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

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 $\chi^2-$test, the modified $C-$test and the $F-$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

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, $\eta$, 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 $\eta$ = 1.54$\pm$0.05 which is close to our recently reported value of $\eta$ = 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

GRB000301C with peculiar afterglow emission

The CCD magnitudes in Johnson V and Cousins R and I photometric passbands are determined for GRB 000301C afterglow starting ~ 1.5 day after the gamma-ray burst. In fact we provide the earliest optical observations for this burst. Light curves of the afterglow emissions in U, B, V, R, I, J and K' passbands are obtained by combining the present measurements with the published data. Flux decay shows a very uncommon variation relative to other well observed GRBs. Overall, there is a steepening of the optical and near-infrared flux decay caused by a geometric and sideways expanding jet. This is superimposed by a short term variability especially during early time (Delta t < 8 days). The cause of variability is not well understood, though it has occurred simultaneously with similar amplitude in all the filters. We derive the early and late time flux decay constants using jet model. The late time flux decay is the steepest amongst the GRB OTs observed so far with alpha ~ 3. Steepening in the flux decay seems to have started simultaneously around Delta t ~ 7.6 day in all passbands. The value of spectral index in the optical-near IR region is ~ -1.0. Redshift determination with z=2.0335 indicates cosmological origin of the GRB having a luminosity distance of 16.6 Gpc. Thus it becomes the second farthest amongst the GRBs with known distances. An indirect estimate of the fluence > 20 keV indicates, if isotropic,> =10^53 ergs of release of energy. The enormous amount of released energy will be reduced, if the radiation is beamed which is the case for this event. Using a jet break time of 7.6 days, we infer a jet opening angle of ~ 0.15 radian. This means the energy released is reduced by a factor of ~ 90 relative to the isotropic value.Comment: LaTeX file, 11 pages including 4 figures, uses psfig.sty, Bull. Astron. Society of India(accepted, Sept, 2000 issue

Assessment of urban growth using Shannon’s Entropy Index: A case study of Chennai, Detroit of India

The Remote Sensing (R/ S) and Geographical Information System (GIS) play a vital role to evaluate and study the urban expansion pattern. In this study, the Chennai city was selected to perform the urban sprawl study. Five different periods of satellite imageries for the time elapsed between 1994 and 2016 were used. The main aim of this paper was to identify the urban sprawl of Chennai as a patterning process. The extended areas of urban in the period of 1994, 2001, 2006, 2011 and 2016 were extracted by the sub-pixel classification method from the satellite imageries. Furthermore, Shannon’s entropy index was used for assessing urban expansion. The findings of this study proved that Chennai city has sprawled by urban expansion during the period between 1994 and 2016. Likewise, the dispersion rate of urban sprawl for the periods of 1994, 2001, 2006, 2011 and 2016 were 0.671, 0.679, 0.688, 0.693 and 0.695 respectively. Consequently, this uncontrolled dispersed urban development had resulted in the study area losses their green space

Intra-night Optical Variability of BL Lacs, Radio-Quiet Quasars and Radio-Loud Quasars

We report optical monitoring observations of 20 high-luminosity AGN, 12 of which are radio-quiet quasars (RQQs). Intra-night optical variability (INOV) was detected for 13 of the 20 objects, including 5 RQQs. The variations are distinctly stronger and more frequent for blazars than for the other AGN classes. By combining these data with results obtained earlier in our program, we have formed an enlarged sample consisting of 9 BL Lacs, 19 RQQs and 11 lobe-dominated radio-loud quasars. The moderate level of rapid optical variability found for both RQQs and radio lobe-dominated quasars argues against a direct link between INOV and radio-loudness. We supplemented the present observations of 3 BL Lacs with additional data from the literature. In this extended sample of 12 well observed BL Lacs, stronger INOV is found for the EGRET detected BL Lacs.Comment: 8 pages, 3 Postscript figures, Accepted for publication in MNRAS, uses mn2e.cl

Echocardiographic Evaluation of Left Ventricular Systolic and Diastolic Dysfunction in Patients with Acute Myocardial Infarction

INTRODUCTION: Acute Myocardial Infarction is one of the leading causes of death among men and women worldwide. Most of the early deaths are due to Ventricular Arrhythmias. These Arrhythmias are responsible for the sudden deaths associated with Myocardial Infarction. The late mortality associated with Myocardial Infarction is typically due to left ventricular dysfunction and its complications. Residual Left Ventricular function after Myocardial Infarction is an important prognostic marker. Left Ventricular dysfunction can be systolic, diastolic or both. Echocardiography is the most widely used and readily available, non-invasive tool in the arsenal of cardiologist for evaluating the left ventricular function. Echocardiographic evaluation of Left Ventricular function is an integral part of evaluation of a patient with Acute Myocardial Infarction. Two Dimensional echocardiography is useful for the assessment of systolic function, and Doppler Echocardiography is well suited for studies of diastolic function. An acute Trans-mural Myocardial Infarction causes a loss of contractile fibres which reduces systolic function. Parallel to the effect on systolic function, a myocardial infarction also impacts diastolic function, as evidenced by the raise in left ventricular end diastolic pressure. This study is performed to estimate the prevalence of left ventricular systolic and diastolic dysfunction using various Echocardiographic indices in patients with Acute ST elevation Myocardial Infarction and to find out its significance in determining early in-hospital morbidity, especially early Congestive Heart Failure in such patients. AIMS AND OBJECTIVES: 1. To assess the prevalence of Left Ventricular Systolic and Diastolic dysfunction in patients with Acute Myocardial Infarction. 2. To study the association between Left Ventricular Systolic, Diastolic dysfunction and the variables such as Age, Sex, Smoking, Diabetes, Hypertension, Killip Class, Type of Myocardial Infarction. 3. To assess the relationship between the echocardiographic indices of systolic and diastolic function and the development of early in-hospital congestive heart failure (as defined by Killip Class ≥ II). MATERIALS AND METHODS: Individuals who were admitted for acute Myocardial Infarction in the Intensive Coronary Care Unit, Department of Cardiology, Govt. Stanley Hospital from April 2011 to September 2011 were evaluated in this study. Their Left Ventricular Systolic and Diastolic function was assessed by 2D Doppler Echocardiography within 48 hours of admission. Left Ventricular Ejection Fraction – the most well accepted expression of systolic Left Ventricular function is measured with the help of 2D echocardiography. Regional Wall Motion Abnormalities are also assessed and graded as: 1. Normal, 2. Hypokinesia, 3. Severe Hypokinesia –akinesia, 4. Dyskinesia, 5. Aneurysm. Inclusion Criteria: 1. Patients of both sex, aged between 30 and 60 with Acute Myocardial Infarction (STEMI) who are admitted in the Intensive Coronary Care Unit. 2. Patients undergoing thrombolysis using streptokinase. Exclusion Criteria: 1. Patients with Non ST elevation myocardial infarction. 2. Patients who have contraindications for thrombolysis. 3. Patients with previous history of myocardial infarction. 4. Patients with complete heart block. 5. Patients with atrial fibrillation. 6. Patients with other co-morbidities such as Chronic Kidney disease, Chronic Obstructive Pulmonary Disease. 7. Patients with prior history of heart failure symptoms. 8. Patients with valvular heart disease. 9. Patients with cardiomyopathies. Statistical Analysis: Data were represented as mean ± SD or percentage of the total, unless otherwise specified. Statistical analysis was done using SPSS ver. Comparison between continuous variables was done using Mann Whitney U test or ANOVA. ROC curves were plotted to determine the ideal cutoff for Echocardiographic variables for predicting heart failure. Univariate logistic regression was used to compare the clinical and echocardiographic variables with heart failure. The significant variables in univariate analysis were added to a complete model of multivariate logistic regression. P value of <0.05 was considered significant. OBSERVATIONS AND DATA ANALYSIS: All the 50 patients included in the study presented with isolated acute ST elevation Myocardial Infarction. All the patients had regional wall motion abnormalities in their Echocardiogram and underwent thrombolysis. The study group included 36 males and 14 females. The difference in sex wise distribution is obvious, as only patients between the age of 30 and 60 were included in the study and in this age group STEMI is more common in males. The age wise distribution chart shows that the incidence of STEMI increases as the age advances. It is also seen that the maximum number of female patients are in the 56-60 group, implying that the risk for MI increases during the post menopausal period. CONCLUSIONS: In this study population of 50 patients with first AMI and without previous heart failure symptoms, the incidence of early in-hospital congestive heart failure was 62% (n=31). • 48% of the patients with first AMI had diastolic dysfunction. • 50% of patients had systolic dysfunction (defined as ejection fraction of ≤ 40%). • 22% of patients had a Regional Wall Motion Scoring Index of ≥1.7. • Left ventricular ejection fraction was the most important predictor of early heart failure (p=0.004). • The cut off ≤ 40% of LVEF had a high predictive value (74% sensitivity 90% specificity) in detecting patients who are likely to develop heart failure symptoms. • Presence of Diastolic dysfunction also predicted early heart failure following AMI accurately (p=0.035). • Regional Wall Motion Index was inferior compared to LVEF and presence of DD in predicting heart failure (p=0.218). • Smokers were more likely to develop early in-hospital heart failure following AMI (p=0.045). • Diabetes was one of the important risk factors for the development of heart failure following AMI (p=0.036)

Intranight optical variability of blazars

We present results of a multi-epoch intranight optical monitoring of 11 blazars consisting of six BL Lac objects and five radio core-dominated quasars (CDQs). These densely sampled and sensitive R-band CCD observations, carried out from 1998 November to 2002 May during a total of 47 nights with an average of 6.5 h per night, have enabled us to detect variability amplitudes as low as ~1 per cent on intranight time-scales. A distinction is found for the first time between the intranight optical variability (INOV) properties of the these two classes of relativistically beamed radio-loud active galactic nuclei (AGNs). BL Lacs are found to show a duty cycle (DC) of INOV of ~60 per cent, in contrast to CDQs, which show a much smaller INOV DC of ~20 per cent, the difference being attributable mainly to the weakly polarized CDQs. On longer time-scales (i.e. between a week to a few years) variability is seen from all the CDQs and BL Lacs in our sample. The results reported here form part of our long-term programme to understand the intranight optical variability characteristics of the four main classes of luminous AGNs, i.e. radio-quiet quasars (RQQs) and radio lobe-dominated quasars (LDQs), as well as CDQs and BL Lac objects

Intranight optical variability of radio-quiet and radio lobe-dominated quasars

We present results of a programme of multi-epoch, intranight optical monitoring of a sample of non-blazar-type active galactic nuclei (AGN), which includes seven radio-quiet quasars (RQQs) and an equal number of radio-loud, lobe-dominated quasars (LDQs), covering a redshift range from about 0.2 to 2.0. These two sets of optically bright and intrinsically luminous quasi-stellar objects (QSOs) are well matched in the redshift-optical luminosity (z-MB) plane. Our CCD monitoring covered a total of 61 nights with an average of 6.1 hours of densely sampled monitoring of just a single QSO per night, thereby achieving a typical detection threshold of ~1 per cent variation over the night. Unambiguous detection of intranight optical variability (INOV) amplitudes in the range 1-3 per cent on day-like or shorter time-scales were thus made for both RQQs and LDQs. Based on these clear detections of INOV, we estimate duty cycles of 17 and 9 per cent for RQQs and LDQs, respectively; inclusion of the two cases of probable variations of LDQs would raise the duty cycle to 15 per cent for LDQs. The similarity in the duty cycle and amplitude of INOV for the RQQs and LDQs suggests, first, that the radio loudness alone does not guarantee an enhanced INOV in QSOs and, secondly, that as in LDQs, relativistic jets may also be present in RQQs. We argue that, as compared to BL Lacs, the conspicuously milder, rarer and possibly slower INOV of RQQs and LDQs can in fact be readily understood in terms of their having optical synchrotron jets which are modestly misaligned from us, but are otherwise intrinsically as relativistic and active as the jets in BL Lacs. This points toward an orientation-based unifying scheme for the INOV of radio-loud and radio-quiet quasars. Variability of up to ~0.3 mag on month- to year-like time-scales is seen for nearly all those RQQs and LDQs in our sample for which sufficient temporal coverage is available. These data have revealed an interesting event that seems most likely explained as an occultation, lasting less than six months, of much of the nuclear optical continuum source in an RQQ. The observations reported here form part of a larger ongoing project to study the intranight optical variability of four major classes of powerful AGN, including blazars