HXD/PIN spectrum (open circles), together with the background spectrum (NXB+CXB; small crosses) and the net spectrum (open squares) of Mrk 273, PKS 1345+12, and Arp 220. The net spectrum for Mrk 273, PKS 1345+12, and Arp 220 is 5.4%, 3.4%, and 2.2% above the background, respectively. Mrk 273 is the only source that is detected above the background beyond the uncertainties of the background modeling (at the 1.8σ level). The spectra of F05189–2524 and F08572+3915 do not lie above the background, so they are not shown here.