We present results from a 200 ks Suzaku observation of 1H 0419-577 taken during 2007 July. The source shows a strong excess of counts above 10 keV compared to the extrapolation of models based on previous data in the 0.5-10 keV band. The 'hard excess' in 1H 0419-577 can be explained by the presence of a Compton-thick partial-covering absorber that covers ~ 70% of the source. The Compton-thick gas likely originates from a radius inside of the optical BLR and may form part of a clumpy disk wind. The fluorescent Fe Ka luminosity measured by Suzaku is consistent with that expected from an equatorial disk wind.
Deep Dive into Suzaku Observation of a Hard Excess in 1H 0419-577: Detection of a Compton-Thick Partial-Covering Absorber.
We present results from a 200 ks Suzaku observation of 1H 0419-577 taken during 2007 July. The source shows a strong excess of counts above 10 keV compared to the extrapolation of models based on previous data in the 0.5-10 keV band. The ‘hard excess’ in 1H 0419-577 can be explained by the presence of a Compton-thick partial-covering absorber that covers ~ 70% of the source. The Compton-thick gas likely originates from a radius inside of the optical BLR and may form part of a clumpy disk wind. The fluorescent Fe Ka luminosity measured by Suzaku is consistent with that expected from an equatorial disk wind.
1H 0419-577 is a broad-line Seyfert 1 galaxy located at a redshift z=0.104 (Grupe 1996;Thomas et al. 1998;Turner et al. 1999) with a strong ultraviolet flux (Marshall et al. 1995). The X-ray properties of this AGN have been the subject of much discussion, as the source shows a strong steepening to soft energies and marked spectral variability (Guainazzi et al. 1998;Turner et al. 1999;Page et al. 2002). The extreme nature of the spectral variability of this source is especially interesting since systematic flattening at low flux levels is a common property of Seyfert galaxies (e.g. Papadakis et al. 2002;Pounds et al. 2004a,b;Vaughan & Fabian 2004;Miller et al. 2007Miller et al. , 2008;;Turner et al. 2008). Understanding the origin of the observed phenomenon should lead to important insight as to the physical processes that dominate in such sources. The AGN low-state spectra have been suggested by some (e.g. Vaughan & Fabian 2004;Miniutti & Fabian 2004) to represent blurred reflection arising within 20r g and by others to represent a complex absorbed state (e.g. Inoue & Matsumoto 2003;Pounds et al. 2003;Miller et al. 2008). In the context of the former model, spectral variability has been attributed to changes in the degree of light bending as the continuum source location moves; for absorption-based models spectral variability is attributed to changes in the ionization, column or covering of absorbing gas (e.g. Netzer et al. 2002;Kraemer et al. 2005). As for many sources, detailed models for 1H 0419-577 have been suggested whereby the spectral form and variability can be explained either by a partial-covering absorber (Pounds et al. 2004a,b) or blurred reflection from the inner accretion disk (Fabian et al. 2005); data prior to Suzaku were unable to provide a definitive preference for either of the two scenarios.
Recent improvements in the quality of data available in the Fe K regime has led to the detection in AGN of relatively narrow absorption lines of high EW (> 50 eV, e.g. Pounds et al. 2003;Miller et al. 2007;Dadina et al. 2005;Braito et al. 2007;Turner et al. 2008), indicative of an origin in very large columns of ionized gas. Narrow absorption lines cannot arise from blurred reflection so their detection motivates a reconsideration of the importance of absorption in shaping the observed X-ray properties of AGN. This, and the extended bandpass afforded by the combination of XIS and PIN data motivated a Suzaku observation of 1H 0419-577 that is the subject of this paper.
Suzaku (Mitsuda et al. 2007) has four X-ray telescopes each focusing X-rays on to a CCD forming part of the X-ray Imaging Spectrometer (XIS Koyama et al. 2007) suite. XIS units 0,2,3 are front-illuminated (FI) and cover ∼ 0.6 -10.0 keV with energy resolution FWHM ∼ 150 eV at 6 keV. Use of XIS2 was discontinued after a charge leak was discovered in 2006 November. XIS 1 is a backilluminated CCD and has an enhanced soft-band response (down to 0.2 keV) but lower area at 6 keV than the FI CCDs as well as a larger background level at high energies. Suzaku also carries a nonimaging, collimated Hard X-ray Detector (HXD Takahashi et al. 2007) whose PIN detector provides useful AGN data typically over 15-70 keV.
The Suzaku observation was made 2007 July 25 (OBSID 702041010). We re-ran the pipeline processing of the raw data to utilize the most recent calibration with hxdpi and hxdgrade versions 2008-03-03. The data were then reduced using v6.4.1 of HEAsoft. We screened the events to exclude data during and within 500 seconds of entry/exit from the South Atlantic Anomaly (SAA). Additionally we excluded data with an Earth elevation angle less than 10 • and cut-off rigidity > 6 GeV. The source was observed at the nominal center position for the XIS. The FI CCDs were in 3 × 3 and 5 × 5 edit-modes, with normal clocking mode. For the CCDs utilized we selected good events with grades 0,2,3,4, and 6 and removed hot and flickering pixels using the SISCLEAN script. The spaced-row charge injection (SCI) was utilized. The exposure time was 179 ks for the FI CCDs.
The XIS products were extracted from circular regions of 2.9 ′ radius while background spectra were extracted from a region of the same size offset from the source (and avoiding the chip corners where calibration source data are registered). The response and ancillary response files were then created using xisrmfgen v2007 May and xissimarfgen v2008 Mar. The background was 1% of the total XIS count rate in the full XIS band for each CCD.
1H 0419-577 is too faint to be detected in the HXD GSO instrument, but was detectable in the PIN. For the analysis we used the model “D” background (released 2008 June 17 1 ). As the PIN background rate is strongly variable around the orbit, we first selected source data to discard events within 500 s of an SAA passage, we also rejected events with day/night elevation angles > 5 o . The time filter resulting from the screening was then applied to the background
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