Aborted jets and the X–ray emission of radio–quiet AGNs

¹ Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italy
² Dipartimento di Scienze di Como, Università dell'Insubria, via Valleggio 11, Como, 22100 Italy
³ Dipartimento di Fisica, Università degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy

Corresponding author: G. Ghisellini; gabriele@merate.mi.astro.it

Received: 13 January 2003
Accepted: 30 September 2003

Abstract

We propose that radio–quiet quasars and Seyfert galaxies have central black holes powering outflows and jets which propagate only for a short distance, because the velocity of the ejected material is smaller than the escape velocity. We call them “aborted" jets. If the central engine works intermittently, blobs of material may be produced, which can reach a maximum radial distance and then fall back, colliding with the blobs produced later and still moving outwards. These collisions dissipate the bulk kinetic energy of the blobs by heating the plasma, and can be responsible (entirely or at least in part) for the generation of the high energy emission in radio–quiet objects. This is alternative to the more conventional scenario in which the X–ray spectrum of radio–quiet sources originates in a hot (and possibly patchy) corona above the accretion disk. In the latter case the ultimate source of energy of the emission of both the disk and the corona is accretion. Here we instead propose that the high energy emission is powered also by the extraction of the rotational energy of the black hole (and possibly of the disk). By means of Montecarlo simulations we calculate the time dependent spectra and light curves, and discuss their relevance to the X–ray spectra in radio–quiet AGNs and galactic black hole sources. In particular, we show that time variability and spectra are similar to those observed in Narrow Line Seyfert 1 galaxies.