Barrio Uña, Juan AbelContreras González, José LuisFidalgo, David Friedrich CarretoFonseca González, María VictoriaHoang, Kim DinhLópez Moya, MarcosMiranda Pantoja, José MiguelMorcuende, D.Nievas Rosillo, MireiaPeñil Del Campo, PabloSaha, Lab2023-06-162023-06-162020-02-200004-637X10.3847/1538-4357/ab6612https://hdl.handle.net/20.500.14352/6202© 2020. The American Astronomical Society. All rights reserved. Artículo firmado por 259 autores. This research is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation, the Smithsonian Institution, and NSERC in Canada. This research used resources provided by the Open Science Grid, which is supported by the National Science Foundation and the U.S. Department of Energy's Office of Science, and the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under contract No. DE-AC0205CH11231. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and the collaborating institutions in the construction and operation of the instrument.; The MAGIC collaboration would like to thank the Instituto de Astrofisica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2015-69818-P, FPA2012-36668, FPA2015-68378-P, FPA2015-69210-C6-2R, FPA2015-69210-C6-4-R, FPA2015-69210-C6-6-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP201571662-C2-2-P, FPA201790566REDC), the Indian Department of Atomic Energy, the Japanese JSPS and MEXT, and the Bulgarian Ministry of Education and Science, National RI Roadmap Project DO1-153/28.08.2018 is gratefully acknowledged. This work was also supported by the Spanish Centro de Excelencia "Severo Ochoa" SEV-2016-0588 and SEV2015-0548 and Unidad de Excelencia "María de Maeztu" MDM-2014-0369, the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782, the University of Rijeka Project 13.12.1.3.02, the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382, and the Brazilian MCTIC, CNPq, and FAPERJ.; This publication makes use of data obtained at Metsahovi Radio Observatory, operated by Aalto University, Finland, and the OVRO 40 m monitoring program, which is supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G and NSF grants AST-0808050 and AST1109911. The UMRAO data were obtained through NSF grant AST 0607523 and NASA Fermi GI award NNX09AU16G. The St. Petersburg University team acknowledges support from Russian RFBR foundation, grant 12-02-00452. The Abastumani Observatory team acknowledges financial support by the Shota Rustaveli National Science Foundation through project FR/577/6-320/13. The Steward Observatory data were obtained under Fermi Guest Investigator Program grant NNX09AU10G. The research at Boston University is supported by NASA grant 80NSSC17K0649 and NSF grant AST-1615796.We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of similar to 27 Crab Units above 1 TeV was measured in very high energy (VHE) gamma-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE gamma-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE gamma-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy gamma-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsahovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of similar to 25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (delta greater than or similar to 33) and the size of the emission region (delta R--1(B) less than or similar to 3.8 x 10(13) cm) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.engjournal articlehttps://doi.org/10.3847/1538-4357/ab6612https://iopscience.iop.org/open access537Active galactic nucleiRay light curvesBl-lac objectsX-rayCrab-nebulaBlazar flaresRadio-sourcesTev photonsEmissionRadiationElectricidadElectrónica (Física)2202.03 Electricidad