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Sat., June 4
Vera Nievas - Very-high-energy gamma-rays from the Universe's middle age: detection of B0218+357 and PKS1441+25 with the MAGIC telescopes telescopes
Toggle Cloak Cloak Flat Spectrum Radio Quasars (FSRQs) remain uncommon members of the Very High Energy (VHE, E$>$100GeV) source family. The reason is twofold. First, they typically have strong emission in the optical-UV coming from the Broad Line Region, which can interact with the gamma-rays, determining a strong absorption. Second, their spectrum is typically soft and may exhibit intrinsic cut-offs.
The FSRQs B0218+357 (z=0.944) and PKS1441+25 (z=0.940) were first detected at VHE with MAGIC in July 2014 and April 2015 respectively, and are the most distant VHE blazars known to date. The detection of this new z~1 blazar class by the MAGIC telescopes gives us a chance to study the processes that allow a typically VHE-obscured blazar to emit sub-TeV photons when strong flares occur and set limits on the EBL density at redshift ~1 for the first time with the Cherenkov technique.
The VHE observations of both blazars were triggered after a high-state alert coming from Fermi-LAT in the High Energy band (HE, 100MeV$<$E$<$100GeV). For B0218+357, a known gravitationally lensed blazar with two image components separated by ~0.3 arcsec and with a delay of 10-12 days, MAGIC observations were scheduled for the trailing pulse after a strong flare in July 2014 and resulted in a detection during only 2 nights. For PKS1441+25, the long-lasting flare allowed the MAGIC collaboration to cover the highest activity state and its gradual decay to the quiescent state.Stephan O’Brien - TeV Observations of Hard Spectrum BL Lac objects with VERITAS
Toggle Cloak Cloak High-Frequency-Peaked BL Lac objects (HBLs) are the most-intense sources of VHE emission, dominating the extragalactic VHE (E > 100 GeV) night sky. HBLs have been observed to vary across all wavelengths and on timescales ranging from minutes to years. VHE observations of a number of HBLs made with the VERITAS telescope array will be reported. Combined data taken between 2007 and 2016 will be used to derive time-averaged spectra, compare spectral models and determine the highest energies probed by the observations. This will be done using advanced forward-folding spectral reconstruction methods. Flux variability will also be investigated on nightly and seasonal timescales. Methods for combining the VHE spectra with Fermi-LAT data, allowing constraints to be placed on the extragalactic background light (EBL), will also be discussed.
Paul Morris
- Zhaoqiang Shen
Bing Li
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