Chandra Grating Observations of Seyfert 1 Galaxies

We present new results from a Chandra HETG observation of NGC 5548 and give a comparison of absorption and emission features found in Seyfert 1 galaxies using Chandra grating observations. Deep soft X-ray edges are seen in Mkn 509 and NGC 3783, consistent with ASCA data. In NGC 5548 and NGC 4501 the edges are weak but consistent with the low column densities. We show that the detection of a narrow, probably non-disk, component of the iron line is very common. We show the effect of removing this narrow component from the ASCA Fe-K line profile in NGC 4151, revealing the underlying true shape of the relativistic Fe-K line component. Our preliminary HETG spectra of NGC 5548 (exposure time ∼ 80 ks) taken in 2000, February, are shown in Fig. 1 and Fig. 2(a) (see also George, Turner, Yaqoob 2001). The strongest features (apart from Fe Kα – see Yaqoob et al. 2001) – are the Ovii He-like triplet and absorption features due to Ne and O Lyα, and Ovii 1s 2 − 3p 1 P 1. See Table 1 for a comparison with Kaastra et al. (2000). Ovii (f) is particularly strong compared to (i) and (r), indicating a photoionization-dominated plasma. It is consistent with being at the systemic velocity but we measure a range of blueshifts for the absorption lines. These, and detailed analysis will be reported in McKernan et al. (in preparation). Detailed Chandra grating spectroscopy has now been published for five Seyfert 1 galaxies, as summarized in Table 1. Kaspi et al. (2001a) present the highest S/N grating data available for any AGN (∼ 900 ks on NGC 3783; Table 1 refers only to the shorter 53 ks observation). NGC 3227 was too weak for searching for narrow absorption/emission features; 3C 273 is bright but no absorption/emission features were detected (see George et al.