Correlation between optical and γ-ray flux variations in BL Lacs

Rajput, Bhoomika; Shah, Zahir; Stalin, C. S.; Sahayanathan, S.; Rakshit, Suvendu

doi:10.1093/mnras/stab970

Cited by 7 publications

(7 citation statements)

References 79 publications

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“…The counterclockwise looping was observed between flux and PD variations on 2014 February 20 by Pasierb et al (2020). The optical and γ-ray flux variations in this source were found to be correlated (Rajput et al 2021). The possible quasi-periodic oscillation of ∼ 314 days in the 9.5 year γ-ray light curve was studied by Kushwaha et al (2020).…”

Section: Oj 287mentioning

confidence: 56%

“…We collected γ-ray data in the energy range 0.1-300 GeV for 11 BL Lac sources detected by the Fermi Large Area Telescope (Fermi-LAT; Atwood et al 2009). To generate the one-day binned γ-ray light curves of these sources we followed the same strategy given in Rajput et al (2021). If the test statistics (TS) ≥ 25 (which corresponds to 5σ; Mattox et al 1996), the source is considered to be detected in the one-day binned γ-ray light curve.…”

Section: γ-Ray Data Reductionmentioning

confidence: 99%

“…Furthermore, the nature of the γ-ray emission process can be constrained by analysis of the correlation between γ-ray flux and optical polarization position angle. The observation obtained from Fermi Gamma-ray Space Telescope (hereinafter Fermi) reported the various behaviour of correlation between γ-ray flux and optical flux (Bonning et al 2009;Chatterjee et al 2012;Cohen et al 2014;MacDonald et al 2015;Rajput et al 2019Rajput et al , 2020Amaya-Almazán et al 2021;Rajput et al 2021) and between γ-ray flux and optical polarization position angle (Abdo et al 2010b;Marscher et al 2010;Blinov et al 2015Blinov et al , 2018. However, these findings show that the polarization degree and position angle, and their correlation with different energy bands, have a complex behaviour.…”

Section: Introductionmentioning

confidence: 99%

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Study of correlation between optical flux and polarization variations in BL Lac objects

Rajput,

Pandey,

Stalin

et al. 2022

Preprint

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Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energy, which also shows variations. We present here our results on the correlation analysis between optical flux and polarization degree (PD) variations in a sample of 11 BL Lac objects using ∼ 10 years of data from the Steward Observatory. We carried out the analysis on long-term (∼ several months) as well as on short-term timescales (∼ several days). On long-term timescales, for about 85% of the observing cycles, we found no correlation between optical flux and PD. On short-term timescales, we found a total of 58 epochs with a significant correlation between optical flux and PD, where both positive and negative correlation were observed. In addition, we also found a significant correlation between optical flux and γ-ray flux variations on long-term timescales in 11% of the observing cycles. The observed PD variations in our study cannot be explained by changes in the power-law spectral index of the relativistic electrons in the jets. The shock-in-jet scenario is favoured for the correlation between optical flux and PD, whereas the anti-correlation can be explained by the presence of multi-zone emission regions. The varying correlated behaviour can also be explained by the enhanced optical flux caused by the newly developed radio knots in the jets and their magnetic field alignment with the large scale jet magnetic field.

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Section: Oj 287mentioning

confidence: 56%

Section: γ-Ray Data Reductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of correlation between optical flux and polarization variations in BL Lac objects

Rajput,

Pandey,

Stalin

et al. 2022

Preprint

Self Cite

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“…On the contrary, there can be instances of an optical flare with no counterpart in the X-ray band. Also, the multi-band flux variability characteristics of blazars are highly complex, as revealed from recent observations Rajput et al (2019Rajput et al ( , 2020Rajput et al ( , 2021. However, inspection of Figure 1 indicate that the source is in a relatively faint state across different bands of the electromagnetic spectrum during 2017.…”

Section: Observation and Data Reductionmentioning

confidence: 91%

Flux and spectral variability of Mrk 421 during its moderate activity state using NuSTAR: Possible accretion disc contribution?

Mondal,

Rani,

Stalin

et al. 2022

Preprint

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Context. The X-ray emission in BL Lac objects is believed to be dominated by synchrotron emission from their relativistic jets. However, when the jet emission is not strong, one could expect signatures of X-ray emission from inverse Compton scattering of accretion disc photons by hot and energetic electrons in the corona. Moreover, the observed X-ray variability can also originate in the disc, and gets propagated and amplified by the jet.Aims. Here, we present results on the BL Lac object Mrk 421 using the Nuclear Spectroscopic Telescope Array data acquired during 2017 when the source was in a moderate X-ray brightness state. For comparison with high jet activity state, we also considered one epoch data in April 2013 when the source was in a very high X-ray brightness state. Our aim is to explore the possibility of the signature of accretion disc emission in the overall X-ray emission from Mrk 421 and also examine changes in accretion parameters considering their contribution to spectral variations. Methods. We divided each epoch of data into different segments in order to find small scale variability. Data for all segments were fitted using simple powerlaw model. We also fitted the full epoch data using the two component advective flow model to extract the accretion flow parameters. Furthermore, we estimated the X-ray flux coming from the different components of the flow using the lowest normalization method and analysed the relations between them. For consistency, we performed the spectral analysis using available models in the literature. Results. The simple powerlaw function does not fit the spectra well, and a cutoff needs to be added. The spectral fitting of the data using the two component advective flow model shows that the data can be explained with a model where (a) the size of the dynamic corona at the base of the jet from ∼ 28 to 10 r s , (b) the disc mass accretion rate from 0.021 to 0.051 ṀEdd , (c) the halo mass accretion rate from 0.22 to 0.35 ṀEdd , and (d) the viscosity parameter of the Keplerian accretion disc from 0.18 − 0.25. In the assumed model, the total flux, disc and jet flux correlate with the radio flux observed during these epochs. Conclusions. From the spectral analysis, we conclude that the spectra of all the epochs of Mrk 421 in 2017 are well described by the accretion disc based two component accretion flow model. The estimated disc and jet flux relations with radio flux show that accretion disc can contribute to the observed X-ray emission, when X-ray data (that covers a small portion of the broad band spectral energy distribution of Mrk 421) is considered in isolation. However, the present disc based models are disfavoured with respect to the relativistic jet models when considering the X-ray data in conjunction with data at other wavelengths.

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“…On the contrary, there can be instances of an optical flare with no counterpart in the X-ray band. Also, the multiband flux variability characteristics of blazars are highly complex, as revealed from recent observations Rajput et al (2019Rajput et al ( , 2020Rajput et al ( , 2021. However, inspection of Fig.…”

Section: Observation and Data Reductionmentioning

confidence: 92%

Flux and spectral variability of Mrk 421 during its moderate activity state usingNuSTAR: Possible accretion disc contribution?

Mondal

Rani

Stalin

et al. 2022

A&A

View full text Add to dashboard Cite

Context. The X-ray emission in BL Lac objects is believed to be dominated by synchrotron emission from their relativistic jets. However, when the jet emission is not strong, one could expect signatures of X-ray emission from inverse Compton scattering of accretion disc photons by hot and energetic electrons in the corona. Moreover, the observed X-ray variability can also originate in the disc, and get propagated and amplified by the jet. Aims. Here, we present results on the BL Lac object Mrk 421 using the Nuclear Spectroscopic Telescope Array data acquired during 2017 when the source was in a moderate X-ray brightness state. For comparison with high jet activity state, we also considered one epoch of data in April 2013 when the source was in a very high X-ray brightness state. Our aim is to explore the possibility of the signature of accretion disc emission in the overall X-ray emission from Mrk 421 and also examine changes in accretion parameters considering their contribution to spectral variations. Methods. We divided each epoch of data into different segments in order to find small-scale variability. Data for all segments were fitted using a simple power-law model. We also fitted the full epoch data using the two component advective flow (TCAF) model to extract the accretion flow parameters. Furthermore, we estimated the X-ray flux coming from the different components of the flow using the lowest normalisation method and analysed the relations between them. For consistency, we performed the spectral analysis using models available in the literature. Results. The simple power-law function does not fit the spectra well, and a cutoff needs to be added. The spectral fitting of the data using the TCAF model shows that the data can be explained with a model where (a) the size of the dynamic corona at the base of the jet is from ∼28 to 10 rs, (b) the disc mass accretion rate is from 0.021 to 0.051 ṀEdd, (c) the halo mass accretion rate is from 0.22 to 0.35 ṀEdd, and (d) the viscosity parameter of the Keplerian accretion disc from 0.18 to 0.25. In the assumed model, the total flux, disc and jet flux correlate with the radio flux observed during these epochs. Conclusions. From the spectral analysis, we conclude that the spectra of all the epochs of Mrk 421 in 2017 are well described by the accretion-disc-based TCAF model. The estimated disc and jet flux relations with radio flux show that accretion disc can contribute to the observed X-ray emission, when X-ray data (that cover a small portion of the broad band spectral energy distribution of Mrk 421) are considered in isolation. However, the present disc-based models are disfavoured with respect to the relativistic jet models when considering the X-ray data in conjunction with data at other wavelengths.

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Correlation between optical and γ-ray flux variations in BL Lacs

Cited by 7 publications

References 79 publications

Study of correlation between optical flux and polarization variations in BL Lac objects

Study of correlation between optical flux and polarization variations in BL Lac objects

Flux and spectral variability of Mrk 421 during its moderate activity state using NuSTAR: Possible accretion disc contribution?

Flux and spectral variability of Mrk 421 during its moderate activity state usingNuSTAR: Possible accretion disc contribution?

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