First Detection of Polarization in X-Rays for PSR B0540-69 and Its Nebula
Fei Xie, Josephine Wong, Fabio La Monaca, Roger W. Romani, Jeremy Heyl, P. Kaaret, Alessandro Di Marco, N. Bucciantini, Kuan Liu, C.‐Y. Ng, Niccolò Di Lalla, Martin C. Weisskopf, E. Costa, P. Soffitta, Fabio Muleri, Matteo Bachetti, M. Pilia, John Rankin, Sergio Fabiani, I. Agudo, L. A. Antonelli, L. Baldini, W. H. Baumgartner, R. Bellazzini, S. Bianchi, Stephen D. Bongiorno, R. Bonino, A. Brez, Fiamma Capitanio, Simone Castellano, E. Cavazzuti, Chien‐Ting Chen, S. Ciprini, Alessandra De Rosa, E. Del Monte, Laura Di Gesu, I. Donnarumma, Victor Doroshenko, Michal Dovčiak, Steven R. Ehlert, Teruaki Enoto, Y. Evangelista, Riccardo Ferrazzoli, Javier A. García, Shuichi Gunji, Kiyoshi Hayashida, W. Iwakiri, Svetlana G. Jorstad, V. Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, H. Krawczynski, L. Latronico, Ioannis Liodakis, S. Maldera, Alberto Manfreda, Frédéric Marin, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, F. Massaro, G. Matt, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Michela Negro, Stephen L. O’Dell, N. Omodei, C. Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, M. Perri, M. Pesce-Rollins, Pierre-Olivier Petrucci, Andrea Possenti, Juri Poutanen, Simonetta Puccetti, Brian D. Ramsey, Ajay Ratheesh, O. J. Roberts, C. Sgró, Patrick Slane, G. Spandre, Douglas A. Swartz, Toru Tamagawa, F. Tavecchio, Roberto Taverna, Yuzuru Tawara, Allyn F. Tennant, Nicholas E. Thomas, Francesco Tombesi, A. Trois, Sergey S. Tsygankov, Roberto Turolla, Jacco Vink, Kinwah Wu, Silvia Zane, Zorawar Wadiasingh, Wynn C. G. Ho
Abstract
Abstract We report on X-ray polarization measurements of the extragalactic Crab-like PSR B0540-69 and its Pulsar Wind Nebula (PWN) in the Large Magellanic Cloud, using a ∼850 ks Imaging X-ray Polarimetry Explorer (IXPE) exposure. The PWN is unresolved by IXPE. No statistically significant polarization is detected for the image-averaged data, giving a 99% confidence polarization upper limit (MDP 99 ) of 5.3% in the 2–8 keV energy range. However, a phase-resolved analysis detects polarization for both the nebula and pulsar in the 4–6 keV energy range. For the PWN defined as the off-pulse phases, the polarization degree (PD) of (24.5 ± 5.3)% and polarization angle (PA) of (78.1 ± 6.2)° is detected at 4.6 σ significance level, consistent with the PA observed in the optical band. In a single on-pulse window, a hint of polarization is measured at 3.8 σ with PD of (50.0 ± 13.1)% and PA of (6.2 ± 7.4)°. A “simultaneous” PSR/PWN analysis finds two bins at the edges of the pulse exceeding 3 σ PD significance, with PD of (68 ± 20)% and (62 ± 20)%; intervening bins at 2–3 σ significance have lower PD, hinting at additional polarization structure.