Discovery of very high energy gamma-ray emission from the low-frequency-peaked Bl Lacertae object Bl Lacertae
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2007
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IOP Publishing
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Albert, J., Aliu, E., Anderhub, H. et al. «Discovery of Very High Energy γ-Ray Emission from the Low-Frequency-Peaked BL Lacertae Object BL Lacertae». The Astrophysical Journal, vol. 666, n.o 1, agosto de 2007, p. L17. iopscience.iop.org, https://doi.org/10.1086/521550.
Abstract
The MAGIC collaboration observed BL Lacertae for 22.2 hr during 2005 August to December and for 26 hr during 2006 July to September. The source is the historical prototype and eponym of a class of low-frequency-peaked BL Lacertae (LBL) objects. A very high energy (VHE) gamma-ray signal was discovered with a 5.1 sigma excess in the 2005 data. Above 200 GeV, an integral flux of (0.6 +/- 0.2) x 10(-11) cm(-2) S-1 was measured, corresponding to approximately 3% of the Crab flux. The differential spectrum between 150 and 900 GeV is rather steep with a photon index of -3.6 +/- 0.5. The light curve shows no significant variability during the observations in 2005. For the first time a clear detection of VHE gamma-ray emission from an LBL object was obtained with a signal below previous upper limits. The 2006 data show no significant excess. This drop in flux follows the observed trend in optical activity.
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© The American Astronomical Society. We thank the IAC for the excellent working conditions at the ORM. The support of the German BMBF and MPG, Italian INFN, and Spanish CICYT is gratefully acknowledged. This work is also supported by ETH Research Grant TH34/043 and the Polish MNiI Grant 1P03D01028. We thank H. Aller and M. Aller (UMRAO), and A. Lähteenmäki (Metsähovi) for providing the radio data.