Optical Polarimetry of A0535+262 in February and March 2015

ATel #7435; Iain A Steele (Liverpool JMU)
on 23 Apr 2015; 13:26 UT
Credential Certification: Iain Steele (iainsteele@mac.com)

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Following the report of the start of increased X-ray activity from the high mass Be/X-ray binary source A0535+262 (ATel #7015) I began a programme of regular monitoring of the optical polarisation of the counterpart (HD245770). Data were obtained using the RINGO3 polarimeter of the Liverpool Telescope. This carries out optical polarisation measurements simultaneously in three bands ("near IR" 770-1000nm, "Red" 650-760nm, and "Visible" 350-640 nm).

I measure the following degree of polarisation (percentage) in the three filters. Typical errors on each measurement are ~0.5 per-cent and are due to systematic effects in the instrument.

 
UT DATE  near-IR  Vis       Red 
 
20150206  0.9      1.3      1.0 
20150211  0.9      1.6      1.5 
20150213  1.1      1.6      1.8 
20150215  1.2      0.9      0.8 
20150224  0.6      1.5      1.8 
20150301  1.0      0.3      0.3 
20150304  0.6      1.8      2.0   
20150311  0.8      1.3      1.7 
20150313  1.0      1.6      1.2 
20150315  0.8      1.3      1.7 
20150327  0.7      1.2      1.1 

Inspection of the SWIFT/BAT light curve of the source (http://swift.gsfc.nasa.gov/results/transients/1A0535p262/) shows that the outburst began on 20150128, reached its peak on 20150205 and ended on 20150214. Weakening of the H-alpha line strength in optical spectra at the time of the outburst is presented in ATel #7029 and Atel #7030 and can be interpreted as a possible interaction between the neutron star and the Be star disk.

The first three polarimetric data points presented correspond to the time of X-ray activity, with the remainder in quiescence. No difference is apparent between the two epochs. The measured degree of polarisation is consistent with that expected for a Be star disk (Waters & Marlborough, 1992, A&A, 256, 195) with no evidence for an additional polarimetric component associated with the interaction of the neutron star with the disk as is suggested may be occurring in the source EXO2030+375 (Reig et al., 2014, MNRAS, 445, 4235).

Liverpool Telescope