Properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

Abstract

We have conducted a multiwavelength survey of 42 radio loud narrow-1ine Seyfert 1 galaxies (RLNLS1s), selected by searching among all the known sources of this type and omitting those with steep radio spectra. We analyse data from radio frequencies to X-rays, and supplement these with information available from online catalogues and the literature in order to cover the full electromagnetic spectrum. This is the largest known multiwavelength survey for this type of source. We detected 90% of the sources in X-rays and found 17% at γ rays. Extreme variability at high energies was also found, down to timescales as short as hours. In some sources, dramatic spectral and flux changes suggest interplay between a relativistic jet and the accretion disk. The estimated masses of the central black holes are in the range ∼ 10 6−8 M ⊙ , lower than those of blazars, while the accretion luminosities span a range from ∼ 0.01 to ∼ 0.49 times the Eddington limit, with an outlier at 0.003, similar to those of quasars. The distribution of the calculated jet power spans a range from ∼ 10 42.6 to ∼ 10 45.6 erg s −1 , generally lower than quasars and BL Lac objects, but partially overlapping with the latter. Once normalised by the mass of the central black holes, the jet power of the three types of active galactic nuclei are consistent with each other, indicating that the jets are similar and the observational differences are due to scaling factors. Despite the observational differences, the central engine of RLNLS1s is apparently quite similar to that of blazars. The historical difficulties in finding radio-loud narrow-line Seyfert 1 galaxies might be due to their low power and to intermittent jet activity.

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

“…Both paradigms are also discussed for γ-NLS1(e.g., Abdo et al 2009c;Foschini et al 2015;Berton et al 2015), and it has been proposed that CSS and RL-NLS1 are linked (e.g., Komossa et al 2006;Doi et al 2012;Caccianiga et al 2014;Komossa et al 2015;Gu et al 2015). Recently, Caccianiga et al (2015) have found evidence of significant star formation activity in a sample of RL-NLS1s, favouring the scenario that RL-NLS1s are young AGNs.…”

“…Among the small sample of γ-NLS1s (see Foschini et al 2015;D'Ammando et al 2015;Yao et al 2015), the sources besides PKS 2004−447, which were studied best so far in the radio regime and which yielded a significant 5 γ-ray detection by Fermi/LAT, are listed in Table 4. PKS 2004−447 is the only γ-NLS1 detected that is located in the southern hemisphere, and it is the radio loudest of them.…”

“…Then, Yuan et al (2008) compiled a genuine sample of 23 RL-NLS1s with RL 1.4 GHz > 100, with black hole masses of 10 6 -10 8 M and Eddingtion ratios R Edd ≈ 1. Based on these and other studies, Foschini et al (2015) and Berton et al (2015) have a combined sample of 60 sources with RL 5 GHz > 10. Only a few RL-NLS1s have been detected by Fermi/LAT (γ-NLS1, Abdo et al 2009b;Foschini et al 2015;D'Ammando et al 2015;Yao et al 2015, see Sect.…”

“…Based on these and other studies, Foschini et al (2015) and Berton et al (2015) have a combined sample of 60 sources with RL 5 GHz > 10. Only a few RL-NLS1s have been detected by Fermi/LAT (γ-NLS1, Abdo et al 2009b;Foschini et al 2015;D'Ammando et al 2015;Yao et al 2015, see Sect. 4.3) with most of them listed in the Third Fermi/LAT Catalog of AGNs with b < −10 • and b > 10 • (3LAC, Ackermann et al 2015).…”

“…As a result, its NLS1 classification has been under discussion (e.g., Zhou et al 2006;Yuan et al 2008). Despite its steep spectral index, it was included in the sample of flat spectrum RL-NLS1 studied by Foschini et al (2015). This is the second in a series of papers presenting results from broadband observations of PKS 2004−447.…”