Kavli Affiliate: Nicola Omodei
| First 5 Authors: Riccardo Ferrazzoli, Dmitry Prokhorov, Niccolò Bucciantini, Patrick Slane, Jacco Vink
| Summary:
Supernova remnants (SNRs) provide insights into cosmic-ray acceleration and
magnetic field dynamics at shock fronts. Recent X-ray polarimetric measurements
by the Imaging X-ray Polarimetry Explorer (IXPE) have revealed radial magnetic
fields near particle acceleration sites in young SNRs, including Cassiopeia A,
Tycho, and SN 1006. We present here the spatially-resolved IXPE X-ray
polarimetric observation of the northwestern rim of SNR RX J1713.7-3946. For
the first time, our analysis shows that the magnetic field in particle
acceleration sites of this SNR is oriented tangentially with respect to the
shock front. Because of the lack of precise Faraday-rotation measurements in
the radio band, this was not possible before. The average measured polarization
degree (PD) of the synchtrotron emission is 12.5 {pm} 3.3%, lower than the one
measured by IXPE in SN 1006, comparable to the Tycho one, but notably higher
than the one in Cassiopeia A. On sub-parsec scales, localized patches within RX
J1713.7-3946 display PD up to 41.5 {pm} 9.5%. These results are compatible
with a shock-compressed magnetic field. However, in order to explain the
observed PD, either the presence of a radial net magnetic field upstream of the
shock, or partial reisotropization of the turbulence downstream by radial
magneto-hydrodynamical instabilities, can be invoked. From comparison of PD and
magnetic field distribution with {gamma}-rays and 12 CO data, our results
provide new inputs in favor of a leptonic origin of the {gamma}-ray emission.
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