Presentation #133.02 in the session Planetary Nebulae, Supernova Remnants.
We present SOFIA HAWC+ band D (at 154 microns) polarization observations of the young supernova remnant (SNR) Cas A. The polarization map shows high polarization fractions at 5–30 percent level and their variation across the SNR, indicating that SNRs may be a strong polarization source in far-IR. The high polarization is direct evidence that grains are highly elongated and aligned to a high degree. We observe an inverse correlation between the intensity and polarization degree. The polarization is well-aligned but weaker where the emission is bright at the central unshocked ejecta and the southeastern shell. In contrast, stronger polarization is detected between the bright structures. The observed polarization is that the grain alignment efficiency is lower where the gas density is higher because of a higher rate of dust’s collision with gas. HAWC+ polarization map at 154 microns differs from the polarization of SCUBA 850 micron, where the northern shell shows the highest polarization (and did not cover the south). We will present the magnetic field strength using the Davis-Chandrasekhar-Fermi (DCF) method and constraints of dust composition, the average grain size, dust mass, and other dust properties of the freshly produced grains from the dust polarization maps.