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 similar to 0.3-0.6, core radii r(c) similar to 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 similar to 3-5 keV) and luminosity (L0.4-5 (keV) similar to 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.