THE SIMULTANEOUS OPTICAL-TO-X-RAY SPECTRAL ENERGY DISTRIBUTION OF SOFT X-RAY SELECTED ACTIVE GALACTIC NUCLEI OBSERVED BY SWIFT

Abstract

We report Swift observations of a sample of 92 bright soft X-ray selected active galactic nuclei (AGN). This sample represents the largest number of AGN observed to study the spectral energy distribution (SED) of AGN with simultaneous optical/UV and X-ray data. The principal motivation of this study is to understand the SEDs of AGN in the optical/UV to X-ray regime and to provide bolometric corrections which are important in determining the Eddington ratio L/L Edd . In particular, we rigorously explore the dependence of the UV-EUV contribution to the bolometric correction on the assumed EUV spectral shape. We find strong correlations of the spectral slopes α X and α UV with L/L Edd . Although Narrow-Line Seyfert 1 galaxies (NLS1s) have steeper α X and higher L/L Edd than Broad-Line Seyfert 1 galaxies (BLS1s), their optical/UV to X-ray spectral slopes α ox and optical/UV slopes α UV are very similar. The mean SED of NLS1s shows that in general this type of AGN appears to be fainter in the UV and at hard X-ray energies than BLS1s. We find a strong correlation between α X and α UV for AGN with X-ray spectral slopes α X <1.6. For AGN with steeper X-ray spectra, both this relation and the relation between α X and L/L Edd break down. At α X ≈1.6, L/L Edd reaches unity. We note an offset in the α UV -L/L Edd relation between NLS1s and BLS1s. We argue that α UV is a good estimator of L/L Edd and suggest that α UV can be used to estimate L/L Edd in high-redshift QSOs. Although NLS1s appear to be highly variable in X-rays they only vary marginally in the UV.

A comprehensive approach to analyzing theXMM-Newtondata of Seyfert 1 galaxies

“…This is a characteristic value for AGNs with a small-amplitude soft excess as is the case of ESO 359-G19. In a recent work, Grupe et al (2010) using two Swift observations data in the same soft band (0.2-2 keV) found soft power law photon indices of 1.72 ± 0.10 and 1.60 ± 0.14, which are more typical of the spectral indices observed in the 2-10 keV energy band. This behavior could indicate that the soft excess is variable both in flux and shape as seen in NLS1 objects.…”

“…It was previously observed in X-rays with the ROSAT (1990 August; Voges et al 1999; Thomas et al 1998) and Einstein (Elvis et al 1992) satellites, as part of the study of the general properties of objects with X-ray emission (Simcoe et al 1997;Grupe et al 2001;Jahnke & Wisotzki 2003;Fuhrmeister & Schmitt 2003). More recently, it has been observed by Swift (2008 October) as part of a sample of 92 bright soft X-ray selected AGNs (Grupe et al 2010).…”

“…From optical spectroscopy covering a narrow spectral range, between 4300 and 5700 Å, Boroson & Green (1992) estimated a full width at half maximum (FWHM) of 2120 km s −1 for the Hβ emission line, and observed a very broad Hei 4471 Å emission line. More recently, Grupe et al (2010) have derived a FWHM of 1760 ± 50 km s −1 for Hβ, less than the value used as one of the criteria to distinguish Narrow Line Seyfert 1 (NLS1) from Seyfert 1 galaxies. Nevertheless, the objects was classified as a NLS1 by Véron-Cetty & Véron (2006).…”

“…Analyzing ROSAT data of ESO 359-G19 (taken in 1990 with the source in a high flux state, in the 0.1-2.4 keV range), Grupe et al (2001Grupe et al ( , 2004 fitted the soft X-ray continuum with a power law with a photon index of Γ ∼ 2.4 that is consistent with the presence of the soft excess component. In Grupe et al (2010), these authors analyzed Swift data (taken in 2008 with the source in low state) reporting that the continuum in the 0.3-10 keV range could be described with a power law with a photon index of Γ ∼ 1.7. This value is consistent with the hard power law index, i.e.…”

Properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

“…The average spectral index in the 0.3-10 keV energy range is α X = 1.0 ± 0.5, with a median value of 0.8 (see Online Material Table 8), as compared with the values of 0.58 (FSRQs), 1.3 (BL Lac objects), 1.1 (BLS1s), and 1.7 (RQNLS1s). These values were calculated from the samples of γ−ray blazars from Ghisellini et al ( , 2010 and Tavecchio et al (2010) and radio-quiet Seyferts from Grupe et al (2010). The corresponding distributions are displayed in Fig.…”