We have studied the variability of the H
β
line and the adjacent continuum in the spectrum of the Seyfert galaxy Ark 120, based on spectral observations of the galaxy’s nucleus obtained in the Crimea ...in 1992–2005, supplemented by published data for 1988–1996. Irregular variability on various timescales (years to days) can be accompanied by periodic brightness variations in both the continuum and the H
β
line, with a period of
P
∼ 430 days and an amplitude of Δ
m
∼ 0.2
m
in the continuum, which were traced for more than 13 cycles. In total, in 1988–2005, the flux variations in the line lag those in the continuum by 55 ± 9 days if calculated from the peak of the cross correlation function, or by 72 ± 7 days, if calculated from the centroid of the CCF. The delay is correlated with the continuum brightness, increasing when the continuum flux increases. The H
β
line profiles indicate both a high degree of diversity and the presence of features that recur after various extended time intervals. Analysis of the evolution of the differences between each individual normalized line profile and the mean normalized profile indicates systematic motion of excesses relative to the average profile from negative to positive radial velocities. In contrast, parts of the H
β
line with low radiation relative to the mean normalized profile evolve in the opposite direction (from the red to the blue H
β
wing). This pattern is also typical for the rotating broad-line region, if this region has the form of a disk. The rotation period exceeds 9000–10000 days, or 25–27 years. The size of the broad-line region calculated form this period corresponds to a reverberation time of no fewer than 30 days, consistent with the results of cross-correlation analysis.
A multifrequency campaign on the BL Lac object PG 1553+113 was organized by the Whole Earth Blazar Telescope (WEBT) in 2013 April–August, involving 19 optical, two near-IR, and three radio ...telescopes. The aim was to study the source behaviour at low energies during and around the high-energy observations by the Major Atmospheric Gamma-ray Imaging Cherenkov telescopes in April–July. We also analyse the UV and X-ray data acquired by the Swift and XMM–Newton satellites in the same period. The WEBT and satellite observations allow us to detail the synchrotron emission bump in the source spectral energy distribution (SED). In the optical, we found a general bluer-when-brighter trend. The X-ray spectrum remained stable during 2013, but a comparison with previous observations suggests that it becomes harder when the X-ray flux increases. The long XMM–Newton exposure reveals a curved X-ray spectrum. In the SED, the XMM–Newton data show a hard near-UV spectrum, while Swift data display a softer shape that is confirmed by previous Hubble Space Telescope/Cosmic Origins Spectrograph and International Ultraviolet Explorer observations. Polynomial fits to the optical–X-ray SED show that the synchrotron peak likely lies in the 4–30 eV energy range, with a general shift towards higher frequencies for increasing X-ray brightness. However, the UV and X-ray spectra do not connect smoothly. Possible interpretations include: (i) orientation effects, (ii) additional absorption, (iii) multiple emission components, and (iv) a peculiar energy distribution of relativistic electrons. We discuss the first possibility in terms of an inhomogeneous helical jet model.
Deep-Water Neutrino Telescope in Lake Baikal Allakhverdyan, V. A.; Avrorin, A. D.; Avrorin, A. V. ...
Physics of atomic nuclei,
12/2021, Letnik:
84, Številka:
9
Journal Article
Recenzirano
The Baikal-GVD deep-water neutrino telescope of the cubic kilometer scale, focused on research in the field of astrophysics and particle physics, is being built in Lake Baikal. As of 2021, the ...effective volume of the detector reaches 0.4 km
3
for cascades generated by high-energy astrophysical neutrinos. The paper describes the design and basic characteristics of the telescope data acquisition system, discusses some aspects of deep-water engineering related to the deployment of the detector, and presents selected results obtained with the partially complete detector.
Deep-Underwater Cherenkov Detector in Lake Baikal Avrorin, A.V.; Avrorin, A. D.; Ayinutdinov, V. M. ...
Journal of experimental and theoretical physics,
04/2022, Letnik:
134, Številka:
4
Journal Article
Recenzirano
Neutrino telescope Baikal-CVD is a deep-underwater Cherenkov detector of elementary particles of the 1-km
3
scale, which has been developed beginning from 2016 in Lake Baikal. The telescope is ...assembled from separate blocks (clusters of optical modules), which makes it possible to perform scientific research even at early stages of its development. In the 2021 configuration, the detector contains eight clusters with 2304 optical modules in total and is the largest neutrino telescope in the Northern hemisphere. The design and main characteristics of the Baikal-GVD data acquisition system are described, the problems of deep-underwater engineering associated with the development of the detector are considered, and some physical results obtained on the facility are presented
Results of a long-term monitoring (≳10 years) of the broad line and continuum fluxes of three Active Galactic Nuclei (AGN), 3C 390.3, NGC 4151, and NGC 5548, are presented. We analyze the H
α and H
β ...profile variations during the monitoring period and study different details (as bumps, absorption bands) which can indicate structural changes in the Broad Line Region (BLR). The BLR dimensions are estimated using the time lags between the continuum and the broad lines flux variations. We find that in the case of 3C 390.3 and NGC 5548 a disk geometry can explain both the broad line profiles and their flux variations, while the BLR of NGC 4151 seems more complex and is probably composed of two or three kinematically different regions.
The neutrino telescope Baikal-GVD is designed for search for high energy neutrinos whose sources are not yet reliably identified. It currently includes total of 3456 optical modules arranged on 96 ...strings, providing an effective volume of 0.6 km
for cascades with energy above 1 PeV. We discuss the first results from the partially built experiment, which is currently the largest neutrino telescope in the Northern Hemisphere and still growing up.
Currently, the Baikal-GVD Deep Underwater Neutrino Telescope is being successfully deployed in Lake Baikal. It comprises 96 strings with 3456 optical modules. We present the status and plans for ...further deployment of the Baikal-GVD telescope and discuss the issues related to the development of the next-generation neutrino telescope in Lake Baikal.
The light curve of Mrk 6 for 1970–2002 is presented and discussed. The amplitudes of variability were 1.6m, 1.1m, and 0.8m in UBV bands, respectively. The magnitudes of the underlying galaxy in the ...27.5'' aperture were found to be $U_{\rm g}=15.82$, $B_{\rm g}=15.42$ and $V_{\rm g}=14.36$. The mean color indices of the variable component are $(U-B)_{\rm var}=-0.49$ and $(B-V)_{\rm var}=0.75$ without correction for reddening. In the time intervals from 10 days to 1300 days the structure function can be presented as a power function, $S\!F\propto\tau^b$, where $b=0.72\pm0.04$. The time where the SF for Mrk 6 reaches the upper plateau is about 3300 days. The observed SF can be interpreted by the superposition of independent flares model with the maximal duration of flares ~800 days. If these flares are located in the radiation pressure dominated region of the accretion disk, the size of this region is about 70, 330 RS, assuming the viscous parameter α is 0.1, 0.01, respectively. It is concluded that the optical long-term variability of Seyfert galaxies can be explained by thermal instability in the accretion disk.
Data are presented from observations in the B, V, R, and I bands of 200 comparison stars in the fields of 18 active galactic nuclei (AGN) with right ascensions from 0 to 9 hours over a wide range of ...stellar magnitudes. Most of the AGN are blazars and quasars. The B, V, R, and I magnitudes of the overwhelming majority of these AGN were not known previously. Finding charts for these stars are provided. These observations can be used for differential photometry of galactic nuclei.
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