The RoboPol pipeline and control system

King, O. G.; Blinov, D.; Ramaprakash, A. N.; Myserlis, I.; Angelakis, E.; Baloković, Mislav; Feiler, R.; Fuhrmann, L.; Hovatta, T.; Khodade, P.; Kougentakis, A.; Kylafis, N. D.; Kus, A. J.; Modi, Deepa; Paleologou, E. V.; Panopoulou, G. V.; Papadakis, I. E.; Papamastorakis, I.; Paterakis, George; Pavlidou, V.; Pazderska, B.; Pazderski, E.; Pearson, T. J.; Rajarshi, C.; Readhead, A. C. S.; Reig, P.; Steiakaki, A.; Tassis, Konstantinos; Zensus, J. A.

doi:10.1093/mnras/stu176

Cited by 59 publications

(109 citation statements)

References 18 publications

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“…Noise q err,i , u err,i is then drawn from a Gaussian distribution N(0, σ q,i ) and it is added to each random walk data point. The data points and uncertainties are then transformed into m l , χ and the corresponding uncertainties following King et al (2014), Eqs. (5), (6).…”

Section: Simulated Evpa Errorsmentioning

confidence: 99%

Polarization angle swings in blazars: The case of 3C 279

Kiehlmann

Savolainen

Jorstad

et al. 2016

A&A

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Context. Over the past few years, on several occasions, large, continuous rotations of the electric vector position angle (EVPA) of linearly polarized optical emission from blazars have been reported. These events are often coincident with high energy γ-ray flares and they have attracted considerable attention, since they could allow us to probe the magnetic field structure in the γ-ray emitting region of the jet. The flat-spectrum radio quasar 3C 279 is one of the most prominent examples showing this behaviour. Aims. Our goal is to study the observed EVPA rotations and to distinguish between a stochastic and a deterministic origin of the polarization variability. Methods. We have combined multiple data sets of R-band photometry and optical polarimetry measurements of 3C 279, yielding exceptionally well-sampled flux density and polarization curves that cover a period of [2008][2009][2010][2011][2012]. Several large EVPA rotations are identified in the data. We introduce a quantitative measure for the EVPA curve smoothness, which is then used to test a set of simple random walk polarization variability models against the data. Results. 3C 279 shows different polarization variation characteristics during an optical low-flux state and a flaring state. The polarization variation during the flaring state, especially the smooth ∼360• rotation of the EVPA in mid-2011, is not consistent with the tested stochastic processes. Conclusions. We conclude that, during the two different optical flux states, two different processes govern polarization variation, which is possibly a stochastic process during the low-brightness state and a deterministic process during the flaring activity.

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Section: Simulated Evpa Errorsmentioning

confidence: 99%

Polarization angle swings in blazars: The case of 3C 279

Kiehlmann

Savolainen

Jorstad

et al. 2016

A&A

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“…The observations were reduced using the pipeline described in King et al (2014), which uses aperture photometry. The TeV sources were measured with a fixed 3 aperture diameter.…”

Section: Robopol Observationsmentioning

confidence: 99%

Optical polarization of high-energy BL Lacertae objects

Hovatta

Lindfors

Blinov

et al. 2016

A&A

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Context. We investigate the optical polarization properties of high-energy BL Lac objects using data from the RoboPol blazar monitoring program and the Nordic Optical Telescope. Aims. We wish to understand if there are differences in the BL Lac objects that are detected with the current-generation TeV instruments compared to those that have not yet been detected. Methods. We use a maximum likelihood method to investigate the optical polarization fraction and its variability in these sources. In order to study the polarization position angle variability, we calculate the time derivative of the electric vector position angle (EVPA) change. We also study the spread in the Stokes Q/I − U/I-plane and rotations in the polarization plane. Results. The mean polarization fraction of the TeV-detected BL Lacs is 5% while the non-TeV sources show a higher mean polarization fraction of 7%. This difference in polarization fraction disappears when the dilution by the unpolarized light of the host galaxy is accounted for. The TeV sources show somewhat lower fractional polarization variability amplitudes than the non-TeV sources. Also the fraction of sources with a smaller spread in the Q/I − U/I-plane and a clumped distribution of points away from the origin, possibly indicating a preferred polarization angle, is larger in the TeV than in the non-TeV sources. These differences between TeV and non-TeV samples seems to arise from differences between intermediate and high spectral peaking sources instead of the TeV detection. When the EVPA variations are studied, the rate of EVPA change is similar in both samples. We detect significant EVPA rotations in both TeV and non-TeV sources, showing that rotations can occur in high spectral peaking BL Lac objects when the monitoring cadence is dense enough. Our simulations show that we cannot exclude a random walk origin for these rotations. Conclusions. These results indicate that there are no intrinsic differences in the polarization properties of the TeV-detected and nonTeV-detected high-energy BL Lac objects. This suggests that the polarization properties are not directly related to the TeV-detection, but instead the TeV loudness is connected to the general flaring activity, redshift, and the synchrotron peak location.

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“…The program performs aperture photometry of all point sources in the field of view, calculates their normalized Stokes parameters q and u and also provides relative photometry. A detailed description of the RoboPol control system and pipeline is given in King et al (2014a). Upgrades made to the pipeline, mainly with regards to analysis in the wider FOV, are described in Panopoulou et al (2015).…”

Section: Control System and Data Reduction Pipelinementioning

confidence: 99%

“…By default, the data are reduced and corrected for the instrumental polarization according to the instrument model described in King et al (2014a) (see also section 3). The parameters of the model are fit anew each observing season, as the instrument is removed from the GAM at the end of the observatory seasonal operations (typically November) and re-installed at the start of the following season (typically March).…”

Section: Control System and Data Reduction Pipelinementioning

confidence: 99%

RoboPol: a four-channel optical imaging polarimeter

Ramaprakash

Rajarshi

Das

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present the design and performance of RoboPol, a four-channel optical polarimeter operating at the Skinakas Observatory in Crete, Greece. RoboPol is capable of measuring both relative linear Stokes parameters q and u (and the total intensity I) in one sky exposure. Though primarily used to measure the polarization of point sources in the R-band, the instrument features additional filters (B, V and I), enabling multi-wavelength imaging polarimetry over a large field of view (13.6 ′ × 13.6 ′ ). We demonstrate the accuracy and stability of the instrument throughout its five years of operation. Best performance is achieved within the central region of the field of view and in the R band. For such measurements the systematic uncertainty is below 0.1% in fractional linear polarization, p (0.05% maximum likelihood). Throughout all observing seasons the instrumental polarization varies within 0.1% in p and within ∼1 • in polarization angle.

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The RoboPol pipeline and control system

Cited by 59 publications

References 18 publications

Polarization angle swings in blazars: The case of 3C 279

Polarization angle swings in blazars: The case of 3C 279

Optical polarization of high-energy BL Lacertae objects

RoboPol: a four-channel optical imaging polarimeter

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