The expanding light echoes from supernova 2014J in M82
  We present the measurement of the size and surface brightness of the
expanding light echoes from supernova (SN) 2014J in the nearby starburst galaxy
M82. Hubble Space Telescope (HST) ACS/WFC images were taken ~277 and ~416 days
(after the time of B-band maximum light) in the filters F475W, F606W, and
F775W, each combined with the three polarizing filters: POL0V, POL60V, and
POL120V. The two epochs' imaging reveals the time evolution of at least two
major echoes. Three concentric bright regions between position angles (PA,
0^{\circ} from North, counterclockwise). 80^{\circ} ~ 170^{\circ} have
projected radius of 0.60" on the sky on ~277 days and expanding to 0.75" on
~416 days, corresponding to scattering materials at a foreground distance of
222\pm37 pc. Another fainter but evident light echo extending over a wide range
of PA has radii of 0.75" and 0.96" on ~277 and ~416 days. This corresponds to
scattering material at a foreground distance of 367\pm61 pc. Multiple light
echoes with S/N > 2.5 reside at smaller radii on ~277 days but become less
significant on ~416 days indicating a complex structure of foreground
interstellar medium (ISM). The light echo shows bluer color than predicted
under a Rayleigh scattering case. We also found the light echo brightened from
V_{echo}=21.68\pm0.07 on 2014 September 5, to V_{echo}=21.05\pm0.08 on 2014
November 6, suggesting an enhancement of echoing materials at different
distances projected on to the plane of the sky.
