Abstract
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.
Abstract
BL Lacertae underwent a series of historical high flux activity over a year from 2020 August in the optical to VHE
γ
-rays. In this paper, we report on optical flux and spectral variability ...of the first historical maxima outburst event during October–November in the
g
,
r
, and
i
bands with the 1.26 m telescope at the Xinglong Observatory, China. We detected significant intranight variations with amplitude rising up to ∼30%, where the fastest variability timescale was found to be a few tens of minutes, giving an emitting region size of the order 10
−3
pc, which corresponds to ∼100 Schwarzschild radius of the central black hole, likely coming from some jet mini-structures. Unlike on the intranight timescale, a clear frequency-dependent pattern along symmetric timescales (∼11 days) of flux variation is detected on a long timescale. The spectral evolution was predominated by flattening of the spectra with increasing brightness i.e., a bluer-when-brighter trend in 96% of the cases. On the night before the outburst peak, the color indices shown in a color–magnitude diagram, clustered into two distinct branches, within a period of ∼6 hr, which is connected to a hard-soft-hard spectral evolution trend extracted from time-resolved spectra. To the best of our knowledge, such a trend has never been seen in BL Lac or any other blazars before. The results obtained in this study can be explained in the context of shock-induced particle acceleration or magnetic reconnection in the jet where turbulent processes most likely resulted in the asymmetric flux variation on a nightly timescale.
The “Blazar Sequence” in the TeV Band Ouyang, Zhihao; Xiao, Hubing; Chen, Jianzhen ...
The Astrophysical journal,
06/2023, Letnik:
949, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
The “blazar sequence” has been proposed for more than 20 yr, yet its nature is still unclear. In this work, for the first time we expand this topic to the TeV band by using a sample of 58 ...TeV blazars, including 48 blazars in the quiescent state and 21 blazars in the flaring state (11 blazars show in both quiescent and flaring state). We investigate the correlation between the TeV luminosity, which has been compensated for attenuation from extragalactic background light, and the synchrotron peak frequency. We note that there is no correlation between TeV luminosity and peak frequency in the quiescent state and a strong anticorrelation in the flaring state for the observed value. However, there is a strong positive correlation in both the quiescent state and the flaring state for the intrinsic value. This indicates that the blazar sequence is shown in the flaring state rather than in the quiescent state for the observed value and the blazar sequence is not present in both states after removing the beaming effect. In addition, to confirm whether the beaming effect results in the blazar sequence, we compare the Fermi
γ
-ray luminosity between the quiescent state and the flaring state. We find the Fermi
γ
-ray luminosity in the flaring state is greater than that in the quiescent state, and the Doppler factor in the flaring state is greater. We suggest the blazar sequence in the flaring state may be due to a stronger beaming effect.
We study the long term Kepler light curve of the blazar W2R 1926+42 (∼1.6 yr) which indicates a variety of variability properties during different intervals of observation. The normalized excess ...variance, F
var ranges from 1.8 per cent in the quiescent phase and 43.3 per cent in the outburst phase. We find no significant deviation from linearity in the F
var-flux relation. Time series analysis is conducted using the Fourier power spectrum and the wavelet analysis methods to study the power spectral density (PSD) shape, infer characteristic time-scales and statistically significant quasi-periodic oscillations (QPOs). A bending power law with an associated time-scale of
$T_\mathrm{B} = 6.2^{+6.4}_{-3.1}$
hours is inferred in the PSD analysis. We obtain a black hole mass of M
• = (1.5–5.9) × 107 M⊙ for the first time using F
var and the bend time-scale for this source. From a mean outburst lifetime of days, we infer a distance from the jet base r ≤ 1.75 pc indicating that the outburst originates due to a shock. A possible QPO peaked at 9.1 d and lasting 3.4 cycles is inferred from the wavelet analysis. Assuming that the QPO is a true feature, r = (152–378)GM•/c
2 and supported by the other timing analysis products such as a weighted mean PSD slope of −1.5 ± 0.2 from the PSD analysis, we argue that the observed variability and the weak and short duration QPO could be due to jet based processes including orbital features in a relativistic helical jet and others such as shocks and turbulence.
We monitored BL Lacertae frequently during 2014–2016 when it was generally in a high state. We searched for intra-day variability for 43 nights using quasi-simultaneous measurements in the B, V, R, ...and I bands (totaling 143 light curves); the typical sampling interval was about eight minutes. On hour-like timescales, BL Lac exhibited significant variations during 13 nights in various optical bands. Significant spectral variations are seen during most of these nights such that the optical spectrum becomes bluer when brighter. The amplitude of variability is usually greater for longer observations but is lower when BL Lac is brighter. No evidence for periodicities or characteristic variability time-scales in the light curves was found. The color variations are mildly chromatic on long timescales.
We present results of optical observations of the extremely violently variable blazar S4 0954+65 on intra-night time scales. The object showed flux changes of up to 100% within a few hours. Time ...delays between optical bands, color changes and “rms-flux” relations are investigated and the results are discussed in terms of existing models of blazar variability.
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, ~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.
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 0.58 ± 0.11 in
V
-band magnitude within ∼2.64 h and a corresponding minimum variability timescale of 18.21 ± 4.87 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 1.37 ± 0.04. 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.
ABSTRACT
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 colour changes, but no firmly detectable time delays between the optical bands. The linear polarization was also highly variable in both polarization degree and angle (electric vector polarization angle). The object was observed from several observatories throughout the world, covering a total of almost 300 h 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 time-scales.
ABSTRACT
We present an extensive recent multiband 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 monitored the blazar quasi-simultaneously during three nights in B, V, R, and I bands; four nights in B, V, and R; two nights in V, R, and I; five nights in B and R; and two 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 colour variations in the light curves of the blazar on intraday time-scales. Out of 12, 11, 53, and 5 nights observations, intraday variations with amplitudes between ∼3 and ∼20 per cent 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 per cent. These duty cycles are lower than those typically measured at earlier times. On these time-scales colour 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.
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