57 research outputs found
A comparative study of multiwavelength blazar variability on decades to minutes timescales
Multiwavelength blazar variability is produced by noise-like processes with the power-law form of power spectral density (PSD). We present the results of our detailed investigation of multiwavelength ( γ -ray and optical) light curves covering decades to minutes timescales, of two BL Lac objects namely, PKS 0735+178 and OJ 287. The PSDs are derived using discrete Fourier transform (DFT) method. Our systematic approach reveals that OJ 287 is, on average, more variable than PKS 0735+178 at both optical and γ -ray energies on the corresponding time scales. On timescales shorter than ∼10 days, due to continuous and dense monitoring by the Kepler satellite, a steepening of power spectrum is observed for OJ 287. This indicates the necessity of an intermittent process generating variability on intra-night timescales for OJ 287
PKS 2155-304 : a case study of blazar variability power spectrum at the highest energies and on the longest timescales
We present the results of our Power Spectral Density (PSD) analysis for the BL Lac object PKS 2155-304, utilizing the nightly-binned long-term light curve from the decade-long monitoring, as well as the minute-binned intra-night light curve from the High Energy Stereoscopic Survey (H.E.S.S.; >200 GeV). The source is unique for exhibiting the shortest flux-doubling timescale at Very High Energy (VHE) among its class and thus provides a rare opportunity to study the particle acceleration on the smallest spatial scales in blazar jets. The light curves are modeled in terms of the Continuous-Time Auto-Regressive Moving Average (CARMA) process. The combined long-term and intra-night PSD extends up to ∼6 decades in the temporal frequency range; unprecedented at the TeV energies for a blazar source. Our systematic approach reveals that PKS 2155-304 shows, on average, a complex shape of variability power spectrum, with more variability power on longer timescales. The long-term variability is best modeled by the CARMA(2,1) process, while the intra-night variability is modeled by a CARMA(1,0) process. We note that the CARMA(1,0) process refers to an Ornstein–Uhlenbeck process where the power-law PSD slope (PSD varies as a function of variability frequency to the power of the negative slope) changes from two to zero, above a certain “characteristic/relaxation” timescale. Even though the derived power spectrum of the intra-night light curve did not reveal a flattening, we speculate such relaxation must occur on timescales longer than a few hours for the source
Blazar variability power spectra from radio up to TeV photon energies: Mrk 421 and PKS 2155-304
We present the results of the power spectral density (PSD) analysis for the
blazars Mrk\,421 and PKS\,2155304, using good-quality, densely sampled light
curves at multiple frequencies, covering 17 decades of the electromagnetic
spectrum, and variability timescales from weeks up to a decade. The data were
collected from publicly available archives of observatories at radio from OVRO,
optical and infrared (B, V, R, I, J, H, and K-bands), X-rays from the {\it
Swift} and the {\it Rossi} X-ray Timing Explorer, high and very high energy
rays from the {\it Fermi} and Very Energetic Radiation Imaging
Telescope Array System as well as the High Energy Stereoscopic System. Our
results are: (1) the power-law form of the variability power spectra at radio,
infra-red and optical frequencies have slopes 1.8, indicative of
random-walk type noise processes; (2) the power-law form of the variability
power spectra at higher frequencies, from X-rays to very high energy
\,-rays, however, have slopes 1.2, suggesting a flicker noise
type process; (3) there is significantly more variability power at X-rays, high
and very high energy -rays on timescales 100 days, as
compared to lower energies. Our results do not easily fit into a simple model,
in which a single compact emission zone is dominating the radiative output of
the blazars across all the timescales probed in our analysis. Instead, we argue
that the frequency-dependent shape of the variability power spectra points out
a more complex picture, with highly inhomogeneous outflow producing non-thermal
emission over an extended, stratified volume.Comment: MNRAS accepte
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
Catalogue with visual morphological classification of 32,616 radio galaxies with optical hosts
We present the catalogue of Radio sources associated with Optical Galaxies
and having Unresolved or Extended morphologies I (ROGUE I). It was generated by
cross-matching galaxies from the Sloan Digital Sky Survey Data Release 7 (SDSS
DR 7) as well as radio sources from the First Images of Radio Sky at Twenty
Centimetre (FIRST) and the National Radio Astronomical Observatory VLA Sky
Survey (NVSS) catalogues. We created the largest handmade catalogue of visually
classified radio objects and associated with them optical host galaxies,
containing 32,616 galaxies with a FIRST core within 3 arcsec of the optical
position. All listed objects possess the good quality SDSS DR 7 spectra with
the signal-to-noise ratio 10 and spectroscopic redshifts up to . The
radio morphology classification was performed by a visual examination of the
FIRST and the NVSS contour maps overlaid on a DSS image, while an optical
morphology classification was based on the 120 arcsec snapshot images from SDSS
DR 7.
The majority of radio galaxies in ROGUE I, i.e. 93%, are unresolved
(compact or elongated), while the rest of them exhibit extended morphologies,
such as Fanaroff-Riley (FR) type I, II, and hybrid, wide-angle tail,
narrow-angle tail, head-tail sources, and sources with intermittent or
reoriented jet activity, i.e. double-double, X-shaped, and Z-shaped. Most of FR
IIs have low radio luminosities, comparable to the luminosities of FR Is.
Moreover, due to visual check of all radio maps and optical images, we were
able to discover or reclassify a number of radio objects as giant,
double-double, X-shaped, and Z-shaped radio galaxies. The presented sample can
serve as a database for training automatic methods of identification and
classification of optical and radio galaxies.Comment: Proceedings paper under the IAU symposium "Nuclear Activity in
Galaxies Across Cosmic Time", eds. M. Povic, P. Marziani, J. Masegosa, H.
Netzer, S. H. Negu, and S. B. Tessem
On the photometric error calibration for the `differential light curves' of point-like Active Galactic Nuclei
It is important to quantify the underestimation of rms photometric errors
returned by the commonly used \emph APPHOT algorithm in the \emph IRAF
software, in the context of differential photometry of point-like AGN, because
of the crucial role it plays in evaluating their variability properties.
Published values of the underestimation factor, , using several different
telescopes, lie in the range 1.3 - 1.75. The present study aims to revisit this
question by employing an exceptionally large data set of 262 differential light
curves (DLCs) derived from 262 pairs of non-varying stars monitored under our
ARIES AGN monitoring program for characterizing the intra-night optical
variability (INOV) of prominent AGN classes. The bulk of these data were taken
with the 1-m Sampurnanad Telescope (ST). We find = 1.540.05 which
is close to our recently reported value of = 1.5. Moreover, this
consistency holds at least up to a brightness mismatch of 1.5 mag between the
paired stars. From this we infer that a magnitude difference of at least up to
1.5 mag between a point-like AGN and comparison star(s) monitored
simultaneously is within the same CCD chip acceptable, as it should not lead to
spurious claims of INOV.Comment: 20 pages, 3 figures and 1 table; accepted for publication in JAp
A review on characteristics and analytical methods of atovaquone – a potent antimalarial agent
Drugs used in the treatment of malaria that is caused by various plasmosium species i.e. P. falciparum, P. vivax are most irresistible disease throughout the world. The different medications are utilized in the treatment of malaria incorporated the Aryl aminoalcohol mixes: Quinine, Quinidine, Chloroquine, Mefloquine; Antifolate compound: Pyrimethamine, Proguanil, Chlorproguanil, Trimethoprim and Atovaquone. Atovaquone is most effective drug utilized in the treatment of malaria. It must be given in single or in mixture with different antimalarials. An enormous number of methodologies including High Performance Liquid chromatography (HPLC), UV–Visible spectroscopy and Liquid Chromatography-Mass Spectroscopy (LC-MS) are utilized for the determination of atovaquone. Various analytical methods are used for the analysis of pharmaceutical products and these methods were validated according to ICH guidelines (Q1A R2). Thus, this technique can be safely used for the standard quality control analysis of atovaquone
Ectopic pregnancy: a five year retrospective study in a tertiary care hospital
Background: A ruptured ectopic pregnancy is a true emergency and remains the leading cause of pregnancy related first trimester deaths. The objective was to study the clinical profile of ectopic pregnancy in a tertiary care hospital.Methods: It was a retrospective study conducted at Christian Medical College & Hospital, Ludhiana from 1st June 2009 to 31st May 2014. A total of 108 patients with ectopic pregnancy were analysed on clinical presentation, clinical findings, investigations, operative findings and outcome.Results: A majority of women (44.44%) were in the age group of 26-30 years and 50% were multigravida. Risk factors were identifiable in 71.29% patients. Amenorrhea (91.6%) and pain abdomen (92.82%) were the most common presenting symptoms. Twenty (18.51%) women had laparoscopy, 72 (66.67%) underwent an exploratory laparotomy and sixteen (14.81%) women received medical management. There were no maternal deaths and post-operative morbidity in the form of febrile illness (11.11%), and wound sepsis (4.62%) was seen.Conclusions: Ectopic pregnancy still remains one of the major causes of maternal morbidity and mortality. Early diagnosis and referral in hemodynamically stable state along with use of minimal access surgery or medical management can change the scenario of ectopic pregnancy in the developing world.
Multi-wavelength variability study of the classical BL Lac object PKS 0735+178 on timescales ranging from decades to minutes
We present the results of our power spectral analysis for the BL Lac object
PKS 0735+178 utilizing the Fermi-LAT survey at high-energy -rays,
several ground-based optical telescopes, and single-dish radio telescopes
operating at GHz frequencies. The novelty of our approach is that, by combining
long-term and densely sampled intra-night light curves in the optical regime,
we were able to construct for the first time the optical power spectrum of the
blazar for a time domain extending from 23 years down to minutes. Our analysis
reveals that: (i) the optical variability is consistent with a pure red noise,
for which the power spectral density can well be approximated by a single
power-law throughout the entire time domain probed; (ii) the slope of power
spectral density at high-energy -rays (), is significantly
flatter than that found at radio and optical frequencies () within the
corresponding time variability range; (iii) for the derived power spectra we
did not detect any low-frequency flattening, nor do we see any evidence for
cut-offs at the highest frequencies down to the noise floor levels due to
measurement uncertainties. We interpret our findings in terms of a model where
the blazar variability is generated by the underlying single stochastic process
(at radio and optical frequencies), or a linear superposition of such processes
(in the -ray regime). Along with the detailed PSD analysis, we also
present the results of our extended (1998-2015) intra-night optical monitoring
program and newly acquired optical photo-polarimetric data for the source.Comment: The Astrophysical Journal, in pres
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