Mkn 766 (NGC 4253)

Note: The blazar 1ES 1218+304 is located about 0.73 degrees away, at (α = 12 21 21.94, δ = +30 10 37.1). Its 2-10 keV flux measurements are typically 1.5 to 2.6 × 10⁻¹¹ erg cm⁻² s⁻¹ (e.g., from XMM-Newton, Blustin et al. 2004; BeppoSAX, Giommi et al. 2005; Suzaku, Sato et al. 2008). Given the FWHM ∼ 1 degree angular response of the PCA, 1ES 1218+304 could thus contribute a contaminating flux of roughly 2-4 × 10⁻¹² erg cm⁻² s⁻¹ to the flux/spectrum of Mkn 766 (that is, contamination at the ∼7-15% level). The blazar RGB J1217+301 (ON 325) lies about 0.33 degrees away, at (α = 12 17 52.1, δ= +30 07 01). Its 2-10 keV flux, following references on NED, is usually 6-10 × 10⁻¹³ erg cm⁻² s⁻¹ and so the level of contamination to the measured flux/spectrum of Mkn 766 is likely only ∼5 × 10⁻¹³ erg cm⁻² s⁻¹.