The relativistic jet of the γ-ray emitting narrow-line Seyfert 1 galaxy 1H 0323+342

Abstract

The detection of several radio-loud narrow-line Seyfert 1 (NLS1) galaxies by the Fermi Gamma-Ray Space Telescope hints at the existence of a rare, new class of γ-ray emitting active galactic nuclei with low black hole masses. Like flat spectrum radio quasars (FSRQs), their γ-ray emission is thought to be produced via the external Compton mechanism whereby relativistic jet electrons upscatter a photon field external to the jet, e.g. from the accretion disc, broad line region (BLR) and dusty torus, to higher energies. Here we study the origin of the γ-ray emission in the lowest-redshift candidate among the currently-known γ-ray emitting NLS1s, 1H 0323+342, and take a new approach. We observationally constrain the external photon field using quasisimultaneous near-IR, optical and X-ray spectroscopy. Applying a one-zone leptonic jet model, we simulate the range of jet parameters for which this photon field, when Compton scattered to higher energies, can explain the γ-ray emission. We find that the site of the γ-ray emission lies well within the BLR and that the seed photons mainly originate from the accretion disc. The jet power that we determine, 1.0 × 10 45 erg s −1 , is approximately half the accretion disc luminosity. We show that this object is not simply a low-mass FSRQ, its jet is intrinsically less powerful than predicted by scaling a typical FSRQ jet by black hole mass and accretion rate. That γ-ray emitting NLS1s appear to host underpowered jets may go some way to explaining why so few have been detected to date.

Relativistic Jets in Gamma-Ray-Emitting Narrow-Line Seyfert 1 Galaxies

“…The spectra are hard above 2 keV (Γ X < 2), which is similar to what is observed in FSRQ rather than radio-quiet NLSy1, suggesting that a significant contribution of inverse Compton (IC) radiation from a relativistic jet dominates that part of the X-ray spectrum. Differently from FSRQ, a narrow Fe line at 6.4 keV has been reported for one source, 1H 0323+342 (Figure 3, right panel), which has the softest X-ray spectrum of the γ-ray-emitting NLSy1 [97,98]. The majority of γ-ray-emitting NLSy1 for which good-quality X-ray spectra are available show an excess of emission at low energies with respect to the extrapolation of the hard X-ray spectral continuum model, making them different from typical blazars.…”

“…As an example, the left panel of Figure 3 shows this excess below 2 keV in the X-ray spectrum of PMN J0948+0022. The 0.3-10 keV energy range spectra of γ-ray-emitting NLSy1 are usually well fitted by a broken power-law with a break around 2 keV [99] 5 , being the spectrum below the break due to disc/coronal emission, a typical feature of Seyfert 5 In case of 1H 0323+342 a more complex X-ray spectrum was observed (e.g., [98]). galaxies, and the emission above the break dominated by the jet emission, a typical feature of blazars.…”

“…A model including two power-laws and two Gaussian Iron emission lines with the Galactic value in the direction of the source fixed to N H, Gal = 2.33 × 10 21 cm −2 is applied to the data. Adapted from[98].…”

Comparative intranight optical variability of X-ray and γ-ray-detected narrow-line Seyfert 1 galaxies

“…The unexpected discovery of γ-ray emissions from Narrowline Seyfert 1 (NLSy1) galaxies (Abdo et al 2009a,b,c;Foschini et al 2010;Foschini 2011;D'Ammando et al 2012D'Ammando et al , 2015Yao et al 2015;Yang et al 2018;Paliya et al 2018;Yao et al 2019) and the realisation that essentially all of them have detection (> 3σ) in the radio band too (Komossa et al 2006;Yuan et al 2008;Yao et al 2015;Kynoch et al 2018;Lähteenmäki et al 2018), suggesting a possible relationship between some NLSy1s and blazars. This hypothesis is further corroborated by the finding that the Spectral Energy Distributions (SEDs) of some NLSy1 galaxies show the canonical double-humped profile such that the lower energy hump representing the relativistic jet's synchrotron emissions peaks somewhere between the near-infrared and Xray frequencies.…”

The baryon loading effect on relativistic astrophysical jet transport in the interstellar medium

“…Among them, relativistic jets are often connected with the observed exciting high-energy astrophysical phenomena, such as gamma-ray burst [4][5][6], active galactic nucleus (AGNs) [7][8][9], tidal disruption events [10,11] and compact binary stars [12,13]. Recently, the Fermi Gamma-Ray Space Telescope has detected a typical AGN [14], in which the jet bulk Lorentz factor is about 10∼20. However, despite the growing interest in relativistic astrophysical jets, our understanding of them is still limited.…”