Systematic search for VHE gamma-ray emission from X-ray bright high-frequency BL Lac objects

Abstract

All but three (M87, BL Lac and 3C 279) extragalactic sources detected so far at very high energy (VHE) gamma-rays belong to the class of high-frequency peaked BL Lac (HBL) objects. This suggested to us a systematic scan of candidate sources with the MAGIC telescope, based on the compilation of X-ray blazars by Donato et al. (2001). The observations took place from December 2004 to March 2006 and cover sources on the northern sky visible under small zenith distances zd < 30 degrees at culmination. The sensitivity of the search was planned for detecting X-ray bright F(1 keV) > 2 uJy) sources emitting at least the same energy flux at 200 GeV as at 1 keV. In order to avoid strong gamma-ray attenuation close to the energy threshold, the redshift of the sources was constrained to values z<0.3. Of the fourteen sources observed, 1ES 1218+304 and 1ES 2344+514 have been detected in addition to the known bright TeV blazars Mrk 421 and Mrk 501. A marginal excess of 3.5 sigma from the position of 1ES 1011+496 was observed and has been confirmed as a source of VHE gamma-rays by a second MAGIC observation triggered by a high optical state (Albert et al. 2007). For the remaining sources, we present here the 99% confidence level upper limits on the integral flux above ~200 GeV. We characterize the sample of HBLs (including all HBLs detected at VHE so far) by looking for correlations between their multi-frequency spectral indices determined from simultaneous optical, archival X-ray, and radio luminosities, finding that the VHE emitting HBLs do not seem to constitute a unique subclass. The absorption corrected gamma-ray luminosities at 200 GeV of the HBLs are generally not higher than their X-ray luminosities at 1 keV.

15 pages, 7 figures, 5 tables, submitted to ApJ (revised version)

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Cited by in corpus (22)

• Fermi observations of TeV-selected AGN
• Discovery of Very High Energy gamma-rays from 1ES 1011+496 at z=0.212
• Detection of Intra-day Variability Timescales of Four High Energy Peaked Blazars with XMM-Newton
• Synoptic studies of seventeen blazars detected in very high-energy gamma-rays
• The RINGO2 and DIPOL Optical Polarisation Catalogue of Blazars
• Contribution to the Extragalactic Gamma-ray Background from the Cascades of Very-high Energy Gamma Rays from Blazars
• The blazar-like radio structure of the TeV source IC310
• Discovery of High-energy and Very High Energy Gamma-ray Emission from the Blazar RBS 0413
• MAXI investigation into the longterm X-ray variability from the very-high-energy gamma-ray blazar Mrk 421
• Multiwavelength observations of the AGN 1ES 0414+009 with VERITAS, Fermi-LAT, Swift-XRT, and MDM
• 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
• Gamma-ray excess from a stacked sample of high- and intermediate-frequency peaked blazars observed with the MAGIC telescope
• Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012
• A two-zone photohadronic scenario for EHBL-like behavior of Mrk 501
• Multi-Wavelength Observations of the Blazar 1ES 1011+496 in Spring 2008
• Multi-Wavelength Observations of the HBL Object 1ES 1011+496 in Spring 2008
• Spectral energy distributions and high-energy emission of BL Lac type objects
• Successful ToO triggers on the extragalactic sources with the MAGIC telescope
• Physics Insights from Recent MAGIC AGN Observations
• Observations of VHE gamma-Ray Sources with the MAGIC Telescope
• INTEGRAL View of TeV Sources: A Legacy for the CTA Project