47 research outputs found
On Energetics and Structure of Sub-parsec Jets in Quasars
This paper reviews the topic of sub-parsec - scale jets in quasars, and
covers the the following issues: observations of parsec and sub-parsec scale
jets; energy dissipation and particle acceleration; radiative processes;
magnetic fields, pair content, and energetics; and variability and its relation
to the central engine activity. In particular, we describe how internal shocks
can explain properties of gamma-ray flares and demonstrate that MeV blazars
(those with luminosity peak in the 1-30 MeV range) can be unified with GeV
blazars (those with luminosity peak at GeV energies) assuming that in GeV
blazars the gamma-ray flares are produced via Comptonization of broad emission
lines, whereas in the MeV blazars they result from Comptonization of infrared
radiation of hot dust. We also make predictions about the radiative effects of
bulk Compton process in the soft X-ray band and show how spectral and
variability properties in that band can be used to constrain structure of jets
near their bases.Comment: To appear in the Proceedings of the 2nd KIAS Astrophysics Workshop
"Current High Energy Emission Around Black Holes," Seoul, Korea, Sep. 3 - 8,
2001 (15 pages
Are Quasar Jets Matter or Poynting Flux Dominated?
If quasar jets are accelerated by magnetic fields but terminate as matter
dominated, where and how does the transition occur between the
Poynting-dominated and matter-dominated regimes? To address this question, we
study constraints which are imposed on the jet structure by observations at
different spatial scales. We demonstrate that observational data are consistent
with a scenario where the acceleration of a jet occurs within 10^{3-4} R_g. In
this picture, the non-thermal flares -- important defining attributes of the
blazar phenomenon - are produced by strong shocks formed in the region where
the jet inertia becomes dominated by matter. Such shocks may be formed due to
collisions between the portions of a jet accelerated to different velocities,
and the acceleration differentiation is very likely to be related to global MHD
instabilities.Comment: to appear in "Astrophysical Sources of High Energy Particles and
Radiation", AIP Proceedings Series, eds. T. Bulik, G. Madejski, and B. Rudak
(20-24 June 2005, Torun, Poland
MAXI and GLAST Studies of Jets in Active Galaxies
The recent launch of Fermi / GLAST - coinciding with the MAXI workshop -
opens a new era for studies of jet-dominated active galaxies, known as blazars.
While the emission processes operating in various spectral bands in blazars are
reasonably well understood, the knowledge of the details of the structure of
the jet, location of the dissipation region with respect to the accreting black
hole, and coupling of the jet to the accretion process are known only at a
rudimentary level. Blazars are variable, and this provides an opportunity to
use the variability in various bands - and in particular, the relationship of
respective time series to each other - to explore the relative location of
regions responsible for emission in the respective bands. Observationally, this
requires well-sampled time series in as many spectral bands as possible. To
this end, with its all-sky, sensitive monitoring capability, the recently
launched GLAST, and MAXI, to be deployed in 2009, are the most promising
instruments bound to provide good sampling in respectively the energetic
gamma-ray, and the soft X-ray band. This paper highlights the inferences
regarding blazar jets that can be gleaned from such joint observations.Comment: Submitted to the proceedings of 3rd MAXI workshop "Astrophysics with
All-Sky X-ray Observations," 10-12 June 2008, RIKEN, Wako, Saitama, Japa
Constraining jet production scenarios by studies of Narrow-Line-Radio-Galaxies
We study a large sample of narrow-line radio galaxies (NLRGs) with extended
radio structures. Using 1.4 GHz radio luminosities, , narrow optical
emission line luminosities, L_{\oiii} and , as well as black
hole masses derived from stellar velocity dispersions measured from
the optical spectra obtained with the Sloan Digital Sky Survey, we find that:
(i) NLRGs cover about 4 decades of the Eddington ratio, ; (ii) strongly
correlates with ; (iii) radio-loudness, , strongly anti-correlates with . A very broad range
of the Eddington ratio indicates that the parent population of NLRGs includes
both radio-loud quasars (RLQs) and broad-line radio galaxies (BLRGs). The
correlations they obey and their high jet production efficiencies favor a jet
production model which involves the so-called 'magnetically choked' accretion
scenario. In this model, production of the jet is dominated by the
Blandford-Znajek mechanism, and the magnetic fields in the vicinity of the
central black hole are confined by the ram pressure of the accretion flow.
Since large net magnetic flux accumulated in central regions of the accretion
flow required by the model can take place only via geometrically thick
accretion, we speculate that the massive, 'cold' accretion events associated
with luminous emission-line AGN can be accompanied by an efficient jet
production only if preceded by a hot, very sub-Eddington accretion phase.Comment: 24 pages, 6 figures, published in ApJ, moderate revisions to match
the published versio