X-ray perspective of Narrow-line Seyfert 1 galaxies

Abstract

It is arguably in the X-ray regime that Narrow-line Seyfert 1 galaxies (NLS1s) exhibit the most extreme behaviour. Spectral complexity, rapid and large amplitude flux variations, and exceptional spectral variability are well known characteristics. However, NLS1s are not eccentric, but form a continuous sequence with typical Seyfert 1 galaxies. Understanding the extreme behaviour displayed by NLS1s will provide insight to the general AGN phenomenon. In this review, I will examine some of the important NLS1 X-ray discoveries over the past twenty years. I will then explore recent work that looks at the nature of the primary X-ray source (i.e. the corona) in NLS1s, demonstrating how the corona can be compact, dynamic, and in some cases consistent with collimated outflow. X-ray observations of NLS1s will be key in determining the nature of the corona, resolving the disc-jet connection, and determining the origin of the radio loud/quiet dichotomy in AGN.

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

“…A conference on NLS1s was held in Padova in 2018, the third specific on NLS1s, after the first one held in 1999 (Joint MPE-AIP-ESO workshop on Observational and Theoretical Progress in the Study of Narrow-Line Seyfert 1 Galaxies, 8-11 December 1999, Bad Honnef, Germany, [132]), and the second one held in 2011 (Narrow-Line Seyfert 1 Galaxies and their place in the Universe, 4-6 April 2011, Milano, Italy, [133]). In the proceedings of the 2018 Padova conference [134], there are many invited reviews worth mentioning: Komossa on the multiwavelength properties [135], Lister on the radio characteristics [136], Gallo about the X-ray emission [137], and Czerny to put NLS1s in the wide context of the quasar main sequence [138].…”

A small satellite version of a soft x-ray polarimeter

“…Some AGN, such as the subclass known as narrow line Seyfert 1s (NLS1s), 30 have an X-ray spectral component below 1 keV -a soft X-ray excess over a power law component that dominates the spectrum above 2 keV. 31 The flatter power law that dominates the 2-10 keV band is most often modeled as reflection of X-rays from a hot corona off of an accretion disk, 32,33 and its polarization properties are observable by IXPE .…”

“…Several NLS1s show evidence of collimated outflows contributing to the X-ray emission. 30,43 A detection of >10% polarization would favor a jet model of the soft excess, linking these sources to blazars and rule out thermal and coronal models. RE J1034+396 is an interesting case with a 3550 s quasi-periodic oscillation.…”

A dynamic black hole corona in an active galaxy through X-ray reverberation mapping

“…At high accretion rates, the disc could have some geometric thickness, changing the path length from corona to the disc, the effects of which are not expected to affect the current results 27 . Once these models are fully developed, X-ray reverberation will be a powerful method for determining the fine details of the accretion process.Understanding how the disc-corona system couples together, how the corona is powered and their relation to jets, are longstanding problems in accretion physics 12,28 . Changes in coronal height coupled with long-term source flux have been observed using time-averaged spectra in similar AGN 29 .…”

“…Observations of AGN tell us there must be a hot 'corona' of electrons close to the black hole, which constitutes a significant fraction of their total luminosity 11,12 . The origin and geometry of this corona is unknown, but it irradiates the inflowing matter, with gravitational light bending focusing most of the radiation on the inner edge of the accretion disc, before being reprocessed and directed toward the observer (see Figure 1).…”