Narrow-line Seyfert 1 Galaxies Research Articles

On the Nature of the Radio Calibrator and Gamma-Ray Emitting NLS1 Galaxy 3C 286 and Its Multiwavelength Variability

The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of the radio-loudest NLS1 galaxies known to date. 3C 286 is also one of very few known compact steep-spectrum (CSS) sources detected in the gamma-ray regime. Observations in the X-ray regime, rarely carried out so far, revealed evidence for variability, raising the question whether it is driven by the accretion disk or jet. 3C 286 is also well known for its damped Lyman alpha system from an intervening absorber at z = 0.692, triggering a search for the corresponding X-ray absorption along the line-of-sight. Here, we present new observations in the radio, X-ray, optical, and UV bands. The nature of the X-ray variability is addressed. Spectral evidence suggests that it is primarily driven by the accretion disk (not the jet), and the X-ray spectrum is well fit by a powerlaw plus soft excess model. The radio flux density and polarization remain constant at the Effelsberg telescope resolution, reconfirming the use of 3C 286 as radio calibrator. The amount of reddening/absorption along the line-of-sight intrinsic to 3C 286 is rigorously assessed. None is found, validating the derivation of a high Eddington ratio (L/LEdd ∼ 1) and of the very high radio-loudness index of 3C 286. Based on the first deep Chandra image of 3C 286, tentative evidence for hard X-ray emission from the SW radio lobe is reported. A large variety of models for the gamma-ray emission of 3C 286 are briefly discussed.

A comparative analysis of the active galactic nucleus and star formation characteristics of broad- and narrow-line Seyfert 1 galaxies

We report here our comparative analysis of the active galactic nucleus (AGN) and star formation (SF) characteristics of a sample of narrow-line Seyfert 1 (NLS1) and broad-line Seyfert 1 (BLS1) galaxies. Our sample consisted of 373 BLS1 and 240 NLS1 galaxies and spanned the redshift 0.02 $<$ $z$ $<$ 0.8. The broad-band spectral energy distribution, constructed using data from the ultra-violet to the far-infrared, was modelled using CIGALE to derive the basic properties of our sample. We searched for differences in stellar mass (M$_ ast $), star formation rate (SFR), and AGN luminosity (L$_ AGN $) in the two populations. We also estimated new radiation-pressure-corrected black hole masses for our sample of BLS1 and NLS1 galaxies. While the virial black hole mass (M$_ BH $) of BLS1 galaxies is similar to their radiation-pressure-corrected M$_ BH $ values, the virial M$_ BH $ values of NLS1 galaxies are underestimated. We found that NLS1 galaxies have a lower M$_ BH $ of log (M$_ BH M$_ odot ) = 7.45 pm 0.27 and a higher Eddington ratio of log ($ Edd $) = $-$0.72 pm 0.22 than BLS1 galaxies, which have log (M$_ BH M$_ odot ) and $ Edd $ values of 8.04 pm 0.26 and $-$1.08 pm 0.24, respectively. The distributions of M$_ ast $, SFR, and specific star formation (sSFR = SFR/M$_ ast $) for the two populations are indistinguishable. This analysis is based on an independent approach and contradicts reports in the literature that NLS1 galaxies have a higher SF than BLS1 galaxies. While we found that L$_ AGN $ increases with M$_ ast $, L$_ SF $ flattens at high M$_ ast $ for both BLS1 and NLS1 galaxies. The reason may be that SF is suppressed by AGN feedback at M$_ ast $ higher than sim 1011 M$_ odot $ or that the AGN fuelling mechanism is decoupled from SF. Separating the sample into radio-detected and radio-undetected subsamples, we found no difference in their SF properties suggesting that the effect of AGN jets on SF is negligible.

Superluminal Motion and Jet Parameters in the Gamma-ray-Emitting Narrow-Line Seyfert 1 Galaxy TXS 1206+549

Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of radio-loud and γ-ray-emitting NLS1 galaxies. We focus on the radio properties of this galaxy by analysing archival, high-resolution, very long baseline interferometry (VLBI) imaging observations taken at 8 GHz frequency in six epochs between 1994 and 2018. Using the milliarcsecond-scale radio structure, we can resolve a core and a jet component whose angular separation increases by (0.055±0.006) mas yr−1. This corresponds to an apparent superluminal jet component motion of (3.5±0.4)c. From the core brightness temperature and the jet component proper motion, we determine the characteristic Doppler-boosting factor, the bulk Lorentz factor, and the jet viewing angle. We find no compelling evidence for a very closely aligned blazar-type jet. The parameters for TXS 1206+549 resemble those of radio-loud quasar jets with a moderate Lorentz factor (Γ≈4) and ϑ≈24∘ inclination to the line of sight.

Changing-Look Narrow-Line Seyfert 1 Galaxies, their Detection with SVOM, and the Case of NGC 1566

We discuss applications of the study of the new and barely explored class of changing-look (CL) narrow-line Seyfert 1 (NLS1) galaxies and comment on their detection with the space mission SVOM (Space Variable Objects Monitor). We highlight the case of NGC 1566, which is outstanding in many respects, for instance as one of the nearest known CL AGN undergoing exceptional outbursts. Its NLS1 nature is discussed, and we take it as a nearby prototype for systems that could be discovered and studied in the near future, including with SVOM. Finally, we briefly examine the broader implications and applications of CL events in NLS1 galaxies and show that such systems, once discovered in larger numbers, will greatly advance our understanding of the physics of the environment of rapidly growing supermassive black holes. This White Paper is part of a sequence of publications which explore aspects of our understanding of (CL) NLS1 galaxy physics with future missions.

Multiwavelength variability of γ-ray emitting narrow-line Seyfert 1 galaxies

ABSTRACT As one of the drivers of feedback in active galactic nuclei (AGNs), the jets launched from supermassive black holes (SMBHs) are important for understanding the co-evolution of SMBHs and their host galaxies. However, the formation of AGN jets is far from clear. The discovery of γ-ray narrow-line Seyfert 1 (NLS1) galaxies during the past two decades has provided us with a new means of studying the link between jets and accretion processes and the formation of jets. Here, we explore the coupling of jet and accretion discs in seven bright γ-ray NLS1 galaxies by studying simultaneous optical/ultraviolet and X-ray observations of these systems taken by Swift. The results show that, except for 1H 0323+342 in which the X-rays are significantly contributed from the accretion disc, the observed X-ray emission of the other sources is dominated by the jet, and accretion process makes little contribution if not absent. Although the origin of the X-ray emission is different, the broad-band spectral shape characterized by αox and the X-ray flux is found to follow the same evolutionary trend in 1H 0323+342, PMN J0948+0022, and PKS 1502+036. For the remaining sources, the trend is not observed or the sampling is not dense enough.

Revisiting Emission-line Measurement Methods for Narrow-line Active Galactic Nuclei

Measuring broad emission-line widths in active galactic nuclei (AGN) is not straightforward owing to the complex nature of flux variability in these systems. Line width measurements become especially challenging when the signal-to-noise ratio is low, profiles are narrower, or spectral resolution is low. We conducted an extensive correlation analysis between emission-line measurements from the optical spectra of Markarian 142 (Mrk 142; a narrow-line Seyfert galaxy) taken with the Gemini North Telescope (Gemini) at a spectral resolution of 185.6 ± 10.2 km s−1 and the Lijiang Telescope (LJT) at 695.2 ± 3.9 km s−1 to investigate the disparities in the measured broad-line widths from both telescopes’ data. Due to its narrow broad-line profiles, which were severely affected by instrumental broadening in the lower-resolution LJT spectra, Mrk 142 posed a challenge. We discovered that allowing the narrow-line flux of permitted lines having broad and narrow components to vary during spectral fitting caused a leak in the narrow-line flux to the broad component, resulting in broader broad-line widths in the LJT spectra. Fixing the narrow-line flux ratios constrained the flux leak and yielded the Hβ broad-line widths from LJT spectra ∼54% closer to the Gemini Hβ widths than with flexible narrow-line ratios. The availability of spectra at different resolutions presented this unique opportunity to inspect how spectral resolution affected emission-line profiles in our data and adopt a unique method to accurately measure broad-line widths. Reconsidering line measurement methods while studying diverse AGN populations is critical for the success of future reverberation-mapping studies. Based on the technique used in this work, we offer recommendations for measuring line widths in narrow-line AGN.

The rise and fall of the iron-strong nuclear transient PS16dtm

Context. Thanks to the advent of large-scale optical surveys, a diverse set of flares from the nuclear regions of galaxies has recently been discovered. These include the disruption of stars by supermassive black holes at the centers of galaxies – nuclear transients known as tidal disruption events (TDEs). Active galactic nuclei (AGN) can show extreme changes in the brightness and emission line intensities, often referred to as changing-look AGN (CLAGN). Given the physical and observational similarities, the interpretation and distinction of nuclear transients as CLAGN or TDEs remains difficult. One of the obstacles of making progress in the field is the lack of well-sampled data of long-lived nuclear outbursts in AGN. Aims. Here, we study PS16dtm, a nuclear transient in a Narrow Line Seyfert 1 (NLSy1) galaxy, which has been proposed to be a TDE candidate. Our aim is to study the spectroscopic and photometric properties of PS16dtm, in order to better understand the outbursts originating in NLSy1 galaxies. Methods. Our extensive multiwavelength follow-up that spans around 2000 days includes photometry and spectroscopy in the UV/optical, as well as mid-infrared (MIR) and X-ray observations. Furthermore, we improved an existing semiempirical model in order to reproduce the spectra and study the evolution of the spectral lines. Results. The UV/optical light curve shows a double peak at ∼50 and ∼100 days after the first detection, and it declines and flattens afterward, reaching preoutburst levels after 2000 days of monitoring. The MIR light curve rises almost simultaneously with the optical, but unlike the UV/optical which is approaching the preoutburst levels in the last epochs of our observations, the MIR emission is still rising at the time of writing. The optical spectra show broad Balmer features and the strongest broad Fe II emission ever detected in a nuclear transient. This broad Fe II emission was not present in the archival preoutburst spectrum and almost completely disappeared +1868 days after the outburst. We found that the majority of the flux of the broad Balmer and Fe II lines is produced by photoionization. We detect only weak X-ray emission in the 0.5−8 keV band at the location of PS16dtm, at +848, +1130, and +1429 days past the outburst. This means that the X-ray emission continues to be lower by at least an order of magnitude, compared to archival, preoutburst measurements. Conclusions. We confirm that the observed properties of PS16dtm are difficult to reconcile with normal AGN variability. The TDE scenario continues to be a plausible explanation for the observed properties, even though PS16dtm shows differences compared to TDE in quiescent galaxies. We suggest that this event is part of a growing sample of TDEs that show broad Balmer line profiles and Fe II complexes. We argue that the extreme variability seen in the AGN host due to PS16dtm may have easily been misclassified as a CLAGN, especially if the rising part of the light curve had been missed. This implies that some changing look episodes in AGN may be triggered by TDEs. Imaging and spectroscopic data of AGN with good sampling are needed to enable testing of possible physical mechanisms behind the extreme variability in AGN.

Jetted narrow-line Seyfert 1 galaxies breaking the jet paradigm: A comprehensive study of host-galaxy morphologies

Narrow-line Seyfert 1 (NLS1) galaxies are unevolved active galactic nuclei (AGNs) that exist predominantly in spiral galaxies. However, mostly due to the small number of sources studied, it has been under debate whether also the hosts of jetted NLS1 galaxies, a particular subclass of these sources hosting a relativistic jet, are disk-like or elliptical, as the hosts of more powerful jetted AGNs. We studied the host morphologies of 14 NLS1 galaxies, 11 of which have been detected at 37 GHz, indicating that these sources harbour relativistic jets. TheJ- andKs-band data used in this study were obtained with the Nordic Optical Telescope (NOT). We performed the photometric decomposition of the host galaxy using the band that gave a better fit and additionally created colour maps of all sources that had both aJ- and aKs-band observation. We were able to successfully model 12 sources, nine of which most likely have disk-like morphologies. Of the remaining sources, one source could possibly be hosted either in a disk-like or a dwarf galaxy, and in two cases the results are inconclusive. Only one of our sources shows clear signs of interaction, but the colour maps of most of our sources hint at ample dust in the nuclei, possibly indicating earlier minor mergers, which can go unnoticed due to the limited resolution of these observations. Our results further support disk-like galaxies as the predominant host type of jetted NLS1 galaxies. Most importantly, with the number of modelled hosts of jetted NLS1s now exceeding 50, with only a few elliptical hosts, it seems to be safe to conclude that also disk-like galaxies are able to launch and maintain relativistic jets, and that the traditional jet paradigm stating that only massive elliptical galaxies are capable of hosting relativistic jets is severely outdated.

Multicolor Optical Monitoring of the γ -Ray Emitting Narrow-line Seyfert 1 Galaxy PMN J0948+0022 from 2020 to 2021

In order to study the physical properties of the γ-ray emitting narrow-line Seyfert 1 (NLS1) galaxy population, photometric and spectral observations of the γ-ray emitting NLS1 PMN J0948+0022 were made with the Lijiang 2.4 m optical telescope of Yunnan Observatories, Chinese Academy of Sciences. Photometric data in the B and R bands were collected for 50 nights from 2020 January to 2021 December. During the observation epoch, the variability amplitudes are 73.67% in the B band and 79.96% in the R band. Intra-day variability is found in two observation nights, and the duty cycle value is 29% with variability amplitude > 12.9% in the R band, which support the presence of the relativistic jets in the target. The redder-when-brighter (RWB) chromatic trend (or steeper-when-brighter trend) appears on intra-day and long timescales. The RWB trend is dominated by the radiation of accretion disk and jet, and resembles those in flat spectrum radio quasars. When PMN J0948+0022 is brighter than 17.ͫ5 in the R band, there is no color change trend. By analyzing the spectral data of PMN J0948+0022, we obtained the black hole mass of M • = 1.61 × 107 M ⊙ and accretion rate of , and confirmed that PMN J0948+0022 is a super-Eddington accreting NLS1. The redshifts of reverberation mapped super-Eddington accreting active galactic nuclei can be expanded by PMN J0948+0022 up to above 0.5. Super-Eddington accreting NLS1 galaxies were chosen as a new type of cosmological candle in the literature. PMN J0948+0022 may be used as a target for the next step of reverberation mapping monitoring project of super-Eddington accreting massive black holes.

A comparative study of the physical properties for a representative sample of Narrow and Broad-line Seyfert galaxies

ABSTRACT We present a comparative study of the physical properties of a homogeneous sample of 144 Narrow line Seyfert 1 (NLSy1) and 117 Broad-line Seyfert 1 (BLSy1) galaxies. These two samples are in a similar luminosity and redshift range and have optical spectra available in the 16th data release of Sloan Digital Sky Survey (SDSS-DR16) and X-ray spectra in either XMM-NEWTON or ROSAT. Direct correlation analysis and a principal component analysis (PCA) have been performed using ten observational and physical parameters obtained by fitting the optical spectra and the soft X-ray photon indices as another parameter. We confirm that the established correlations for the general quasar population hold for both types of galaxies in this sample despite significant differences in the physical properties. We characterize the sample also using the line shape parameters, namely the asymmetry and kurtosis indices. We find that the fraction of NLSy1 galaxies showing outflow signatures, characterized by blue asymmetries, is higher by a factor of about 3 compared to the corresponding fraction in BLSy1 galaxies. The presence of high iron content in the broad-line region of NLSy1 galaxies in conjunction with higher Eddington ratios can be the possible reason behind this phenomenon. We also explore the possibility of using asymmetry in the emission lines as a tracer of outflows in the inner regions of Active Galactic Nuclei. The PCA results point to the NLSy1 and BLSy1 galaxies occupying different parameter spaces, which challenges the notion that NLSy1 galaxies are a subclass of BLSy1 galaxies.

Revisiting the spectral energy distribution of I Zw 1 under the CaFe Project

The CaFe Project involves the study of the properties of the low ionization emission lines (LILs) pertaining to the broad-line region (BLR) in active galaxies. These emission lines, especially the singly-ionized iron (Fe II) in the optical and the corresponding singly-ionized calcium (Ca II) in the near-infrared (NIR) are found to show a strong correlation in their emission strengths, i.e. with respect to the broad H$\beta$ emission line, the latter also belonging to the same category of LILs. The origin of this correlation is attributed to the similarity in the physical conditions necessary to emit these lines - especially in terms of the strength of the ionization from the central continuum source and the local number density of available matter in these regions. In this paper, we focus on the issue of the spectral energy distribution (SED) characteristic to a prototypical Type-1 Narrow-line Seyfert galaxy (NLS1) - I Zw 1. We extract the continuum from quasi-simultaneous spectroscopic measurements ranging from the near-UV (~1200A) to the near-infrared (~24000A) to construct the SED and supplement it with archival X-ray measurements available for this source. Using photoionization code CLOUDY, we assess and compare the contribution of the prominent "Big Blue Bump" seen in our SED versus the SED used in our previous work, wherein the latter was constructed from archival, multi-epoch photometric measurements. Following the prescription from our previous work, we constrain the physical parameter space to optimize the emission from these LILs and discuss the implication of the use of a "better" SED.

A Family Tree of Optical Transients from Narrow-line Seyfert 1 Galaxies

Abstract The Zwicky Transient Facility (ZTF) has discovered five events (0.01 < z < 0.4) belonging to an emerging class of active galactic nuclei (AGNs) undergoing smooth, large-amplitude, and rapidly rising flares. This sample consists of several transients initially classified as supernovae with narrow spectral lines. However, upon closer inspection, all of the host galaxies display Balmer lines with FWHM(Hβ) ∼ 900–1400 km s−1, characteristic of a narrow-line Seyfert 1 (NLSy1) galaxy. The transient events are long lived, over 400 days on average in the observed frame. We report UV and X-ray follow-up of the flares and observe persistent UV emission, with two of the five transients detected with luminous X-ray emission, ruling out a supernova interpretation. We compare the properties of this sample to previously reported flaring NLSy1 galaxies and find that they fall into three spectroscopic categories: 1) Balmer line profiles and Fe ii complexes typical of NLSy1s, 2) strong He ii profiles, and 3) He ii profiles including Bowen fluorescence features. The latter are members of the growing class of AGN flares attributed to enhanced accretion reported by Trakhtenbrot et al. We consider physical interpretations in the context of related transients from the literature. For example, two of the sources show high-amplitude rebrightening in the optical, ruling out a simple tidal disruption event scenario for those transients. We conclude that three of the sample belong to the Trakhtenbrot et al. class and two are tidal disruption events in NLSy1s. We also hypothesize as to why NLSy1s are preferentially the sites of such rapid enhanced flaring activity.

The CaFe project: Optical Fe II and near-infrared Ca II triplet emission in active galaxies: simulated EWs and the co-dependence of cloud size and metal content

Aims. Modelling the low-ionisation lines (LILs) in active galactic nuclei (AGNs) still faces problems in explaining the observed equivalent widths (EWs) when realistic covering factors are used and the distance of the broad-line region (BLR) from the centre is assumed to be consistent with the reverberation mapping measurements. We re-emphasise this problem and suggest that the BLR ‘sees’ a different continuum from that seen by a distant observer. This change in the continuum reflected in the change in the net bolometric luminosity from the AGN is then able to resolve the above problem. Methods. We carefully examine the optical Fe II and near-infrared (NIR) Ca II triplet (CaT) emission strengths with respect to Hβ emission using the photoionisation code CLOUDY and a range of physical parameters. Prominent among these parameters are (a) the ionisation parameter (U), (b) the local BLR cloud density (nH), (c) the metal content in the BLR cloud, and (d) the cloud column density. Using an incident continuum for I Zw 1 –a prototypical Type-1 narrow-line Seyfert galaxy– our basic setup is able to recover the line ratios for the optical Fe II (i.e. RFeII) and for the NIR CaT (i.e. RCaT) in agreement with the observed estimates. Nevertheless, the pairs of (U,nH) that reproduce the conforming line ratios do not relate to agreeable line EWs. We therefore propose a way to mitigate this issue. The LIL region of the BLR cloud does not see the same continuum emitted by the accretion disc as that seen by a distant observer; rather it sees a filtered version of the original continuum which brings the radial sizes into agreement with the reverberation mapped estimates for the extension of the BLR. This is achieved by scaling the radial distance of the emitting regions from the central continuum source using the photoionisation method in correspondence with the reverberation mapping estimates for I Zw 1. Taking inspiration from past studies, we suggest that this collimation of the incident continuum can be explained by the anisotropic emission from the accretion disc, which modifies the spectral energy distribution such that the BLR receives a much cooler continuum with a reduced number of line-ionising photons, allowing reconciliation in the modelling with the line EWs. Results. (1) The assumption of the filtered continuum as the source of BLR irradiation recovers realistic EWs for the LIL species, such as the Hβ, Fe II, and CaT. However, our study finds that to account for the adequate RFeII (Fe II/Hβ flux ratio) emission, the BLR needs to be selectively overabundant in iron. On the other hand, the RCaT (CaT/Hβ flux ratio) emission spans a broader range from solar to super-solar metallicities. In all these models, the BLR cloud density is found to be consistent with our conclusions from prior studies, that is, nH ∼ 1012 cm−3 is required for the sufficient emission of Fe II and CaT. (2) We extend our modelling to test and confirm the co-dependence between metallicity and cloud column density for these two ionic species (Fe II and CaT), further allowing us to constrain the physical parameter space for the emission of these LILs. Adopting the estimates from line ratios that diagnose the metallicity in these gas-rich media –which suggest super-solar values (≳5−10 Z⊙)–, we arrive at cloud columns that are of the order of 1024 cm−2. (3) Finally, we test the effect of inclusion of a micro-turbulent velocity within the BLR cloud and find that the Fe II emission is positively affected. An interesting result obtained here is the reduction in the value of the metallicity by up to a factor of ten for the RFeII cases when the microturbulence is invoked, suggesting that microturbulence can act as an apparent metallicity controller for the Fe II. On the contrary, the RCaT cases are relatively unaffected by the inclusion of microturbulence.

Mrk 1239: a Type-2 Counterpart of Narrow-line Seyfert-1?

Abstract We present new spectrophotometric and spectropolarimetric observations of Mrk 1239, one of the 8 prototypes that defines type-1 narrow-line Seyfert galaxies (NLS1s). Unlike the other typical NLS1s though, a high degree of polarization (P ∼ 5.6%) and red optical–IR (g–W 4 = 12.35) colors suggest that Mrk 1239 is more similar to type-2 active galactic nuclei like NGC 1068. Detailed analysis of spectral energy distribution in the UV–optical–IR yields two components from the nucleus: a direct and transmitted component that is heavily obscured (E B–V ≈ 1.6), and another indirect and scattered one with mild extinction (E B–V ∼ 0.5). Such a two-light-paths scenario is also found in previous reports based on the X-ray data. Comparison of emission lines and the detection of He i*λ10830 BAL at [−3000, −1000] km s−1 indicates that the obscuring clouds are at physical scale between the sublimation radius and that of the narrow emission line regions. The potential existence of powerful outflows is found as both the obscurer and scatterer are outflowing. Similar to many other type-2s, jet-like structure in the radio band is found in Mrk 1239, perpendicular to the polarization angle, suggesting polar scattering. We argue that Mrk 1239 is very probably a type-2 counterpart of NLS1s. The identification of 1 out of 8 prototype NLS1s as a type-2 counterpart implies that there can be a substantial amount of analogs of Mrk 1239 misidentified as type-1s in the optical band. Properties of these misidentified objects are going to be explored in our future works.

Intra-night optical variability of γ −ray detected narrow-line Seyfert1 galaxies

Abstract We report the first attempt to systematically characterise intra-night optical variability (INOV) of the rare and enigmatic subset of Narrow-Line Seyfert1 galaxies (NLSy1s), which is marked by detection in the γ-ray band and is therefore endowed with Doppler boosted relativistic jets, like blazars. However, the central engines in these two types of AGN are thought to operate in different regimes of accretion rate. Our INOV search in a fairly large and unbiased sample of 15 γ-ray NLSy1s was conducted in 36 monitoring sessions, each lasting ≥ 3 hrs. In our analysis, special care has been taken to address the possible effect on the differential light curves, of any variation in the seeing disc during the session, since that might lead to spurious claims of INOV from such AGN due to the possibility of a significant contribution from the host galaxy to the total optical emission. From our observations, a duty cycle (DC) of INOV detection in the γ-ray NLSy1s is estimated to be around 25% - 30%, which is comparable to that known for blazars. This estimate of DC will probably need an upward revision, once it becomes possible to correct for the dilution of the AGN’s nonthermal optical emission by the (much steadier) optical emission contributed not only by the host galaxy but also the nuclear accretion disc in these high Eddington rate accretors. Finally, we also draw attention to the possibility that sharp optical flux changes on sub-hour time scale are less rare for γ-ray NLSy1s, in comparison to blazars.

A Suzaku sample of unabsorbed narrow-line and broad-line Seyfert 1 galaxies – I. X-ray spectral properties

ABSTRACT A sample of narrow-line Seyfert 1 (NLS1) and broad-line Seyfert 1 (BLS1) galaxies observed with Suzaku is presented. The final sample consists of 22 NLS1s and 47 BLS1s, for a total of 69 active galactic nuclei (AGNs) that are all at low redshift (z < 0.5) and exhibit low host-galaxy column densities (<1022${\rm cm}^{-2}\,$). The average spectrum for each object is fit with a toy model to characterize important parameters, including the photon index, soft excess, Compton hump (or hard excess), narrow iron line strength, luminosity, and X-ray Eddington ratio (Lx/LEdd). We confirm previous findings that NLS1s have steeper power laws and higher X-ray Eddington ratios, but also find that NLS1 galaxies have stronger soft and hard excesses than their BLS1 counterparts. Studying the correlations between parameters shows that the soft and hard excesses are correlated for NLS1 galaxies, while no such correlation is observed for BLS1s. Performing a principal component analysis (PCA) on the measured X-ray parameters shows that while the X-ray Eddington ratio is the main source of variations within our sample (PC1), variations in the soft and hard excesses form the second principal component (PC2) and it is dominated by the NLS1s. The correlation between the soft and hard excesses in NLS1 galaxies may suggest a common origin for the two components, such as a blurred reflection model. The presented Suzaku sample of Seyfert 1 galaxies is a useful tool for the analysis of the X-ray properties of AGNs, and for the study of the soft and hard excesses observed in AGNs.

A Relativistic Orbit Model for Temporal Properties of AGN

We present a unified model for X-ray quasi-periodic oscillations (QPOs) seen in Narrow-line Seyfert 1 (NLSy1) galaxies, γ-ray and optical band QPOs that are seen in Blazars. The origin of these QPOs is attributed to the plasma motion in corona or jets of these AGN. In the case of X-ray QPOs, we applied the general relativistic precession model for the two simultaneous QPOs seen in NLSy1 1H 0707-945 and deduce orbital parameters, such the radius of the emission region, and spin parameter a for a circular orbit; we obtained the Carter’s constant Q, a, and the radius in the case of a spherical orbit solution. In other cases where only one X-ray QPO is seen, we localized the orbital parameters for NLSy1 galaxies REJ 1034+396, 2XMM J123103.2+110648, MS 2254.9-3712, Mrk 766, and MCG-06-30-15. By applying the lighthouse model, we found that a kinematic origin of the jet based γ-ray and optical QPOs, in a relativistic MHD framework, is possible. Based on the inbuilt Hamiltonian formulation with a power-law distribution in the orbital energy of the plasma consisting of only circular or spherical trajectories, we show that the resulting Fourier power spectral density (PSD) has a break corresponding to the energy at ISCO. Further, we derive connection formulae between the slopes in the PSD and that of the energy distribution. Overall, given the preliminary but promising results of these relativistic orbit models to match the observed QPO frequencies and PSD at diverse scales in the inner corona and the jet, it motivates us to build detailed models, including a transfer function for the energy spectrum in the corona and relativistic MHD jet models for plasma flow and its polarization properties.

A Comparison of X-Ray Photon Indices among the Narrow- and Broad-line Seyfert 1 Galaxies

Abstract We present a detailed comparative systematic study using a sample of 221 narrow-line Seyfert 1 (NLSy1) galaxies in comparison to a redshift-matched sample of 154 broad-line Seyfert 1 (BLSy1) galaxies based on their observations using ROSAT and/or XMM-Newton in soft X-ray band (0.1–2.0 keV). A homogeneous analysis is carried out to estimate their soft X-ray photon indices ( ) and its correlations with other parameters of nuclear activities such as Eddington ratios (R Edd), bolometric luminosities (L bol), black hole masses (M BH), and the widths of the broad component of Hβ lines (FWHM(Hβ)). In our analysis, we found clear evidence of the difference in the and R Edd distributions among NLSy1 and BLSy1 galaxies, with steeper and higher R Edd for the former. Such a difference also exists in the spectral index distribution in hard X-ray ( ), based on the analysis of 53 NLSy1 and 46 BLSy1 galaxies in the 2–10 keV energy band. The difference in R Edd distributions does exist even after applying the average correction for the difference in the inclination angle of NLSy1 and BLSy1 galaxies. We also estimated R Edd, based on SED fitting of 34 NLSy1 and 30 BLSy1 galaxies over the 0.3–10 keV energy band, and found that results are still consistent with R Edd estimates based on the optical bolometric luminosity. Our analysis suggests that the higher R Edd in NLSy1 is responsible for its steeper X-ray spectral slope compared to the BLSy1, consistent with the disk-corona model as proposed for the luminous AGNs.

Properties of Broad and Narrow Line Seyfert galaxies selected from SDSS

A comparative study of a representative sample of Broad and Narrow line Seyfert galaxies is presented. These galaxies have been selected from the 16th data release of the Sloan Digital Sky Survey (SDSS-DR16). Some of the properties derived from single epoch spectrum vary significantly between the two populations. We find that the emission regions of Narrow line Seyfert galaxies are rich in iron content and the accretion rate is higher compared to the Broad line Seyfert galaxies. In our analysis, the H emission line is found to be asymmetric in few of the galaxies with more number of Narrow-line Seyfert 1 (NlSy1) galaxies showing blue asymmetries i.e. traces of outflowing gas as compared to the Broad-line Seyfert 1 (BlSy1) galaxies. This behaviour may be explained by the higher iron content present in the emission line regions of NlSy1 galaxies.

Two Quasi-periodic Oscillations in ESO 113-G010

In the narrow-line Seyfert galaxy (NLS1) ESO 113-G010, two quasi-periodic oscillation (QPO) signals are detected in the XMM-Newton data collected in 2005 November. The XMM-Newton telescope has an exposure longer than 100ks in the energy range of 0.3–10 keV. The data are analyzed using the Lomb-Scargle periodogram (LSP) and the weighted wavelet Z-transform (WWZ) methods. It is found that there are ∼2.24 hour and ∼4.09 hour QPOs in the observation with the confidence levels of 7.3σ and 4.8σ, respectively. The two QPO signals have a relationship of approximately 1:2 (1:1.83). The absence of QPO in another observation of the object suggests that it is a transient phenomenon. The relationship between the mass of the ESO 113-G010 central black hole (BH) MBH and its frequency fQPO satisfies the known logarithmic linear relation in highly accreting BH systems, from stellar-mass BHs to supermassive BHs. The energy spectrum analysis reveals that the source has a soft X-ray excess below 1 keV.