ABSTRACT
We report here the first results from a 15-yr long variability monitoring of the z = 2.0 quasar QSO B1312+7837. It shows luminosity changes with a period P ∼ 6.13 yr (P ∼ 2.04 yr at rest ...frame) and amplitude of ∼0.2 mag, superimposed on a gradual dimming at a rate of ∼0.55 mag per 100 yr. Two false periods associated with power peaks in the data windowing function were discarded. The measured period is confirmed with a bootstrapping Monte Carlo simulation. A damped random walk model yields a better fit to the data than a sine-function model, but at the cost of employing some high-frequency variations which are typically not seen in quasars. We consider the possible mechanisms driving this variability, and conclude that orbital motion of two supermassive black holes – result from a recent galaxy merger – is a possible explanation.
Whiting 1 is a member of the fast-growing group of young globular clusters in the Milky Way halo. Preliminary estimates of its fundamental parameters have been provided using optical photometry and ...low-resolution spectroscopy. In an attempt to strengthen our knowledge of Whiting 1, in this study we employ a complementary approach. Isochrone fitting method was applied on the near-infrared colour–magnitude diagram and yields an age t = 5.7 ± 0.3 Gyr, metallicity z = 0.006 ± 0.001 (Fe/H = −0.5 ± 0.1) and distance modulus (m − M)0 = 17.48 ± 0.10. Our results confirm that Whiting 1 is a young and moderately metal-rich globular cluster. It is one of the youngest from the Sgr dSph. We fitted an Elson, Fall and Freeman (EFF) profile to the near-infrared number counts, and measured cluster core radius r
c = 9.1 arcsec ± 3.9 arcsec. Two probable eclipsing variables in the cluster were found from multi-epoch V-band photometry. Finally, an unknown galaxy cluster was identified on our K versus (J − K) colour–magnitude diagram. It has a redshift z ∼ 1, and it is located at about 1 arcmin from the centre of Whiting 1 at
$\alpha _{\rm J2000} = 02^{\rm h} 02^{\rm m} 56 {.\!\!^{{\mathrm{s}}}6$
, δJ2000 = −03°16′09′
′, contaminating the cluster photometry.
Context. The BL Lac object 3C 371 was observed by the Transiting Exoplanet Survey Satellite (TESS) for approximately a year, between July 2019 and July 2020, with an unmatched two-minute imaging ...cadence. In parallel, the Whole Earth Blazar Telescope (WEBT) Collaboration organized an extensive observing campaign, providing three years of continuous optical monitoring between 2018 and 2020. These datasets allow for a thorough investigation of the variability of the source. Aims. The goal of this study is to evaluate the optical variability of 3C 371. Taking advantage of the remarkable cadence of TESS data, we aim to characterize the intra-day variability (IDV) displayed by the source and identify its shortest variability timescale. With this estimate, constraints on the size of the emitting region and black hole mass can be calculated. Moreover, WEBT data are used to investigate long-term variability (LTV), including in terms of the spectral behavior of the source and the polarization variability. Based on the derived characteristics, we aim to extract information on the origin of the variability on different timescales. Methods. We evaluated the variability of 3C 371 by applying the variability amplitude tool, which quantifies variability of the emission. Moreover, we employed common tools, such as ANOVA (ANalysis Of VAariance) tests, wavelet and power spectral density (PSD) analyses to characterize the shortest variability timescales present in the emission and the underlying noise affecting the data. We evaluated the short- and long-term color behavior to understand its spectral behavior. The polarized emission was analyzed, studying its variability and possible rotation patterns of the electric vector position angle (EVPA). Flux distributions of the IDV and LTV were also studied with the aim being to link the flux variations to turbulent and/or accretion-disk-related processes. Results. Our ANOVA and wavelet analyses reveal several entangled variability timescales. We observe a clear increase in the variability amplitude with increasing width of the time intervals evaluated. We are also able to resolve significant variations on timescales of as little as ∼0.5 h. The PSD analysis reveals a red-noise spectrum with a break at IDV timescales. The spectral analysis shows a mild bluer-when-brighter (BWB) trend on long timescales. On short timescales, mixed BWB, achromatic and redder-when-brighter signatures can be observed. The polarized emission shows an interesting slow EVPA rotation during the flaring period, where a simple stochastic model can be excluded as the origin with a 3 σ significance. The flux distributions show a preference for a Gaussian model for the IDV, and suggest it may be linked to turbulent processes, while the LTV is better represented by a log-normal distribution and may have a disk-related origin.
Context. M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 – the first event of this kind observed in M 31 since 1988. Very few similar events have been confirmed as of 2015. ...Most of them are considered to be products of stellar mergers. Aims. Results of an extensive optical monitoring of the transient in the period January–March 2015 are presented. Methods. Eight optical telescopes were used for imaging. Spectra were obtained on the Large Altazimuth Telescope (BTA), the Gran Telecsopio Canarias (GTC) and the Rozhen 2 m telescope. Results. We present a highly accurate 70 d light curve and astrometry with a 0.05′′uncertainty. The colour indices reached a minimum of 2−3 d before peak brightness and rapidly increased afterwards. The spectral type changed from F5I to F0I in 6 d before the maximum and then to K3I in the next 30 d. The luminosity of the transient was estimated to be 8.7+3.3-2.2 × 105 L⊙ during the optical maximum. Conclusions. Both the photometric and the spectroscopic results confirm that the object is a red nova, similar to V838 Monocerotis.
We report the results of quasi-simultaneous two-filter optical monitoring of two high-energy peaked blazars, 1ES 1959+650 and 1ES 2344+514, to search for microvariability and short-term variability ...(STV). We carried out optical photometric monitoring of these sources in an alternating sequence of B and R passbands, and have 24 and 19 nights of new data for these two sources, respectively. No genuine microvariability (intranight variability) was detected in either of these sources. This non-detection of intranight variations is in agreement with the conclusions of previous studies that high-energy peaked BL Lacs are intrinsically less variable than low-energy peaked BL Lacs in the optical bands. We also report the results of STV studies for these two sources between 2009 July and 2010 August. Genuine STV is found for the source 1ES 1959+650 but not for 1ES 2344+514. We briefly discuss possible reasons for the difference between the intranight variability behaviour of high- and low-energy peaked blazars.
Introduction
: Lumbar disc herniation is a common pathology of young and middle-aged patients. Fissures and tears in the annulus fibrosus become weak points that facilitate herniation of the nucleus ...pulposus, especially when extreme forces ‘attack’ the intervertebral disc. A significant biomechanical force applied to a healthy (‘normal’) disc can have the same effect. Disc protrusions and herniations to varying degrees penetrate the spinal canal.
Aim
: This study aims to present features of lumbar disc herniation in pediatric and elderly patients and evaluate them with respect to data reported in the literature.
Materials and methods
: Five hundred eighty-nine patients were assessed, 64 of whom were children (0-18 years), and 98 were elderly patients (>60 years). The operated patients were followed up for at least three years. All data were recorded at the regular follow-ups (at 1 and 3 months, and at 1 and 3 years after surgery). We used chi-square tests and directional measures to determine statistically significant data. Operative treatment in children and elderly patients was 28% (162) of our cohort’s total number of patients.
Results
: Analyzing postoperative MacNaB, our result showed that children have 23.4% excellent and 76.6 good self-assessment, while in elderly patients, on the one hand, MacNaB used to be excellent or good in 78.5%, and on the other hand, 21.5% had fair or poor self-assessment (
p
<0.05).
Conclusions
: Long-term postoperative outcomes were worse in elderly patients than in children. This was mainly due to the poor status of the intervertebral discs according to the Phirman scale and the associated pathologies at other levels.
We have measured multiband optical flux and colour variations for a sample of 12 low-energy peaked blazars (LBLs) on short, day-to-month, time-scales. Our sample contains six BL Lacertae objects (BL ...Lacs) and six flat spectrum radio quasars (FSRQs). These photometric observations, made during 2008 September to 2009 June, used five optical telescopes, one in India and four in Bulgaria. We detected short-term flux variations in 11 of these blazars and colour variability in eight of them. Our data indicate that six blazars (3C 66A, AO 0235+164, S5 0716+714, PKS 0735+178, OJ 287 and 3C 454.3) were observed in pre- or post-outburst states, five (PKS 0420−014, 4C 29.45, 3C 279, PKS 1510−089 and BL Lac) were in a low state, while one (3C 273) was in an essentially steady state. The duty cycles for flux and colour variations on short time-scales in these LBLs are ∼92 and ∼33 per cent, respectively. The colour versus magnitude correlations seen here support the hypothesis that BL Lac objects tend to become bluer with increase in brightness; however, FSRQs may show the opposite trend, and there are exceptions to these trends in both categories of blazar. We briefly discuss emission models for active galactic nuclei that might explain our results.
Optical photopolarimetry of blazar OJ287 Bozhilov, V; Ovcharov, E; Nikolov, G
Monthly notices of the Royal Astronomical Society,
03/2014, Letnik:
439, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present results from an original observational campaign comprising five epoch optical photopolarimetrical observations of the BL Lac-type AGN OJ287 in the period 2012 November-2013 April. The data ...are gathered with the Focal Reducer Rozhen 2 (FoReRo2) on the 2-m RCC telescope at NAO Rozhen, Bulgaria. We derive photometry and polarization in the R band as well as position angle (PA). There are indications for correlation between polarization and brightness in the R band. Furthermore, observed variation in PA corresponds to a rotation of the plane of polarization of 5.80 deg d−1.
We present the results of our study of spectral energy distributions (SEDs) of a sample of 10 low- to intermediate-synchrotron-peaked blazars. We investigate some of the physical parameters most ...likely responsible for the observed short-term variations in blazars. To do so, we focus on the study of changes in the SEDs of blazars corresponding to changes in their respective optical fluxes. We model the observed spectra of blazars from radio to optical frequencies using a synchrotron model that entails a log-parabolic distribution of electron energies. A significant correlation among the two fitted spectral parameters (a, b) of log-parabolic curves and a negative trend among the peak frequency and spectral curvature parameter, b, emphasize that the SEDs of blazars are fitted well by log-parabolic curves. On considering each model parameter that could be responsible for changes in the observed SEDs of these blazars, we find that changes in the jet Doppler factors are most important.
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