197 research outputs found
Further evidence for intra-night optical variability of radio-quiet quasars
Although well established for BL Lac objects and radio-loud quasars, the
occurrence of intra-night optical variability (INOV) in radio-quiet quasars is
still debated, primarily since only a handful of INOV events with good
statistical significance, albeit small amplitude, have been reported so far.
This has motivated us to continue intra-night optical monitoring of bona-fide
radio-quiet quasars (RQQs). Here we present the results for a sample of 11 RQQs
monitored by us on 19 nights. On 5 of these nights a given RQQ was monitored
simultaneously from two well separated observatories. In all, two clear cases
and two probable case of INOV were detected. From these data, we estimate an
INOV duty cycle of 8% for RQQs which would increase to 19% if the
`probable variable' cases are also included. Such comparatively small INOV duty
cycles for RQQs, together with the small INOV amplitudes (1%), are in
accord with the previously deduced characteristics of this phenomenon.Comment: 15 Pages, 4 Tables, 24 Figures; Accepted in BAS
Jet stability, dynamics and energy transport
Relativistic jets carry energy and particles from compact to very large
scales compared with their initial radius. This is possible due to their
remarkable collimation despite their intrinsic unstable nature. In this
contribution, I review the state-of-the-art of our knowledge on instabilities
growing in those jets and several stabilising mechanisms that may give an
answer to the question of the stability of jets. In particular, during the last
years we have learned that the limit imposed by the speed of light sets a
maximum amplitude to the instabilities, contrary to the case of classical jets.
On top of this stabilising mechanism, the fast growth of unstable modes with
small wavelengths prevents the total disruption and entrainment of jets. I also
review several non-linear processes that can have an effect on the collimation
of extragalactic and microquasar jets. Within those, I remark possible causes
for the decollimation and decelleration of FRI jets, as opposed to the
collimated FRII's. Finally, I give a summary of the main reasons why jets can
propagate through such long distances.Comment: For the proceedings of High Energy Phenomena in Relativistic Outflows
III (HEPRO III, IJMPD, accepted). 12 page
A COMPARATIVE CLINICAL STUDY TO EVALUATE THE EFFECT OF CHARAKOKTA MUTRAVIRECHANIYA MAHAKASHAYA IN MUTRAKRICHRA OR LOWER URINARY TRACT INFECTION
Mutrakrichra the disease of Mutravaha Srotas is caused due to Sanga (obstruction). Mutrakrichra means difficulty in micturition. Mutrakrichra can be compared to lower urinary tract infection (LUTI) symptoms. LUTI is the most common infection known to mankind and a common condition seen in general practice. Urinary tract infection affects more than 150 million people every year worldwide. Objective: To evaluate the effect of Mutravirechaniya Mahakashaya in LUTI and to compare its efficacy with Tab. Norfloxacin. Methods: 45 patients of either gender with the symptoms of LUTI were randomized into three groups of 15 patients each. Group A- received Mutravirechaniya Mahakashaya 50ml. Group B- received Tab. Norfloxacin 400mg and Group C- Mutravirechaniya Mahakashaya and Tab. Norfloxacin in the above mentioned dose for ten days. Efficacy outcomes were assessed through subjective parameters and routine urine and microscopic examination. Observation and results: When compared all the groups showed better results in relieving the clinical symptoms of LUTI. Overall patients treated with Mutravirechaniya Mahakashaya and Tab. Norfloxacin showed better results, but there was no significant difference between the groups (P<0.351). Conclusion: Mutravirechaniya Mahakashaya was able to meet the efficacy outcomes measures in comparison to Tab. Norfloxacin. Clinical effects of Mutravirechaniya Mahakashaya were similar to Tab. Norfloxacin owing to its diuretic, analgesic and anti-inflammatory properties
Was the Cosmic Web of Protogalactic Material Permeated by Lobes of Radio Galaxies During the Quasar Era?
Evidence for extended active lifetimes (> 10^8 yr) for radio galaxies implies
that many large radio lobes were produced during the `quasar era', 1.5 < z < 3,
when the comoving density of radio sources was 2 -- 3 dex higher than the
present level. However, inverse Compton losses against the intense microwave
background substantially reduce the ages and numbers of sources that are
detected in flux-limited surveys. The realization that the galaxy forming
material in those epochs was concentrated in filaments occupying a small
fraction of the total volume then leads to the conclusion that radio lobes
permeated much of the volume occupied by the protogalactic material during that
era. The sustained overpressure in these extended lobes is likely to have
played an important role in triggering the high inferred rate of galaxy
formation at z > 1.5 and in the magnetization of the cosmic network of
filaments.Comment: 5 pages, 0 figures, submitted to ApJ Letters; uses emulateapj
Understanding BL Lac objects Structural & kinematic mode changes in the BL Lac object PKS 0735+178
Context. We present evidence that parsec-scale jets in BL Lac objects may be
significantly distinct in kinematics from their counterparts in quasars. We
argued this previously for the BL lac sources 1803+784 and 0716+714, report
here a similar pattern for another well-known BL Lac object, PKS 0735+178,
whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. A
detailed study of the jet components' motion reveals that the standard AGN
paradigm of apparent superluminal motion does not always describe the
kinematics in BL Lac objects. We study 0735+178 here to augment and improve the
understanding of the peculiar motions in the jets of BL Lac objects as a class.
Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations
(2cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91.
Results. We found a drastic structural mode change in the VLBI jet of 0735+178,
between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a
linear shape.We further found that this jet had undergone a similar transition
sometime between December 1981 and June 1983. A mode change, occurring in the
reverse direction (between mid-1992 and mid-1995) has already been reported in
the literature. These structural mode changes are found to be reflected in
changed kinematical behavior of the nuclear jet, manifested as an apparent
superluminal motion and stationarity of the radio knots. In addition, we found
the individual mode changes to correlate in time with the maxima in the optical
light curve. The last two transitions occurred before a (modest) radio flare.
The behavior of this pc-scale jet appears to favor a scenario involving
non-ballistic motions of the radio knots, produced by the precession of a
continuous jet within the ambient medium.Comment: Accepted for publication in A&A (Abstract reduced for astro-ph
Extragalactic radio sources with sharply inverted spectrum at metre wavelengths
We present the first results of a systematic search for the rare
extragalactic radio sources showing an inverted (integrated) spectrum, with
spectral index , a previously unexplored spectral domain. The
search is expected to yield strong candidates for , for which
the standard synchrotron self-absorption (characterized by a single power-law
energy distribution of relativistic electron population) would not be a
plausible explanation, even in an ideal case of a perfectly homogeneous source
of incoherent synchrotron radiation. Such sharply inverted spectra, if found,
would require alternative explanations, e.g., free-free absorption, or
non-standard energy distribution of relativistic electrons which differs from a
power-law (e.g., Maxwellian).
The search was carried out by comparing two sensitive low-frequency radio
surveys made with sub-arcminute resolution, namely, the WISH survey at 352 MHz
and TGSS/DR5 at 150 MHz. The overlap region between these two surveys contains
7056 WISH sources classified as `single' and brighter than 100 mJy at 352 MHz.
We focus here on the seven of these sources for which we find .
Two of these are undetected at 150 MHz and are particularly good candidates for
. Five of the seven sources exhibit a
`Gigahertz-Peaked-Spectrum' (GPS).Comment: 8 pages, 2 figures, accepted for publication in MNRA
Intra-night optical variability of core dominated radio quasars: the role of optical polarization
Context. Rapid variations in optical flux are seen in many quasars and all blazars. The amount of variability in different classes of active galactic nuclei has been studied extensively but many questions remain unanswered. Aims. We present the results of a long-term programme to investigate the intra-night optical variability (INOV) of powerful flat spectrum radio core-dominated quasars (CDQs), with a focus on probing the relationship of INOV to the degree of optical polarization. Methods. We observed a sample of 16 bright CDQs showing strong broad optical emission lines and consisting of both high and low optical polarization quasars (HPCDQs and LPCDQs). In this first systematic study of its kind, we employed the 104-cm Sampurnanand telescope, the 201-cm Himalayan Chandra telescope and the 200-cm IUCAA-Girawali Observatory telescope, to carry out R-band monitoring on a total of 47 nights. Using the CCD as an N-star photometer to densely monitor each quasar for a minimum duration of about 4 h per night, INOV exceeding ~1–2 per cent could be reliably detected. Combining these INOV data with those taken from the literature, after ensuring conformity with the basic selection criteria we adopted for the 16 CDQs monitored by us, we were able to increase the sample size to 21 CDQs (12 LPCDQs and 9 HPCDQs) monitored on a total of 73 nights. Results. As the existence of a prominent flat-spectrum radio core signifies that strong relativistic beaming is present in all these CDQs, the definitions of the two sets differ primarily in fractional optical polarization, with the LPCDQs showing a very low median Pop ≃ 0.4 per cent. Our study yields an INOV duty cycle (DC) of ~28 per cent for the LPCDQs and ~68 percent for HPCDQs. If only strong INOV with fractional amplitude above 3 per cent is considered, the corresponding DCs are ~7 per cent and ~40 per cent, respectively. Conclusions. From this strong contrast between the two classes of luminous, relativistically beamed quasars, it is apparent that relativistic beaming is normally not a sufficient condition for strong INOV and a high optical polarization is the other necessary condition. Moreover, the correlation is found to persist for many years after the polarization measurements were made. Some possible implications of this result are pointed out, particularly in the context of the recently detected rapid γ-ray variability of blazars
On Pair Content and Variability of Sub-Parsec Jets in Quasars
X-ray observations of blazars associated with the OVV (Optically Violently
Variable) quasars put strong constraints on the electron - positron pair
content of radio-loud quasar jets. From those observations, we infer that jets
in quasars contain many more electron - positron pairs than protons, but
dynamically are still dominated by protons. In particular, we show that pure
electron - positron jet models can be excluded, as they overpredict soft X-ray
radiation; likewise, pure proton - electron jets can be excluded, as they
predict too weak nonthermal X-ray radiation. An intermediate case is viable. We
demonstrate that jets which are initially proton-electron ("proto-jets") can be
pair-loaded via interaction with 100 - 300 keV photons produced in hot
accretion disc coronae, likely to exist in active galactic nuclei in general.
If the coronal radiation is powered by magnetic flares, the pair loading is
expected to be non-uniform and non-axisymmetric. Together with radiation drag,
this leads to velocity and density perturbations in a jet and formation of
shocks, where the pairs are accelerated. Such a scenario can explain rapid
(time scale of about a day) variability observed in OVV quasars.Comment: Accepted for publication in the Astrophysical Journa
Unification of Radio Galaxies and Their Accretion/Jet Properties
We investigate the relation between black hole mass, M_bh, and jet power,
Q_jet, for a sample of BL Lacs and radio quasars. We find that BL Lacs are
separated from radio quasars by the FR I/II dividing line in M_bh-Q_jet plane,
which strongly supports the unification scheme of FR I/BL Lac and FR II/radio
quasar. The Eddington ratio distribution of BL Lacs and radio quasars exhibits
a bimodal nature with a rough division at L_bol/L_Edd~0.01, which imply that
they may have different accretion modes. We calculate the jet power extracted
from advection dominated accretion flow (ADAF), and find that it require
dimensionless angular momentum of black hole j~0.9-0.99 to reproduce the
dividing line between FR I/II or BL Lac/radio quasar if dimensionless accretion
rate mdot=0.01 is adopted, which is required by above bimodal distribution of
Eddington ratios. Our results suggest that black holes in radio galaxies are
rapidly spinning.Comment: To appear JAA in Jun
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