mura (LIP, Portugal) on behalf of the Fermi Large Area Telescope Collaboration
on 17 Oct 2022; 07:27 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed renewed gamma-ray activity from a source positionally consistent with BL Lacertae, also known as 4FGL J2202.7+4216 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 330.68038 deg, Decl. = +42.27778 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z = 0.0686 (Vermeulen et al. 1995, ApJ, 452, L5).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on October 15, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (5.0+/-0.6) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 15 relative to the average flux reported in the third release of the fourth Fermi-LAT catalog (4FGL-DR3, Abdollahi et al. 2022, ApJS, 260, 53). The corresponding photon index is 2.07+/-0.09, and is smaller than the 4FGL-DR3 value of 2.18+/-0.01, similar to what has been observed in previous episodes of gamma-ray flaring activity of BL Lacertae (ATels #14330, #14583 and #14777). The gamma-ray enhancement occurred during an optical brightness increase (ATel #15684) and the spectral hardening resulted in the detection of two high-energy photons, having probability to be associated with the source larger than p = 0.9999, observed on October 15 at 03:47:29 UT, with E = 19 GeV, and at 10:19:27 UT, with E = 31 GeV.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source belongs to the list of daily monitored LAT sources, therefore a preliminary gamma-ray light curve is available at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/BL_Lac. The light curve of this source can also be accessed through the Fermi-LAT Light Curve Repository (LCR) at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J2202.7+4216. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Simone Garrappa (simone.garrappa at desy.de).
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.
