TY - JOUR

T1 - X-Ray Polarization Detection of Cassiopeia A with IXPE

AU - Vink, Jacco

AU - Prokhorov, Dmitry

AU - Ferrazzoli, Riccardo

AU - Slane, Patrick

AU - Zhou, Ping

AU - Asakura, Kazunori

AU - Baldini, Luca

AU - Bucciantini, Niccoló

AU - Costa, Enrico

AU - Di Marco, Alessandro

AU - Heyl, Jeremy

AU - Marin, Frédéric

AU - Mizuno, Tsunefumi

AU - Ng, C.-Y.

AU - Pesce-Rollins, Melissa

AU - Ramsey, Brian D.

AU - Rankin, John

AU - Ratheesh, Ajay

AU - Sgró, Carmelo

AU - Soffitta, Paolo

AU - Swartz, Douglas A.

AU - Tamagawa, Toru

AU - Weisskopf, Martin C.

AU - Yang, Yi-Jung

AU - Bellazzini, Ronaldo

AU - Bonino, Raffaella

AU - Cavazzuti, Elisabetta

AU - Costamante, Luigi

AU - Di Lalla, Niccoló

AU - Latronico, Luca

AU - Maldera, Simone

AU - Manfreda, Alberto

AU - Massaro, Francesco

AU - Mitsuishi, Ikuyuki

AU - Omodei, Nicola

AU - Oppedisano, Chiara

AU - Zane, Silvia

AU - Agudo, Ivan

AU - Antonelli, Lucio A.

AU - Bachetti, Matteo

AU - Baumgartner, Wayne H.

AU - Bianchi, Stefano

AU - Bongiorno, Stephen D.

AU - Brez, Alessandro

AU - Capitanio, Fiamma

AU - Castellano, Simone

AU - Ciprini, Stefano

AU - Rosa, Alessandra De

AU - Del Monte, Ettore

AU - Gesu, Laura Di

AU - Donnarumma, Immacolata

AU - Doroshenko, Victor

AU - Dovčiak, Michal

AU - Ehlert, Steven R.

AU - Enoto, Teruaki

AU - Evangelista, Yuri

AU - Fabiani, Sergio

AU - Garcia, Javier A.

AU - Gunji, Shuichi

AU - Hayashida, Kiyoshi

AU - Iwakiri, Wataru

AU - Jorstad, Svetlana G.

AU - Karas, Vladimir

AU - Kitaguchi, Takao

AU - Kolodziejczak, Jeffery J.

AU - Krawczynski, Henric

AU - La Monaca, Fabio

AU - Liodakis, Ioannis

AU - Marinucci, Andrea

AU - Marscher, Alan P.

AU - Marshall, Herman L.

AU - Matt, Giorgio

AU - Muleri, Fabio

AU - O’Dell, Stephen L.

AU - Papitto, Alessandro

AU - Pavlov, George G.

AU - Peirson, Abel L.

AU - Perri, Matteo

AU - Pilia, Maura

AU - Possenti, Andrea

AU - Poutanen, Juri

AU - Puccetti, Simonetta

AU - Romani, Roger W.

AU - Spandre, Gloria

AU - Tavecchio, Fabrizio

AU - Taverna, Roberto

AU - Tawara, Yuzuru

AU - Tennant, Allyn F.

AU - Thomas, Nicolas E.

AU - Tombesi, Francesco

AU - Trois, Alessio

AU - Tsygankov, Sergey

AU - Turolla, Roberto

AU - Wu, Kinwah

AU - Xie, Fei

PY - 2022

Y1 - 2022

N2 - We report on a ∼5σ detection of polarized 3–6 keV X-ray emission from the supernova remnant Cassiopeia A (Cas A) with the Imaging X-ray Polarimetry Explorer (IXPE). The overall polarization degree of 1.8% ± 0.3% is detected by summing over a large region, assuming circular symmetry for the polarization vectors. The measurements imply an average polarization degree for the synchrotron component of ∼2.5%, and close to 5% for the X-ray synchrotron-dominated forward shock region. These numbers are based on an assessment of the thermal and nonthermal radiation contributions, for which we used a detailed spatial-spectral model based on Chandra X-ray data. A pixel-by-pixel search for polarization provides a few tentative detections from discrete regions at the ∼ 3σ confidence level. Given the number of pixels, the significance is insufficient to claim a detection for individual pixels, but implies considerable turbulence on scales smaller than the angular resolution. Cas A’s X-ray continuum emission is dominated by synchrotron radiation from regions within ≲1017 cm of the forward and reverse shocks. We find that (i) the measured polarization angle corresponds to a radially oriented magnetic field, similar to what has been inferred from radio observations; (ii) the X-ray polarization degree is lower than in the radio band (∼5%). Since shock compression should impose a tangential magnetic-field structure, the IXPE results imply that magnetic fields are reoriented within ∼1017 cm of the shock. If the magnetic-field alignment is due to locally enhanced acceleration near quasi-parallel shocks, the preferred X-ray polarization angle suggests a size of 3 × 1016 cm for cells with radial magnetic fields.

AB - We report on a ∼5σ detection of polarized 3–6 keV X-ray emission from the supernova remnant Cassiopeia A (Cas A) with the Imaging X-ray Polarimetry Explorer (IXPE). The overall polarization degree of 1.8% ± 0.3% is detected by summing over a large region, assuming circular symmetry for the polarization vectors. The measurements imply an average polarization degree for the synchrotron component of ∼2.5%, and close to 5% for the X-ray synchrotron-dominated forward shock region. These numbers are based on an assessment of the thermal and nonthermal radiation contributions, for which we used a detailed spatial-spectral model based on Chandra X-ray data. A pixel-by-pixel search for polarization provides a few tentative detections from discrete regions at the ∼ 3σ confidence level. Given the number of pixels, the significance is insufficient to claim a detection for individual pixels, but implies considerable turbulence on scales smaller than the angular resolution. Cas A’s X-ray continuum emission is dominated by synchrotron radiation from regions within ≲1017 cm of the forward and reverse shocks. We find that (i) the measured polarization angle corresponds to a radially oriented magnetic field, similar to what has been inferred from radio observations; (ii) the X-ray polarization degree is lower than in the radio band (∼5%). Since shock compression should impose a tangential magnetic-field structure, the IXPE results imply that magnetic fields are reoriented within ∼1017 cm of the shock. If the magnetic-field alignment is due to locally enhanced acceleration near quasi-parallel shocks, the preferred X-ray polarization angle suggests a size of 3 × 1016 cm for cells with radial magnetic fields.

U2 - 10.3847/1538-4357/ac8b7b

DO - 10.3847/1538-4357/ac8b7b

M3 - Article

VL - 938

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

ER -