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Optical polarimetric observations of 4C +21.35 (PKS 1222+21) during the gamma-ray flare

ATEL # 2693; T. Dominici (MCT/LNA), A. Pereyra (MCT/ON), Z. Abraham (IAG/USP), U. Barres de Almeida (Durham University), C. Boisson (Observatoire de Paris-Meudon), P. Chadwick (Durham University), A. M. Magalhaes (IAG/USP) & M. Ward (Durham University)
on 23 Jun 2010; 12:05 UT
Password Certification: Tania Dominici (tdominici@lna.br)

Subjects: Optical
Referred to by ATEL #: 2708

We report optical polarimetric observations of the blazar 4C +21.35 (PKS 1222+21) gathered during the intense gamma-ray emission that has been detected and followed by MAGIC experiment (Atel #2684), AGILE (Atel #2686) and Fermi (Atel #2687) satellites. The polarimetric observations were carried out using the B&C 60 cm telescope at Pico dos Dias Observatory (Brazopolis, MG, Brazil, MCT/LNA) equipped with an imaging polarimeter (IAGPOL, Magalhaes et al. 1996).

Two measurements were obtained in the R band on June 19, as follow:

UT 22:11:51.89: P(R) = (4.31 +/- 0.08)% ; theta = 160.5 +/- 0.5 degrees

UT 22:51:41.54: P(R) = (4.05 +/- 0.18)%; theta = 160.3 +/- 1.3 degrees

The source was observed again on June 20 UT 21:57:01.09 and has exhibited variability in both, polarization degree and position angle: P(R) = (1.47 +/- 0.19)%; theta = 15.6 +/- 3.7 degrees

The light curve provided by Catalina Real-time Transient Survey of Fermi blazars (http://nesssi.cacr.caltech.edu/catalina/Blazars/501021210634100112p.html, Drake et al. 2009) shows a brightness decrease of about 0.34 magnitudes between its first measurement of 19 June and the last one on 22 June (14.21 and 14.55 +/- 0.02, respectively, in the V band). Additionally, we estimated R magnitude from polarimetric frames and obtained 14.53 and 14.92 for the first and second nights, respectively, with uncertainties of about 0.1 magnitudes. Based on that, the polarization seems to be correlated with total light.

4C +21.35 is not an usual source for polarimetric monitoring programs and few data are available from the literature. For a comparison, Sluse et al. (2005) observed the blazar on 23 March, 2002, and found P(R) = (1.52 +/- 0.13)% and theta = 167 +/- 3 degrees, using 3.6 m La Silla telescoped equipped with EFOSC2. We encourage further polarimetric observations to look for correlations with the gamma-ray activity.

References

Drake, A.J., et al., 2009, ApJ, 696, 870

Magalhaes, A.M., et al., 2006, ASP Conf. Ser. 355 (M. Kraus & A.S. Miroshnichenko), p. 147

Sluse, D. et al., 2005, A&A, 433, 757


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