15 research outputs found
Investigating the origin of optical flares from the TeV blazar S4 0954+65
Aims. We aim to investigate the extreme variability properties of the TeV
blazar S4 0954+65 using optical photometric and polarisation observations
carried out between 2017 and 2023 using three ground-based telescopes.
Methods. We examined an extensive dataset comprised of 138 intraday
(observing duration shorter than a day) light curves (LCs) of S4 0954+65 for
flux, spectral, and polarisation variations on diverse timescales. For the
variable LCs, we computed the minimum variability timescales. We investigated
flux-flux correlations and colour variations to look for spectral variations on
long (several weeks to years) timescales. Additionally, we looked for
connections between optical R-band flux and polarisation degree.
Results. We found significant variations in 59 out of 138 intraday LCs. We
detected a maximum change of 0.580.11 in V-band magnitude within
2.64 h and a corresponding minimum variability timescale of
18.214.87 mins on 2017 March 25. During the course of our observing
campaign, the source brightness changed by 4 magnitudes in V and R bands;
however, we did not find any strong spectral variations. The slope of the
relative spectral energy distribution was 1.370.04. The degree of
polarisation varied from 3% to 39% during our monitoring. We observed a
change of 120 degrees in polarisation angle (PA) within 3 h on 2022
April 13. No clear correlation was found between optical flux and the degree of
polarisation.
Conclusions. The results of our optical flux, colour, and polarisation study
provide hints that turbulence in the relativistic jet could be responsible for
the intraday optical variations in the blazar S4 0954+65. However, the
long-term flux variations may be caused by changes in the Doppler factor.Comment: 9 pages, 10 figures, 4 tables, 4 appendix, Astronomy & Astrophysics
journal (in press
Intra-night optical flux and polarization variability of BL~Lacertae during its 2020 2021 high state
In this work, we report the presence of rapid intra-night optical variations
in both -- flux and polarization of the blazar BL Lacertae during its
unprecedented 2020--2021 high state of brightness. The object showed
significant flux variability and some color changes, but no firmly detectable
time delays between the optical bands. The linear polarization was also highly
variable in both -- polarization degree and angle (EVPA). The object was
observed from several observatories throughout the world, covering in a total
of almost 300 hours during 66 nights. Based on our results, we suggest, that
the changing Doppler factor of an ensemble of independent emitting regions,
travelling along a curved jet that at some point happens to be closely aligned
with the line of sight can successfully reproduce our observations during this
outburst. This is one of the most extensive variability studies of the optical
polarization of a blazar on intra-night timescales.Comment: 23 pages,7 figures, 5 Tables (2 as appendix). Accepted for
publication in MNRA
Optical intra-day variability of the blazar S5 0716+714
We present an extensive recent multi-band optical photometric observations of
the blazar S5 0716+714 carried out over 53 nights with two telescopes in India,
two in Bulgaria, one in Serbia, and one in Egypt during 2019 November -- 2022
December. We collected 1401, 689, 14726, and 165 photometric image frames in B,
V, R, and I bands, respectively. We montiored the blazar quasi-simultaneously
during 3 nights in B, V, R, and I bands; 4 nights in B, V, and R; 2 nights in
V, R, and I; 5 nights in B and R; and 2 nights in V and R bands. We also took
37 nights of data only in R band. Single band data are used to study intraday
flux variability and two or more bands quasi-simultaneous observations allow us
to search for colour variation in the source. We employ the power-enhanced
F-test and the nested ANOVA test to search for genuine flux and color
variations in the light curves of the blazar on intraday timescales. Out of 12,
11, 53, and 5 nights observations, intraday variations with amplitudes between
~3% and ~20% are detected in 9, 8, 31 and 3 nights in B, V, R, and I bands,
respectively, corresponding to duty cycles of 75%, 73%, 58% and 60%. These duty
cycles are lower than those typically measured at earlier times. On these
timescales color variations with both bluer-when-brighter and
redder-when-brighter are seen, though nights with no measurable colour
variation are also present. We briefly discuss possible explanations for this
observed intraday variability.Comment: 19 pages, 5 figures, 4 tables, Accepted for Publication in MNRA
A search for chaos in the optical light curve of a blazar: W2R 1926+42
Aims. In this work we search for the signatures of low-dimensional chaos in the temporal behavior of the Kepler-field blazar W2R 1946+42. Methods. We use a publicly available, similar to 160 000-point-long and mostly equally spaced light curve of W2R 1946+42. We apply the correlation integral method to both real datasets and phase randomized surrogates. Results. We are not able to confirm the presence of low-dimensional chaos in the light curve. This result, however, still leads to some important implications for blazar emission mechanisms, which are discussed
Characterizing the emission region property of blazars
The studies and constraints on the emission region are crucial to the blazar
radiation mechanism. Yet the previous works mainly focus on individual sources.
In this work, we make use of the largest and the latest spectral energy
distribution (SED) fitting results in the literature to statistically study the
blazar emission region property in the framework of leptonic one-zone. Our
results reveal (1) FSRQs show lower electron energy () than BL Lacs and tend to have a stronger magnetic field
() and smaller electron-to-magnetic energy ratio ()
than BL Lacs; (2) we find the electro-magnetic equipartition would rather
happen in the jets of BL Lacs than happen in the jets of FSRQs; (3) there are
682 blazars with a magnetic field weaker critical value of generating the
Kelvin-Helmholtz instability, thus one-third of the blazars in our sample are
able to produce this instability; (4) the distance () between the
emission region and the central black hole (BH) is in the scale of 0.1
pc, the location of the emission region may be evenly distributed inside and
outside the broad line region (BLR).Comment: 13 pages, 5 figures, 2 tables. Accepted to ApJ
Characterizing the Emission Region Properties of Blazars
Studies and constraints on the emission region are crucial to the blazar radiation mechanism. Yet previous works have mainly focused on individual sources. In this work, we make use of the largest and the latest spectral energy distribution fitting results in the literature to statistically study the blazar emission region properties in the framework of a one-zone leptonic model. Our results reveal: (1) that flat-spectrum radio quasars (FSRQs) show lower electron energy ( γ _p ≲ 1.6 × 10 ^3 ) than BL Lacertae objects (BL Lacs) and tend to have a stronger magnetic field ( B ) and smaller electron-to-magnetic energy ratio ( U _e / U _B ) than BL Lacs; (2) we find that the electromagnetic equipartition would rather happen in the jets of BL Lacs than happen in the jets of FSRQs; (3) there are 682 blazars with a magnetic field weaker than the critical value for generating the Kelvin–Helmholtz instability, thus one-third of the blazars in our sample are able to produce this instability; and (4) the distance ( d _em ) between the emission region and the central black hole is on the scale of ∼0.1 pc, so the location of the emission region may be evenly distributed inside and outside the broad-line region