- ID:
- ivo://CDS.VizieR/J/ApJS/237/30
- Title:
- 6-yr light curves of 10 blazars
- Short Name:
- J/ApJS/237/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out multi-color optical monitoring of a sample of 10 blazars from 2005 to 2011. The sample contains 3 LBLs, 2 IBLs, 4 HBLs, and 1 FSRQ. Our monitoring focused on the long-term variability and the sample included nine BL Lac objects and one flat-spectrum radio quasar (FSRQ). A total of 14,799 data points were collected. This is one of the largest optical databases for a sample of 10 blazars. All objects showed significant variability except for OT 546. Because of the low sampling on each single night, only BL Lacertae were observed to have intraday variability on 2006 November 6. Most BL Lac objects showed a bluer-when-brighter (BWB) chromatism, while the FSRQ, 3C 454.3, displayed a redder-when-brighter trend. The BWB color behaviors of most BL Lacs can be at least partly attributed to the trend of increasing variation amplitude with increasing frequency observed in these objects. The average spectral index of LBLs is around 1.5, as expected from the model dominated by synchrotron self-Compton loss. The optical emission of HBL is probably contaminated by the thermal emission from the host galaxies. Correlation analysis did not reveal any time delay between variations at different wavelengths.
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- ID:
- ivo://CDS.VizieR/J/ApJS/222/6
- Title:
- 4.5yr obs. of Mrk421 with ARGO-YBJ & Fermi
- Short Name:
- J/ApJS/222/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the extensive multi-wavelength observations of the blazar Markarian 421 (Mrk 421) covering radio to {gamma}-rays, during the 4.5yr period of ARGO-YBJ and Fermi common operation time, from 2008 August to 2013 February. These long-term observations, extending over an energy range of 18 orders of magnitude, provide a unique chance to study the variable emission of Mrk 421. In particular, due to the ARGO-YBJ and Fermi data, the entire energy range from 100MeV to 10TeV is covered without any gap. In the observation period, Mrk 421 showed both low- and high-activity states at all wavebands. The correlations among flux variations in different wavebands were analyzed. The X-ray flux is clearly correlated with the TeV {gamma}-ray flux, while the GeV {gamma}-rays only show a partial correlation with the TeV {gamma}-rays. Radio and UV fluxes seem to be weakly or not correlated with the X-ray and {gamma}-ray fluxes. Seven large flares, including five X-ray flares and two GeV {gamma}-ray flares with variable durations (3-58d), and one X-ray outburst phase were identified and used to investigate the variation of the spectral energy distribution with respect to a relative quiescent phase. During the outburst phase and the seven flaring episodes, the peak energy in X-rays is observed to increase from sub-keV to a few keV. The TeV {gamma}-ray flux increases up to 0.9-7.2 times the flux of the Crab Nebula. The behavior of GeV {gamma}-rays is found to vary depending on the flare, a feature that leads us to classify flares into three groups according to the GeV flux variation. Finally, the one-zone synchrotron self-Compton model was adopted to describe the emission spectra. Two out of three groups can be satisfactorily described using injected electrons with a power-law spectral index around 2.2, as expected from relativistic diffuse shock acceleration, whereas the remaining group requires a harder injected spectrum. The underlying physical mechanisms responsible for different groups may be related to the acceleration process or to the environment properties.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/170
- Title:
- 10yr of radio-to-gamma-ray obs. of 1ES 1215+30.3
- Short Name:
- J/ApJ/891/170
- Date:
- 19 Jan 2022 09:02:08
- Publisher:
- CDS
- Description:
- Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100MeV to 30TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.
- ID:
- ivo://CDS.VizieR/J/ApJS/232/7
- Title:
- 8yr R-band photopolarimetric data of blazar Mrk 421
- Short Name:
- J/ApJS/232/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of 8yr R-band photopolarimetric data of blazar Mrk 421 collected from 2008 February to 2016 May are presented, along with extensive multiwavelength observations covering radio to TeV {gamma}-rays around the flares observed in 2008 May, 2010 March, and 2013 April. The most important results are found in 2013, when the source displayed in the R band a very high brightness state of 11.29+/-0.03mag (93.60+/-1.53mJy) on April 10 and a polarization degree of 11.00%+/-0.44% on May 13. The analysis of the optical data shows that the polarization variability is due to the superposition of two polarized components that might be produced in two distinct emitting regions. An intranight photopolarimetric variability study carried out over seven nights after the 2013 April maximum found flux and polarization variations on the nights of April 14, 15, 16, and 19. In addition, the flux shows a minimum variability timescale of {Delta}t=2.34+/-0.12hr, and the polarization degree presents variations of~1%-2% on a timescale of {Delta}t~minutes. Also, a detailed analysis of the intranight data shows a coherence length of the large-scale magnetic field of l_B_~0.3pc, which is the same order of magnitude as the distance traveled by the relativistic shocks. This result suggests that there is a connection between the intranight polarimetric variations and spatial changes of the magnetic field. Analysis of the complete R-band data along with the historical optical light curve found for this object shows that Mrk 421 varies with a period of 16.26+/-1.78yr.
- ID:
- ivo://CDS.VizieR/J/ApJ/884/92
- Title:
- 7yrs of VRI obs. of S5 0716+714 and its flares
- Short Name:
- J/ApJ/884/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The typical blazar S5 0716+714 is very interesting due to its rapid and large-amplitude variability and high duty cycle of microvariability in the optical band. We analyze the observations in the I, R, and V bands obtained with the 1.0m telescope at Weihai observatory of Shandong University from 2011 to 2018. The model of synchrotron radiation from turbulent cells in a jet has been proposed as a mechanism for explaining microvariability seen in blazar light curves. Parameters such as the sizes of turbulent cells, the enhanced particle densities, and the location of the turbulent cells in the jet can be studied using this model. The model predicts a time lag between variations, as observed in different frequency bands. An automatic model fitting method for microvariability is developed, and the fitting results of our multi-frequency microvariability observations support the model. The results show that both the amplitude and duration of flares decomposed from the microvariability light curves conform to the log-normal distribution. The turbulent cell size is within the range of about 5-55au, and the time lags of the microvariability flares between the I-R and R-V bands should be several minutes. The time lags obtained from the turbulence model are consistent with the fitting statistical results, and the time lags of flares are correlated with the time lags of the whole light curve.
- ID:
- ivo://CDS.VizieR/J/ApJ/848/103
- Title:
- ~1.5yr Swift observations of Mrk 421
- Short Name:
- J/ApJ/848/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the Swift observations of the nearby BL Lac object Mrk421 during 2013 November-2015 June. The source exhibited a strong long-term variability in the 0.3-10keV band, with a maximum-to-minimum flux ratio of 13, and underwent X-ray flares by a factor of 1.8-5.2 on timescales of a few weeks or shorter. The source showed 48 instances of intraday flux variability in this period, which sometimes was observed within the 1 ks observational run. It was characterized by fractional amplitudes of 1.5(0.3)%-38.6(0.4)% and flux doubling/halving times of 2.6-20.1hr. The X-ray flux showed a lack of correlation with the TeV flux on some occasions (strong TeV flares were not accompanied by comparable X-ray activity and vice versa), indicating that the high-energy emission in Mrk421 was generated from an emission region more complex than a single zone. The best fits of the 0.3-10keV spectra were mainly obtained using the log-parabola model, showing a strong spectral variability that generally followed a "harder-when-brighter" trend. The position of the synchrotron spectral energy distribution peak showed an extreme range from a few eV to ~10keV that happens rarely in blazars.