The γ-ray sky seen at X-ray energies. I. Searching for the connection between X-rays and γ-rays in Fermi BL Lac objects

The γ-ray sky seen at X-ray energies. I. Searching for the connection between X-rays and γ-rays in Fermi BL Lac objectsMarchesini, E. J.Paggi, A.Massaro, F.Masetti, N.D'Abrusco, RaffaeleAndruchow, I.de Menezes, R.DOI: info:10.1051/0004-6361/201936285v. 631A150
Marchesini, E. J., Paggi, A., Massaro, F., Masetti, N., D'Abrusco, Raffaele, Andruchow, I., and de Menezes, R. 2019. "The γ-ray sky seen at X-ray energies. I. Searching for the connection between X-rays and γ-rays in Fermi BL Lac objects." Astronomy and Astrophysics 631:A150. https://doi.org/10.1051/0004-6361/201936285
ID: 154594
Type: article
Authors: Marchesini, E. J.; Paggi, A.; Massaro, F.; Masetti, N.; D'Abrusco, Raffaele; Andruchow, I.; de Menezes, R.
Abstract: Context. BL Lac objects are an extreme type of active galactic nuclei (AGNs) that belong to the largest population of γ-ray sources: blazars. This class of AGNs shows a double-bumped spectral energy distribution that is commonly described in terms of a synchrotron self-Compton (SSC) emission process, whereas the low-energy component that dominates their emission between the infrared and the X-ray band is tightly connected to the high-energy component that peaks in the γ-rays. Two strong connections that link radio and mid-infrared emission of blazars to the emission in the γ-ray band are well established. They constitute the basis for associating γ-ray sources with their low-energy counterparts. Aims: We searched for a possible link between X-ray and γ-ray emissions for the subclass of BL Lacs using all archival Swift/XRT observations combined with Fermi data for a selected sample of 351 sources. Methods: Analyzing ̃2400 ks of Swift/XRT observations that were carried out until December 2018, we discovered that above the γ-ray flux threshold Fγ ≈ 3 × 10-12 erg cm-2 s-1, 96% of all Fermi BL Lacs have an X-ray counterpart that is detected with signal-to-noise ratio > 3. Results: We did not find any correlation or clear trend between X-ray and γ-ray fluxes and/or spectral shapes, but we discovered a correlation between the X-ray flux and the mid-infrared color. Finally, we discuss on a possible interpretation of our results in the SSC framework. Full Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/631/A150