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We report observations of a transient source fermi from radio to grs. fermi was discovered by the {it Fermi-LAT} in May 2017. Follow-up {it Swift-XRT} observations revealed three flaring episodes through March 2018, and the peak X-ray flux is about $10^3$ higher than the {it ROSAT all-sky survey (RASS)} flux upper limit. Optical spectral measurements taken by the {it Magellan 6.5-m telescope} and the {it Lick-Shane telescope} both show a largely featureless spectrum, strengthening the BL Lac interpretation first proposed by citet{Bruni18}. The optical and mid-infrared (MIR) emission goes to a higher state in 2018, when the flux in high energies goes down to a lower level. Our {it RATAN-600m} measurements at 4.8~GHz and 8.2~GHz do not indicate any significant radio flux variation over the monitoring seasons in 2017 and 2018, nor deviate from the archival {it NVSS} flux level. During GeV flaring times, the spectrum is very hard ($Gamma_gammasim$1.7) in the GeV band and at times also very hard (($Gamma_{rm X}lesssim2$) in the X-rays, similar to a high-synchrotron-peak (or even an extreme) BL Lac object, making fermi a good target for ground-based {it Cherenkov telescopes}.
On May 15th, 2017, the emph{FERMI}/LAT gamma-ray telescope observed a transient source not present in any previous high-energy catalogue: J1544-0649. It was visible for two consecutive weeks, with a flux peak on May 21st. Subsequently observed by a e
1RXS J101015.9-311909 is a galaxy located at a redshift of z=0.14 hosting an active nucleus belonging to the class of bright BL Lac objects. Observations at high (HE, E > 100 MeV) and very high (VHE, E > 100 GeV) energies provide insights into the or
We present results from VERITAS observations of the BL Lac object PG 1553+113 spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured between 160 and 560,GeV, is well described by a power law with a spectral index of $4.33 pm 0.
On 2017 September 22, the IceCube Neutrino Observatory reported the detection of the high-energy neutrino event icnu, of potential astrophysical origin. It was soon determined that the neutrino direction was consistent with the location of the gamma-
Since the launch of the Fermi satellite, BL Lacertae has been moderately active at gamma-rays and optical frequencies until May 2011, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST-AGILE Supp