Related papers: Polarized x-rays from a magnetar

Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements

We report spectro-polarimetric results of an observational campaign of the bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by IXPE, NICER and INTEGRAL. Consistently with previous results, the broad-band spectrum is…

High Energy Astrophysical Phenomena · Physics 2023-01-18 R. Farinelli , S. Fabiani , J. Poutanen , F. Ursini , C. Ferrigno , S. Bianchi , M. Cocchi , F. Capitanio , A. De Rosa , A. Gnarini , F. Kislat , G. Matt , R. Mikusincova , F. Muleri , I. Agudo , L. A. Antonelli , M. Bachetti , L. Baldini , W. H. Baumgartner , R. Bellazzini , S. D. Bongiorno , R. Bonino , A. Brez , N. Bucciantini , S. Castellano , E. Cavazzuti , S. Ciprini , E. Costa , E. Del Monte , L. Di Gesu , N. Di Lalla , A. Di Marco , I. Donnarumma , V. Doroshenko , M. Dovčiak , S. R. Ehlert , T. Enoto , Y. Evangelista , R. Ferrazzoli , J. A. Garcia , S. Gunji , K. Hayashida , J. Heyl , W. Iwakiri , S. G. Jorstad , V. Karas , T. Kitaguchi , J. J. Kolodziejczak , H. Krawczynski , F. La Monaca , L. Latronico , I. Liodakis , S. Maldera , A. Manfreda , F. Marin , A. P. Marscher , H. L. Marshall , I. Mitsuishi , T. Mizuno , C. -Y. Ng , S. L. O'Dell , N. Omodei , C. Oppedisano , A. Papitto , G. G. Pavlov , A. L. Peirson , M. Perri , M. Pesce-Rollins , P. O. Petrucci , M. Pilia , A. Possenti , S. Puccetti , B. D. Ramsey , J. Rankin , A. Ratheesh , R. W. Romani , C. Sgrò , P. Slane , P. Soffitta , G. Spandre , T. Tamagawa , F. Tavecchio , R. Taverna , Y. Tawara , A. F. Tennant , N. E. Thomas , F. Tombesi , A. Trois , S. S. Tsygankov , R. Turolla , J. Vink , M. C. Weisskopf , K. Wu , F. Xie , S. Zane

IXPE Polarizations of the Lighthouse Pulsar, Trail, and Filament

The Lighthouse pulsar (PSR J1101$-$6101) sports a bright X-ray trail and filament. The synchrotron emission from both structures is expected to be polarized, with electric vector position angle (EVPA) perpendicular to the magnetic field…

High Energy Astrophysical Phenomena · Physics 2026-05-13 Jack T. Dinsmore , Roger W. Romani , S. Zhang , C. -Y. Ng , Stefano Silvestri , Oleg Kargaltsev , Niccolo' Bucciantini , Philip Kaaret , Josephine Wong , Patrick Slane , Paolo Soffitta , Martin C. Weisskopf

Probing Magnetic Fields in Young Supernova Remnants with IXPE

Synchrotron emission from the shocked regions in supernova remnants provides, through its polarization, crucial details about the magnetic field strength and orientation in these regions. This, in turn, provides information on particle…

High Energy Astrophysical Phenomena · Physics 2024-10-07 Patrick Slane , Riccardo Ferrazzoli , Ping Zhou , Jacco Vink

Unobscured radio-quiet Active Galactic Nuclei under the eyes of IXPE

We present the results of the X-ray polarimetric analyses performed on unobscured radio-quiet Active Galactic Nuclei (AGN) with the Imaging X-ray Polarimetry Explorer (IXPE), with simultaneous XMM-Newton and NuSTAR data. The synergy of…

Astrophysics of Galaxies · Physics 2024-07-01 V. E. Gianolli , S. Bianchi , P-O. Petrucci , A. Marinucci , A. Ingram , D. Tagliacozzo , D. E. Kim , F. Marin , G. Matt , P. Soffitta , F. Tombesi

Uncovering the geometry of the hot X-ray corona in the Seyfert galaxy NGC4151 with IXPE

We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy NGC4151. The source has been observed with the Imaging X-ray Polarimetry Explorer (IXPE) for 700 ks, complemented with simultaneous XMM-Newton (50 ks) and NuSTAR…

Astrophysics of Galaxies · Physics 2023-06-12 V. E. Gianolli , D. E. Kim , S. Bianchi , B. Agís-González , G. Madejski , F. Marin , A. Marinucci , G. Matt , R. Middei , P-O. Petrucci , P. Soffitta , D. Tagliacozzo , F. Tombesi , F. Ursini , T. Barnouin , A. De Rosa , L. Di Gesu , A. Ingram , V. Loktev , C. Panagiotou , J. Podgorny , J. Poutanen , S. Puccetti , A. Ratheesh , A. Veledina , W. Zhang , I. Agudo , L. A. Antonelli , M. Bachetti , L. Baldini , W. H. Baumgartner , R. Bellazzini , S. D. Bongiorno , R. Bonino , A. Brez , N. Bucciantini , F. Capitanio , S. Castellano , E. Cavazzuti , C. -T. Chen , S. Ciprini , E. Costa , E. Del Monte , N. Di Lalla , A. Di Marco , I. Donnarumma , V. Doroshenko , M. Dovčiak , S. R. Ehlert , T. Enoto , Y. Evangelista , S. Fabiani , R. Ferrazzoli , J. A. García , S. Gunji , J. Heyl , W. Iwakiri , S. G. Jorstad , P. Kaaret , V. Karas , F. Kislat , T. Kitaguchi , J. J. Kolodziejczak , H. Krawczynski , F. La Monaca , L. Latronico , I. Liodakis , S. Maldera , A. Manfreda , A. P. Marscher , H. L. Marshall , F. Massaro , I. Mitsuishi , T. Mizuno , F. Muleri , M. Negro , C. -Y. Ng , S. L. ODell , N. Omodei , C. Oppedisano , A. Papitto , G. G. Pavlov , A. L. Peirson , M. Perri , M. Pesce-Rollins , M. Pilia , A. Possenti , B. D. Ramsey , J. Rankin , O. J. Roberts , R. W. Romani , C. Sgrò , P. Slane , G. Spandre , D. A. Swartz , T. Tamagawa , F. Tavecchio , R. Taverna , Y. Tawara , A. F. Tennant , N. E. Thomas , A. Trois , S. S. Tsygankov , R. Turolla , J. Vink , M. C. Weisskopf , K. Wu , F. Xie , S. Zane

New polarimetric study of the galactic X-ray burster GX 13+1

Weakly magnetized neutron stars (WMNS) are complicated sources with challenging phenomenology. For decades, they have been studied via spectrometry and timing. It has been established that the spectrum of WMNSs consists of several…

High Energy Astrophysical Phenomena · Physics 2024-08-28 Anna Bobrikova , Alessandro Di Marco , Fabio La Monaca , Juri Poutanen , Sofia V. Forsblom , Vladislav Loktev

IXPE observation of PKS 2155-304 reveals the most highly polarized blazar

We report the X-ray polarization properties of the high-synchrotron-peaked (HSP) blazar PKS 2155$-$304 based on observations with the Imaging X-ray Polarimetry Explorer (IXPE). We observed the source between Oct 27 and Nov 7, 2023. We also…

High Energy Astrophysical Phenomena · Physics 2024-09-11 Pouya M. Kouch , Ioannis Liodakis , Riccardo Middei , Dawoon E. Kim , Fabrizio Tavecchio , Alan P. Marscher , Herman L. Marshall , Steven R. Ehlert , Laura Di Gesu , Svetlana G. Jorstad , Iván Agudo , Grzegorz M. Madejski , Roger W. Romani , Manel Errando , Elina Lindfors , Kari Nilsson , Ella Toppari , Stephen B. Potter , Ryo Imazawa , Mahito Sasada , Yasushi Fukazawa , Koji S. Kawabata , Makoto Uemura , Tsunefumi Mizuno , Tatsuya Nakaoka , Hiroshi Akitaya , Callum McCall , Helen E. Jermak , Iain A. Steele , Ioannis Myserlis , Mark Gurwell , Garrett K. Keating , Ramprasad Rao , Sincheol Kang , Sang-Sung Lee , Sang-Hyun Kim , Whee Yeon Cheong , Hyeon-Woo Jeong , Emmanouil Angelakis , Alexander Kraus , Francisco José Aceituno , Giacomo Bonnoli , Víctor Casanova , Juan Escudero , Beatriz Agís-González , César Husillos , Daniel Morcuende , Jorge Otero-Santos , Alfredo Sota , Rumen Bachev , Lucio Angelo Antonelli , Matteo Bachetti , Luca Baldini , Wayne H. Baumgartner , Ronaldo Bellazzini , Stefano Bianchi , Stephen D. Bongiorno , Raffaella Bonino , Alessandro Brez , Niccolò Bucciantini , Fiamma Capitanio , Simone Castellano , Elisabetta Cavazzuti , Chien-Ting Chen , Stefano Ciprini , Enrico Costa , Alessandra De Rosa , Ettore Del Monte , Niccolò Di Lalla , Alessandro Di Marco , Immacolata Donnarumma , Victor Doroshenko , Michal Dovčiak , Teruaki Enoto , Yuri Evangelista , Sergio Fabiani , Riccardo Ferrazzoli , Javier A. Garcia , Shuichi Gunji , Kiyoshi Hayashida , Jeremy Heyl , Wataru Iwakiri , Philip Kaaret , Vladimir Karas , Fabian Kislat , Takao Kitaguchi , Jeffery J. Kolodziejczak , Henric Krawczynski , Fabio La Monaca , Luca Latronico , Simone Maldera , Alberto Manfreda , Frédéric Marin , Andrea Marinucci , Francesco Massaro , Giorgio Matt , Ikuyuki Mitsuishi , Fabio Muleri , Michela Negro , C. -Y. Ng , Stephen L. O'Dell , Nicola Omodei , Chiara Oppedisano , Alessandro Papitto , George G. Pavlov , Abel Lawrence Peirson , Matteo Perri , Melissa Pesce-Rollins , Pierre-Olivier Petrucci , Maura Pilia , Andrea Possenti , Juri Poutanen , Simonetta Puccetti , Brian D. Ramsey , John Rankin , Ajay Ratheesh , Oliver J. Roberts , Carmelo Sgrò , Patrick Slane , Paolo Soffitta , Gloria Spandre , Douglas A. Swartz , Toru Tamagawa , Roberto Taverna , Yuzuru Tawara , Allyn F. Tennant , Nicholas E. Thomas , Francesco Tombesi , Alessio Trois , Sergey S. Tsygankov , Roberto Turolla , Jacco Vink , Martin C. Weisskopf , Kinwah Wu , Fei Xie , Silvia Zane

X-ray and optical polarization aligned with the radio jet ejecta in GX 339-4

We present the first X-ray polarization measurements of GX 339-4. IXPE observed this source twice during its 2023-2024 outburst, once in the soft-intermediate state and again during a soft state. The observation taken during the…

High Energy Astrophysical Phenomena · Physics 2024-08-14 G. Mastroserio , B. De Marco , M. C. Baglio , F. Carotenuto , S. Fabiani , T. D. Russell , F. Capitanio , Y. Cavecchi , S. Motta , D. M. Russell , M. Dovciak , M. Del Santo , K. Alabarta , A. Ambrifi , S. Campana , P. Casella , S. Covino , G. Illiano , E. Kara , E. V. Lai , G. Lodato , A. Manca , I. Mariani , A. Marino , C. Miceli , P. Saikia , A. W. Shaw , J. Svoboda , F. M. Vincentelli , J. Wang

Active galactic nuclei in the era of the Imaging X-ray Polarimetry Explorer

In about four years, the National Aeronautics and Space Administration (NASA) will launch a small explorer mission named the Imaging X-ray Polarimetry Explorer (IXPE). IXPE is a satellite dedicated to the observation of X-ray polarization…

Instrumentation and Methods for Astrophysics · Physics 2017-08-08 F. Marin , M. C. Weisskopf

X-ray polarimetry and spectroscopy of the neutron star low-mass X-ray binary GX 9+9: an in-depth study with IXPE and NuSTAR

We report on a comprehensive analysis of simultaneous X-ray polarimetric and spectral data of the bright atoll source GX 9+9 with the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR. The source is significantly polarized in the 4--8…

High Energy Astrophysical Phenomena · Physics 2023-08-02 F. Ursini , R. Farinelli , A. Gnarini , J. Poutanen , S. Bianchi , F. Capitanio , A. Di Marco , S. Fabiani , F. La Monaca , C. Malacaria , G. Matt , R. Mikušincová , M. Cocchi , P. Kaaret , J. J. E. Kajava , M. Pilia , W. Zhang , I. Agudo , L. A. Antonelli , M. Bachetti , L. Baldini , W. H. Baumgartner , R. Bellazzini , S. D. Bongiorno , R. Bonino , A. Brez , N. Bucciantini , S. Castellano , E. Cavazzuti , C. -T. Chen , S. Ciprini , E. Costa , A. De Rosa , E. Del Monte , L. Di Gesu , N. Di Lalla , I. Donnarumma , V. Doroshenko , M. Dovčiak , S. R. Ehlert , T. Enoto , Y. Evangelista , R. Ferrazzoli , J. A. Garcia , S. Gunji , K. Hayashida , J. Heyl , W. Iwakiri , S. G. Jorstad , V. Karas , F. Kislat , T. Kitaguchi , J. J. Kolodziejczak , H. Krawczynski , L. Latronico , I. Liodakis , S. Maldera , A. Manfreda , F. Marin , A. Marinucci , A. P. Marscher , H. L. Marshall , F. Massaro , I. Mitsuishi , T. Mizuno , F. Muleri , M. Negro , C. -Y. Ng , S. L. O'Dell , N. Omodei , C. Oppedisano , A. Papitto , G. G. Pavlov , A. L. Peirson , M. Perri , M. Pesce-Rollins , P. -O. Petrucci , M. Pilia , A. Possenti , S. Puccetti , B. D. Ramsey , J. Rankin , A. Ratheesh , O. J. Roberts , R. W. Romani , C. Sgrò , P. Slane , P. Soffitta , G. Spandre , D. A. Swartz , T. Tamagawa , F. Tavecchio , R. Taverna , Y. Tawara , A. F. Tennant , N. E. Thomas , F. Tombesi , A. Trois , S. S. Tsygankov , R. Turolla , J. Vink , M. C. Weisskopf , K. Wu , F. Xie , S. Zane

Modelling polarized X-ray pulses from accreting millisecond pulsars with X-PSI, using different hot spot locations and shapes

We present an analysis of polarized X-ray pulses based on simulated data for accreting millisecond pulsars (AMPs). We used the open-source X-ray Pulse Simulation and Inference code (previously applied to NICER observations), which we…

High Energy Astrophysical Phenomena · Physics 2025-04-02 Tuomo Salmi , Bas Dorsman , Anna L. Watts , Anna Bobrikova , Alessandro Di Marco , Vladislav Loktev , Alessandro Papitto , Maura Pilia , Juri Poutanen , John Rankin

First X-ray and radio polarimetry of the neutron star low-mass X-ray binary GX 17+2

We report the first polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) Z-source GX 17+2 using the Imaging X-ray Polarimetry Explorer (IXPE) and the Very Large Array (VLA). We find that the X-ray source was polarized…

High Energy Astrophysical Phenomena · Physics 2025-10-08 Unnati Kashyap , Thomas J. Maccarone , Eliot C. Pattie , Mason Ng , Swati Ravi , Alexandra J. Tetarenko , Pau Bosch Cabot , Herman L. Marshall

First Detection of X-ray Polarization and Its Short-term Increase Pre- and Post-Eclipse in HMXB 4U 1700-377

We report the first statistically significant detection of X-ray polarization from the high-mass X-ray binary (HMXB) 4U 1700-377, observed using the Imaging X-ray Polarimetry Explorer (IXPE). A polarization degree exceeding 10% was detected…

High Energy Astrophysical Phenomena · Physics 2025-09-19 Kaito Ninoyu , Keisuke Uchiyama , Shinya Yamada , Ryota Hayakawa , Shunji Kitamoto , Nao Kominato , Takayoshi Kohmura , Misaki Mizumoto , Yuusuke Uchida , Toru Tamagawa , Ryota Tomaru , Seoru Ito

Polarized X-rays from Magnetized Neutron Stars

We review the polarization properties of X-ray emission from highly magnetized neutron stars, focusing on emission from the stellar surfaces. We discuss how x-ray polarization can be used to constrain neutron star magnetic field and…

High Energy Astrophysical Phenomena · Physics 2016-06-01 Dong Lai , Wynn C. G. Ho , Matthew van Adelsberg , Chen Wang , Jeremy S. Heyl

Pulsed and Polarized X-ray Emission from Neutron Star Surfaces

The intense magnetic fields of neutron stars naturally lead to strong anisotropy and polarization of radiation emanating from their surfaces, both being sensitive to the hot spot position on the surface. Accordingly, pulse phase-resolved…

High Energy Astrophysical Phenomena · Physics 2025-02-21 Matthew G. Baring , Hoa Dinh Thi , George A. Younes , Kun Hu

Highly Significant Detection of X-Ray Polarization from the Brightest Accreting Neutron Star Sco X-1

The Imaging X-ray Polarimetry Explorer (IXPE) measured with high significance the X-ray polarization of the brightest Z-source Scorpius X-1, resulting in the nominal 2-8 keV energy band in a polarization degree of 1.0(0.2)% and a…

High Energy Astrophysical Phenomena · Physics 2024-01-25 Fabio La Monaca , Alessandro Di Marco , Juri Poutanen , Matteo Bachetti , Sara E. Motta , Alessandro Papitto , Maura Pilia , Fei Xie , Stefano Bianchi , Anna Bobrikova , Enrico Costa , Wei Deng , Mingyu Ge , Giulia Illiano , Shu-Mei Jia , Henric Krawczynski , Eleonora V. Lai , Kuan Liu , Guglielmo Mastroserio , Fabio Muleri , John Rankin , Paolo Soffitta , Alexandra Veledina , Filippo Ambrosino , Melania Del Santo , Wei Chen , Javier A. Garcia , Philip Kaaret , Thomas D. Russell , Wen-Hao Wei , Shuang-Nan Zhang , Chao Zuo , Zaven Arzoumanian , Massimo Cocchi , Andrea Gnarini , Ruben Farinelli , Keith C. Gendreau , Francesco Ursini , Martin C. Weisskopf , Silvia Zane , Ivan Agudo , Lucio Angelo Antonelli , Luca Baldini , Wayne H. Baumgartner , Ronaldo Bellazzini , Stephen D. Bongiorno , Raffaella Bonino , Alessandro Brez , Niccolò Bucciantini , Fiamma Capitanio , Simone Castellano , Elisabetta Cavazzuti , Chien-Ting J. Chen , Stefano Ciprini , Alessandra De Rosa , Ettore Del Monte , Laura Di Gesu , Niccolò Di Lalla , Immacolata Donnarumma , Victor Doroshenko , Michal Dovciak , Steven R. Ehlert , Teruaki Enoto , Yuri Evangelista , Sergio Fabiani , Riccardo Ferrazzoli , Shuichi Gunji , Kiyoshi Hayashidadag , Jeremy Heyl , Wataru Iwakiri , Svetlana G. Jorstad , Vladimir Karas , Fabian Kislat , Takao Kitaguchi , Jeffery J. Kolodziejczak , Luca Latronico , Ioannis Liodakis , Simone Maldera , Alberto Manfreda , Fre'de'ric Marin , Andrea Marinucci , Alan P. Marscher , Herman L. Marshall , Francesco Massaro , Giorgio Matt , Ikuyuki Mitsuishi , Tsunefumi Mizuno , Michela Negro , Stephen Chi-Yung Ng , Stephen L. O'Dell , Nicola Omodei , Chiara Oppedisano , George Pavlov , Abel L. Peirson , Matteo Perri , Melissa Pesce-Rollins , Pierre-Olivier Petrucci , Andrea Possenti , Simonetta Puccetti , Brian Ramsey , Ajay Ratheesh , Oliver J. Roberts , Roger W. Romani , Carmelo Sgrò , Patrick Slane , Gloria Spandre , Douglas A. Swartz , Toru Tamagawa , Fabrizio Tavecchio , Roberto Taverna , Yuzuru Tawara , Allyn F. Tennant , Nicholas Thomas , Francesco Tombesi , Alessio Trois , Sergey S. Tsygankov , Roberto Turolla , Jacco Vink , Kinwah Wu

Evaluation of several explanations of the strong X-ray polarization of the black hole X-ray binary 4U 1630-47

The Imaging X-ray Polarimetry Explorer (IXPE) observations of the X-ray binary 4U 1630-47 in the high soft state revealed high linear polarization degrees (PDs) rising from 6% at 2 keV to 10% at 8 keV. We discuss in this letter three…

High Energy Astrophysical Phenomena · Physics 2024-10-11 Henric Krawczynski , Yajie Yuan , Alexander Y. Chen , Kun Hu , Nicole Rodriguez Cavero , Sohee Chun , Ephraim Gau , James F. Steiner , Michal Dovčiak

Light curves and polarization of accretion- and nuclear-powered millisecond pulsars

We study theoretical X-ray light curves and polarization properties of accretion-powered millisecond pulsars. We assume that the radiation is produced in two antipodal spots at the neutron star surface which are associated with the magnetic…

Astrophysics · Physics 2009-11-10 Kerttu Viironen , Juri Poutanen

X-ray polarization study of the neutron star low-mass X-ray binary GX 349+2

We report the first X-ray polarimetric results of the neutron star (NS) low-mass X-ray binary (LMXB) Z-source GX 349+2 using the Imaging X-ray Polarimetry Explorer (IXPE). We discovered that the X-ray source was polarized at PD = 1.1 +/-…

High Energy Astrophysical Phenomena · Physics 2025-05-20 Unnati Kashyap , Thomas J. Maccarone , Mason Ng , Eliot C. Pattie , Swati Ravi , Herman L. Marshall

IXPE observation confirms a high spin in the accreting black hole 4U 1957+115

We present the results of the first X-ray polarimetric observation of the low-mass X-ray binary 4U 1957+115, performed with the Imaging X-ray Polarimetry Explorer in May 2023. The binary system has been in a high-soft spectral state since…

High Energy Astrophysical Phenomena · Physics 2024-02-09 L. Marra , M. Brigitte , N. Rodriguez Cavero , S. Chun , J. F. Steiner , M. Dovčiak , M. Nowak , S. Bianchi , F. Capitanio , A. Ingram , G. Matt , F. Muleri , J. Podgorný , J. Poutanen , J. Svoboda , R. Taverna , F. Ursini , A. Veledina , A. De Rosa , J. A. Garcia , A. A. Lutovinov , I. A. Mereminskiy , R. Farinelli , S. Gunji , P. Kaaret , T. Kallman , H. Krawczynski , Y. Kan , K. Hu , A. Marinucci , G. Mastroserio , R. Mikušincová , M. Parra , P. O. Petrucci , A. Ratheesh , P. Soffitta , F. Tombesi , S. Zane , I. Agudo , L. A. Antonelli , M. Bachetti , L. Baldini , W. H. Baumgartner , R. Bellazzini , S. D. Bongiorno , R. Bonino , A. Brez , N. Bucciantini , S. Castellano , E. Cavazzuti , C. Chen , S. Ciprini , E. Costa , E. Del Monte , L. Di Gesu , N. Di Lalla , A. Di Marco , I. Donnarumma , V. Doroshenko , S. R. Ehlert , T. Enoto , Y. Evangelista , S. Fabiani , R. Ferrazzoli , K. Hayashida , J. Heyl , W. Iwakiri , S. G. Jorstad , V. Karas , F. Kislat , T. Kitaguchi , J. J. Kolodziejczak , F. La Monaca , L. Latronico , I. Liodakis , S. Maldera , A. Manfreda , F. Marin , A. P. Marscher , H. L. Marshall , F. Massaro , I. Mitsuishi , T. Mizuno , M. Negro , C. Y. Ng , S. L. O'Dell , N. Omodei , C. Oppedisano , A. Papitto , G. G. Pavlov , A. L. Peirson , M. Perri , M. Pesce-Rollins , M. Pilia , A. Possenti , S. Puccetti , B. D. Ramsey , J. Rankin , O. J. Roberts , R. W. Romani , C. Sgro , P. Slane , G. Spandre , D. A. Swartz , T. Tamagawa , F. Tavecchio , Y. Tawara , A. F. Tennant , N. E. Thomas , A. Trois , S. S. Tsygankov , R. Turolla , J. Vink , M. C. Weisskopf , K. Wu , F. Xie