Ultraviolet characteristics, outflow properties and variability of active galactic nucleus Markarian 1513

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1 Advance Access publication 2014 March 3 doi: /mnras/stu211 Ultraviolet characteristics, outflow properties and variability of active galactic nucleus Markarian 1513 Barton W. Tofany, 1 Lisa M. Winter, 1 Benoit Borguet, 2 Doug Edmonds, 2 Charles Danforth, 1 James Green 1 and Nahum Arav 2 1 Center for Astrophysics and Space Astronomy, University of Colorado, 593 UCB, Boulder, CO 80309, USA 2 Department of Physics, Virginia Polytechnic Institute and State University, Robeson Hall (0435), Blacksburg, VA 24061, USA Accepted 2014 January 29. Received 2014 January 22; in original form 2013 June 28 ABSTRACT We analysed data from the Cosmic Origins Spectrograph (COS) to characterize the spectral properties and outflows of the active galactic nucleus (AGN), Markarian Further investigation using previous data collected by the Space Telescope Imaging Spectrograph (STIS), Goddard High Resolution Spectrograph (GHRS), and International Ultraviolet Explorer (IUE) was used to examine variability in the outflows along with the AGN emission and continuum luminosity spanning 32 yr. The COS data contained two sets of intrinsic absorption systems. The first, which is associated with an outflow, was observed in Lyman α, NV, SiIV, and C IV, with an outflow velocity of 1521 ± 20 km s 1. This absorption system prevailed through the historical Hubble Space Telescope observations spanning 15 yr, and COS data revealed a previously unobserved Si IV outflow absorption feature. A second absorption system was observed at 17 ± 20 km s 1 in Lyman α, NV, and the blue component of C IV ( Å), indicating the presence of an intervening cloud, but not necessarily an outflow. Variability was also observed in the continuum levels of the AGN spectrum, which dropped by nearly a factor of 2 in both the power-law index and flux level between the GHRS and COS data. Key words: galaxies: active galaxies: Seyfert. 1 INTRODUCTION Active galactic nuclei (AGN) are powerful sources of emission across the entire electromagnetic spectrum. AGN are believed to be powered by supermassive black holes (SMBHs), with masses on the order of M, in the centre of massive galaxies that are actively accreting matter. The SMBHs are surrounded by a hot accretion disc that peaks in the ultraviolet (UV) and optical. Under the unified model proposed by Antonucci (1993), differences in AGN classification result from our viewing angle to the central engine. For instance, clouds of energetic gas orbiting close to the SMBH, with velocities on the order of km s 1, produce the broad emission lines viewed in type 1 Seyferts. This inner region surrounding the black hole is enveloped in a dusty torus that may, depending on the viewing angle, obscure the central broad line emitting region leaving only narrow emission features from more distant slow moving clouds not obscured by the torus, resulting in a type 2 Seyfert classification. In addition, many type 1 Seyferts exhibit variability in luminosity, with time-scales ranging from hours to barton.tofany@colorado.edu Atmospheric and Environmental Research, Superior, CO. years across all bands of the electromagnetic spectrum. Often the most dramatic and short-term variation is found in the X-ray and higher energy wavebands. One prevalent feature of many AGN that is not fully understood is AGN outflows. In the UV, over half of type 1 Seyferts exhibit intrinsic absorption lines which are blueshifted with respect to the corresponding AGN emission features, indicating outflowing gas (e.g. Crenshaw et al. 1999; Crenshaw, Kraemer & George 2003). When UV outflows are present, they are always observed in Lyman α (Lyα), C IV, NV, andovi, with smaller percentages of type 1 Seyferts exhibiting absorption due to Si IV (40 per cent) and Mg II (10 per cent; Crenshaw et al. 2003). A similar outflow detection rate is found in the soft X-rays (Reynolds et al. 1997), while recent results suggest that the covering fraction may be much higher (C f 1 as in Winter 2010; Winter et al. 2012). The source of these outflows is still unknown but there are many theories as to their origin such as Compton heating (Begelman, McKee & Shields 1983), outflows driven by radiation pressure (Liu et al. 2013, and references therein), or accretion winds driven by magnetic fields within the disc and broad-line regions (Rees 1987). Further study is required to determine both the mechanism that causes these winds and the affect the AGN outflows have on their host galaxy and the interstellar medium (ISM) through enrichment and kinematic excitation. C 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society

2 3650 B. W. Tofany et al. Table 1. UV observations of Mrk Instrument Data set PI Date Exp. time Spectral coverage COS LB4Q070 Green Å STIS O4EC10FKQ Stocke Å GHRS Z2KU0206 Heap Å IUE SWP01909 Boggess Å IUE SWP19799 Sargent Å IUE SWP23257 Malkan Å IUE SWP27211 Elvis Å Notes. Listed are details of each observation utilized in this study, including the HST COS guaranteed time observations and archived data from HST (STIS and GHRS) and IUE. We include the observation identification listed in MAST, the PI, date, exposure time (s), and spectral coverage in the AGN rest frame. The approximate spectral resolution (λ/ λ) is 200 for IUE and for the HST observations. Figure 1. UV spectra for COS, STIS, and GHRS. Primary emission features are labelled along with the geocoronal Lyα feature ( ). Additionally, multiple observations over various time-scales can help to constrain the spatial distribution of the outflowing material (Gabel et al. 2005b; Moe et al. 2009). The target for the outflow study presented in this work is Markarian 1513 (Mrk 1513, II Zw 136, UGC 11763, PG ). Mrk 1513 has been a target of interest for many UV studies due to its sightline through the high-velocity clouds (HVCs) which make up the Magellanic Stream extension (Collins, Shull & Giroux 2005). UV spectra of Mrk 1513 reveal the presence of several ionized species in the intergalactic medium (IGM), which has warranted multiple observations with successively better instruments. The bright AGN provides the continuum radiation that these studies rely upon for absorption line studies of HVC components from our own Galaxy. However, there is no extensive previous investigation of the intrinsic UV properties of Mrk 1513 despite the fact that archived observations exist from both the Hubble Space Telescope s (HST) Goddard High Resolution Spectrograph (GHRS; Crenshaw et al. 1999) and Space Telescope Imaging Spectrograph (STIS; Penton, Stocke & Shull 2004) instruments. The recent observation by the HST Cosmic Origins Spectrograph (COS) provides an unprecedented opportunity to study the new high-resolution spectra as well as the archived UV data, which when including the International Ultraviolet Explorer (IUE) spectra, allows us to search for variability in the emission and absorption properties over a 30 yr baseline. In this paper, we present the first in-depth UV study of Mrk 1513 to both characterize the AGN continuum and emission line properties and investigate AGN outflows. In addition to the new COS spectrum, we present an analysis of the archived data from IUE, GHRS, and STIS. Details of the observations are included in Section 2. The UV spectral analysis, including the continuum, emission, and outflow absorption fits are included in Section 3. We compared our results with those reported by other wavelength observations of Mrk 1513 by Far Ultraviolet Spectroscopic Explorer (FUSE)

3 Ultraviolet characteristics of AGN Mrk Figure 2. UV spectra for all four IUE exposures. Prominent emission features from Lyα and C IV are labelled along with the geocoronal Lyα feature ( ). and XMM Newton in Section 4. The wealth of historical data on Mrk 1513 allows us to characterize variability in the UV spectra, which we discuss in Section 5. Finally, we present our conclusions in Section 6. 2 OBSERVATIONS Mrk 1513 was observed during the COS guaranteed time observer s (GTO) program (PI: Green), and was originally targeted for a study of HVCs surrounding the Milky Way. However, the data also lend itself to an analysis of the emitting AGN as well. Data were acquired during a single set of exposures (2010 October 28) with both the G130M ( Å) and G160M ( Å) mediumresolution gratings (R λ/ λ ) and an aperture size of 2.5 arcsec. Total exposure times were and s for the G160 and G130 gratings, respectively. Four observations were taken with each grating to produce continuous spectral coverage from 1066 to 1690 Å with minimal instrumentation effects (Osterman et al. 2011). The four exposures in each grating were reduced using CALCOS v2.11f. Flat-fielding, alignment, and co-addition were carried out using IDL routines developed by the COS GTO team specifically for COS far-ultraviolet (FUV) data 1 and described in detail in Danforth et al. (2010). Briefly, each exposure was corrected for narrow, 15 per cent opaque shadows from ion repeller grid wires. The local exposure time in these regions was reduced to give them less weight in the final co-addition. Similarly, exposure times for data at the edges of the detectors were decreased to de-weight these data in the final co-addition. With four different central wavelength settings per grating, any residual instrumental artefacts from grid-wire shadows and detector boundaries should have negligible effect on the final spectrum. Next, strong interstellar features in each exposure were aligned via cross-correlation and interpolated on to a common wavelength scale. The wavelength shifts were typically on the order of a resolution element ( 0.07 Å, 17 km s 1 ) or less. The co-added flux at each wavelength was taken to be the exposure-weighted mean of flux in each exposure. Additional observations were included in this study to investigate the long-term variability of Mrk 1513 and its associated outflows. Four IUE exposures were taken between 1978 July 3 and 1985 December 2, which provide low-resolution spectra and the processed data were downloaded from Multimission Archive at Space 1 IDL routines available at danforth/costools.html

4 3652 B. W. Tofany et al. Figure 3. UV spectra for COS (blue), STIS (red), and GHRS (green). Galactic (black), AGN outflow (magenta), and IGM (cyan) absorption lines are labelled. The IGM line was found at z = and is present in all observations. Table 2. Continuum power-law fit parameters. Observation a 0 α χ 2 COS 4.30 ± ± GHRS 7.72 ± ± IUE ± ± IUE ± ± IUE ± ± IUE ± ± Notes. Continuum fits from a simple power law of the form a 0 (λ/1100 Å) α,wherea 0 is the continuum flux density at 1100 Å (in units of erg s 1 cm 2 Å 1 ) and α is the power-law index. χ 2 is the reduced χ 2 value from our spectral fits. Telescope Science Institute (MAST). 2 IUE data was collected with a 20-arcsec aperture which allowed significant contamination from the galaxy. Data from STIS and GHRS were also acquired from MAST. The GHRS data cover a range ( Å) comparable to that of COS but with reduced spectral resolution. The GHRS observations consisted of four separate subexposures on the G140L grating with a 2-arcsec aperture that were combined into a single composite spectrum. The STIS data utilized the G140M grating and only cover 110 Å around Lyα but provide comparable resolution to the COS data, though it required a significantly longer exposure time. The STIS data were processed as described in Penton et al. (2004). All of the observation times, exposures, PIs, and other relevant information on the observations used in this investigation are found in Table 1 and a comparison of the UV spectra with major 2 emission lines labelled is illustrated in both Fig. 1 (COS, STIS, GHRS) and Fig. 2 (IUE). 3 UV SPECTRAL ANALYSIS This section deals primarily with the spectral analysis for Mrk 1513 for all available UV spectra. Identification of the various absorption and emission sources is found in Section 3.1. Best-fitting parameters from spectral fits to both the AGN continuum radiation as well as primary emission features are included in Section 3.2. Outflow properties for the COS, GHRS, and STIS data are discussed in Section UV spectrum feature identification We corrected all spectra for Galactic reddening using the intervening hydrogen column density of N H I = cm 2, based on Dickey & Lockman (1990) 3 which results in an E(B V) = from the relationship derived by Predehl & Schmitt (1995). Using the calculated E(B V), along with the extinction function of Cardelli, Clayton & Mathis (1989), the data were reddening corrected. Next we shifted the spectrum into the rest frame of the AGN (z = ). 4 This shift allowed for easier identification of primary AGN emission and absorption features. With the reddening corrected and AGN frame shifted spectra, the first priority was emission and absorption line identification to determine if any outflows were present. In both the COS and 3 N H I value determined through the NASA s High Energy Astrophysics Science Archive Research Center (HEASARC) data base at 4 Redshift found through NASA/IPAC Extragalactic Database (NED) at

5 Ultraviolet characteristics of AGN Mrk Table 3. COS emission line properties. Component FWHM (km s 1 ) Offset (kms 1 ) Integrated flux (10 13 erg s 1 cm 2 Å 1 ) Strong emission lines Lyα λ= Å χ 2 /dof = /8048 (303.9) ± ± ± ± 0.1 N V λ = , Å χ 2 /dof = /8048 (303.9) ± ± ± ± 0.1 Si IV + O IV] λ = , , Å χ 2 /dof = /11029 (6.1) ± ± ± ± 0.1 O IV] ± ± 0.1 C IV λ = , Å χ 2 /dof = /9784 (5.3) ± ± ± ± ± ± 0.1 Weak emission lines Si II λ = Å χ 2 /dof = /5331 (4.8) ± ± ± 0.1 C II λ = Å χ 2 /dof = /5330 (3.9) ± ± ± 0.1 He II λ = Å χ 2 /dof = /9784 (5.3) ± ± ± 0.1 Notes. Best-fitting parameters for Gaussian fits to the prominent COS emission lines. The primary emission features (Lyα, C IV, Si IV+O IV, andnv) were fit with a combination of a narrow and broad Gaussian. The FWHM of the Lyα, SiIV+O IV, andnv lines are fixed to those from C IV. The weak emission lines (Si II,CII,andHeII) were fit with a single Gaussian. Full details of the fitting procedure are included in Section σ errors are listed. GHRS data broad-line emission features were detected in Lyα,N V, Si IV+O IV], and CIV, along with less significant features due to C II, He II, and Si II. Several absorption components were present due to gas originating in our own Galaxy, IGM, and AGN intrinsic absorption (outflow) components. Only one prominent IGM feature was found at z = in Lyα. Because of the large number of absorption lines present in this region we utilized the line finding procedure provided by Dr Charles Danforth. This IGM feature is clearly present in the COS, STIS and GHRS observations along with several galactic absorption signatures illustrated in Fig. 3. AGN outflow features were observed to be caused by the same ions as the strongest of the broad-line emission features: Lyα, NV, Si IV,and C IV. All of these lines exhibited an average blueshift from the AGN rest frame of 1521 ± 20 km s 1 in the COS spectrum (which we quantify in Section 3.3). This outflow system was also detected in both the STIS and GHRS spectra, however, due to the reduced resolution of the GHRS data outflow absorption due to Si IV was not detected. The IUE data do not exhibit any outflows due to the low spectral resolution of the data. An additional set of intrinsic absorption lines was also detected in Lyα, NV, and the blue component of C IV ( Å) for the COS, GHRS, and STIS (Lyα and N V only) data with a velocity of 17 ± 20 km s 1.The latter set of lines is possibly associated with a low-velocity outflow or a cloud of intervening gas near the AGN. Previous analysis of the GHRS outflows can be found in Crenshaw et al. (1999), where both absorption systems were detected for Lyα,NV,andCIV. 3.2 Continuum and emission line fits The AGN continuum spectra were modelled using a power law of the form F λ (λ) = a 0 (λ/1100 Å) α. In the power-law model, α is the power-law index and a 0 provides the continuum flux density in units of erg s 1 cm 2 Å 1 at 1100 Å (following the analysis of Mrk 817 in Winter et al. 2011). The choice of 1100 Å was based on the lack of prominent emission and absorption features near that region. The same analysis was performed with a 0 at 1350 Å which produced the same accuracy of fit and the same power-law index. The power law was fitted using 10 separate wavebands for the GHRS and COS data and four wavebands in the IUE data, all of various sizes between 5 and 150 Å that were free from absorption or emission features. The fitting procedure utilized the PyMINUIT 5 interface for the MINUIT Function Minimization and Error Analysis code (CERN). The best-fitting parameters along with goodness of fit, indicated by χ 2 /dof of this continuum modelling are included in Table 2. We were unable to find a continuum function for the 5 Code found at

6 3654 B. W. Tofany et al. Figure 4. Emission line fits for the COS data. The plots above correspond to C IV, Lyα/N V, Si IV, CII, Si II, and He II. The black line represents the data after performing a 21 pixels boxcar smoothing function. The individual Gaussians are represented by the dashed blue lines, with the combined Gaussian fit illustrated by the dashed red line. Details of the fits are included in Section 3.2. STIS data because it was limited to such a small range of wavelengths ( 110 Å). The STIS data also only include the wavelengths between the AGN and geocoronal Lyα features where we expect significant underlying absorption from the IGM to distort the continuum emission that is present. Emission models were based off a series of Gaussian curves for Lyα, NV, SiIV + O IV], and C IV. The MINUIT code was used to fit the full width at half-maximum (FWHM), total amplitude, and position of the Gaussian centroids. Several of the lines were also doublets (N V, Si IV, and CIV). These Li-like doublets exhibit two

7 Ultraviolet characteristics of AGN Mrk Table 4. GHRS emission line properties. Component FWHM (km s 1 ) Offset (kms 1 ) Integrated flux (10 13 erg s 1 cm 2 Å 1 ) Strong emission lines Lyα λ= Å χ 2 /dof = /560 (167.3) ± ± ± ± 0.1 N V λ = , Å χ 2 /dof = /560 (167.3) ± ± ± ± 0.1 Si IV + O IV] λ = , , Å χ 2 /dof = /853 (5.2) ± ± ± ± 0.1 O IV] ± ± 0.1 C IV λ = , Å χ 2 /dof = /836 (5.1) ± ± ± ± ± ± 0.1 Weak emission lines Si II λ = Å χ 2 /dof = /5331 (4.8) ± ± ± 0.1 C II λ = Å χ 2 /dof = /5330 (3.9) ± ± ± 0.1 Notes. Best-fitting parameters for Gaussian fits to the prominent GHRS emission lines. 1σ errors are listed. Description as in Table 3 with full details in Section 3.2. lines associated with the different spin orbit coupling states of the 2p 2s transition. 6 This transition exhibits a line ratio of 2:1 between the blue and red doublet component, which had to be accounted for when fitting the emission features. The first ion fitted was the C IV doublet ( and Å) due to its high flux and lack of blending with other species. The model was composed of a narrowline doublet and a broad-line doublet (4 Gaussians total) with the doublet separation and amplitude ratio set to the laboratory values (2.3 Å and 2:1, respectively). The FWHM found in the C IV fit was used for the Si IV ( and Å ) fit leaving only the amplitude and the centroid displacement parameters free. The intrinsic forbiddend emission from O IV] also contributed weak emission lines which are blended with the Si IV doublet. This O IV] emission was modelled using a single Gaussian at Å (similar to Shull, Stevans & Danforth 2012) with a FWHM equal to that found in the narrow component of C IV. As with the C IV fit, the doublet separation and amplitude ration were set to the laboratory values of Å and 2:1. Since the Lyα and N V doublet lines are blended, they were fit simultaneously. N V ( and Å) was fit in the same manner as the C IV doublet. Two sets of Gaussian doublets (broad and narrow) were used and the doublet separation was set to the laboratory value of 3.98 Å. The amplitudes of the N V doublet components were set so the blue line was twice the magnitude of the red line. The FWHM of the N V Gaussians was set to the best-fitting values for 6 Atomic transitions found at C IV.TheLyα emission ( Å) was modelled with a broad-line Gaussian and a narrow-line Gaussian, with the FWHMs set to those value determined in the C IV fit. The weaker emission features: C II, He II, and Si II were fit with single Gaussians (singlet lines), with the same free parameters of FWHM, amplitude, and centroid displacement. Best-fitting parameters for all COS emission lines are shown in Table 3 with the spectral model fits in Fig. 4. The GHRS emission features were fit in the same manner as the COS lines. The best-fitting parameters are listed in Table 4 and plots of the model fits are found in Fig. 5. The STIS data only covered part of the Lyα emission line, thus we set the FWHM values to those found for COS. Best-fitting values for the amplitude and velocity offset can be found in Table 5 and Fig. 6 illustrates the best fit and data. For the IUE spectra the FWHM values were fixed to values from the COS C IV fit. Only the amplitude and velocity offsets of the Gaussian centroid parameters were free. This process was necessary due to the low spectral resolution of the IUE data. The fit values obtained for both Lyα and C IV are presented in Table 6 for all four IUE exposures. All emission fit tables list 1σ errors. The best-fitting models to the IUE spectra are also shown in Figs 7 and Intrinsic absorption properties Intrinsic absorption that is blueshifted with respect to the AGN is indicative of strong outflows of ionized gas (e.g. Crenshaw et al. 1999, 2003). The COS, GHRS, and STIS data for Mrk 1513 revealed two significant absorption systems. An outflow feature is

8 3656 B. W. Tofany et al. Figure 5. Emission line fits for the GHRS data. These plots show the best-fitting models for the GHRS emission lines: C IV, Lyα/N V,SiIV, CII, andsiii. apparent in Lyα, NV, SIV, andciv with an average outflow velocity of 1521 ± 20 km s 1 in the COS data, 1547 ± 26 km s 1 in GHRS, and 1510 ± 20 km s 1 in the STIS data. (Henceforth this outflow system will be referred to as the 1521 km s 1 outflow for all data sets.) The second absorption system at 17 ± 20 km s 1 was only conclusively found in Lyα and N V. Each of the primary absorption systems for COS and GHRS are plotted in Figs 9 and 10, respectively with both absorption systems indicated. We simultaneously fit the absorption features from multiple species (Lyα, N V, C IV,andSiIV) to determine the column densities of the outflowing

9 Ultraviolet characteristics of AGN Mrk Table 5. STIS emission line properties. Component FWHM (km s 1 ) Offset (kms 1 ) Integrated flux (10 13 erg s 1 cm 2 Å 1 ) Lyα λ= Å χ 2 /dof = /739 (1235.8) ± ± ± ± 0.1 Notes. Best-fitting parameters for Gaussian fits to the Lyα emission in the STIS observation. The FWHM was fixed to the best-fitting value from the COS observations. 1σ errors are listed. Full details are included in Section 3.2. Figure 6. The only emission feature found in the limited range of the STIS data was Lyα. We used the FWHM value from the COS C IV line to help fit the truncated emission profile. gas using two different methods in Section Determination of the ionization state of the gas for the COS data is described in Section Column density calculations The first concern for determination of the properties (e.g. column density) of the absorption features is an accurate modelling of the emission features and continuum; so that they can be properly divided out of the spectrum, leaving only the absorption lines. In the optical/uv, AGN have three distinct emission sources: continuum emission, the broad line emitting region (BLER), and the narrow line emitting region (NLER). The continuum emission arises from thermal emission in the accretion disc. The BLER consists of clouds of gas orbiting close to the black hole resulting in dramatic Doppler broadening of the lines on the order of km s 1, while the NLER is located further from the SMBH resulting in lower velocities. A discussion of our continuum and emission line fits is found in Section 3.2. After dividing out the continuum and emission features only the absorption features remain. Our analysis of the intrinsic absorption features used two different covering models to represent the outflowing gas. The simplest model was that of an apparent optical depth (AOD), which assumes that a slab of intervening gas has a uniform optical depth and completely covers the background emission source. This method has long been used to fit interstellar absorption lines, with a good overview of the procedure found in Savage & Sembach (1991). We show an illustration of the geometry of this uniform covering model in Fig. 11. For the AOD modelling, we first solved for the observed intensity, I obs (v), as a function of radial velocity v with optical depth τ(v), and the unabsorbed intensity I 0 (v), such that I obs (v) = I 0 (v)e τ(v). (1) For doublet lines such as C IV and N V, we use the red component to solve for τ because the red component will saturate after the stronger blue component. An accurate uniform covering model would produce absorption lines that follow the doublet line ratio for Li-like ions of 2:1. However, our data clearly violate this ratio. In addition we observed that the Lyα trough, as well as the blue components of N V and C IV, share a similar depth and exhibit flat bottoms, indicating that these absorption profiles are saturated as seen in Fig. 12. However these absorption features are not black saturated, which along with the deviation from the expected 2:1 ratio indicate that the outflowing gas only partially covers the background emission source (Barlow & Sargent 1997; Aravetal.2005). By partial covering, we imply that the gas distribution per velocity bin over the background emitting source follows a piecewise function as shown in Fig. 11. This model is similar to the uniform covering model in that it assumes a slab of gas with uniform optical depth, but introduces a new parameter, C(v), which represents the fraction of the emission source that is covered by the slab of gas. By introducing the covering parameter we have to use absorption equations for both the red and blue troughs to fully constrain the solution. We assume that the optical depth of the blue component is twice that of the red component for these Li-like doublets (2τ red = τ blue ) as in Gabel et al. (2005a) and Arav et al. (2005). The resulting set of equations is I obs,b (v) = I 0,B (v)[(1 C(v)) + C(v)e 2τ(v) ], (2) I obs,r (v) = I 0,R (v)[(1 C(v)) + C(v)e τ(v) ]. (3) This system of equations allows us to solve for the covering fraction, C(v), and optical depth of the red trough, τ(v) (Barlow& Sargent 1997; Aravetal.2005; Gabel et al. 2005a): C(v) = 1 + ( Iobs,R I 0,R τ(v) = ln ) 2 2 ( Iobs,R 1 + ( Iobs,B I 0,B ) 2 I 0,R ) ( ) ( Iobs,R Iobs,B I 0,R ( ) Iobs,R 1 I 0,R ( Iobs,R I 0,R ), (4) I 0,B ). (5) The obvious flaw in this technique is that the parameters are underconstrained for single lines such as Lyα. The partial covering model can still be used on singlet lines, however, we have to assume

10 3658 B. W. Tofany et al. Table 6. IUE emission line properties. Component FWHM (km s 1 ) Offset (kms 1 ) Integrated flux (10 13 erg s 1 cm 2 Å 1 ) SWP Lyα λ= Å χ 2 /dof = /48 (109.78) ± ± ± ± ± ± 0.1 N V λ = , Å χ 2 /dof = /48 (109.78) ± ± ± ± ± ± 0.1 C IV λ = , Å χ 2 /dof = /71 (6.16) ± ± ± ± ± ± 0.2 SWP Lyα λ= Å χ 2 /dof = /48 (16.96) ± ± ± ± ± ± 0.1 N V λ = , Å χ 2 /dof = /48 (16.96) ± ± ± ± ± ± 0.1 C IV λ = , Å χ 2 /dof = /71 (3.00) ± ± ± ± ± ± 0.2 Lyα λ= Å χ 2 /dof = /48 (44.26) ± ± ± ± ± ± 0.1 N V λ = , Å χ 2 /dof = /48 (44.26) ± ± ± ± ± ± 0.1 C IV λ = , Å χ 2 /dof = /71 (4.68) ± ± ± ± ± ± 0.2 Lyα λ= Å χ 2 /dof = /48 (44.39) ± ± ± ± ± ± 0.1 N V λ = , Å χ 2 /dof = /48 (44.39) ± ± ± ± ± ± 0.1 C IV λ = , Å χ 2 /dof = /836 (5.1) ± ± ± ± ± ± 0.3 Notes. Best-fitting parameters for Gaussian fits to the prominent IUE emission lines. 1σ errors are listed. Description with full details in Section 3.2. that the covering fraction is the same for both a reference doublet, C IV in our case, and the singlet. This allows us to solve for the optical depth in the singlet line, however, this is a poor assumption since the covering fraction often differs between ionic species as shown in Barlow & Sargent (1997). A plot showing the covering fraction for each velocity bin as well as a comparison of the optical depth between the AOD and partial covering models for the COS C IV outflow feature can be found in Fig As seen in this figure several of the velocity bins on the wings exhibited flux in the blue component that exceeded the flux in the red component. The 7 Fig. 13 along with calculations of column density based on COL10.PRO IDL package provided by Benoit Borguet.

11 Ultraviolet characteristics of AGN Mrk Figure 7. Emission line fits for the first two IUE exposures. These plots show the best-fitting models for the IUE emission lines: C IV and Lyα. maximum blue to red flux ratio is 1:1, and any bins that violate this limit represent errors in the data that cannot properly model the physical situation. These unrealistic bins resulted in very large optical depths that persisted despite changing both emission models and velocity bin distribution. The partial covering absorption equations will always produce a solution for τ, however, non-linear propagation of measurement errors often causes the τ solution to increase drastically with little change in the observed flux (Gabel et al. 2005a). This resulted in very large upper limits on the column densities often an order of magnitude in excess of the calculated column density values. As a result, only the AOD results are presented with the caveat that these are only lower limits for the ionic column densities. Once the AOD (τ) was determined, we proceeded to determine the column density using the relationship from Edmonds et al. (2011), adapted from Savage & Sembach (1991): N ion (v) = f j λ j τ j (v) (cm 2 km 1 s), (6) where λ j and f j are the wavelength and oscillator strength for line j, respectively. The average optical depth τ j (v) is different for each absorption model. For the AOD/uniform covering model τ j (v) =τ j (v). The computed column densities for the AOD model are found in Table 7 for the COS observations, in Table 8 for the GHRS observations, and in Table 9 for the STIS data Photoionization calculations We also consider that in a highly energetic gas a large fraction of the hydrogen will be ionized. Ionized hydrogen causes no absorption so with the above column density determination we are missing a significant portion of the gas. However if we use the column densities of the other ions we can estimate how energetic the gas is, determine the ionization parameter, and deduce what the total hydrogen density is. We estimate the ionization parameter U = Q H /4πcR 2 n H and total hydrogen column density (N H )ofthe 1521 km s 1 trough using the spectral synthesis code CLOUDY (most recently Ferland et al. 2013). The spectral energy distribution (SED) is given by the photometric data collected in the NED. At the COS epoch, this SED gives a bolometric luminosity of erg s 1.Using the column densities determined from the COS data set, we find log U = and log N H = cm 2. The errors in the two parameters are correlated. Unfortunately only the AOD model produced significant results so these parameters are only lower limits.

12 3660 B. W. Tofany et al. 4 PREVIOUS OBSERVATIONS IN THE FAR-UV (FUSE) AND X-RAY (XMM NEWTON) All type 1 Seyfert galaxies that exhibit UV outflows have absorption due to Lyα ( Å), C IV ( and Å), N V ( and Å), and O VI ( and Å; Crenshaw et al. 1999, 2003). We detected the Lyα, CIV, andnv outflow features but the COS spectra did not cover the wavelength range necessary to detect O VI. However, previous observations by the FUV spectrograph have observed and detected outflows in both O VI and Lyβ (Dunn et al. 2008). Crenshaw et al. (1999) also found that outflows were detected in all AGN that exhibited absorption in the X-ray. Observation by XMM Newton reveal the presence of warm absorbers in Mrk 1513 (Cardaci et al. 2009). 4.1 AGN outflows in the FUV There are several observations of Mrk 1513 in the FUV using FUSE. Observations were taken between 2000 November and 2004 November with results presented in Dunn et al. (2007, 2008). Outflow features with velocities corresponding to the two systems discussed in this paper ( 1521 and 17 km s 1 ) were detected in O VI although the second component is heavily obscured by Fe II and H 2 Figure 8. Emission line fits for the second two IUE exposures. ISM features for the blue line. The occurrence of O VI was anticipated since O VI outflow absorption is commonly found when C IV and N V outflows are detected (Crenshaw et al. 2003) due to the similar ionization potentials of these species. Any future studies would benefit from concurrent observations of the O VI, CIV, NV, and both Lyα and β. The absorption present in O VI could provide a third column density parameter (along with C IV and N V) which would help constrain the ionization parameter models. Additionally, the Lyβ absorption feature could constrain a partial covering solution for hydrogen. 4.2 X-ray spectra from XMM Newton Mrk 1513 has also been observed at X-ray wavelengths, most recently by Cardaci et al. (2009)usingXMM Newton EPIC and RGS spectra in 2003 May. The EPIC spectra was fit with a power law (Ɣ = 1.63 ± 0.02), a blackbody to model the soft excess (kt = ± 0.002), and Gaussian emission line representing Fe-Kα. In the high-resolution RGS spectra indicated the presence of two warm absorbers. The first absorption feature is associated with the Fe unresolved transition array (UTA) around 15 Å, which is due to a blend of n = 2ton = 3 transitions for several Fe ionization species between Fe I and Fe XVI (Behar, Sako & Kahn 2001).

13 Ultraviolet characteristics of AGN Mrk Figure 9. The COS data plotted in velocity space, showing the four ions where intrinsic absorption lines were detected. For doublet lines (C IV,Si IV, and N V) the red and blue components are plotted separately. Uniform absorption at the same velocity for several ions is indicative of outflows. Both the 1521 and 17 km s 1 features are indicated by the dashed lines. Figure 10. GHRS data plotted in velocity space, with doublet components plotted separately to reveal the presence of outflows at 1547 and 21 km s 1.

14 3662 B. W. Tofany et al. of over 2000 km s 1 (almost 7σ ) points to a different origin for the Cardaci et al. (2009) inflow system and the outflows examined in this study. Figure 11. The gas distribution assumed by the two outflow models. The top AOD model assumes that the outflowing gas completely and uniformly covers the background emission source (i.e. uniform covering). The partial covering model involves a uniform slab of gas which only partially covers the emission source, with the fraction covered given by the parameter C(v). Figure 12. The absorption profiles for Lyα, CIV, andnv. Both blue components of CIV and NV along with Lyα exhibit flat bottoms and similar minimum flux values, suggesting these troughs are saturated. A second feature likely due to a similar iron line complex near 11 Å was also detected and both features appear to be blueshifted by 500 ± 300 km s 1 (Cardaci et al. 2009). Combined studies of X-ray and UV absorbers found that when outflows are present in the UV/Xray they are also detected in the X-ray/UV (Crenshaw et al. 1999). The X-ray observations of Mrk 1513 are also consistent with this finding. Based on the photoionization estimation we placed a lower constraint on the hydrogen column density of Significant iron UTA features are associated with hydrogen columns which are at least an order of magnitude larger than our estimation. This discrepancy in hydrogen column densities and a difference in measured velocities 5 VARIABILITY Variability is one of the primary characteristics of AGN over a variety of time-scales and wavelengths. With our 30 yr baseline of UV observations from IUE and HST, we searched for variability in the continuum and emission lines of Mrk Additionally, the high-resolution spectroscopy from GHRS and COS provides a 15 yr baseline for comparison of the absorption line/outflow properties. In this section, we discuss details of the UV variability observed in Mrk In Fig. 14, we show both the change in luminosity and continuum level between the IUE, GHRS, and COS observations. Since the STIS spectrum covered a small wavelength range, it is not included in our comparison. From the IUE observations, taken from 1978 to 1984, we find that the continuum and the power-law index (Table 2) are variable. The continuum varies by a factor of 2 while the slope varies from 1.55 to Changes in the steepness of the slope do not correlate with luminosity during this time period. However, if we consider both the continuum luminosity and steep slopes ( α = 1.70) from the IUE and GHRS spectra compared to the lower luminosity and flat slope (α = 1.01) measured in the COS spectrum, we find that steeper slopes are correlated with higher luminosities. This is consistent with results from X-ray analysis, which find steeper slopes correlate with higher luminosities when examining multiple observations from the same low-redshift AGN (e.g. Winter et al. 2008). It should be noted that the IUE observations present high flux levels in part due to the larger aperture used for those observations. However the greatest variability is observed between GHRS and COS epochs which had similar apertures. We find that there is less variability measured in the line luminosities of the IUE observations. The lack of variation could be a result of the IUE observation s larger aperture. The 20 arcsec field of view encompassed the entire host galaxy which will not exhibit the same variation that is expected of the central AGN region. While the N V appears to vary considerably, this is likely due to difficulties measuring this doublet, which is blended with the prominent Lyα emission, in the low-resolution spectra. Over the 32 yr time span, however, the line luminosities also vary by factors of 2. In particular, we find that the Lyα luminosity decreases while the luminosity of the more ionized lines (C IV, NV, andsiiv) increases. This suggests that the Lyα changes are correlated with the continuum, while the ionized lines are inversely correlated. Our analysis showed no variation in the velocity of either outflow system. Both the 1521 and 17 km s 1 outflow systems exhibited velocities that were consistent to within 1σ between all observations. Also there was no conclusive detection of column density variability since the AOD model only provides lower limits for column density. The most significant find was the appearance of the Si IV outflow in the COS data. Previous analysis of the GHRS data only revealed absorption in Lyα, CIV, andnv (Crenshaw et al. 1999). The COS observations revealed a Si IV component of the 1521 km s 1 outflow. As seen in Fig. 15 Si IV exhibits intrinsic absorption at the same velocity as the other ionic species for both the red and blue doublet components while absorption is evident in the GHRS data. As previously stated, Si IV outflows are only found in about 40 per cent of type 1 Seyfert galaxies and here is an example of an AGN outflow that has a transient Si IV feature. Since the other ionic species are not affected it is unlikely that the

15 Ultraviolet characteristics of AGN Mrk Figure 13. Shown are the absorption profile, calculated N ion (v), optical depth and covering fraction for C IV from the COS data. The top frame compares to normalized flux from both red and blue doublet components. Included as well (dashed cyan line) is the flux predicted for the blue component by the AOD model of the red component assuming the 2:1 ratio for Li-like doublet amplitudes is fulfilled. The second and third frames compare the number density and optical depth for both the partial covering and AOD models. Note that any unphysical bins (those where the flux in the blue component is greater than the flux in the red component) are dropped from the N ion (v) calculation. The bottom frame illustrates the covering fractions calculated for the partial covering model. Table 7. COS absorption line properties. Ionic species Velocity (km s 1 ) Apparent optical depth Lyα N V C IV Si IV Notes. Best-fitting column densities (units of cm 2 ) for simultaneous fits to the intrinsic absorption features in the COS data using the AOD. Note that the AOD values are only a lower limit since the AOD model fails to account for non-black saturation and deviations from the expected line ratios. Description with full details in Section 3.3. Table 8. GHRS absorption line properties. Ionic species Velocity (km s 1 ) Apparent optical depth Lyα N V C IV Notes. Best-fitting column densities (units of cm 2 ) for simultaneous fits to the intrinsic absorption features in the GHRS data. Description with full details in Section 3.3. Table 9. STIS absorption line properties. Ionic species Velocity (km s 1 ) Apparent optical depth Lyα Notes. Best-fitting column densities (units of cm 2 ) for simultaneous fits to the intrinsic absorption features in the STIS data. Description with full details in Section 3.3. appearance of the Si IV absorption is due to changes in the outflow materials position. One possible explanation for the appearance of the Si IV outflow feature results from the current low energy state of Mrk 1513 evident in the continuum variability previously discussed. The ionization potential for Si IV is 34.8 ev which is 13.1 ev lower than the potential for C IV. The lower energy output from the central AGN may have reduced the energy within the outflow such that the Si IV transition became more prevalent (Crenshaw et al. 2003; Winter et al. 2011). 6 CONCLUSIONS We present the UV spectra for Mrk 1513 including an analysis of the AGN continuum, emission, and outflow features. Data from IUE, STIS, GHRS, and COS were analysed to characterize variability in the emission and absorption. We modelled both the continuum and broad emission features from the AGN and analysed variability present over the 30 yr baseline covered by UV observations. We detected an AGN outflow feature at 1521 ± 20 km s 1 in Lyα, N V, SiIV, andciv, and a secondary cloud of intervening gas in Lyα and N V with a velocity of 17 ± 20 km s 1 in the COS data. The column densities and ionization parameter were determined

16 3664 B. W. Tofany et al. pronounced emission signatures from C II, He II, and O I. The prominent lines were modelled using Gaussians with separate components for both the blue and red components of each doublet and separate sets of Gaussians to represent both the broad and narrow emission features. The weaker lines (C II, He II, and O I) were modelled with a single Gaussian for the GHRS and COS spectra since the IUE observations lacked the spectral resolution to detect these weak features. Figure 14. Both the line luminosity in prominent emission and the continuum flux density (at 1100 Å) are shown as a function of the observation date. We find that the strong emission lines of Lyα and C IV do not vary much between the IUE spectra, while the continuum level varies considerably. Both the Lyα luminosity and continuum decrease from the GHRS to COS observations, 15 yr later, while the luminosity of the ionized lines increases. Dashed lines represent the average level in each of the indicated lines or the continuum. Errors in both of these graphs are smaller that the symbols used. Flux levels for the IUE observation combine AGN and host galaxy emission and thus measure an increased flux level. for these outflow systems and their evolution tracked between the GHRS, STIS, and COS data. 6.1 AGN continuum and emission features We modelled the AGN continuum using the standard power law: F λ (λ) = a 0 (λ/1100 Å) α, with a 0 measured at 1100 Å. We found the average power-law index for the IUE and GHRS observations to be α = 1.70 ± 0.06 but the COS data differed greatly with α = 1.01 ± The variations between these observations were discussed in Section 5. The power-law index measured in the COS data is consistent with the value found by Zheng et al. (1997) of α = 0.99 ± 0.05 for local AGN. However, the older data are consistent with a power-law index closer to the average value of α = 1.76 ± 0.12 found in higher redshift (z >0.33) quasi-stellar objects (QSOs) by Telfer et al. (2002). The UV spectrum of Mrk 1513 contains significant broad emission features from Lyα, NV, SiIV+O IV, andciv, along with less 6.2 AGN outflows Two intrinsic absorption systems were detected in the COS spectra of Mrk The first system was present in Lyα and N V at a velocity of 17 ± 20 km s 1. This system was also present in both the GHRS and STIS observations. The second system was an outflow detected in Lyα, NV,CIV, andsiiv. The outflow exhibited a velocity of 1521 ± 20 km s 1 in the COS data and 1547 ± 26 km s 1 for the GHRS. The Lyα outflow feature was also observed in the STIS data at a velocity of 1510 ± 20 km s 1. The column densities were then determined for the COS and GHRS features using a uniform covering model. Utilizing the spectral synthesis code CLOUDY we determined the ionization parameter (log U = ) and total hydrogen column density(log N H = cm 2 )ofthe 1521 km s 1 COS outflow based on our column density determinations. Both the ionization parameters and column densities are lower limits due to the restrictions of the uniform covering model. All of the outflows examined in Crenshaw et al. (1999) had column densities between and cm 2 just as we found for the outflow systems of Mrk It should be noted that especially with higher column densities (10 15 cm 2 ) the AOD model only provides a lower limit. In the same study only three out of 13 AGN exhibited outflows at a higher velocity than Mrk Variability Both the continuum and the emission lines of Mrk 1513 exhibited variability. The continuum emission had a mostly constant flux level and power-law index from the IUE data through the GHRS data (a 0 = 7.4 ± 1.02, α = 1.7 ± 0.1), followed by a profound decrease in both the overall luminosity and the power-law index for COS (a 0 = 4.3 ± 10.1, α = 1.01 ± 0.1), indicating a quiescent state compared to earlier observations. The emission lines showed slight changes in the offset velocities and FWHM between the COS and GHRS data along with variability in the amplitudes. The velocity of the outflow systems remained constant, however, the COS observation revealed a previously undetected outflow in Si IV. Unfortunately due to the calculated column densities providing only lower limit we were unable to accurately compare column density variations between the GHRS and COS observations to determine if the appearance of Si IV absorption is due to changes in outflow density or energy. Most outflows do not show significant variability in column density, however, several studies (Crenshaw et al. 1999; Winter et al. 2011) have shown that for select objects outflow column densities can change by a factor of 5 over only a few years. There is a possibility that Mrk 1513 will show column density variations in the future as a result of the dramatic change in continuum luminosity detected in this study. The decrease in energy released by the AGN between the COS and GHRS observations could change the ionization state of the gas resulting in dramatic column density variations (Crenshaw et al. 1999). It is possible the