On the Photometric Error Calibration for the Differential Light Curves of Point-like Active Galactic Nuclei

Goyal, A.; Mhaskey, Mukul; Gopal-Krishna, . .; Wiita, Paul J.; Stalin, C. S.; Sagar, Ram

doi:10.1007/s12036-013-9183-7

Cited by 19 publications

(23 citation statements)

References 49 publications

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“…As emphasized in several independent studies, the photometric errors returned by APPHOT are significantly underestimated (by factors of η = 1.3-1.7; Gopal- Garcia et al 1999;Stalin et al 2004;Bachev et al 2005;Zhang et al 2018). Goyal et al (2013a) obtained η =1.54±0.05, using 262 steady star-star DLCs and involving intra-night observations with three different telescopes located in India. Thus, η =1.54 has been used in the present analysis to scale up the photometric magnitude errors returned by IRAF.…”

Section: Determination Of Microvariability Parameters In the Dlcsmentioning

confidence: 99%

Multiband optical flux density and polarization microvariability study of optically bright blazars

Pasierb

Goyal

Ostrowski

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present the results of flux density, spectral index, and polarization intra-night monitoring studies of a sample of eight optically bright blazars, carried out by employing several small to moderate aperture (0.4 m to 1.5 m diameter) telescopes fitted with CCDs and polarimeters located in Europe, India, and Japan. The duty cycle of flux variability for the targets is found to be ∼ 45 percent, similar to that reported in earlier studies. The computed two-point spectral indices are found to be between 0.65 to 1.87 for our sample, comprised of low-and intermediate frequency peaked blazars, with one exception; they are also found to be statistically variable for about half the instances where 'confirmed' variability is detected in flux density. In the analysis of the spectral evolution of the targets on hourly timescale, a counter-clockwise loop (soft-lagging) is noted in the flux-spectral index plane on two occasions, and in one case a clear spectral flattening with the decreasing flux is observed. In our data set, we also observe a variety of flux-polarization degree variability patterns, including instances with a relatively straightforward anti-correlation, correlation, or counterclockwise looping. These changes are typically reflected in the flux-polarization angle plane: the anti-correlation between the flux and polarization degree is accompanied by an anti-correlation between the polarization angle and flux, while the counterclockwise flux-PD looping behaviour is accompanied by a clockwise looping in the flux-polarization angle representation. We discuss our findings in the framework of the internal shock scenario for blazar sources.

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Section: Determination Of Microvariability Parameters In the Dlcsmentioning

confidence: 99%

Multiband optical flux density and polarization microvariability study of optically bright blazars

Pasierb

Goyal

Ostrowski

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Different values were calculated by different authors e.g Before subsequent analysis, we should estimate the scale factor η for each telescope. The method of Goyal et al (2013) is adopted. First, for each light curve, we calculate the χ 2 value of differential magnitudes of the check star by using the equation as follow:…”

Section: Error Scalingmentioning

confidence: 99%

Intra-day optical multi-band quasi-simultaneous observation of BL Lacertae object S5 0716+714 from 2013 to 2016

Zhang

Meng

2018

Monthly Notices of the Royal Astronomical Society

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We perform quasi-simultaneous optical multi-band monitoring of BL Lac object S5 0716+714 on seven nights from 2013 to 2016. Intra-day variability (IDV) is found on all seven nights. The source was faintest on JD 2456322 with 14.15 mags and brightest on JD 2457437 with 12.51 mags in the R band. The maximum intra-day variation we observed is 0.15 mags in the B band on JD 2456322. Both bluer-whenbrighter and achromatic spectral behaviours were observed on the intra-day timescale. On the longer-term scale, the object exhibited a mild bluer-when-brighter behaviour between the B and R bands. We estimate the inter-band lags using two independent methods. The variation in the B band was observed to lag that in the I band by about 15 minutes on JD 2457315. We compare this lag with one reported previously and discussed the origin of these lags.

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“…We trace the cause of the difference to the re-sampling process in SWarp of sub-pixel shifted images for stacking that decreases background noise of the stacked image (Bertin et al 2002). Note that a similar factor has been introduced in other AGN variability studies (e.g., Goyal et al 2013b). Thus, we used Equation (4) to model the true photometry error σ cal , as…”

Section: Variability Of Agnmentioning

confidence: 91%

Intra-night optical variability of AGN in the COSMOS field with the KMTNet

Kim,

Karouzos,

et al. 2018

Preprint

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Active Galactic Nucleus (AGN) variability can be used to study the physics of the region in the vicinity of the central black hole. In this paper, we investigated intra-night optical variability of AGN in the COSMOS field in order to understand the AGN instability at the smallest scale. Observations were performed using the KMTNet on three separate nights for 2.5-5 hour at a cadence of 20-30 min. We find that the observation enables the detection of the short-term variability as small as ∼ 0.02 and 0.1 mag for R ∼ 18 and 20 mag sources, respectively. Using four selection methods (X-rays, mid-infrared, radio, and matching with SDSS quasars), 394 AGNs are detected in the 4 deg 2 field of view. After differential photometry and χ 2 −test, we classify intra-night variable AGNs. But the fraction of variable AGNs (0-8 %) is consistent with a statistical fluctuation from null result. Eight out of 394 AGNs are found to be intra-night variable in two filters or two nights with a variability level of 0.1 mag, suggesting that they are strong candidates for intra-night variable AGNs. Still they represent a small population (2 %). There is no sub-category of AGNs that shows a statistically significant intra-night variability.

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On the Photometric Error Calibration for the Differential Light Curves of Point-like Active Galactic Nuclei

Cited by 19 publications

References 49 publications

Multiband optical flux density and polarization microvariability study of optically bright blazars

Multiband optical flux density and polarization microvariability study of optically bright blazars

Intra-day optical multi-band quasi-simultaneous observation of BL Lacertae object S5 0716+714 from 2013 to 2016

Intra-night optical variability of AGN in the COSMOS field with the KMTNet

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