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Register a new userOn the multiwavelength properties of several {gamma}-ray detected narrow-line Seyfert 1 galaxies
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The {gamma}-ray detection from several radio-loud (RL) narrow-line Seyfert 1 (NLS1) galaxies has enabled us to study powerful relativistic jets in active galactic nuclei (AGNs) with smaller black hole masses and higher accretion rates than classical blazars. However, the sample of those {gamma}-ray detected NLS1s available is still not large enough for a comprehensive and statistical study. We provide a summary of our detections and follow-up studies of three {gamma}-ray-emitting NLS1s: SDSS J211852.96-073227.5 with flaring {gamma}-ray radiation (Yang et al. 2018, Paliya et al. 2018) and SDSS J122222.55+041315.7 with the highest redshift by far (z~1) (Yao et al. 2015a), along with the prototype 1H 0323+342 (Zhou et al. 2007, Yao et al. 2015b). And we will discuss their multiwavelength properties and variability properties, including implications from high-energy observations in {gamma}-rays and X-rays, infrared and radio properties, and correlated variability between several wavebands.
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Vaidehi S. Paliya (Deutsches Elektronen Synchrotron DESY
, n Platanenallee 6
, D-15738 Zeuthen
2019
This article reviews our current understanding about $gamma$-ray detected narrow-line Seyfert 1 ($gamma$-NLSy1) galaxies. The detection with the Large Area Telescope onboard {it Fermi}~Gamma-ray Space Telescope has provided the strongest evidence for the presence of closely aligned relativistic jet in these intriguing active galactic nuclei (AGN) and opened up a realm to explore the physical conditions needed to launch the jet in a different central engine and host galaxy environment than that is known for blazars. Promising results acquired from various multi-wavelength campaigns are converging to a scenario in which the $gamma$-NLSy1 galaxies can be considered as `young blazars. These enigmatic sources hold the key to unravel the jet triggering mechanism and evolution of the AGN phase of a galaxy, in general. As such, $gamma$-NLSy1s should be considered as one of the top priority targets for next generation observational facilities.
The detection of gamma rays from a small number of Narrow Line Seyfert 1 galaxies by the LAT instrument onboard Fermi seriously challenged our understanding of AGN physics. Among the most important findings associated with their discovery has been the realisation that smaller-mass black holes seem to be hosted by these systems. Immediately after their discovery a radio multi- frequency monitoring campaign was initiated to understand their jet radio emission. Here the first results of the campaign are presented. The light curves and some first variability analyses are discussed, showing that the brightness temperatures and Doppler factors are moderate. The phenomenologies are typically blazar-like. The frequency domain on the other hand indicates intense spectral evolution and the variability patterns indicate mechanisms similar to those acting in the jets of BL Lacs and FSRQs. Finally, the linear polarisation also reveals the presence of a quiescent, optically thin jet in certain cases.
Radio and $gamma$-ray loud narrow-line Seyfert 1 galaxies (NLS1s) are unique objects to study the formation and evolution of relativistic jets, as they are believed to have high accretion rates and powered by low mass black holes contrary to that known for blazars. However, only about a dozen $gamma$-ray detected NLS1s ($gamma$-NLS1s) are known to date and all of them are at $zle1$. Here, we report the identification of a new $gamma$-ray emitting NLS1 TXS 1206+549 at $z=1.344$. A near-infrared spectrum taken with the Subaru telescope showed H$beta$ emission line with FWHM of $1194pm77$ km s$^{-1}$ and weak [O III] emission line but no optical Fe II lines, due to the limited wavelength coverage and poor signal-to-noise ratio. However, UV Fe II lines are present in the SDSS optical spectrum. The source is very radio-loud, unresolved, and has a flat radio spectrum. The broadband SED of the source has the typical two hump structure shown by blazars and other $gamma$-NLS1s. The source exhibits strong variability at all wavelengths such as the optical, infrared, and $gamma$-ray bands. All these observed characteristics show that TXS 1206+549 is the most distant $gamma$-NLS1 known to date.
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 $gamma$-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 $gamma$-ray NLSy1s was conducted in 36 monitoring sessions, each lasting $geq$ 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 $gamma$-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 AGNs 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 $gamma$-ray NLSy1s, in comparison to blazars.
A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be gamma-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multi-frequency analysis of FBQS J1644+2619, one of the most recently discovered gamma-ray emitting NLSy1s. We analyse an ~80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multi-wavelength observations covering the radio - gamma-ray range. The spectral energy distribution of the source is similar to the other gamma-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterised by a hard photon index (Gamma = 1.66) above 2 keV and a soft excess at lower energies.The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonisation in a warm, optically thick corona. We discuss our results in the context of the other gamma-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.
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