High synchrotron peak blazars X-ray spectral fits

We present the results of a multi-wavelength study of a population of X-ray bright (log(F(0.2-12keV))>-12.5), non-Gamma-ray detected high and extreme high synchrotron peak (HSP, EHSP; log(Nu,peak,Hz)>16) BL Lacs to i) put stronger constraints on the synchrotron peak location and shape and ii) model their expected behaviour in the very high-energy band. First, we performed an X-ray spectral analysis, using XMM-Newton, Chandra, Swift-XRT, and eROSITA data, and fitting the spectra using both a power law and a log parabola model.

Out of 78 sources in the initial sample, 17 were best described by a log parabola model, a result that supports a scenario where the synchrotron peak falls in the X-ray band. Among these 17 sources, we further selected the 10 objects dominated by the jet emission, with no significant contamination of the host galaxy. We performed a gamma-ray analysis of Fermi-LAT data for these objects, obtaining upper limits providing information on their flux in the 100MeV-300GeV energy range.