Vol 18, No 5

Analysis of the 3C 445 soft X-ray spectrum as observed by Chandra high-energy gratings

Fu-Tong Dong, Shu-Hua Shao, Yan Cheng, Jiao-Long Zeng


Abstract We present a detailed analysis of the soft X-ray emission of 3C 445 using an archival Chandra High Energy Transmission Grating (HETG) spectrum. Highly-ionized H- and He-like Mg, Si and S lines, as well as a resolved low-ionized Si Kα line, are detected in the high resolution spectrum. The He-like triplets of Mg and Si are resolved into individual lines, and the calculated R ratios indicate a high density for the emitter. The low values of G ratios indicate the lines originate from collisionally ionized plasmas. However, the detection of a resolved narrow Ne X radiative recombination continua (RRC) feature in the spectrum seems to prefer a photoionized environment. The spectrum is subsequently modeled with a photoionization model, and the results are compared with those of a collisional model. Through a detailed analysis of the spectrum, we exclude a collisional origin for these emission lines. A one-component photoionization model provides a great fit to the emission features. The best-fit parameters are \(\log \xi = 3.3^{+0.4}_{-0.3}\) erg cm s\(^{-1}\), \(n_{\rm H}=5^{+15}_{-4.5}\times 10^{10}\) cm\(^{-3}\), and \(N_{\rm H} = 2.5^{+3.8}_{-1.7}\times10^{20}\) cm\(^{-2}\). According to the calculated high density for the emitter, the measured velocity widths of the emission lines and the inferred radial distance (6 × 10\(^{14}\) − 8 × 10\(^{15}\) cm), we suggest the emission lines originating from matter are located in the broad line region (BLR).


Keywords galaxies: active — X-rays: galaxies — galaxies: individual (3C 445)

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