@article{discovery10196344,
          volume = {9},
           month = {August},
       publisher = {NATURE PORTFOLIO},
         journal = {Nature Astronomy},
            year = {2024},
           title = {Complex rotational dynamics of the neutron star in Hercules X-1 revealed by X-ray polarization},
           pages = {1047--1053},
            note = {This version is the author accepted manuscript. For information on re-use, please refer to the publisher's terms and conditions.},
        abstract = {In an accreting X-ray pulsar, a neutron star accretes matter from a companion star through an accretion disk. The magnetic field of the rotating neutron star disrupts the inner edge of the disk, funnelling the gas to flow onto the poles on its surface. Hercules X-1 is a prototypical persistent X-ray pulsar about 7 kpc from Earth. Its emission varies on three distinct timescales: the neutron star rotates every 1.2 s, it is eclipsed by its companion each 1.7 d, and the system exhibits a superorbital period of 35 d, which has remained stable since its discovery. Several lines of evidence point to the source of this variation as the precession of the accretion disk or that of the neutron star. Despite the many hints over the past 50 yr, the precession of the neutron star itself has yet not been confirmed or refuted. X-ray polarization measurements (probing the spin geometry of Her X-1) with the Imaging X-ray Polarimetry Explorer suggest that free precession of the neutron star crust sets the 35 d period; this has the important implication that its crust is somewhat asymmetric by a few parts per ten million.},
             url = {http://dx.doi.org/10.1038/s41550-024-02295-8},
          author = {Heyl, J and Doroshenko, V and Gonz{\'a}lez-Caniulef, D and Caiazzo, I and Poutanen, J and Mushtukov, A and Tsygankov, SS and Kirmizibayrak, D and Bachetti, M and Pavlov, GG and Forsblom, SV and Malacaria, C and Suleimanov, VF and Agudo, I and Antonelli, LA and Baldini, L and Baumgartner, WH and Bellazzini, R and Bianchi, S and Bongiorno, SD and Bonino, R and Brez, A and Bucciantini, N and Capitanio, F and Castellano, S and Cavazzuti, E and Chen, CT and Ciprini, S and Costa, E and De Rosa, A and Del Monte, E and Di Gesu, L and Di Lalla, N and Di Marco, A and Donnarumma, I and Dov{\vc}iak, M and Ehlert, SR and Enoto, T and Evangelista, Y and Fabiani, S and Ferrazzoli, R and Garcia, JA and Gunji, S and Hayashida, K and Iwakiri, W and Jorstad, SG and Kaaret, P and Karas, V and Kislat, F and Kitaguchi, T and Kolodziejczak, JJ and Krawczynski, H and La Monaca, F and Latronico, L and Liodakis, I and Maldera, S and Manfreda, A and Marin, F and Marinucci, A and Marscher, AP and Marshall, HL and Massaro, F and Matt, G and Mitsuishi, I and Mizuno, T and Muleri, F and Negro, M and Ng, CY and O'Dell, SL and Omodei, N and Oppedisano, C and Papitto, A and Peirson, AL and Perri, M and Pesce-Rollins, M and Petrucci, PO and Pilia, M and Possenti, A and Puccetti, S and Ramsey, BD and Rankin, J and Ratheesh, A and Roberts, OJ and Romani, RW and Sgr{\`o}, C and Slane, P and Soffitta, P and Spandre, G and Swartz, DA and Tamagawa, T and Tavecchio, F and Taverna, R and Tawara, Y and Tennant, AF and Thomas, NE and Tombesi, F and Trois, A and Turolla, R and Vink, J and Weisskopf, MC}
}