The Pierre Auger Observatory, which is the largest air-shower experiment in the world, offers unprecedented exposure to neutral particles at the highest energies. Since the start of data collection more than 18 years ago, various searches for ultra-high-energy (UHE, E & 1017 eV) photons have been performed, either for a diffuse flux of UHE photons, for point sources of UHE photons or for UHE photons associated with transient events such as gravitational wave events. In the present paper, we summarize these searches and review the current results obtained using the wealth of data collected by the Pierre Auger Observatory.
Argentina-Comision Nacional de Energia Atomica
ANPCyT
Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET)
Gobierno de la Provincia de Mendoza
Municipalidad de Malargue
NDM Holdings
Valle Las Lenas
Australian Research Council
Belgium-Fonds de la Recherche Scientifique (FNRS)
FWO
Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) Fundacao de Apoio a Pesquisa do Distrito Federal (FAPDF) Financiadora de Inovacao e Pesquisa (Finep) Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio De Janeiro (FAPERJ) Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) 2019/10151-2 2010/07359-6 1999/05404-3
Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes (MCTIC)
France-Centre de Calcul IN2P3/CNRS Centre National de la Recherche Scientifique (CNRS) Region Ile-de-France Centre National de la Recherche Scientifique (CNRS) Departement Sciences de l'Univers (SDU-INSU/CNRS) French National Research Agency (ANR) LABEX ANR-10-LABX-63 ANR-11-IDEX-0004-02
Federal Ministry of Education & Research (BMBF) German Research Foundation (DFG) Finanzministerium Baden-Wurttemberg Helmholtz Alliance for Astroparticle Physics (HAP) Helmholtz Association Ministerium fur Kultur und Wissenschaft des Landes Nordrhein-Westfalen Ministerium fur Wissenschaft, Forschung und Kunst des Landes Baden-Wurttemberg
Italy-Istituto Nazionale di Fisica Nucleare (INFN) Istituto Nazionale Astrofisica (INAF)
Ministry of Education, Universities and Research (MIUR)
CETEMPS Center of Excellence
Ministry of Foreign Affairs and International Cooperation (Italy)
Consejo Nacional de Ciencia y Tecnologia (CONACyT) 167733 Universidad Nacional Autonoma de Mexico Programa de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT) Universidad Nacional Autonoma de Mexico
Netherlands-Ministry of Education, Culture and Science Netherlands Organization for Scientific Research (NWO)
SURF Cooperative
Poland-Ministry of Education and Science DIR/WK/2018/11 National Science Centre, Poland 2016/22/M/ST9/00198 2016/23/B/ST9/01635 2020/39/B/ST9/01398
Portuguese Foundation for Science and Technology FEDER funds within Programa Operacional Factores de Competitividade through FundacAo para a Ciencia e a Tecnologia (COMPETE)
Romania-Ministry of Research, Innovation and Digitization, CNCS/CCCDI UEFISCDI within the National Nucleus Program PN19150201/16N/2019 PN1906010 PNCDI III TE128 PN-III-P1-1.1-TE-2021-0924/TE57/2022 PED289
Slovenian Research Agency - Slovenia P1-0031 P1-0385 I0-0033 N1-0111
Spanish Government FPA2017-85114-P PID2019-104676GB-C32
Xunta de Galicia
European Commission ED431C 2017/07
Junta de Andalucia SOMM17/6104/UGR P18-FR-4314
European Commission
RENATA Red Nacional Tematica de Astroparticulas FPA2015-68783-REDT
Maria de Maeztu Unit of Excellence MDM-2016-0692
United States Department of Energy (DOE) DE-AC02-07CH11359 DE-FR02-04ER41300 DE-FG02-99ER41107 DE-SC0011689
National Science Foundation (NSF) 0450696
Grainger Foundation
Marie Curie-IRSES/EPLANET
European Particle Physics Latin American Network
UNESCO
MSMT CR LTT18004 LM2015038 LM2018102 CZ.02.1.01/0.0/0.0/16_013/0001402 CZ.02.1.01/0.0/0.0/18_046/0016010 CZ.02.1.01/0.0/0.0/17_049/0008422