Related papers: HAWC J2227+610 and its association with G106.3+2.7…

Potential PeVatron supernova remnant G106.3+2.7 seen in the highest-energy gamma rays

Cosmic rays (protons and other atomic nuclei) are believed to gain energies of petaelectronvolts (PeV) and beyond at astrophysical particle accelerators called 'PeVatrons' inside our Galaxy. Although a characteristic feature of a PeVatron…

High Energy Astrophysical Phenomena · Physics 2021-09-08 M. Amenomori , Y. W. Bao , X. J. Bi , D. Chen , T. L. Chen , W. Y. Chen , Xu Chen , Y. Chen , Cirennima , S. W. Cui , Danzengluobu , L. K. Ding , J. H. Fang , K. Fang , C. F. Feng , Zhaoyang Feng , Z. Y. Feng , Qi Gao , Q. B. Gou , Y. Q. Guo , Y. Y. Guo , H. H. He , Z. T. He , K. Hibino , N. Hotta , Haibing Hu , H. B. Hu , J. Huang , H. Y. Jia , L. Jiang , H. B. Jin , K. Kasahara , Y. Katayose , C. Kato , S. Kato , K. Kawata , W. Kihara , Y. Ko , M. Kozai , Labaciren , G. M. Le , A. F. Li , H. J. Li , W. J. Li , Y. H. Lin , B. Liu , C. Liu , J. S. Liu , M. Y. Liu , W. Liu , Y. -Q. Lou , H. Lu , X. R. Meng , K. Munakata , H. Nakada , Y. Nakamura , H. Nanjo , M. Nishizawa , M. Ohnishi , T. Ohura , S. Ozawa , X. L. Qian , X. B. Qu , T. Saito , M. Sakata , T. K. Sako , J. Shao , M. Shibata , A. Shiomi , H. Sugimoto , W. Takano , M. Takita , Y. H. Tan , N. Tateyama , S. Torii , H. Tsuchiya , S. Udo , H. Wang , H. R. Wu , L. Xue , Y. Yamamoto , Z. Yang , Y. Yokoe , A. F. Yuan , L. M. Zhai , H. M. Zhang , J. L. Zhang , X. Zhang , X. Y. Zhang , Y. Zhang , Yi Zhang , Ying Zhang , S. P. Zhao , Zhaxisangzhu , X. X. Zhou

VER J2227+608: A Hadronic PeVatron Pulsar Wind Nebula?

We report the detection of GeV $\gamma$-ray emission from the very-high-energy (VHE) $\gamma$-ray source VER J2227+608 associated with the "tail" region of SNR G106.3+2.7. The GeV $\gamma$-ray emission is extended and spatially coincident…

High Energy Astrophysical Phenomena · Physics 2020-01-08 Yuliang Xin , Houdun Zeng , Siming Liu , Yizhong Fan , Daming Wei

Observation of the Galactic Center PeVatron Beyond 100 TeV with HAWC

We report an observation of ultra-high energy (UHE) gamma rays from the Galactic Center region, using seven years of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like…

High Energy Astrophysical Phenomena · Physics 2024-09-06 A. Albert , R. Alfaro , C. Alvarez , A. Andrés , J. C. Arteaga-Velázquez , D. Avila Rojas , H. A. Ayala Solares , R. Babu , E. Belmont-Moreno , A. Bernal , K. S. Caballero-Mora , T. Capistrán , A. Carramiñana , S. Casanova , U. Cotti , J. Cotzomi , S. Coutiño de León , E. De la Fuente , C. de León , D. Depaoli , N. Di Lalla , N. Di Lalla , R. Diaz Hernandez , B. L. Dingus , M. A. DuVernois , J. C. Díaz-Vélez , K. Engel , T. Ergin , C. Espinoza , K. L. Fan , K. Fang , N. Fraija , S. Fraija , J. A. García-González , F. Garfias , H. Goksu , M. M. González , J. A. Goodman , S. Groetsch , J. P. Harding , S. Hernández-Cadena , I. Herzog , J. Hinton , D. Huang , F. Hueyotl-Zahuantitla , T. B. Humensky , P. Hüntemeyer , A. Iriarte , S. Kaufmann , D. Kieda , A. Lara , W. H. Lee , J. Lee , H. León Vargas , J. T. Linnemann , A. L. Longinotti , G. Luis-Raya , K. Malone , O. Martinez , J. Martínez-Castro , J. A. Matthews , P. Miranda-Romagnoli , J. A. Montes , J. A. Morales-Soto , E. Moreno , M. Mostafá , M. Najafi , L. Nellen , M. Newbold , M. U. Nisa , R. Noriega-Papaqui , L. Olivera-Nieto , N. Omodei , M. Osorio-Archila , Y. Pérez Araujo , E. G. Pérez-Pérez , C. D. Rho , D. Rosa-González , E. Ruiz-Velasco , H. Salazar , D. Salazar-Gallegos , A. Sandoval , M. Schneider , G. Schwefer , J. Serna-Franco , A. J. Smith , Y. Son , R. W. Springer , O. Tibolla , K. Tollefson , I. Torres , R. Torres-Escobedo , R. Turner , F. Ureña-Mena , E. Varela , X. Wang , Z. Wang , I. J. Watson , E. Willox , H. Wu , S. Yu , S. Yun-Cárcamo , H. Zhou

An Enigmatic PeVatron in an Area around HII Region G35.6$-$0.5

Identifying Galactic PeVatrons (PeV particle accelerators) from the ultra-high-energy (UHE, >100 TeV) $\gamma$-ray sources plays a crucial role in revealing the origin of Galactic cosmic rays. The UHE source 1LHAASO J1857+0203u is suggested…

High Energy Astrophysical Phenomena · Physics 2026-01-07 The LHAASO Collaboration , Zhen Cao , F. Aharonian , Axikegu , Y. X. Bai , Y. W. Bao , D. Bastieri , X. J. Bi , Y. J. Bi , W. Bian , A. V. Bukevich , Q. Cao , W. Y. Cao , Zhe Cao , J. Chang , J. F. Chang , A. M. Chen , B. Q. Chen , E. S. Chen , H. X. Chen , Liang Chen , Lin Chen , Long Chen , M. J. Chen , M. L. Chen , Q. H. Chen , S. Chen , S. H. Chen , S. Z. Chen , T. L. Chen , Y. Chen , N. Cheng , Y. D. Cheng , M. C. Chu , M. Y. Cui , S. W. Cui , X. H. Cui , Y. D. Cui , B. Z. Dai , H. L. Dai , Z. G. Dai , Danzengluobu , X. Q. Dong , K. K. Duan , J. H. Fan , Y. Z. Fan , J. Fang , J. H. Fang , K. Fang , C. F. Feng , H. Feng , L. Feng , S. H. Feng , X. T. Feng , Y. Feng , Y. L. Feng , S. Gabici , B. Gao , C. D. Gao , Q. Gao , W. Gao , W. K. Gao , M. M. Ge , T. T. Ge , L. S. Geng , G. Giacinti , G. H. Gong , Q. B. Gou , M. H. Gu , F. L. Guo , J. Guo , X. L. Guo , Y. Q. Guo , Y. Y. Guo , Y. A. Han , O. A. Hannuksela , M. Hasan , H. H. He , H. N. He , J. Y. He , Y. He , Y. K. Hor , B. W. Hou , C. Hou , X. Hou , H. B. Hu , Q. Hu , S. C. Hu , C. Huang , D. H. Huang , T. Q. Huang , W. J. Huang , X. T. Huang , X. Y. Huang , Y. Huang , Y. Y. Huang , X. L. Ji , H. Y. Jia , K. Jia , H. B. Jiang , K. Jiang , X. W. Jiang , Z. J. Jiang , M. Jin , M. M. Kang , I. Karpikov , D. Khangulyan , D. Kuleshov , K. Kurinov , B. B. Li , C. M. Li , Cheng Li , Cong Li , D. Li , F. Li , H. B. Li , H. C. Li , Jian Li , Jie Li , K. Li , S. D. Li , W. L. Li , W. L. Li , X. R. Li , Xin Li , Y. Z. Li , Zhe Li , Zhuo Li , E. W. Liang , Y. F. Liang , S. J. Lin , B. Liu , C. Liu , D. Liu , D. B. Liu , H. Liu , H. D. Liu , J. Liu , J. L. Liu , M. Y. Liu , R. Y. Liu , S. M. Liu , W. Liu , Y. Liu , Y. N. Liu , Q. Luo , Y. Luo , H. K. Lv , B. Q. Ma , L. L. Ma , X. H. Ma , J. R. Mao , Z. Min , W. Mitthumsiri , H. J. Mu , Y. C. Nan , A. Neronov , K. C. Y. Ng , L. J. Ou , P. Pattarakijwanich , Z. Y. Pei , J. C. Qi , M. Y. Qi , B. Q. Qiao , J. J. Qin , A. Raza , D. Ruffolo , A. Sáiz , M. Saeed , D. Semikoz , L. Shao , O. Shchegolev , X. D. Sheng , F. W. Shu , H. C. Song , Yu. V. Stenkin , V. Stepanov , Y. Su , D. X. Sun , Q. N. Sun , X. N. Sun , Z. B. Sun , J. Takata , P. H. T. Tam , Q. W. Tang , R. Tang , Z. B. Tang , W. W. Tian , L. H. Wan , C. Wang , C. B. Wang , G. W. Wang , H. G. Wang , H. H. Wang , J. C. Wang , Kai Wang , Kai Wang , L. P. Wang , L. Y. Wang , P. H. Wang , R. Wang , W. Wang , X. G. Wang , X. Y. Wang , Y. Wang , Y. D. Wang , Y. J. Wang , Z. H. Wang , Z. X. Wang , Zhen Wang , Zheng Wang , D. M. Wei , J. J. Wei , Y. J. Wei , T. Wen , C. Y. Wu , H. R. Wu , Q. W. Wu , S. Wu , X. F. Wu , Y. S. Wu , S. Q. Xi , J. Xia , G. M. Xiang , D. X. Xiao , G. Xiao , Y. L. Xin , Y. Xing , D. R. Xiong , Z. Xiong , D. L. Xu , R. F. Xu , R. X. Xu , W. L. Xu , L. Xue , D. H. Yan , J. Z. Yan , T. Yan , C. W. Yang , C. Y. Yang , F. Yang , F. F. Yang , L. L. Yang , M. J. Yang , R. Z. Yang , W. X. Yang , Y. H. Yao , Z. G. Yao , L. Q. Yin , N. Yin , X. H. You , Z. Y. You , Y. H. Yu , Q. Yuan , H. Yue , H. D. Zeng , T. X. Zeng , W. Zeng , M. Zha , B. B. Zhang , F. Zhang , H. Zhang , H. M. Zhang , H. Y. Zhang , J. L. Zhang , Li Zhang , P. F. Zhang , P. P. Zhang , R. Zhang , S. B. Zhang , S. R. Zhang , S. S. Zhang , X. Zhang , X. P. Zhang , Y. F. Zhang , Yi Zhang , Yong Zhang , B. Zhao , J. Zhao , L. Zhao , L. Z. Zhao , S. P. Zhao , X. H. Zhao , F. Zheng , W. J. Zhong , B. Zhou , H. Zhou , J. N. Zhou , M. Zhou , P. Zhou , R. Zhou , X. X. Zhou , X. X. Zhou , B. Y. Zhu , C. G. Zhu , F. R. Zhu , H. Zhu , K. J. Zhu , Y. C. Zou , X. Zuo

HAWC J2227+610: a potential PeVatron candidate for the CTA in the northern hemisphere

Recent observations of the gamma-ray source HAWC J2227+610 by Tibet AS+MD and LHAASO confirm the special interest of this source as a galactic PeVatron candidate in the northern hemisphere. HAWC J2227+610 emits Very High Energy (VHE)…

High Energy Astrophysical Phenomena · Physics 2021-10-18 G. Verna , F. Cassol , H. Costantini

A search for spectral hardening in HAWC sources above 56 TeV

The High Altitude Water Cherenkov (HAWC) Observatory is a wide-field-of-view gamma-ray observatory that is optimized to detect gamma rays between ~300 GeV and several hundred TeV. The HAWC Collaboration recently released their third source…

High Energy Astrophysical Phenomena · Physics 2021-08-02 Kelly Malone , HAWC Collaboration

X-Ray Emission from the PeVatron-candidate Supernova Remnant G106.3+2.7

We report a discovery of diffuse X-ray emission around the supernova remnant (SNR) G106.3+2.7, which is associated with VER J2227+608 and HAWC J2227+610 and is known as a candidate for a PeV cosmic ray accelerator (PeVatron). We analyze…

High Energy Astrophysical Phenomena · Physics 2021-05-25 Yutaka Fujita , Aya Bamba , Kumiko K. Nobukawa , Hironori Matsumoto

Searching for TeV emission from LHAASO J0341+5258 with VERITAS and HAWC

Galactic PeVatrons are astrophysical sources accelerating particles up to a few PeV ($\sim$10$^{15}$ eV) energies. The primary signature of 100 TeV $\gamma$ rays may come from PeV protons or multi-hundred TeV (not PeV) electrons. The search…

High Energy Astrophysical Phenomena · Physics 2023-08-31 P. Bangale , X. Wang

Multiple Galactic Sources with Emission Above 56 TeV Detected by HAWC

We present the first catalog of gamma-ray sources emitting above 56 and 100 TeV with data from the High Altitude Water Cherenkov (HAWC) Observatory, a wide field-of-view observatory capable of detecting gamma rays up to a few hundred TeV.…

High Energy Astrophysical Phenomena · Physics 2020-01-16 HAWC Collaboration , A. U. Abeysekara , A. Albert , R. Alfaro , J. R. Angeles Camacho , J. C. Arteaga-Velázquez , K. P. Arunbabu , D. Avila Rojas , H. A. Ayala Solares , V. Baghmanyan , E. Belmont-Moreno , S. Y. BenZvi , C. Brisbois , K. S. Caballero-Mora , T. Capistrán , A. Carramiñana , S. Casanova , U. Cotti , J. Cotzomi , S. Coutiño de León , E. De la Fuente , C. de León , S. Dichiara , B. L. Dingus , M. A. DuVernois , J. C. Díaz-Vélez , R. W. Ellsworth , K. Engel , C. Espinoza , H. Fleischhack , N. Fraija , A. Galván-Gámez , D. Garcia , J. A. García-González , F. Garfias , M. M. González , J. A. Goodman , J. P. Harding , S. Hernandez , J. Hinton , B. Hona , D. Huang , F. Hueyotl-Zahuantitla , P. Hüntemeyer , A. Iriarte , A. Jardin-Blicq , V. Joshi , S. Kaufmann , D. Kieda , A. Lara , W. H. Lee , H. León Vargas , J. T. Linnemann , A. L. Longinotti , G. Luis-Raya , J. Lundeen , R. López-Coto , K. Malone , S. S. Marinelli , O. Martinez , I. Martinez-Castellanos , J. Martínez-Castro , H. Martínez-Huerta , J. A. Matthews , P. Miranda-Romagnoli , J. A. Morales-Soto , E. Moreno , M. Mostafá , A. Nayerhoda , L. Nellen , M. Newbold , M. U. Nisa , R. Noriega-Papaqui , A. Peisker , E. G. Pérez-Pérez , J. Pretz , Z. Ren , C. D. Rho , C. Rivière , D. Rosa-González , M. Rosenberg , E. Ruiz-Velasco , F. Salesa Greus , A. Sandoval , M. Schneider , H. Schoorlemmer , G. Sinnis , A. J. Smith , R. W. Springer , P. Surajbali , E. Tabachnick , M. Tanner , O. Tibolla , K. Tollefson , I. Torres , R. Torres-Escobedo , L. Villaseñor , T. Weisgarber , J. Wood , T. Yapici , H. Zhang , H. Zhou

VERITAS and HAWC observations of unidentified source LHAASO J2108+5157

Understanding the complete nature of Galactic sources that accelerate cosmic rays up to $10^{15}$ eV energy (Galactic PeVatrons) is still an unsolved problem in high-energy astrophysics. Although supernova remnants have long been considered…

High Energy Astrophysical Phenomena · Physics 2023-09-04 Sajan Kumar , Michael Martin , Xiaojie Wang

Evidence of 100 TeV ${\gamma}$-ray emission from HESS J1702-420: A new PeVatron candidate

The identification of active PeVatrons, hadronic particle accelerators reaching the knee of the cosmic-ray spectrum (at the energy of few PeV), is crucial to understand the origin of cosmic rays in the Galaxy. In this context, we report on…

High Energy Astrophysical Phenomena · Physics 2021-08-23 L. Giunti , B. Khelifi , K. Kosack , R. Terrier

First HAWC Spectra of Galactic Gamma-ray Sources Above 100 TeV and the Implications for Cosmic-ray Acceleration

We present the first catalogs of the highest-energy (above 56 TeV and 100 TeV) gamma-ray sources seen by the High Altitude Water Cherenkov (HAWC) Observatory. The wide field-of-view of HAWC naturally lends itself to unbiased all-sky surveys…

High Energy Astrophysical Phenomena · Physics 2019-08-21 Kelly Malone

Multiwavelength study of Galactic PeVatron LHAASO J0341+5258

Galactic PeVatrons are astrophysical sources accelerating particles up to a few PeV (~10$^{15}$ eV). The primary method to identify both electron and proton PeVatrons is the observation of $\gamma$-ray radiation at ultra-high energies (UHE;…

High Energy Astrophysical Phenomena · Physics 2025-09-26 P. Bangale , X. Wang

Multi-wavelength observations of 2HWC J1928+177: dark accelerator or new TeV gamma-ray binary?

2HWC J1928+177 is a Galactic TeV gamma-ray source detected by the High Altitude Water Cherenkov (HAWC) Observatory up to ~ 56 TeV. The HAWC source, later confirmed by H.E.S.S., still remains unidentified as a dark accelerator since there is…

High Energy Astrophysical Phenomena · Physics 2020-07-22 Kaya Mori , Hongjun An , Qi Feng , Kelly Malone , Raul R. Prado , Yve E. Schutt , Brenda L. Dingus , E. V. Gotthelf , Charles J. Hailey , Jeremy Hare , Oleg Kargaltsev , Reshmi Mukherjee

Ultrahigh-Energy Gamma-Ray Sources Need Not Be Hadronic PeVatrons

Ultrahigh-energy gamma rays ($E_{\gamma}>100 \, {\rm TeV}$) have been detected from a handful of astrophysical sources. Due to the Klein-Nishina suppression of inverse Compton scattering at such high energies, it has sometimes been argued…

High Energy Astrophysical Phenomena · Physics 2026-03-19 Zachary Curtis-Ginsberg , Dan Hooper , Justin Vandenbroucke

HAWC Study on the Ultra-High-Energy Gamma-Ray Emissions from the Pulsar Wind Nebula G32.64+0.53

Multi-TeV gamma-ray emission around eHWC J1850+001 (a source from the first HAWC catalog of gamma-ray sources emitting above 56 TeV) is spatially coincident with the pulsar wind nebula (PWN) G32.64+0.53, powered by PSR J1849-0001. The…

High Energy Astrophysical Phenomena · Physics 2026-03-23 R. Alfaro , C. Alvarez , E. Anita-Rangel , M. Araya , J. C. Arteaga-Velázquez , D. Avila Rojas , H. A. Ayala Solares , R. Babu , P. Bangale , E. Belmont-Moreno , A. Bernal , K. S. Caballero-Mora , T. Capistrán , A. Carramiñana , F. Carreón , S. Casanova , U. Cotti , J. Cotzomi , S. Coutiño de León , E. De la Fuente , P. Desiati , N. Di Lalla , R. Diaz Hernandez , M. A. DuVernois , J. C. Díaz-Vélez , K. Engel , T. Ergin , C. Espinoza , N. Fraija , S. Fraija , J. A. García-González , F. Garfias , N. Ghosh , M. M. González , J. A. González , J. A. Goodman , D. Guevel , J. Gyeong , J. P. Harding , I. Herzog , D. Huang , F. Hueyotl-Zahuantitla , A. Iriarte , S. Kaufmann , D. Kieda , K. Leavitt , W. H. Lee , J. Lee , H. León Vargas , A. L. Longinotti , G. Luis-Raya , K. Malone , O. Martinez , J. Martínez-Castro , J. A. Matthews , P. Miranda-Romagnoli , J. A. Morales-Soto , E. Moreno , M. Mostafá , M. Najafi , A. Nayerhoda , L. Nellen , R. Noriega-Papaqui , N. Omodei , E. Ponce , Y. Pérez Araujo , E. G. Pérez-Pérez , C. D. Rho , A. Rodriguez Parra , D. Rosa-González , M. Roth , H. Salazar , D. Salazar-Gallegos , A. Sandoval , M. Schneider , J. Serna-Franco , M. Shin , A. J. Smith , Y. Son , R. W. Springer , O. Tibolla , K. Tollefson , I. Torres , R. Torres-Escobedo , E. Varela , L. Villaseñor , X. Wang , Z. Wang , I. J. Watson , S. Yu , X. Zhang , H. Zhou , C. de León

GeV emission in the region of HESS J1809-193 and HESS J1813-178: is HESS J1809-193 a proton pevatron?

HESS J1809-193 is an unidentified TeV source discovered by the High Energy Stereoscopic System and originally classified as a pulsar wind nebula (PWN) candidate associated with the pulsar PSR J1809-1917. However, a recent study of deep…

High Energy Astrophysical Phenomena · Physics 2018-06-06 Miguel Araya

Hadronic Origin of Sub-PeV Gamma-Ray Emission from LHAASO J0621+3755

Very High Energy (VHE) gamma-rays in pulsars, and their surrounding halos, are interpreted to originate from the leptonic channel, electromagnetic interactions through electron inverse Compton (IC) scattering. In the hadronic scenario,…

High Energy Astrophysical Phenomena · Physics 2026-05-18 Sonali Sahoo , Ankan Roy , Kritika Yadav , Reetanjali Moharana

The HAWC ultra-high-energy gamma-ray map with more than 5 years of data

In 2020, the HAWC Collaboration presented the first catalog of gamma-ray sources emitting above 56 TeV and 100 TeV. With nine sources detected, this was the highest-energy source catalog to date. Here, we present the results of re-analysis…

High Energy Astrophysical Phenomena · Physics 2023-11-03 Kelly Malone , José Andrés García González , Patrick Harding

Detailed Analysis of the TeV {\gamma}-Ray Sources 3HWC J1928+178, 3HWC J1930+188, and the New Source HAWC J1932+192

The latest High Altitude Water Cherenkov (HAWC) point-like source catalog up to 56 TeV reported the detection of two sources in the region of the Galactic plane at galactic longitude 52\deg < l < 55\deg, 3HWC J1930+188 and 3HWC J1928+178.…

High Energy Astrophysical Phenomena · Physics 2023-03-01 A. Albert , R. Alfaro , C. Alvarez , J. C. Arteaga-Velázquez , D. Avila Rojas , H. A. Ayala Solares , R. Babu , E. Belmont-Moreno , C. Brisbois , K. S. Caballero-Mora , T. Capistrń , A. Carramiñana , S. Casanova , O. Chaparro-Amaro , U. Cotti , J. Cotzomi , S. CoutiñodeLeón , E. De la Fuente , C. de León , R. Diaz Hernandez , J. C. Díaz-Vélez , B. L. Dingus , M. A. DuVernois , M. Durocher , K. Engel , C. Espinoza , K. L. Fan , M. Fernández Alonso , N. Fraija , J. A. García-González , F. Garfias , H. Goksu , M. M. González , J. A. Goodman , J. P. Harding , S. Hernandez , J. Hinton , B. Hona , D. Huang , F. Hueyotl-Zahuantitla , P. Hüntemeyer , A. Iriarte , A. Jardin-Blicq , V. Joshi , S. Kaufmann , D. Kieda , W. H. Lee , H. León Vargas , J. T. Linnemann , A. L. Longinotti , G. Luis-Raya , R. López-Coto , K. Malone , V. Marandon , O. Martinez , J. Martínez-Castro , J. A. Matthews , P. Miranda-Romagnoli , J. A. Morales-Soto , E. Moreno , M. Mostafá , A. Nayerhoda , L. Nellen , M. Newbold , M. U. Nisa , R. Noriega-Papaqui , L. Olivera-Nieto , N. Omodei , A. Peisker , Y. Pérez Araujo , E. G. Pérez-Pérez , C. D. Rho , D. Rosa-González , E. Ruiz-Velasco , H. Salazar , D. Salazar-Gallegos , F. Salesa Greus , A. Sandoval , M. Schneider , J. Serna-Franco , A. J. Smith , Y. Son , R. W. Springer , O. Tibolla , K. Tollefson , I. Torres , R. Torres-Escobedo , R. Turner , F. Ureña-Mena , L. Villaseñor , X. Wang , F. Werner , E. Willox , H. Zhou