Fermi-LAT detection of increasing gamma-ray activity of the blazar BL Lacertae
ATel #12718; S. Garrappa (DESY Zeuthen, DE), S. Buson (Univ. of Wuerzburg, DE; UMBC, USA) on behalf of the Fermi Large Area Telescope Collaboration
on 2 May 2019; 20:43 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)
Subjects: Gamma Ray, >GeV, VHE, Request for Observations, AGN, Blazar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray activity from BL Lacertae (4FGL J2202.7+4216 from The Fermi-LAT Fourth Source Catalog arXiv:1902.10045, VLBI position: R.A.=22:02:43.29137 Dec.=+42:16:39.9799, J2000 from Beasley et al. 2002, ApJS, 141, 13; with a z=0.0686, Vermeulen et al., 1995, ApJ, 452, L5).
BL Lacertae has been detected on 1 May 2019, in a bright state with a daily averaged gamma-ray flux (E>100MeV) of (1.5+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) and a corresponding photon index of 1.7 +/- 0.1, significantly harder than the photon index reported in the 4FGL catalog of 2.23 +/- 0.01. We report also the detection of a 356 GeV photon with a high probability of being associated with the object. Previous flaring activity in gamma-rays was reported in ATel #4028 when the source reached a daily flux level (E > 100MeV) of (2.3 +/- 0.3)x10^-6 photons cm^-2 s^-1.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of the source will continue. The source is included in the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/). We encourage multifrequency observations of BL Lacertae.
For BL Lacertae the 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.
