Pos(ICRC2021)973

PoS(ICRC2021)973 International th 12–23 July 2021 July 12–23 37 SICS CONFERENCE SICS CONFERENCE Berlin | Germany Berlin Berlin | Germany Cosmic Ray Conference Ray Cosmic ICRC 2021 THE ASTROPARTICLE PHY ICRC 2021 THEASTROPARTICLE PHY https://pos.sissa.it/ ONLINE Collaboration b on behalf of the Pierre Auger ∗ a, [email protected] International Cosmic Ray Conference (ICRC 2021) Presenter ∗ th University of Siegen, Walter-Flex-Str. 3, Siegen, Germany Observatorio Pierre Auger, Av. San Martín Norte 304,E-mail: 5613 Malargüe, Argentina Multimessenger astronomy has become increasinglyastronomical objects important have during already been the successfully pastsignals, observed decade. in allowing the for light Some of aAuger multiple Observatory much messenger has deeper taken understanding partof in of the multimessenger their ultra-high-energy astronomy with physical sky. an properties.from In exhaustive the exploration this sources contribution, The of for Pierre gravitational theradiation waves first fields is time, presented. are a expected search Interactionsdistant to for with sources UHE attenuate and the a photons any cosmic non-negligible background possible background ofan flux air unambiguous shower of identification events with ultra-high-energy of hadronic primary photons originhere, photons makes from a a selection challenging strategy task. is appliedmaximum In to the sensitivity both analysis to GW presented a sources and possible airhypothetical photon shower new-physics signal. events processes, aiming At to which the provide mightphotons same allow time, in for a the much window extragalactic is larger medium.selection kept interaction of open GW lengths Preliminary for sources, including of results the binary on neutron the star merger UHE GW170817 photon are presented. fluence from a Copyright owned by the author(s) under the terms of the Creative Commons b a 37 July 12th – 23rd, 2021 Online – Berlin, Germany © Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). (a complete list of authors can be found at the end of the proceedings) Philip Ruehl Follow-up Search for UHE Photons fromWave Gravitational Sources with the Pierre Auger Observatory PoS(ICRC2021)973 γ E Philip Ruehl , respectively ∆ and and photon energies LDF ◦ L 60 could be derived. A dedicated [9]. and ◦ γ eV E 30 17 10 × 2 between θ 2 , an alternative energy reconstruction method has been used γ E . Since the standard energy reconstruction of the Auger SD uses eV 5 . 20 10 and eV 0 . 19 . Thanks to its design, the SD has a duty cycle of almost 100% [5]. 10 The bulk of data received at the Pierre Auger Observatory originates in cosmic rays of hadronic Since the first detection of gravitational waves (GWs) with the advanced LIGO and Virgo With its unique exposure to ultra-high-energy (UHE) radiation, the Pierre Auger Observatory To identify primary photons from transient point sources among the background of hadronic 5 km . 1 between related to the lateral distribution functionoptimized for (LDF) air and showers with to incident the zenith angles rise time of the signal traces.data events They for are the calibration of theair absolute shower energy would be scale, underestimated the due energy to ofestimator its a reduced possible for hadronic photon-induced the component. photon To obtain a energy in less [8]. biased This method is basedphoton-induced on air an showers iterative and procedure the which recursively universalobtain uses profile a the of series elongation the of rate photon of electromagnetic energy shower estimators component which to converges to nature [6]. The identification ofcosmic a rays possible with component of thesignificant UHE Pierre photons excess among of Auger the primary Observatory diffusestringent flux UHE has upper of photon limits been on candidate discussed the events diffuse in has photon flux [7,8]. been above found therein No and, statistically hence, Observatories in 2015, GW observations have become aIn key element the for multimessenger past astronomy. years, theinstruments transient sources throughout of the these accessible GWshigh-energy have part neutrinos. been See of analyzed] [1 by the for various a electromagnetic astronomical description. spectrum and inhas the joined the light global of campaignUHE in neutrinos the [2–4]. multimessenger Here, astronomy we extend of these follow-upin GW observations to sources temporal UHE photons by coincidence beyond searching 10 with EeV for GWUHE observations photons having from a observation limited runs mean freeradiation O1, path fields, O2 due to and we their show O3a. interactions that withinformation Despite the a on cosmic dedicated GW background search sources. inGW To a observations, maintain the multimessenger a surface approach maximum detecor can (SD) susceptibility arraySD provide to of array new the the comprises Pierre still more Auger Observatory sparse than is 1600 numberof used water of here. Cherenkov detectors The on a triangular grid with a spacing 2. Search for UHE Photons cosmic rays, the photon-discriminationmethod utilizes method the data from recorded [8] by thedistribution has SD in and been selects the photon plane adopted candidate perpendicular events in basedmeasured to on by this the the the water signal shower work. Cherenkov SD axis stations. and Two the observables This are shapes used, of the signal time traces Follow-up Photon Search after Gravitational Waves 1. Introduction analysis studying possible steady point sourcesAgain, of no UHE excess photons of has photon-like alsonor events been could in a published be targeted [10, found search11]. neither from in a a set of blind selected search source on candidates. the whole sky PoS(ICRC2021)973 2 − (1) 008 . 0 ± . ◦ starting at 50 g cm . Events are 483 60 Philip Ruehl . after the GW )) is obtained within t LDF ( = 0 and L max ◦ GW X θ = 1000 s 30 = +500 s 0 short t t )) cos( t ∆ ( are rejected. Events which do accounts for the fraction of the is found to be GW eV θ which is not more than ( eV 18 FoV 2 5 starting at . FoV Θ 10 20 max < , an additional event selection has to be X 10 )) Θ energy spectrum, the zenith-angle-averaged hd t ( < 2 LDF E − γ = 1 day γ 1 L GW E which is explained in [9]. E 3 , θ γ is given by of the GW source is between long γ ≤ and E t 0 t E ∆ ( GW ∆ eV θ − 0 ) . 1 t t ( 19 = 10 t A t d ∆ 1 t 0 Z t ) = t ∆ , GW , θ γ E ( before the GW event time and E being the time-dependent aperture of the Auger SD array as determined by the number ) t 500 s ( − A during the obervation period For the search period, two mutual exclusive time windows of To keep the sensitivity to a possible photon signal as high as possible, GW events are carefully The localization of a GW source is communicated by the LIGO/Virgo Collaborations via a To discard low-quality events, a number of selection criteria has been imposed on the data. energy estimator obtained by the standardThe SD shower energy maximum reconstruction is [12]. not directly accessible with the SD. An alternative estimator for 1 2 = GW 0 observation time in which the zenith angle selected by their localization qualityover and distant distance. and Close poorly localized and ones.expected well amount localized of Hence, sources background optimal are at results preferred a can managable level. be obtained while keepingprobability the density distribution on the sky (skyleads localization to map). the An conclusion analysis of that these usingcompromise distributions their between 50% the contour expected as amount the of search background (which region is in proportional the to sky the is solid a angle reasonable with of active hexagons at a given moment. The step-function t event time have been chosenexposure as is a in function of with both [2,4]. right ascensionIntegration and After declination over of a spectral the source sidereal integration, for day a the 1000 inon s spectrum-weighted time practive declination window. makes as shown the in spectrum-weighted1. Fig. exposure only dependent 4. Gravitational Wave Event Selection using CORSIKA [13] simulations.energy and With direction, the the photon exposureθ detection to UHE efficiency photons given from as a a transient function point of source at zenith angle the iterative process of reconstructing the photon energy photon efficiency in the energy range not have a triggered station more thansaturated 1000 low-gain m channel) away are from also the rejected shower axis to (excluding ensure stations a with proper a reconstruction of below ground. These restrictionszenith limit angle of the the primary photon particle. detection Assuming efficiency an depending on energy and also required to have a reconstructed shower maximum Events are required to have 6hexagon”) and active have SD successfully reconstructed stations shower axis, around LDF the and photonthe station energy. with discriminating For the calculating air highest signal shower (“active observables Follow-up Photon Search after Gravitational Waves 3. Exposure applied. Events with reconstructed hadronic energy PoS(ICRC2021)973 140 Mpc Philip Ruehl . Since this has been found for is chosen such that 90 Mpc δ 2 ∼ 80 7 Mpc iso γ = const. 2 h 100 deg 60 declination exposure for A = 2400 km exposure for time-dependent A declination of GW source software framework [14]. 40 line is chosen such as to reject GW sources Off 20 , the sky localization maps of GW sources are 0 3 4 140 Mpc eV 19 20 − which are required to not be farther away than 10 2 40 − 100 deg [15], could not possibly be constrained to be less than its total 60 −

M 18 9 2 80 . . 10 − 1 has been estimated. This photon horizon is the distance beyond which . The blue bars indicate the declination bands that are covered by the four selected × 2 +2 − γ 0 6 . h . This leads to a maximum photon horizon of 0.1 cm 0.7 0.6 0.5 0.4 0.3 0.2 0.8 7

13 s) s) (cm / exposure spectrum-weighted 2 10 level. The maximum distance of × 4 σ 100 EeV . 5 2 The spectrum-weighted exposure during a full sidereal day for a benchmark value of a typical Three classes of GW events have been defined for which the 50% localization region will be Result of a dedicated simulation study using CORSIKA and the for photon-induced air showers above 3 ◦ luminosity. Using CRPropa 3photons [16] in to the simulate extragalactic the medium, propagationphotons a and maximum at attenuation attenuation of length a of flux of UHE analyzed for coincident photon candidatewith events. a maximum The contour first size class of (class 1) comprises GW sources convolved with a corresponding Gaussian distribution before deriving the 50% contour. from which no photons are expected toabout reach the the photon Earth luminosity even under of thea the most source “photon optimistic and assumptions horizon” its emission pattern and spectrum. For this choice, mean value of the distance resolution.the The significance maximum of contour a size of photonabove the candidate event within a 1000 s time window would in any case be the photon luminosity of evenradiated the in brightest GW GW source of so far, i.e. GW190521 with total energy Figure 1: aperture of GW events (see Sec.4) withright: the GW190814, most GW170817, likely GW190701_203306, direction GW170818). markedbeen The by omitted indication for the of GW170817 since dark a the declination line host band galaxyof (GW of has the event-IDs this event from source has left been direction identified to is and,GW hence, negligible. events the taking uncertainty The into account red time solid dependent lines fluctuations display of the the actual aperture. exposure to photons from these of the analyzed sky region)the and search the region. confidence level To1 at also which take the into true account the source directional is resolution localized of within the Auger SD of about Follow-up Photon Search after Gravitational Waves PoS(ICRC2021)973 L D . For 2 Philip Ruehl 720 deg and luminosity distance 50% ) “class 1” ) “class 2” Ω 2 2 ) “class 3”. 2 has been chosen as the search region in ◦ 2 100 deg 720 deg 20 deg (which is the distance of the closest source < < < 50% 50% 50% 5 Ω Ω Ω 40 Mpc ≤ and and and L time window. These events belong to different source D 1 day 40 Mpc 140 Mpc ∞ < < < L L L D D D (c.f. GW170817 [17]) pointing directly towards Earth, only sources with are rejected. For those sources, the exponential attenuation of UHE photons ( ( ( ◦ 3 . and accepted independent of their distance. From such a small region in the sky, the 140 Mpc 2 ∼ γ 20 deg In total, five GW events pass the event selection described above. Four of those, namely > h L such sources with luminosity distance classes which are a BNSGW190701_203306) merger [19, (GW170817)20] [22], and two aThe binary black BNS black hole-neutron event hole star GW170817 mergers merger poses (GW170818, electromagnetic candidate a (GW190814) special follow-up [23]. observations case since as its NGCthan host 4993 through galaxy the [22] has GW been providing observation identified amap, alone. in through much this case, better Instead a localization of circular region using with the angular radius 50% of contour of the convolved sky GW170817, GW170818, GW190701_203306 andof GW190814, view had some of overlap the with SD the field during the Follow-up Photon Search after Gravitational Waves horizon holds for isotropic emission,with it strongly might beamed underestimate jets. the To directionalopening account luminosity also angles of for sources sources which mightD expose narrow jets with half- of GWs observed so far, the binaryto neutron actually star observe (BNS) merger a GW170817), potentialkeep there UHE is a a photon window good flux open chance for orwell potentially place localized unexpected strong sources discoveries, physical is a constraints. introduced. thirdthan subset Finally, These to (class sources 3) are of characterized especially by a 50% contour smaller In2, Fig. the accepted regions in theare visualized space on of top source of localization the distribution ofand all GWTC-2 confident GW [20]. observations published in GWTC-1 [19] 5. Preliminary Results compliance with the analysis of the90% blazar of TXS all 0506+056 UHE in photons [24]. reachingthat This the region. region SD is from chosen NGC4993 such are that expected to be reconstructed within in the extragalactic medium in anyalong case the overweights the beam enhancement axis. ofespecially any close possible A sources photon second to flux class be (class analyzed up 2) to of a accepted maximum GW allowed contour events size is of defined which allows expected background would be negligiblecandidate (c.f. event would be Sec.6) a strong and hintof the towards UHE new detection photons physics capable with of of the a suppressing cosmiccould the coincident background give interactions radiation rise photon such fields. an effect A is possible thecriteria new-physics oscillation process can between that UHE be photons summarized and as axions]. [18 The selection PoS(ICRC2021)973 (2) Philip Ruehl represents the UHE due to the declination GW γ Φ UL F on the spectral fluence inherit the γ E UL γ F GW γ E d dΦ γ 3 E d 6 t d 1 0 E Z E 1 t 0 Z t = : 1 F . The shaded regions define the set of accepted events according to the 50% Ω 2 that has been considered which imposes an additional uncertainty of order 20%, 7] . 1 and localization − , All GW events from GWTC-1 (green dots) and GWTC-2 (blue squares) in the space of source L 3 . D 2 − [ All four GW events have been analyzed with respect to a possible UHE photon signal. No The photon-discrimination method described above has a non-negligible rate of false-positive ∈ Figure 2: distance coincident air shower events have been found inno the coincident data photon of candidates the could Pierre be Auger Observatoy identified.fluence and, As hence, a consequence, upper limits on the spectral selection criteria described inacceptance the region. text while The theoverlap localization numbers with the region refer field to of of the the view of three events, the different that SD. source are classes marked in by the a black circle also have an indicated in3 Fig. by the red bars. 6. Sensitivity detections. In [8], out ofeleven all events air shower passed events recorded the during photon the full candidate operating period selection of and 14.5 yr, were found to be consistent with the Follow-up Photon Search after Gravitational Waves of UHE photons have been placed atphoton 90% flux CL from for each a GW source.declination GW Here, dependence point of source. the exposure. Theband upper covered Therefore, limits by the the variationbars. search of region This differs uncertainty for haslocalized each been in the omitted event. sky. for GW170817 On Itα top since is of its it indicated source there NGC in is 49933 the Fig. is uncertaintyby very due the to well blue the variation of the spectral index PoS(ICRC2021)973 ) 7 − ) = ) for 7 10 − × 10 6 . × Philip Ruehl GW170818 9 = 4 . ( b ( UL = 4 σ F 0 b . ( 5 σ 0 . 5 . For each single GW event the σ 65 . (preliminary) 4 ) for GW170817, 7 − , which means that the hypothesis of such an σ 10 65 × . 4 7 1 . = 7 b ( ) for GW190701_203306 and σ 6 − 95 . are indicated by the blue and red bars respectively. Due to the sky 10 4 α × 6 . = 1 b ( σ 8 . 4 , leads to a photon significance of is not displayed within the axis range. The uncertainty band of this event has no upper bound 6 2 − − 10 Preliminary upper limits (90% CL) on the spectral fluence for the four GW sources that pass the × 2 . = 3 Figure 3: selection criteria defined Sec.4. Uncertainties imposedas by a the limited variation sky of localization the of the spectral sources index as well localization of GW170818 close to the edge of the field of view, the central value of hypothesis of hadronic background events. This number may serverate as an associated estimate for to the background the presentto analysis. a possible Given an signal amountthe of of background primary expected hypothesis photons background, can can the becoincidence be sensitivity rejected with quantified in a through the the GW casegiven confidence event. amount of level of a at For background single which a events, photonobtained given a through candidate number confidence the detection construction interval of described for in observed by theconfidence Feldman photon true level and (CL), candidate Cousins number the (FC) events of lower [21]. limit and photons Depending ofconvenient can a on measure these the be for interval the may or sensitivity, we may definelevel not at be the which the equal photon FC to significance lower limit zero. as is the not Thus,single consistent highest as with photon confidence zero a for candidate the given event. background andsky an Assuming assumed regions a and single time windows photon analyzed candidateb here, event the within expected amount any of of background the events, which four is Follow-up Photon Search after Gravitational Waves 270 MeVcm since the localization region is not fully covered by the field of view. event originating in the background could be rejected at CL of significance would be at a level of for GW170818, GW190814. PoS(ICRC2021)973 level σ 5 Philip Ruehl PoS(ICRC2019)398 PoS(ICRC2019)459 ]. ]. ]. ]. ]. ]. ]. ]. ]. ]. ]. ]. ]. ]. ]. 1603.07142 9711021 ]. 0707.1652 ]. ]. 1810.12927 1710.05834 1502.01323 1612.07155 1612.01517 8 2009.01190 2006.12611 0901.4085 1710.05839 (2016) 38[ 1811.12907 1612.04155 2010.14527 05 (1998) 3873[ 1608.07378 1406.2912 2010.10953 57 (2007) 1485[ (2018) L11[ (2017) L13[ (2015) 172[ (2017) 038[ (2017) 09[ (2020) L13[ (2020) L44[ 580 (2017) L35[ 868 04 04 (2016) 22004. 848 ] (2007). 798 (2016) L25[ (2011) 125019[ Proc. 36th Int. Cosmic Ray Conf., Madison, USA (2019) 900 896 850 (2019) 031040[ 718 (2021) 021053[ 84 837 9 (2014) 160[ (2020) 105[ Phys. Rev. D (2016) 122007[ Proc. 36th Int. Cosmic Ray Conf., Madison, USA (2019) 11 902 789 94 J. Cosmol. Astropart. P. Astrophys. J. Lett. Phys. Rev. D Phys. Rev. X Astrophys. J. Lett. Astrophys. J. Lett. Phys. Rev. X Astrophys. J. Lett. astro-ph/0701583 Astrophys. J. Lett. Nucl. Instrum. Meth. A J. Phys. Conf. Ser. ]. ]. Phys. 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Abbott et al., the SD array of theselection strategy Pierre for both Auger GW sources Observatory and air hasthe shower events sensitivity been has towards been presented. a developed which possible aims photon to For signal keep hadronic this at primaries. a purpose high a With level despite this dedicated an selection irreducible strategy background of a detection at a significance beyond the Follow-up Photon Search after Gravitational Waves 7. Summary is possible. Out ofdetections the in total, GW four catalogs GW GWTC-1 eventsblack – and hole-neutron including GWTC-2, star the which binary merger comprise neutron candidateanalyzed star 50 GW190814 for merger confident – GW170817 UHE GW were and photons. selected the limits following No on this photon the strategy candidate spectral and fluence events of have UHE been photons found were and shown here preliminary for upper theReferences first time. 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Avila 27 1 , , J.A. Chinellato , F. Salamida , C. Hojvat , A.C. Fauth 80 , L. Lu , 36 89 90 , R. Alves Batista 72 81 10 73 13 90 26 64 79 P. Abreu , D. Martello , A. Coleman , B. Keilhauer , T. Fitoussi , J.A. Day 47 , L.M. Domingues Mendes , P.G. Isar , D. Nitz , J. Matthews , I. Caracas , M. Reininghaus , , B. García , F. Convenga , J. Kleinfeller 50 Muñiz S. Andringa P. Assis R.J. Barreira Luz X. Bertou C. Bleve , F. Montanet , E. De Vito 41 76 , I. Epicoco , , M. Gottowik 13 8 , , A.M. Botti , L. Perrone 68 1 47 44 41 81 , B.C. Manning 61 49 11 40 , , , S. Buitink , J. Peña-Rodriguez 20 , 41 , M.R. Hampel 60 , M. Muzio 52 , G. Farrar 77 , U. Giaccari , M. Cerda , , J. Rodriguez Rojo 70 , R. López 41 , , P. Papenbreer , G.C. Hill 32 , , A. Saftoiu , A. Menshikov 58 80 78 65 59 , M. Pothast 32 2 8 52 92 39 34 8 72 21 54 72 , P.F. Gómez Vitale 41 44 80 1 Follow-up Photon Search after Gravitational Waves The Pierre Auger Collaboration N. Borodai A. Bueno F. Canfora L. Cazon R. Colalillo F. Contreras B.R. Dawson V. de Souza J.R.T. de Mello Neto J.C. D’Olivo R. Engel J. Farmer A. Filipčič C. Galelli P.L. Ghia Berisso A. Gorgi P. Hamal D. Heck A. Insolia N. Karastathis M. Kleifges M.A. Leigui de Oliveira L. Lopes D. Mandat G. Marsella H.J. Mathes D. Melo S. Mollerach R. Mussa M. Niechciol J. Pallotta R. Pelayo M. Perlin B. Pont D. Ravignani Carvalho P. Ruehl PoS(ICRC2021)973 , , , , , , , , , , , , 8 4 , ,f 94 73 37 41 46 32 50 40 51 , , , 41 73 34 57 60 , 48 , 56 , V. Verzi Philip Ruehl , D. Stanca , S.J. Sciutto , O. Sima 4 8 , , A. Yushkov , M. Weber 42 , L. Valore 41 c 8 , 41 , T. Suomijärvi , F. Schlüter 8 68 , O. Tkachenko , C. Trimarelli 13 38 , P. Savina 80 , 32 11 81 , J. Schulte , G. Silli 38 43 , R. Sato 8 , B. Wundheiler , A.A. Watson , T. Sudholz 76 , M. Schimp , M. Stadelmaier 38 , P. Travnicek 26 14 8 , 10 10 39 , G. Sigl , I.D. Vergara Quispe , J.F. Valdés Galicia 16 27 , S. Schröder 33 , C. Timmermans 41 52 , L. Zehrer , , 93 76 63 , 77 , A. Travaini , R. Squartini , D. Wittkowski , C. Watanabe 36 4 36 , C. Sarmiento-Cano 42 , M. Vacula , M. Suárez-Durán , C. Ventura • 72 8 10 , 33 , R.C. Shellard 41 , M. Schimassek 39 38 41 , C. Taricco 29 , F.G. Schröder , Z. Torrès , M. Wirtz 32 , M. Zavrtanik 72 70 77 , J. Souchard , , H. Wahlberg 87 76 , R. Sarmento , S. Sehgal , L. Vaclavek , A. Streich 76 , D. Veberič 86 , A. Tapia 47 41 36 , 30 , H. Schieler , B. Tomé 71 53 48 19 , , P. Schovánek 56 15 , , H. Wilczyński , J.F. Soriano , F. Sarazin , P. Stassi 84 , D. Zavrtanik 86 , M. Unger 91 32 70 79 , S. Vorobiov 41 , A. Segreto 83 41 , , Z. Szadkowski 8 8 , V. Scherini , E. Zas , E. Santos 41 14 , O. Scholten , L. Wiencke , C.J. Todero Peixoto 21 , A. Vásquez-Ramírez , R. Ulrich , P. Sommers , J. Stasielak 39 , J. Vink 4 41 32 64 92 76 32 Aires and CONICET, Buenos Aires, Argentina U.N.R., Rosario, Argentina Nacional – Facultad Regional Mendoza (CONICET/CNEA), Mendoza, Argentina Miguelete – San Martín, Buenos Aires, Argentina Republic Centro Atómico Bariloche and Instituto BalseiroCentro (CNEA-UNCuyo-CONICET), de San Investigaciones Carlos en de Láseres Bariloche, y Argentina Departamento Aplicaciones, de CITEDEF Física and and Departamento CONICET, Villa de Martelli, Ciencias de Argentina la Atmósfera y los Océanos, FCEyN,IFLP, Universidad de Universidad Buenos Nacional de La Plata andInstituto CONICET, de La Astronomía Plata, y Argentina Física delInstituto Espacio de (IAFE, CONICET-UBA), Física Buenos Aires, de Argentina Rosario (IFIR) – CONICET/U.N.R.Instituto and de Tecnologías Facultad en de Detección y Ciencias Astropartículas Bioquímicas (CNEA, CONICET, y UNSAM), Farmacéuticas and UniversidadInstituto Tecnológica de Tecnologías en Detección yInternational Astropartículas Center (CNEA, CONICET, of UNSAM), Advanced Buenos Studies Aires, and Argentina Instituto de Ciencias Físicas, ECyT-UNSAM and CONICET, Campus Observatorio Pierre Auger, Malargüe, Argentina Observatorio Pierre Auger and Comisión NacionalUniversidad de Tecnológica Nacional Energía – Atómica, Facultad Malargüe, Regional Argentina BuenosUniversity Aires, of Buenos Adelaide, Adelaide, Aires, S.A., Argentina Australia Université Libre de Bruxelles (ULB), Brussels,Vrije Belgium Universiteit Brussels, Brussels, Belgium Centro Brasileiro de Pesquisas Fisicas, RioCentro de Federal Janeiro, de RJ, Educação Brazil Tecnológica CelsoInstituto Suckow da Federal de Fonseca, Nova Educação, Friburgo, Ciência Brazil eUniversidade Tecnologia de do São Rio Paulo, de Escola Janeiro de (IFRJ),Universidade Engenharia de Brazil de São Lorena, Paulo, Lorena, Instituto SP, de Brazil Universidade Física de de São São Paulo, Carlos, Instituto São de Carlos,Universidade Física, SP, Estadual São Brazil de Paulo, Campinas, SP, IFGW, Brazil Campinas, SP,Universidade Brazil Estadual de Feira de Santana,Universidade Feira Federal de do Santana, ABC, Brazil Santo André,Universidade SP, Federal Brazil do Paraná, Setor Palotina,Universidade Palotina, Federal Brazil do Rio de Janeiro,Universidade Instituto Federal de do Física, Rio Rio de de Janeiro Janeiro,Universidade (UFRJ), Federal RJ, Observatório Fluminense, Brazil do EEIMVR, Valongo, Volta Rio Redonda, de RJ,Universidad Janeiro, de Brazil RJ, Medellín, Brazil Medellín, Colombia Universidad Industrial de Santander, Bucaramanga, Colombia Charles University, Faculty of Mathematics and Physics, Institute of Particle and Nuclear Physics, Prague, Czech 1 2 3 4 5 6 7 8 9 Follow-up Photon Search after Gravitational Waves E.M. Santos R. Šmída D. Schmidt M. Scornavacche C.M. Schäfer S. Stanič A.D. Supanitsky P. Tobiska M. Tueros O. Zapparrata E. Varela A. Weindl J. Vicha 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 PoS(ICRC2021)973 Philip Ruehl 11 IN2P3, Paris, France France (UPIITA-IPN), México, D.F., México Universidade de Lisboa – UL, Lisboa, Portugal Institute of Physics of the CzechPalacky Academy University, of RCPTM, Sciences, Olomouc, Prague, Czech Czech Republic Republic CNRS/IN2P3, IJCLab, Université Paris-Saclay, Orsay, France Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Sorbonne Université, Université deUniv. Grenoble Paris, Alpes, CNRS- CNRS, Grenoble Institute of Engineering Univ. Grenoble Alpes, LPSC-IN2P3, 38000 Grenoble, Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France Bergische Universität Wuppertal, Department of Physics,Karlsruhe Wuppertal, Germany Institute of Technology (KIT), InstituteKarlsruhe for Experimental Institute of Particle Technology Physics, (KIT), Karlsruhe, Institut Germany Karlsruhe für Institute Prozessdatenverarbeitung und of Elektronik, Technology (KIT), Karlsruhe, Institute Germany RWTH for Aachen Astroparticle University, Physics, III. Karlsruhe, Physikalisches Germany Institut A,Universität Aachen, Hamburg, Germany II. Institut für TheoretischeUniversität Physik, Siegen, Hamburg, Department Germany Physik – ExperimentelleGran Teilchenphysik, Siegen, Sasso Germany Science Institute, Italy L’Aquila, INFN Laboratori Nazionali del Gran Sasso,INFN, Assergi Sezione Italy (L’Aquila), di Catania, Catania, Italy INFN, Sezione di Lecce, Lecce, Italy INFN, Sezione di Milano, Milano, Italy INFN, Sezione di Napoli, Napoli, Italy INFN, Sezione di Roma “Tor Vergata”, Roma,INFN, Italy Sezione di Torino, Torino, Italy Istituto di Astrofisica Spaziale e FisicaOsservatorio Cosmica Astrofisico di di Palermo Torino (INAF), (INAF), Palermo, Torino, Italy Italy Politecnico di Milano, Dipartimento di ScienzeUniversità e del Tecnologie Salento, Aerospaziali Dipartimento , di Milano, Matematica Italy Università e dell’Aquila, Dipartimento Fisica di “E. Scienze De Fisiche Giorgi”, e Lecce,Università Chimiche, di Italy Italy L’Aquila, Catania, Dipartimento di FisicaUniversità e di Astronomia, Milano, Catania, Dipartimento Italy di Fisica,Università Milano, di Italy Napoli “Federico II”, DipartimentoUniversità di di Fisica Palermo, “Ettore Dipartimento Pancini”, di Napoli, Fisica Italy Università e di Chimica Roma ”E. “Tor Vergata”, Segrè”, Dipartimento Palermo, diUniversità Italy Fisica, Torino, Roma, Dipartimento Italy di Fisica, Torino, Italy Benemérita Universidad Autónoma de Puebla, Puebla,Unidad México Profesional Interdisciplinaria en Ingeniería yUniversidad Autónoma Tecnologías de Avanzadas Chiapas, Tuxtla del Gutiérrez, Chiapas,Universidad Instituto Michoacana México de Politécnico San Nicolás Nacional deUniversidad Hidalgo, Nacional Morelia, Autónoma Michoacán, de México México, México,Universidad D.F., Nacional México de San Agustin deInstitute Arequipa, of Facultad Nuclear de Physics Ciencias PAN, Naturales Krakow, Poland yUniversity Formales, of Arequipa, Łódź, Peru Faculty of High-EnergyLaboratório Astrophysics,Łódź, Poland de Instrumentação e Física Experimental de“Horia Hulubei” Partículas National Institute – for LIP PhysicsInstitute and of and Nuclear Space Engineering, Instituto Science, Bucharest-Magurele, Bucharest-Magurele, Romania Superior Romania University Politehnica Técnico of – Bucharest, Bucharest, IST, Romania Center for Astrophysics and Cosmology (CAC), UniversityExperimental of Particle Nova Physics Gorica, Department, Nova J. Gorica, Stefan Slovenia Universidad Institute, de Ljubljana, Granada Slovenia and C.A.F.P.E., Granada, Spain Instituto Galego de Física de Altas Enerxías (IGFAE), Universidade de Santiago de Compostela, Santiago de Com- Follow-up Photon Search after Gravitational Waves 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 PoS(ICRC2021)973 Philip Ruehl 12 postela, Spain also at University of Bucharest, Physics Department, Bucharest, Romania Fermi National Accelerator Laboratory, Fermilab, Batavia,Max-Planck-Institut IL, für USA Radioastronomie, Bonn, Germany School of Physics and Astronomy, University ofColorado Leeds, State Leeds, University, Fort United Collins, Kingdom CO,now USA at Hakubi Center for Advanced Research and Graduate School of Science, Kyoto University, Kyoto, Japan IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands Nationaal Instituut voor Kernfysica en HogeStichting Energie Astronomisch Fysica Onderzoek (NIKHEF), in Science Nederland Park, (ASTRON), Amsterdam, Dwingeloo,Universiteit The van The Netherlands Amsterdam, Netherlands Faculty of Science,University Amsterdam, of The Groningen, Netherlands Kapteyn Astronomical Institute,Case Groningen, The Western Reserve Netherlands University, Cleveland, OH, USA Colorado School of Mines, Golden, CO,Department USA of Physics and Astronomy, LehmanLouisiana College, City State University, University Baton of Rouge, New LA, York, Bronx, USA Michigan NY, Technological USA University, Houghton, MI, USA New York University, New York, NY, USA Pennsylvania State University, University Park, PA, USA University of Chicago, Enrico Fermi Institute,University Chicago, of IL, Delaware, USA Department of PhysicsUniversity and of Astronomy, Bartol Wisconsin-Madison, Department Research Institute, of Newark, Physics DE,—– and USA WIPAC, Madison, WI, USA b c e d a f Follow-up Photon Search after Gravitational Waves 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94