PMN J0948 Research Articles

Probing the Heart of Active Narrow-line Seyfert 1 Galaxies with VERA Wideband Polarimetry

We explored the parsec-scale nuclear regions of a sample of radio-loud narrow-line Seyfert 1 galaxies (NLSy1s) using the VLBI Exploration of Radio Astrometry wideband (at a recording rate of 16 Gbps) polarimetry at 22 and 43 GHz. Our targets include 1H 0323+342, SBS 0846+513, PMN J0948+0022, 1219+044, PKS 1502+036, and TXS 2116-077, which are all known to exhibit γ-ray emission indicative of possessing highly beamed jets similar to blazars. For the first time, we unambiguously detected Faraday rotation toward the parsec-scale radio core of NLSy1s, with a median observed core rotation measure (RM) of 2.7 × 103 rad m−2 (or 6.3 × 103 rad m−2 for redshift-corrected). This level of RM magnitude is significantly larger than those seen in the core of BL Lacertae objects (BLOs; a dominant subclass of blazars), suggesting that the nuclear environment of NLSy1s is more gas-rich than that in BLOs. Interestingly, the observed parsec-scale polarimetric properties of NLSy1s (low core fractional polarization, large core RM and jet–EVPA misalignment) are rather similar to those of flat-spectrum radio quasars (FSRQs). Our results are in accordance with the scenario that NLSy1s are in an early stage of active galactic nucleus evolution with their central black hole masses being smaller than those of more evolved FSRQs.

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.

Modelling the variable emission states of γ-ray-emitting narrow-line Seyfert 1 galaxies

ABSTRACT γ-ray-emitting narrow-line Seyfert 1 galaxies (γ-NLS1) constitute an intriguing small population of active galactic nuclei with γ-ray emission resembling low-power flat-spectrum radio quasars (FSRQ), but with differing physical properties. They are jetted, γ/radio-loud Seyfert galaxies, with relatively low black hole masses, accreting at exceptionally high, near-Eddington rates. Certain of these sources exhibit highly variable emission states on relatively short time-scales, the physical origin of which remains elusive. In this work, varying emission states of two bona fide NLS1s, 1H 0323+342 and PMN J0948+0022, and one little-studied FSRQ/intermediate object, B2 0954+25A, are examined. For each source, we analysed quasi-simultaneous multiwavelength data for different states of γ-ray activity and present the results of their broad-band emission modelling, taking into account all available physical constraints to limit the range of the model parameters. Two different scenarios are discussed, in the framework of a one-zone leptonic model, where the high-energy emission is due to the inverse Compton scattering of the disc and broad line region (BLR) or torus photons by relativistic electrons within the jet. The transition from low to high state is well described by variations of the jet parameters, leaving the external photon fields unchanged. The parameterization favours an emission scenario with particle injection on a stationary shock inside the jet. When considering all physical constraints, the disc and BLR scenario is preferred for all three sources. We use the multi-epoch modelling to characterize total jet powers and discuss the intrinsic nature of γ-NLS1 galaxies and FSRQs.

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.

Intraday Mid-infrared Variability of PMN J0948+0022 on 2020 April 26

Abstract We report a new period mid-infrared variability of PMN J0948+0022 on 2020 April 26, observed by the Wide-field Infrared Survey Explore (WISE). This source faded consistently over a period of one day. The amplitude of variability is about 0.21 and 0.18 mag in the W1 (3.4 μm) and W2 (4.6 μm) bands, respectively. The intraday variability constrains the size of the mid-infrared emission region to about 5 × 10−4 pc, which is rather smaller than that of the dust torus but consistent with the base of a jet. The mid-infrared color showed a significant bluer-when-brighter trend, similar to γ-ray emitting blazars. These characteristics suggest that the mid-infrared emission was dominated by the synchrotron emission of relativistic electrons in the jet.

Short time-scale variability of γ-ray-emitting narrow-line Seyfert 1 galaxies in optical and UV bands

ABSTRACT We report the first systematic analysis of single exposures of all optical and ultraviolet (UV) observations performed by the UltraViolet and Optical Telescope (UVOT) on board the Neil Gehrels Swift Observatory satellite available up to 2019 April of six γ-ray-emitting narrow-line Seyfert 1 galaxies (NLSy1). Rapid variability has been significantly detected on hours time-scale for 1H 0323+342, SBS 0846+513, PMN J0948+0022, and PKS 2004−447 in 18 observations for a total of 34 events. In particular, we report the first detection of significant variability on short time-scale (3–6 ks) in optical for PKS 2004–447, and UV for 1H 0323+342 and PMN J0948+0022. The shortest variability time-scale observed for 1H 0323+342, SBS 0846+513, PMN J0948+0022, and PKS 2004−447 (assuming a Doppler factor δ = 10) gives a lower limit on the size of emission region between 9.7 × 1014 (for SBS 0846+513) and 1.6 × 1015 cm (for 1H 0323+342), suggesting that the optical and UV emission during these events is produced in compact regions within the jet. These observations provide unambiguous evidence about the relativistically beamed synchrotron emission in these sources, similar to blazars. A remarkable variability has been observed for PMN J0948+0022 on 2009 June 23 with an increase from ∼1.1 to 0.4 mag going from v to w2 filter in ∼1.6 h and a decrease at the initial level in a comparable time. The higher fractional flux change observed for this and other events at lower frequencies suggests that the synchrotron emission is more contaminated by thermal emission from accretion disc at higher frequencies.

Gamma-ray-emitting narrow-line Seyfert 1 galaxies: the Swift view

ABSTRACT We report the analysis of all Swift observations available up to 2019 April of γ-ray-emitting narrow-line Seyfert 1 galaxies (NLSy1). The distribution of X-ray luminosities (and fluxes) indicates that the jet radiation significantly contributes to their X-ray emission, with Doppler boosting making values higher than other radio-loud NLSy1. The 0.3–10 keV photon indices are on average harder with respect to radio-quiet and radio-loud NLSy1, confirming a dominant jet contribution in X-rays. However, the lower variability amplitude with respect to blazars and the softening of the spectrum in some periods suggests that also the corona radiation contributes to the X-ray emission. In optical and ultraviolet (UV) significant flux changes have been observed on daily, weekly, and monthly time-scale, providing a clear indication of the significant contribution of the jet radiation in this part of spectrum. A strong correlation between X-ray, UV, and optical emission and simultaneous flux variations have been observed in 1H 0323+342, SBS 0846+513, PMN J0948+0022 as expected in case the jet radiation is the dominant mechanism. Correlated multiband variability favours the jet-dominated scenario also in FBQS J1644+2619 and PKS 2004−447. The summed X-ray Telescope spectra of 1H 0323+342, SBS 0846+513, PMN J0948+0022, and FBQS J1644+2619 are well fitted by a broken power law with a break around 2 keV. The spectrum above 2 keV is dominated by the non-thermal emission from a beamed relativistic jet, as suggested by the hard photon index. A Seyfert-like feature like the soft X-ray excess has been observed below 2 keV, making these γ-ray-emitting NLSy1 different from typical blazars.

High-Energy and Very High-Energy Constraints from Log-Parabolic Spectral Models in Narrow-Line Seyfert 1 Galaxies

Narrow-line Seyfert 1 galaxies (NLSy1s) are a well established class of γ -ray sources, showing the presence of a jet like the more common flat-spectrum radio quasars. The evidence of γ -ray emission poses the issue of the location of the γ -ray emitting zone and of the contribution of the γ - γ absorption within the broad-line region (BLR), since such objects have been detected by Fermi-LAT in the MeV-GeV energy range but not by imaging atmospheric Cherenkov telescopes beyond 100 GeV. We discuss how the spectral properties of three NLSy1s (SBS 0846+513, PMN J0948+0022, and PKS 1502+036) derived from the Fermi Large Area Telescope Fourth Source Catalog (4FGL) compared with theoretical models based on the observed properties of the BLR. In particular, we focus on the question on how simple power-law spectral models and log-parabolic ones could be disentangled in γ -ray narrow-line Seyfert 1 galaxies by means of current Fermi-LAT or future imaging atmospheric Cherenkov telescopes data. We found that the only possibility for a log-parabolic model to mimic a power-law model in the energy band above E ∼ 100 GeV is to have a very small value of the curvature parameter β ∼ 0.05 .

Prospects for γ-ray observations of narrow-line Seyfert 1 galaxies with the Cherenkov Telescope Array – II. γ–γ absorption in the broad-line region radiation fields

ABSTRACT Gamma-ray emitting narrow-line Seyfert 1 (γ-NLS1) galaxies possibly harbour relatively low-mass black holes (106–108 M⊙) accreting close to the Eddington limit, and share many characteristics with their sibling sources, flat-spectrum radio quasars. Although they have been detected in the MeV–GeV band with Fermi–LAT, they have never been seen in the very high energy band with current imaging atmospheric Cherenkov telescopes (IACTs). Thus, they are key targets for the next-generation IACT, the Cherenkov Telescope Array (CTA). In a previous work we selected, by means of extensive simulations, the best candidates for a prospective CTA detection (SBS 0846+513, PMN J0948+0022, and PKS 1502+036) taking into account the effects of both the intrinsic absorption (approximated with a cut-off at 30 GeV), and the extragalactic background light on the propagation of γ-rays. In this work, we simulate the spectra of these three sources by adopting more realistic broad-line region (BLR) absorption models. In particular, we consider the detailed treatment of γ–γ absorption in the radiation fields of the BLR as a function of the location of the γ-ray emission region with parameters inferred from observational constraints. We find that, due to the energy range extent and its sensitivity, CTA is particularly well suited to locate the γ-ray emitting region in γ-NLS1. In particular CTA will be able not only to distinguish whether the γ-ray emitting region is located inside or outside the BLR, but also where inside the BLR it may be.

Radio jet structures at ∼100 pc and larger scales of the γ-ray-emitting narrow-line Seyfert 1 galaxy PMN J0948+0022

Abstract The narrow-line Seyfert 1 (NLS1) galaxy PMN J0948+0022 is an archetype of γ-ray-emitting NLS1s in active galactic nuclei (AGNs). In this study, we investigate its radio structures using archival data obtained using the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA). The new VLA images reveal an outermost radio emission separated by 9.1 arcsec. Its resolved structure and steep spectrum suggest a terminal shock in a radio lobe energized by the jet from the PMN J0948+0022 nucleus. This large-scale radio component is found at almost the same position angle as that of the pc-scale jet, indicating a stable jet direction up to ∼1 Mpc. Its apparent one-sidedness implies a moderate advancing speed (β > 0.27). The kinematic age of <1× 107 yr of the jet activity is consistent with the expected NLS1 phase of ∼107 yr in the AGN lifetime. The VLBA image reveals the jet structure at distances ranging from r = 0.82 milliarcsec to 3.5 milliarcsec, corresponding to approximately 100 pc, where superluminal motions were found. The jet width profile (∝ r1.12) and flux-density profile (∝ r−1.44) depending on the distance r along the jet suggest that the jet kinetic energy is converted to internal energy in this region. The jet is causally connected in a nearly conical streamline, which is supported by ambient pressure at 100 pc scales in the host galaxy of PMN J0948+0022.

Prospects for gamma-ray observations of narrow-line Seyfert 1 galaxies with the Cherenkov Telescope Array

Gamma-ray emitting narrow-line Seyfert 1 ($\gamma$-NLSy1) galaxies are thought to harbour relatively low-mass black holes (10$^6$-10$^8$ M$_{\odot}$) accreting close to the Eddington limit. They show characteristics similar to those of blazars, such as flux and spectral variability in the gamma-ray energy band and radio properties which point toward the presence of a relativistic jet. These characteristics make them an intriguing class of sources to be investigated with the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory. We present our extensive set of simulations of all currently known $\gamma$-ray emitters identified as NLS1s (20 sources),investigating their detections and spectral properties, taking into account the effect of both the extra-galactic background light in the propagation of gamma-rays and intrinsic absorption components.We find that the prospects for observations of $\gamma$-NLSy1 with CTA are promising. In particular, the brightest sources of our sample, SBS 0846+513, PMN J0948+0022, and PKS 1502+036 can be detected during high/flaring states, the former two even in the case in which the emission occurs within the highly opaque central regions, which prevent $\gamma$ rays above few tens of GeV to escape. In this case the low-energy threshold of CTA will play a key role. If, on the other hand, high-energy emission occurs outside the broad line region, we can detect the sources up to several hundreds of GeV-depending on the intrinsic shape of the emitted spectrum. Therefore, CTA observations will provide valuable information on the physical conditions and emission properties of their jets.

X-ray and γ-ray emissions from NLSy1 galaxies

The recent observations by Fermi large area telescope (Fermi-LAT) showed that in addition to the radio galaxies and blazars, Narrow-Line Seyfert 1 (NLSy1) galaxies are also [Formula: see text]-rays emitters. NLSy1 are AGNs with optical spectral properties similar to those of Seyfert 1 galaxies, except for having narrow Balmer lines and strong optical lines. They also exhibit strong X-ray variability, steep X-ray spectra and relatively high luminosity. The multiwavelength emission properties of 1H 0323+342, SBS 0846+513 and PMN J0948+0022 are discussed, using the [Formula: see text]-ray data from the last 8.8 years Fermi-LAT observations as well as available Swift(UVOT/XRT) data. It is shown that one-zone synchrotron/synchrotron self-Compton (SSC) model can satisfactorily reproduce their observed broadband spectra.

Fermi-LAT observation of nonblazar AGNs

Context. Fermi Large Area Telescope (Fermi-LAT) has recently detected γ-ray emission from active galactic nuclei (AGN) that do not show clear evidence for optical blazar characteristics or have jets pointing away from the observer (nonblazar AGNs). These are interesting γ-ray emitters providing an alternative approach to studying high energy emission processes. Aims. This paper investigates the spectral and temporal properties of γ-ray emission from nonblazar AGNs using the recent Fermi-LAT observational data. Methods. The data collected by Fermi-LAT during 2008–2015, from the observations of 26 nonblazar AGNs, including 11 Fanaroff–Riley Type I (FRI) and ten FRII radio galaxies and steep spectrum radio quasars (SSRQs) and five narrow line seyfert 1s (NLSy1s) are analysed using the new PASS 8 event selection and instrument response function. Possible spectral changes above GeV energies are investigated with a detailed spectral analysis. Light curves generated with normal and adaptive time bins are used to study the γ-ray flux variability. Results. Non-blazar AGNs have a γ-ray photon index in the range of 1.84–2.86 and a flux varying from a few times 10−9 photon cm−2 s−1 to 10−7 photon cm−2 s−1. Over long time periods, the power law provides an adequate description of the γ-ray spectra of almost all sources. Significant curvature is observed in the γ-ray spectra of NGC 1275, NGC 6251, SBS 0846 + 513, and PMN J0948 + 0022 and their spectra are better described by log parabola or by the power law with exponential cut-off models. The γ-ray spectra of PKS 0625-25 and 3C 380 show a possible deviation from a simple power-law shape, indicating a spectral cut-off around the observed photon energy of Ecut = 131.2 ± 88.04 GeV and Ecut = 55.57 ± 50.74 GeV, respectively. Our analysis confirms the previous finding of an unusual spectral turnover in the γ-ray spectrum of Cen A: the photon index changes from Γ = 2.75 ± 0.02 to 2.31 ± 0.1 at 2.35 ± 0.08 GeV. In the Γ−Lγ plane, the luminosity of nonblazar AGNs is spread in the range of (1041–1047) erg s−1, where those with the lowest luminosity are FRI radio galaxies (but typically appear with a harder photon index) and those with the highest luminosity have are SSRQs/NLSY1s (with softer photon indexes). We confirm the previously reported short-timescale flux variability of NGC 1275 and 3C 120. The γ-ray emission from NLSY1s, 1H 0323 + 342, SBS 0846 + 513, and PMN J0948 + 0022 is variable, showing flares in short scales sometimes accompanied by a moderate hardening of their spectra (e.g., for MJD 56146.8 the γ-ray photon index of SBS 0846 + 513 was Γ = 1.73 ± 0.14). Non-blazar AGNs 3C 111, Cen A core, 3C 207, 3C 275.1, 3C 380, 4C + 39.23B, PKS 1502 + 036, and PKS 2004-447 show a long-timescale flux variability in the γ-ray band.

Multiple-wavelength Variability and Quasi-periodic Oscillation of PMN J0948+0022

Abstract We present a comprehensive analysis of multiple-wavelength observational data of the first GeV-selected narrow-line Seyfert 1 galaxy PMN J0948+0022. We derive its light curves in the γ-ray and X-ray bands from the data observed with Fermi/LAT and Swift/XRT, and generate the optical and radio light curves by collecting the data from the literature. These light curves show significant flux variations. With the LAT data we show that this source is analogous to typical flat spectrum radio quasars in the L γ –Γ γ plane, where L γ and Γ γ are the luminosity and spectral index in the LAT energy band. The γ-ray flux is correlated with the V-band flux with a lag of ∼44 days, and a moderate quasi-periodic oscillation (QPO) with a periodicity of ∼490 days observed in the LAT light curve. A similar QPO signature is also found in the V-band light curve. The γ-ray flux is not correlated with the radio flux in 15 GHz, and no similar QPO signature is found at a confidence level of 95%. Possible mechanisms of the QPO are discussed. We propose that gravitational-wave observations in the future may clarify the current plausible models for the QPO.

The radio structure of the peculiar narrow-line Seyfert 1 galaxy candidate J1100+4421

Narrow-line Seyfert 1 galaxies (NLS1) are an intriguing subclass of active galactic nuclei. Their observed properties indicate low central black hole mass and high accretion rate. The extremely radio-loud NLS1 sources often show relativistic beaming and are usually regarded as younger counterparts of blazars. Recently, the object SDSS J110006.07+442144.3 was reported as a candidate NLS1 source. The characteristics of its dramatic optical flare indicated its jet-related origin. The spectral energy distribution of the object was similar to that of the gamma-ray detected radio-loud NLS1, PMN J0948+0022. Our high-resolution European Very Long Baseline Interferometry Network observations at 1.7 and 5 GHz revealed a compact core feature with a brightness temperature of >~ 10^(10) K. Using the lowest brightness temperature value and assuming a moderate Lorentz factor of ~9 the jet viewing angle is <~ 26 deg. Archival Very Large Array data show a large-scale radio structure with a projected linear size of ~150 kpc reminiscent of double-sided morphology.

Similarity of jet radiation between flat spectrum radio quasars and GeV narrow-line Seyfert 1 galaxies: a universal δ-Lc correlation

By modeling the broadband spectral energy distributions (SEDs) of a typical flat spectrum radio quasar (FSRQ, 3C 279) and two GeV narrow-line Seyfert 1 galaxies (NLS1s, PMN J0948+0022 and 1H 0323+342) in different flux stages with one-zone leptonic models, we find a universal correlation between their Doppler factors (δ) and peak luminosities (Lc) of external Compton scattering bumps. Compiling a combined sample of FSRQs and GeV NLS1s, it is found that both FSRQs and GeV NLS1s in different stages and in different sources follow the same δ-Lc correlation well. This indicates that the variations of observed luminosities may be essentially due to the Doppler boosting effect. The universal δ-Lc relation between FSRQs and GeV NLS1s in different stages may be further evidence that the particle acceleration and radiation mechanisms for the two kinds of sources are similar. In addition, by replacing Lc with the observed luminosity in the Fermi/LAT band (LLAT), this correlation holds and it may serve as an empirical indicator of δ. We estimate the δ values with LLAT for 484 FSRQs in the Fermi/LAT Catalog and they range from 3 to 41, with a median of 16, which are statistically consistent with the values derived by other methods.

The MHz-peaked radio spectrum of the unusualγ-ray source PMN J1603–4904

Context. The majority of bright extragalactic gamma-ray sources are blazars. Only a few radio galaxies have been detected by Fermi/LAT. Recently, the GHz-peaked spectrum source PKS 1718-649 was confirmed to be gamma-ray bright, providing further evidence for the existence of a population of gamma-ray loud, compact radio galaxies. A spectral turnover in the radio spectrum in the MHz to GHz range is a characteristic feature of these objects, which are thought to be young due to their small linear sizes. The multiwavelength properties of the gamma-ray source PMN J1603-4904 suggest that it is a member of this source class. Aims. The known radio spectrum of PMN J1603-4904 can be described by a power law above 1 GHz. Using observations from the Giant Metrewave Radio Telescope (GMRT) at 150, 325, and 610 MHz, we investigate the behaviour of the spectrum at lower frequencies to search for a low-frequency turnover. Methods. Data from the TIFR GMRT Sky Survey (TGSS ADR) catalogue and archival GMRT observations were used to construct the first MHz to GHz spectrum of PMN J1603-4904. Results. We detect a low-frequency turnover of the spectrum and measure the peak position at about 490 MHz (rest-frame), which, using the known relation of peak frequency and linear size, translates into a maximum linear source size of ~1.4 kpc. Conclusions. The detection of the MHz peak indicates that PMN J1603-4904 is part of this population of radio galaxies with turnover frequencies in the MHz to GHz regime. Therefore it can be considered the second, confirmed object of this kind detected in gamma-rays. Establishing this gamma-ray source class will help to investigate the gamma-ray production sites and to test broadband emission models.

THE FIRST GEV OUTBURST OF THE RADIO-LOUD NARROW-LINE SEYFERT 1 GALAXY PKS 1502+036

ABSTRACT The γ-ray-loud narrow-line Seyfert 1 (γ-NLSy1) galaxy PKS 1502+036 (z = 0.409) exhibited its first γ-ray outburst on 2015 December 20. In the energy range of 0.1–300 GeV, the highest flux measured by the Fermi-Large Area Telescope is (3.90 ± 1.52) × 10−6 ph cm &minus; 2 s &minus; 1 ?> , which is the highest γ-ray flux ever detected from this object. The associated spectral shape is soft (Γ0.1–300 GeV = 2.57 ± 0.17) and this corresponds to an isotropic γ-ray luminosity of (1.2 ± 0.6) × 1048 erg s−1. We generate the broadband spectral energy distribution (SED) during the GeV flare and reproduce it using a one-zone leptonic emission model. The optical-UV spectrum can be explained by a combination of synchrotron and accretion disk emission, whereas the X-ray-to-γ-ray SED can be satisfactorily reproduced by inverse-Compton scattering of thermal photons that originated from the torus. The derived SED parameters hint that the increase in the bulk Lorentz factor is a major cause of the flare and the location of the emission region is estimated as being outside the broad-line region but still inside the torus. A comparison of the GeV-flaring SED of PKS 1502+036 with that of two other γ-NLSy1 galaxies, namely, 1H 0323+342 (z = 0.061) and PMN J0948+0022 (z = 0.585), and also with flat spectrum radio quasar (FSRQ) 3C 279 (z = 0.536), has led to the conclusion that the GeV-flaring SEDs of γ-NLSy1 galaxies resemble FSRQs and a major fraction of their bolometric luminosities are emitted at γ-ray energies.

Optical-NIR spectroscopy of the puzzlingγ-ray source 3FGL 1603.9-4903/PMN J1603-4904 with X-Shooter

The Fermi/LAT instrument has detected about two thousands Extragalactic High Energy (E > 100 MeV) gamma-ray sources. One of the brightest is 3FGL 1603.9-4903, associated to the radio source PMN J1603-4904. Its nature is not yet clear, it could be either a very peculiar BL Lac or a CSO (Compact Symmetric Object) radio source, considered as the early stage of a radio galaxy. The latter, if confirmed, would be the first detection in gamma-rays for this class of objects. Recently a redshift z=0.18 +/- 0.01 has been claimed on the basis of the detection of a single X-ray line at 5.44 +/- 0.05 keV interpreted as a 6.4 keV (rest frame) fluorescent line. We aim to investigate the nature of 3FGL 1603.9-4903/PMN J1603-4904 using optical to NIR spectroscopy. We observed PMN J1603-4904 with the UV-NIR VLT/X-shooter spectrograph for two hours. We extracted spectra in the VIS and NIR range that we calibrated in flux and corrected for telluric absorption and we systematically searched for absorption and emission features. The source was detected starting from ~6300 Ang down to 24000 Ang with an intensity comparable to the one of its 2MASS counterpart and a mostly featureless spectrum. The continuum lacks absorption features and thus is non-stellar in origin and likely non-thermal. On top of this spectrum we detected three emission lines that we interpret as the Halpha-[NII] complex, the [SII] 6716,6731 doublet and the [SIII] 9530 line, obtaining a redshift estimate of z= 0.2321 +/- 0.0004. The equivalent width of the Halpha-[NII] complex implies that PMN J1603-4904 does not follow the observational definition of BL Lac, the line ratios suggest that a LINER/Seyfert nucleus is powering the emission. This new redshift measurement implies that the X-ray line previously detected should be interpreted as a 6.7 keV line which is very peculiar.

Redshifted Fe Kαline from the unusualγ-ray source PMN J1603–4904

Multiwavelength observations have revealed the highly unusual properties of the gamma-ray source PMN J1603-4904, which are difficult to reconcile with any other well established gamma-ray source class. The object is either a very atypical blazar or compact jet source seen at a larger angle to the line of sight. In order to determine the physical origin of the high-energy emission processes in PMN J1603-4904, we study the X-ray spectrum in detail. We performed quasi-simultaneous X-ray observations with XMM-Newton and Suzaku in 2013 September, resulting in the first high signal-to-noise X-ray spectrum of this source. The 2-10 keV X-ray spectrum can be well described by an absorbed power law with an emission line at 5.44$\pm$0.05 keV (observed frame). Interpreting this feature as a K{\alpha} line from neutral iron, we determine the redshift of PMN J1603-4904 to be z=0.18$\pm$0.01, corresponding to a luminosity distance of 872$\pm$54 Mpc. The detection of a redshifted X-ray emission line further challenges the original BL Lac classification of PMN J1603-4904. This result suggests that the source is observed at a larger angle to the line of sight than expected for blazars, and thus the source would add to the elusive class of gamma-ray loud misaligned-jet objects, possibly a {\gamma}-ray bright young radio galaxy.