Chandra observations of the X-ray environment of BL Lacs

We present Chandra observations of the X-ray environment of a sample of 6 BL Lacertae objects. The improved sensitivity of the ACIS experiment allows us to separate the core X-ray emission from the contribution of diffuse emission from the host galaxy/cluster scales. Within the short (2–6 ks) ACIS exposures, we find evidence for diffuse X-ray emission in 3 sources (BL Lac, PKS 0548–322, and PKS 2005–489). The diffuse emission can be modeled with a King profile with $\beta \sim 0.3{-}0.6$, core radii $r_{\rm c} \sim 15{-}28$ kpc, and 0.4–5 keV luminosities in the range $10^{41}{-}10^{42}$ erg s-1. In the remaining 3 sources, one (3C 371) has a radial profile entirely consistent with an unresolved source, while two (1ES 2344+514 and 1ES 2321+419) show evidence for weak diffuse emission on kpc scales. These results support current models for radio-loud AGN unifying BL Lacs and FRI radio galaxies through the orientation of their jets. In PKS 0548–322 and PKS 2005–489, we also find evidence for diffuse emission on cluster scales, although the spatial properties of this emission are not constrained. The temperature ($kT \sim 3{-}5$ keV) and luminosity ($L_{0.4-5~{\rm keV}} \sim 10^{42}$ erg s-1) of the cluster gas are typical of normal clusters. Interestingly, these are the two brightest sources of the sample, suggesting a link between environment and nuclear activity.