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Discovery of very high energy gamma-ray emission from RBS 0723 with the MAGIC telescopes

The MAGIC collaboration reports the discovery of very high energy (VHE ; E>100 GeV) gamma-ray emission from RBS 0723 (RA: 08:47:12.9 DEC: +11:33:50, J2000.0) RBS 0723 is a BL Lac object at redshift z=0.198. The source has been detected by Fermi-LAT, in the Second Fermi-LAT source Catalogue (2FGL ; Nolan et al. 2012) with F(>1 GeV) = (5.3+-1.2)e-10 cm^-2 s^-1 and with photon index 1.48+-0.16. It also belongs to the first Fermi-LAT catalog of >10 GeV sources (1FHL ; Ackermann et al, 2013), showing a hard (photon index = 1.4 +- 0.4) and bright (photon flux = 9.6e-11 ph cm^-2 s^-1) emission above 10 GeV, and identified as a good candidate for VHE detection. The shape of the SED indicates it is one of the subclass of the extreme HBL characterized by extremely hard X-ray and VHE continua. RBS 0723 was observed starting on 2013 December 3. Data taken between 2014 Jan 1 and Jan 8 (about 10 hours) yields a source detection with a statistical significance of more than 5 standard deviations. The non-detection in the earlier data taken in 2013 Dec. suggests VHE flux variability. The VHE emission measured with MAGIC has a flux of about 2.5% of the Crab nebula at energies above 200 GeV. Optical monitoring with KVA telescope (La Palma) also shows evidence of an increased flux (R=17.2 in December 2013, R=16.9 in January 2014). MAGIC observations of RBS 0723 will resume on Jan. 22. Multi-wavelength observations are encouraged. The MAGIC contact persons for these observations are R. Mirzoyan (razmik.mirzoyan@mpp.mpg.de) and F. Tavecchio (fabrizio.tavecchio@brera.inaf.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.

Gamma Ray ; >GeV ; TeV ; VHE ; AGN

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