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

Abstract

Before the launch of the Fermi Gamma-ray Space Telescope satellite only two classes of active galactic nuclei (AGN) were known to generate relativistic jets and thus to emit up to the γ-ray energy range: blazars and radio galaxies, both hosted in giant elliptical galaxies. The discovery by the Large Area Telescope (LAT) on-board the Fermi satellite of variable γ-ray emission from a few radio-loud narrow-line Seyfert 1 galaxies (NLSy1) revealed the presence of an emerging third class of AGN with powerful relativistic jets. Considering that NLSy1 are usually hosted in late-type galaxies with relatively small black hole masses, this finding opened new challenging questions about the nature of these objects, the disc/jet connection, the emission mechanisms at high energies, and the formation of relativistic jets. In this review, I will discuss the broad-band properties of the γ-ray-emitting NLSy1 included in the Fourth Fermi LAT source catalog, highlighting major findings and open questions regarding jet physics, black hole mass estimation, host galaxy and accretion process of these sources in the Fermi era.

Jetted Narrow-Line Seyfert 1 Galaxies & Co.: Where Do We Stand?

“…due either to the radiation pressure [14] or a flat BLR [15], by fitting an accretion disk model [16], and by using the black hole-bulge luminosity relationship [44]. The final result is that the masses increase by about one order of magnitude and jetted NLS1s become common FSRQs ( [89][90][91][92]). In addition to the serious flaws already analyzed in the previous sections, there is also an unphysical consequence affecting the large-mass hypothesis: the inconsistency between NLS1s, FSRQs, and the electron cooling [81].…”

“…With reference to other reviews, there are many contributions by D'Ammando et al (including also some papers where NLS1s were only a section of a broader review on relativistic jets, [89,90,[140][141][142][143][144]), Ermash and Komberg [145] (general review on physical and observational properties), Boller (on history of X-ray detections [146]), and Paliya (on gamma-ray NLS1s [91]). More general reviews including sections dedicated to NLS1s were written by Rieger (gamma rays from non-blazar AGN, [147]) and Hada (high-angular resolution radio observations, [148]).…”

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

“…Among them, three sources seem to be the most promising ones to be investigated at energies above a few tens of GeV, namely SBS 0846+513, PMN J0948+0022, and PKS 1502+036. We briefly report here their γ-ray discovery literature, while for a detailed description of their high-energy characteristics we refer to [15][16][17] and references therein. Table 1 shows the γ-ray spectral parameters for the log-parabola model as reported in the 4FGL [14].…”

Relativistic Jets from AGN Viewed at Highest Angular Resolution

“…The discovery of γ-ray emission from NLSy1s indicates the emergence of a new class of AGN that can produce powerful relativistic jets in addition to blazars and radio galaxies. To date, 9 sources have securely been confirmed as "bona fide" γ-ray emitting NLSy1s in the 4FGL catalog [24], whereas some more sources are claimed in Paliya et al [189], although these additional ones should be regarded as "candidate" γ-ray NLSy1s due to their less definitive nature (see [190]). Compared to blazars and radio galaxies, the nature of the NLSy1 jets is still poorly understood, i.e., according to the standard AGN paradigm, the combination of low M BH and highṀ makes it difficult to generate powerful jets.…”

“…For an extensive review on γ-ray emitting NLSy1s and their broadband properties. please see D'Ammando [190].…”