MAGIC detection of very-high-energy gamma-ray flaring activity from BL Lacertae during the current historical optical and high-energy gamma-ray flare

ATel #13963; Oscar Blanch (IFAE-BIST, Barcelona), on behalf of the MAGIC collaboration
on 22 Aug 2020; 13:11 UT
Credential Certification: Oscar Blanch (blanch@ifae.es)

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The MAGIC telescopes have observed an increase in the very-high-energy (VHE; >100 GeV) gamma-ray flux from the eponymous blazar BL Lacertae (22 02 43.29, +42 16 39.98, J2000.0). Observations have been performed on the nights of August 11, 12, 13, 15, 17, 19, and 20, 2020, following the alerts by optical telescopes (showing a historical maximum, see ATel #13930, ATel #13956, ATel #13958) and by the Fermi-LAT instrument in the GeV band (ATel #13933). Preliminary analyses of the MAGIC data show a clear detection (8 sigma above background) during the night of August 19, only (MJD 59080.06 - 59080.17). The preliminary flux estimate for that night is about 15% of the flux from the Crab nebula above 100 GeV. BL Lacertae is a close-by VHE blazar (Albert et al. 2007, ApJ, 666,17) located at redshift z=0.069, which has already shown several VHE flares in the past years (Arlen et al. 2013, ApJ, 762, 92; Abeysekara et al. 2018, ApJ, 856, 95; Acciari et al. 2019, A&A, 623, 175). The last VHE flare happened on May 2019 (ATel #12724), at a flux level similar to the current one. MAGIC observations on BL Lacertae will continue during the next days, and multiwavelength observations are encouraged. The MAGIC contact persons for these observations are Oscar Blanch (blanch@ifae.es), and Giacomo Bonnoli (giacomo.bonnoli@unisi.it). MAGIC is a system of two 17m-diameter Imaging Atmospheric Cherenkov Telescopes located at the Canary island of La Palma, Spain, and designed to perform gamma-ray astronomy in the energy range from 50 GeV to greater than 50 TeV.