A \(Chandra-Swift\) View of Point Sources in Hickson Compact Groups: High AGN fraction but a dearth of strong AGNs

We present \(Chandra\) X-ray point source catalogs for 9 Hickson Compact Groups (HCGs, 37 galaxies) at distances \(34 - 89\) Mpc. We perform detailed X-ray point source detection and photometry, and interpret the point source population by means of simulated hardness ratios. We thus estimate X-ray luminosities (\(L_X\)) for all sources, most of which are too weak for reliable spectral fitting. For all sources, we provide catalogs with counts, count rates, power-law indices (\(\Gamma\)), hardness ratios, and \(L_X\), in the full (\(0.5-8.0\) keV), soft (\(0.5-2.0\) keV) and hard (\(2.0-8.0\) keV) bands. We use optical emission-line ratios from the literature to re-classify 24 galaxies as star-forming, accreting onto a supermassive black hole (AGNs), transition objects, or low-ionization nuclear emission regions (LINERs). Two-thirds of our galaxies have nuclear X-ray sources with \(Swift\)/UVOT counterparts. Two nuclei have \(L_{X,{\rm 0.5-8.0 keV}}\)~\( > 10^{42}\) erg s\(^{-1}\), are strong multi-wavelength AGNs and follow the known \(\alpha_{\rm OX}-\nu L_{\nu,\rm near UV}\) correlation for strong AGNs. Otherwise, most nuclei are X-ray faint, consistent with either a low-luminosity AGN or a nuclear X-ray binary population, and fall in the "non-AGN locus" in \(\alpha_{\rm OX}-\nu L_{\nu,\rm near UV}\) space, which also hosts other, normal, galaxies. Our results suggest that HCG X-ray nuclei in high specific star formation rate spiral galaxies are likely dominated by star formation, while those with low specific star formation rates in earlier types likely harbor a weak AGN. The AGN fraction in HCG galaxies with \(M_R \le -20\) and \(L_{X,{\rm 0.5-8.0 keV}} \ge 10^{41}\) erg s\(^{-1}\) is \(0.08^{+0.35}_{-0.01}\), somewhat higher than the \(\sim 5%\) fraction in galaxy clusters.