Comparison Between TeV and Non-TeV Fermi-detected BL Lacertae Objects

Abstract

In this paper, we compiled a sample of 410 Fermi-detected BL Lacs, including 42 TeV-detected BL Lacs (TBLs) and 368 non-TeV-detected BL Lacs (non-TBLs) with corresponding mid-infrared (mid-IR), TeV and Fermi γ-ray data, and calculated some important parameters including monochromatic luminosities (mid-IR, GeV and TeV bands) and mid-IR spectral indices. Based on those parameters, we discussed the relationship between the mid-IR and the TeV bands and that between the mid-IR and the GeV bands. Main conclusions are drawn as follows: (1) In the color–color and color–magnitude diagrams, our sample forms a WISE-Gamma Strip in the [3.4]–[4.6]–[12] μm color–color diagram, and TBLs occupy the brighter region than the non-TBLs for the similar color-index in the color-magnititue diagram; (2) The mid-IR luminosity of the TBLs is on average higher than that of non-TBLs, while the average mid-IR spectral index of TBLs is smaller than the non-TBLs, suggesting that TBLs are brighter and hold a more flat spectrum than do the non-TBLs in the mid-IR band. Besides, HBLs have a more flat mid-IR spectrum than LBLs and IBLs; (3) The mid-IR luminosity is positively correlated with the GeV luminosity and the intrinsic TeV luminosity. A positive correlation exists between the mid-IR spectral index and the observed TeV spectral index, which is consistent with the expectations of the synchrotron self-Compton mechanism. We suggest that the HBLs with extreme relativistic electrons might scatter the mid-IR photons up to the TeV band.