102 research outputs found
Intranight variability of 3C 454.3 during its 2010 November outburst
Context. 3C 454.3 is a very active flat spectrum radio quasar (blazar) that
has undergone a recent outburst in all observed bands, including the optical.
Aims. In this work we explore the short-term optical variability of 3C 454.3
during its outburst by searching for time delays between different optical
bands. Finding one would be important for understanding the evolution of the
spectrum of the relativistic electrons, which generate the synchrotron jet
emission.
Methods. We performed photometric monitoring of the object by repeating
exposures in different optical bands (BVRI). Occasionally, different telescopes
were used to monitor the object in the same band to verify the reliability of
the smallest variations we observed.
Results. Except on one occasion, where we found indications of a lag of the
blue wavelengths behind the red ones, the results are inconclusive for most of
the other cases. There were either no structures in the light curves to be able
to search for patterns, or else different approaches led to different
conclusions.Comment: 4 pages, 4 figures. Accepted for publication in A&
Nature of Intra-night Optical Variability of BL Lacertae
We present the results of extensive multi-band intra-night optical monitoring
of BL Lacertae during 2010--2012. BL Lacertae was very active in this period
and showed intense variability in almost all wavelengths. We extensively
observed it for a total for 38 nights; on 26 of them observations were done
quasi-simultaneously in B, V, R and I bands (totaling 113 light curves), with
an average sampling interval of around 8 minutes. BL Lacertae showed
significant variations on hour-like timescales in a total of 19 nights in
different optical bands. We did not find any evidence for periodicities or
characteristic variability time-scales in the light curves.
The intranight variability amplitude is generally greater at higher
frequencies and decreases as the source flux increases.
We found spectral variations in BL Lacertae in the sense that the optical
spectrum becomes flatter as the flux increases but in several flaring states
deviates from the linear trend suggesting different jet components contributing
to the emission at different times.Comment: 12 Pages, 5 figures, 3 Tables, Accepted for Publication in MNRA
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1,7,9,10-Tetrasubstituted PMIs Accessible through Decarboxylative Bromination: Synthesis, Characterization, Photophysical Studies, and Hydrogen Evolution Catalysis
In this work, we present a new synthetic strategy for fourfold-substituted perylene monoimides via tetrabrominated perylene monoanhydrides. X-ray diffraction analysis unveiled the intramolecular stacking orientation between the substituents and semicircular packing behavior. We observed the remarkable influence of the substituent on the longevity and nature of the excited state upon visible light excitation. In the presence of poly(dehydroalanine)-graft-poly(ethylene glycol) graft copolymers as solubilizing template, the chromophores are capable of sensitizing [Mo3S13]2− clusters in aqueous solution for stable visible light driven hydrogen evolution over three days. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb
Black sea observing system
The ultimate goal of modern operational oceanography are end user oriented products with high scientific quality. Beneficiaries are the governmental services, coast and offshore based enterprises and research institutions that make use of the products generated by operational oceanography. Direct users are coastal managers, shipping, search and rescue, oil spill combat, offshore industry, ports, fishing, tourism, and recreation industry. Indirect beneficiaries, through climate forecasting based on ocean observations, are food, energy, water and medical suppliers. Availability of updated information on the actual state as well as forecast of marine environment is essential for the success and safety of maritime operations in the offshore industry. Various systems for the collection and presentation of marine data for the needs of different users have been developed and put in operation in the Black Sea. The systems are located both along the coast and in the open sea and the information they provide is used by both the maritime industry and the widest range of users. The Black Sea Monitoring and Forecasting Center in the frame of the Copernicus Marine Service is providing regular and systematic information about the physical state of the ocean, marine ecosystem and wave conditions in the Black Sea area, assimilating observations, keeping efficient operations, advanced technology and high quality modeling products. Combining and optimizing in situ, remote sensing, modeling and forecasting into a Black Sea observing system is a task that has to be solved, and that will allow to get a more complete and comprehensive picture of the state of the marine environment as well as to forecast future changes of physical and biogeochemical state of the Black Sea and the Black Sea ecosystem
Multiwavelength Intraday Variability of the BL Lac S5 0716+714
We report results from a 1 week multi-wavelength campaign to monitor the BL
Lac object S5 0716+714 (on December 9-16, 2009). In the radio bands the source
shows rapid (~ (0.5-1.5) day) intra-day variability with peak amplitudes of up
to ~ 10 %. The variability at 2.8 cm leads by about 1 day the variability at 6
cm and 11 cm. This time lag and more rapid variations suggests an intrinsic
contribution to the source's intraday variability at 2.8 cm, while at 6 cm and
11 cm interstellar scintillation (ISS) seems to predominate. Large and
quasi-sinusoidal variations of ~ 0.8 mag were detected in the V, R and I-bands.
The X-ray data (0.2-10 keV) do not reveal significant variability on a 4 day
time scale, favoring reprocessed inverse-Compton over synchrotron radiation in
this band. The characteristic variability time scales in radio and optical
bands are similar. A quasi-periodic variation (QPO) of 0.9 - 1.1 days in the
optical data may be present, but if so it is marginal and limited to 2.2
cycles. Cross-correlations between radio and optical are discussed. The lack of
a strong radio-optical correlation indicates different physical causes of
variability (ISS at long radio wavelengths, source intrinsic origin in the
optical), and is consistent with a high jet opacity and a compact synchrotron
component peaking at ~= 100 GHz in an ongoing very prominent flux density
outburst. For the campaign period, we construct a quasi-simultaneous spectral
energy distribution (SED), including gamma-ray data from the FERMI satellite.
We obtain lower limits for the relativistic Doppler-boosting of delta >= 12-26,
which for a BL\,Lac type object, is remarkably high.Comment: 16 pages, 15 figures, table 2; Accepted for Publication in MNRA
Optical photometry of GM Cep: evidence for UXor type of variability
Results from optical photometric observations of the pre-main sequence star
GM Cep are reported in the paper. The star is located in the field of the young
open cluster Trumpler 37 - a region of active star formation. GM Cep shows a
large amplitude rapid variability interpreted as a possible outburst from EXor
type in previous studies. Our data from BVRI CCD photometric observations of
the star are collected from June 2008 to February 2011 in Rozhen observatory
(Bulgaria) and Skinakas observatory (Crete, Greece). A sequence of sixteen
comparison stars in the field of GM Cep was calibrated in the BVRI bands. Our
photometric data for a 2.5 years period show a high amplitude variations (Delta
V ~ 2.3m) and two deep minimums in brightness are observed. The analysis of
collected multicolor photometric data shows the typical of UX Ori variables a
color reversal during the minimums in brightness. On the other hand, high
amplitude rapid variations in brightness typical for the Classical T Tauri
stars also present on the light curve of GM Cep. Comparing our results with
results published in the literature, we conclude that changes in brightness are
caused by superposition of both: (1) magnetically channeled accretion from the
circumstellar disk, and (2) occultation from circumstellar clouds of dust or
from features of a circumstellar disk.Comment: 7 pages, 3 figures, accepted for publication in Ap&S
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