GeV-TeV Blazar Population Studies

Source: arXiv


The synergy between the Fermi-LAT and ground-based Cherenkov telescope arrays
gives us the opportunity for the first time to characterize the high energy
emission (100 MeV - 10 TeV) from more than 30 blazars. In this study we
performed a Fermi-LAT spectral analysis for all TeV-detected blazars and
combined it with archival TeV spectra. Our results for low synchrotron-peaked
BL Lacs (LBL) show hints of absorption features in the GeV band that could be
interpreted as internal opacity at the source. We note that simple or broken
power laws cannot describe all the observed GeV-TeV spectra and more complex
spectral shapes seem required.

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    ABSTRACT: We report results from an intensive multiwavelength campaign on the intermediate-frequency-peaked BL Lacertae object W Com (z=0.102) during a strong outburst of very high energy gamma-ray emission in June 2008. The very high energy gamma-ray signal was detected by VERITAS on 2008 June 7-8 with a flux F(>200 GeV) = (5.7+-0.6)x10^-11 cm-2s-1, about three times brighter than during the discovery of gamma-ray emission from W Com by VERITAS in 2008 March. The initial detection of this flare by VERITAS at energies above 200 GeV was followed by observations in high energy gamma-rays (AGILE, E>100 MeV), and X-rays (Swift and XMM-Newton), and at UV, and ground-based optical and radio monitoring through the GASP-WEBT consortium and other observatories. Here we describe the multiwavelength data and derive the spectral energy distribution (SED) of the source from contemporaneous data taken throughout the flare. Comment: 26 pages, 5 figures; Accepted for publication by The Astrophysical Journal
    The Astrophysical Journal 10/2009; 707(1). DOI:10.1088/0004-637X/707/1/612 · 5.99 Impact Factor
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    ABSTRACT: Our understanding of blazars has been greatly increased in recent years by extensive multiwavelength observations, particularly in the radio, X-ray, and gamma-ray regions. Over the past decade the Whipple 10 m telescope has contributed to this with the detection of five BL Lacertae objects at very high gamma-ray energies. The combination of multiwavelength data has shown that blazars follow a well-defined sequence in terms of their broadband spectral properties. Together with providing constraints on emission models, this information has yielded a means by which potential sources of TeV emission may be identified and predictions made as to their possible gamma-ray flux. We have used the Whipple telescope to search for TeV gamma-ray emission from eight objects selected from a list of such candidates. No evidence has been found for very high energy emission from the objects in our sample, and upper limits have been derived for the mean gamma-ray flux above 390 GeV. These flux upper limits are compared with the model predictions, and the implications of our results for future observations are discussed.
    The Astrophysical Journal 12/2003; 599(2). DOI:10.1086/379544 · 5.99 Impact Factor
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    ABSTRACT: The blazar sequence is a scenario in which the bolometric luminosity of the blazar governs the appearance of its spectral energy distribution. The most prominent result is the significant negative correlation between the synchrotron peak frequencies and the synchrotron peak luminosities of the blazar population. Observational studies of the blazar sequence have, in general, neglected the effect of Doppler boosting. We study the dependence of both the synchrotron peak frequency and luminosity with Doppler-corrected quantities. We determine the spectral energy distributions of 135 radio-bright AGN and find the best-fit parabolic function for the distribution to quantify their synchrotron emission. The corresponding measurements of synchrotron peak luminosities and frequencies are Doppler-corrected with a new set of Doppler factors calculated from variability data. The relevant correlations for the blazar sequence are determined for these intrinsic quantities. The Doppler factor depends strongly on the synchrotron peak frequency, the lower energy sources being more boosted. Applying the Doppler correction to the peak frequencies and luminosities annuls the negative correlation between the two quantities, which becomes positive. For BL Lacertae objects, the positive correlation is particularly strong. The blazar sequence, when defined as the anticorrelation between the peak frequency and luminosity of the synchrotron component of the spectral energy distribution, disappears when the intrinsic, Doppler-corrected values are used. It is an observational phenomenon created by variable Doppler boosting across the synchrotron peak frequency range. Comment: 9 pages, 5 figures + 2 tables. The published version with minor changes, the main conclusions are unchanged
    Astronomy and Astrophysics 03/2008; 488(3). DOI:10.1051/0004-6361:200809716 · 4.38 Impact Factor

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