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RINGO2 Optical Polarimetric Observations of PG 1553+113 during a MAGIC Gamma-ray Flare

ATel #4078; Iain Steele (LJMU), Carole Mundell (LJMU), U. Barres de Almeida (MPI for Physics), Elina Lindfors (Tuorla Observatory) and Kari Nilsson (Tuorla Observatory)
on 30 Apr 2012; 07:47 UT
Credential Certification: Ulisses Barres de Almeida (ulisses@mppmu.mpg.de)

Subjects: Optical, AGN, Blazar, Transient

We report optical polarimetric observations of the blazar PG 1553+113 gathered during a period of intense gamma-ray emission detected by the MAGIC experiment (Atel #4069). The polarimetric observations were carried out using the RINGO2 polarimeter (Steele et al. 2010) in the Liverpool Telescope in La Palma, Canary Islands.

The Liverpool optical telescope is monitoring the polarisation of the source since March 2012. Over the course of a week PG 1553+113 has brightened by about 0.25 magnitudes. The polarisation has also varied:

            TIME          DELTA-M     POLARISATION 
    2012-04-15 02:59:10    0.23           1.9%     
    2012-04-17 04:23:22    0.15           4.3%     
    2012-04-21 02:16:56    0.02           3.3%     
    2012-04-23 02:48:55   -0.02           5.0%     

Delta-M indicates the variation in magnitude of the source relative to the nearby comparison start of similar brightness 15:55:46.0 +11:11:20.

Previous polarisation measurements obtained with the KVA telescope in 2009 and in 2011 show that the currently observed values of the polarisation are within the range usually seen for the object.

The Liverpool Telescope polarimetric observations are part of a joint observational programme with MAGIC. The results presented above are preliminary and observations are still ongoing.

Reference:
Steele, I.A., S.D. Bates, C.J. Mottram et al. "RINGO2: an EMCCD-based polarimeter for GRB follow-up", Proc. SPIE 7735, 773549 (2010).