Wide-field one-shot optical polarimeter: HOWPol

Abstract

For prompt optical polarimetry of gamma-ray burst (GRB) afterglow, we require wide-field imaging polarimeter which can produce both Stokes <i>Q</i> and <i>U</i> parameters from only a single exposure, as well as quickly-moving telescope and enclosure system. HOWPol is an optical imaging polarimeter which provides four linearly polarized images at position angles of 0&deg;, 45&deg;, 90&deg; and 135&deg;, i.e., Stokes <i>I</i>, <i>Q</i>, <i>U</i>, simultaneously. The key device is the wedged double Wollaston prism described by Oliva (1997)¹ and Pernechele et al. (2003).² The images are focused on two 2k&times;4k fully depleted CCDs. We report the design and development of the optical devices of HOWPol, which will be mounted to the 1.5-m Kanata telescope at Hiroshima University and stand by the GRB alert.