Fermi Gamma-ray Space Telescope

Hunting Distant VHE Blazars with Fermi-LAT and MAGIC: the Recent Detection of PKS 1441+25

J. Becerra Gonzalez
M. Nievas, F. Tavecchio, M. Manganaro, on behalf of Fermi-LAT and MAGIC coll.

Abstract:

During April 2015, flaring activity was detected by the Large Area Telescope on board Fermi from the flat spectrum radio quasar PKS 1441+25 (z=0.940), displaying a hard spectrum. This activity triggered very high energy (VHE, E>100 GeV) observations using the MAGIC telescopes, leading to its first detection at these energies. Aside from the gravitationally lensed VHE blazar QSO B0218+357 (z = 0.944), also detected by MAGIC, PKS 1441+25 is the most distant VHE blazar detected to date. The multi-wavelength light curve shows two distinct flux states occurring during this flare. The broadband spectral energy distribution can be explained by an external Compton model. For the first time, the VHE gamma-ray spectrum has been used to indirectly probe the extragalactic background light at redshifts out to z ~ 0.94 using sensitive ground Cherenkov observations in the energy range from 40 to 250 GeV.