Gamma-ray excess from a stacked sample of high- and intermediate-frequency peaked blazars observed with the MAGIC telescope

Abstract

Between 2004 and 2009 a sample of 28 X-ray selected high- and intermediate-frequency peaked blazars with a X-ray flux larger than 2 uJy at 1 keV in the redshift range from 0.018 to 0.361 was observed with the MAGIC telescope at energies above 100 GeV. Seven among them were detected and the results of these observations are discussed elsewhere. Here we concentrate on the remaining 21 blazars which were not detected during this observation campaign and present the 3 sigma (99.7 %) confidence upper limits on their flux. The individual flux upper limits lie between 1.6 % and 13.6 % of the integral flux from the Crab Nebula. Applying a stacking method to the sample of non-detections with a total of 394.1 hours exposure time, we find evidence for an excess with a cumulative significance of 4.9 standard deviations. It is not dominated by individual objects or flares, but increases linearly with the observation time as for a constant source with an integral flux level of ~1.5 % of that observed from the Crab Nebula above 150 GeV.

14 pages, 6 figures, accepted by ApJ

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Cited by in corpus (19)

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• MAGIC observations of the giant radio galaxy M87 in a low-emission state between 2005 and 2007
• Upper limits from five years of blazar observations with the VERITAS Cherenkov telescopes
• Optimized analysis method for indirect dark matter searches with Imaging Air Cherenkov Telescopes
• Discovery of VHE gamma-ray emission from the BL Lac object B3 2247+381 with the MAGIC telescopes
• Investigating the peculiar emission from the new VHE gamma-ray source H1722+119
• MAGIC detection of short-term variability of the high-peaked BL Lac object 1ES 0806+524
• Discovery of very high energy gamma-ray emission from the blazar 1ES 1727+502 with the MAGIC Telescopes
• Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012
• Estimating sizes of faint, distant galaxies in the submillimetre regime
• Discovery of very high energy gamma-ray emission from the blazar 1ES 0033+595 by the MAGIC telescopes
• MAGIC detection of very high energy gamma-ray emission from the low-luminosity blazar 1ES 1741+196
• An ALMA survey of sub-millimeter galaxies in the Extended Chandra Deep Field South: Sub-millimeter properties of color-selected galaxies
• Long-term multi-wavelength study of 1ES 0647+250
• Model-independent Redshift Estimation of BL Lac Objects through VHE Observations
• VHE $\gamma$-ray observations of bright BL Lacs with the Large-Sized Telescope prototype (LST-1) of the CTAO
• Multiwavelength temporal and spectral study of TeV blazar 1ES 1727+502 during 2014 to 2021