515 research outputs found
Clear Evidence for Intranight Optical Variability in Radio-quiet Quasars
We present new clues to the problem of the radio loudness dichotomy arising
from an extensive search for intranight optical variability in seven sets of
optically luminous radio-quiet quasars and (radio-loud) BL Lacertae objects,
which are matched in optical luminosity and redshift. Our monitoring of
radio-quiet quasars has for the first time clearly detected such intranight
variability, with peak-to-peak amplitudes ~1%, occurring with a duty cycle of ~
1/6. The matched BL Lacs have both higher variability amplitudes and duty
cycles when observed in the same fashion. We show that the much less pronounced
intranight variability of the radio-quiet quasars relative to BL Lacs can be
understood in terms of a modest misalignment of the jets in radio-quiet quasars
from the line-of-sight. We thus infer that relativistic particle jets may well
also emerge from radio-quiet quasars, but while traversing the short
optical-emitting distances, they could be snuffed out, possibly through inverse
Compton losses in the nuclear region.Comment: 13 pages, 3 figures, in press in ApJ Letters (20 March 2003
WISE view of Narrow-Line Seyfert 1 galaxies: mid-infrared color and variability
We present the color and flux variability analysis at 3.4 {\mu}m (W1-band)
and 4.6 {\mu}m (W 2-band) of 492 narrow-line Seyfert 1 (NLSy1) galaxies using
archival data from the Wide-field Infrared Survey Explorer (WISE). In the WISE
color-color, (W1 - W2) versus (W2 - W3) diagram, ~58% of the NLSy1 galaxies of
our sample lie in the region occupied by the blazar category of active galactic
nuclei (AGN). The mean W1 - W2 color of candidate variable NLSy1 galaxies is
mag. The average amplitude of variability is
mag in long-term (multi-year) with no difference in variability between W1 and
W2-bands. The W1 - W2 color of NLSy1 galaxies is anti-correlated with the
relative strength of [O III] to H{\beta}, strongly correlated with continuum
luminosity, black hole mass, and Eddington ratio. The long-term amplitude of
variability shows weak anti-correlation with the Fe II strength, continuum
luminosity and Eddington ratio. A positive correlation between color as well as
the amplitude of variability with the radio power at 1.4 GHz was found for the
radio-detected NLSy1 galaxies. This suggests non-thermal synchrotron
contribution to the mid-infrared color and flux variability in radio-detected
NLSy1 galaxies.Comment: 10 pages; Accepted for publication in MNRA
Improved characterisation of intra-night optical variability of prominent AGN classes
The incidence of intra-night optical variability (INOV) is known to to differ
significantly among different classes of powerful active galactic nuclei (AGN).
A number of statistical methods have been employed in the literature for
testing the presence of INOV in the light curves, sometimes leading to
discordant results. In this paper we compare the INOV characteristics of six
prominent classes of AGN, as evaluated using three commonly used statistical
tests, namely the test, the modified test and the test, which
has recently begun to gain popularity. The AGN classes considered are:
radio-quiet quasars (RQQs), radio-intermediate quasars (RIQs), lobe-dominated
quasars (LDQs), low optical polarization core-dominated quasars (LPCDQs), high
optical polarization core-dominated quasars (HPCDQs), and TeV blazars. Our
analysis is based on a large body of AGN monitoring data, involving 262
sessions of intra-night monitoring of a total 77 AGN, using 1-2 metre class
optical telescopes located in India. In order to compare the usefulness of the
statistical tests, we have also subjected them to a `sanity check' by comparing
the number of false positives yielded by each test with the corresponding
statistical prediction. The present analysis is intended to serve as a
benchmark for future INOV studies of AGN of different classes.Comment: 26 pages, 2 tables, Accepted for publication in MNRA
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