Faculty Profiles - OKUMURA Akira

Papers - OKUMURA Akira

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Study on the gain and photon detection efficiency drops of silicon photomultipliers under bright background conditions

Okumura A., Wakazono K., Furuta K., Tajima H.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The use of silicon photomultipliers (SiPMs) in imaging atmospheric Cherenkov telescopes is expected to extend the observation times of very-high-energy gamma-ray sources, particularly within the highest energy domain of 50–300 TeV, where the Cherenkov signal from celestial gamma rays is adequate even under bright moonlight background conditions. Unlike conventional photomultiplier tubes, SiPMs do not exhibit quantum efficiency or gain degradation, which can be observed after long exposures to bright illumination. However, under bright conditions, the photon detection efficiency of a SiPM can be undergo temporary degradation because a fraction of its avalanche photodiode cells can saturate owing to photons from the night-sky background (NSB). In addition, the large current generated by the high NSB rate can increase the temperature of the silicon substrate, resulting in shifts in the SiPM breakdown voltages and consequent gain changes. Moreover, this large current changes the effective bias voltage because it causes a voltage drop across the protection resistor of 100–1000 Ω. Hence, these three factors, namely the avalanche photodiode (APD) saturation, Si temperature, and voltage drop must be carefully compensated for and/or considered in the energy calibration of Cherenkov telescopes with SiPM cameras. In this study, we measured the signal output charge of a SiPM and its variation as a function of different NSB-like background conditions up to 1 GHz/pixel. The results verify that the product of the SiPM gain and photon detection efficiency is well characterized by these three factors.

Sensitivity of the Cherenkov Telescope Array to the gamma-ray emission from neutrino sources detected by IceCube

Sergijenko O., Brown A.M., Fiorillo D., de León A.R., Satalecka K., Tung C.F., Taboada I., Abe K., Abe S., Acharyya A., Adam R., Aguasca-Cabot A., Agudo I., Alfaro J., Alvarez-Crespo N., Alves Batista R., Amans J.P., Amato E., Ambrosino F., Angüner E.O., Antonelli L.A., Aramo C., Arcaro C., Arrabito L., Asano K., Aschersleben J., Ashkar H., Augusto Stuani L., Baack D., Backes M., Balazs C., Balbo M., Baquero Larriva A., Barbosa Martins V., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Batzofin R., Baxter J., Beck G., Becker Tjus J., Beiske L., Belardinelli D., Benbow W., Bernardini E., Bernete Medrano J., Bernlöhr K., Berti A., Beshley V., Bhattacharjee P., Bhattacharyya S., Bi B., Biederbeck N., Biland A., Bissaldi E., Blanch O., Blazek J., Boisson C., Bolmont J., Bonnoli G., Bordas P., Bosnjak Z., Bradascio F., Braiding C., Bronzini E., Brose R., Brun F., Brunelli G., Bulgarelli A., Burelli I., Burmistrov L., Burton M., Bylund T., Calisse P.G., Campoy-Ordaz A., Cantlay B.K., Capalbi M., Caproni A., Capuzzo-Dolcetta R., Carlile C., Caroff S., Carosi A., Carosi R., Carrasco M.S., Cascone E., Cassol F., Castrejon N., Catalani F., Cerasole D., Cerruti M., Chaty S., Chen A.W., Chernyakova M., Chiavassa A., Chudoba J., Coimbra Araujo C.H., Conforti V.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

Gamma-ray observations of the astrophysical neutrino sources are fundamentally important for understanding the underlying neutrino production mechanism. We investigate the Cherenkov Telescope Array (CTA) ability to detect the very-high-energy (VHE) gamma-ray counterparts to the neutrino-emitting Active Galaxies. The CTA performance under different configurations and array layouts is computed based on the neutrino and gamma-ray simulations of steady and transient types of sources, assuming that the neutrino events are detected with the IceCube neutrino telescope. The CTA detection probability is calculated for both CTA sites taking into account the visibility constraints. We find that, under optimal observing conditions, CTA could observe the VHE gamma-ray emission from at least 3 neutrino events per year.

Pybkgmodel - a background modelling toolbox for the CTA

Strzys M.C., Abe S., de Bony de Lavergne M., Hütten M., Mender S., Vovk I., Abe K., Abe S., Acharyya A., Adam R., Aguasca-Cabot A., Agudo I., Alfaro J., Alvarez-Crespo N., Alves Batista R., Amans J.P., Amato E., Ambrosino F., Angüner E.O., Antonelli L.A., Aramo C., Arcaro C., Arrabito L., Asano K., Aschersleben J., Ashkar H., Augusto Stuani L., Baack D., Backes M., Balazs C., Balbo M., Baquero Larriva A., Barbosa Martins V., de Almeida U.B., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Batzofin R., Baxter J., Beck G., Becker Tjus J., Beiske L., Belardinelli D., Benbow W., Bernardini E., Bernete Medrano J., Bernlöhr K., Berti A., Beshley V., Bhattacharjee P., Bhattacharyya S., Bi B., Biederbeck N., Biland A., Bissaldi E., Blanch O., Blazek J., Boisson C., Bolmont J., Bonnoli G., Bordas P., Bosnjak Z., Bradascio F., Braiding C., Bronzini E., Brose R., Brown A.M., Brun F., Brunelli G., Bulgarelli A., Burelli I., Burmistrov L., Burton M., Bylund T., Calisse P.G., Campoy-Ordaz A., Cantlay B.K., Capalbi M., Caproni A., Capuzzo-Dolcetta R., Carlile C., Caroff S., Carosi A., Carosi R., Carrasco M.S., Cascone E., Cassol F., Castrejon N., Catalani F., Cerasole D., Cerruti M., Chaty S., Chen A.W., Chernyakova M., Chiavassa A., Chudoba J., Coimbra Araujo C.H., Conforti V., Conte F.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

Despite the advancement in background rejection techniques, observation of the very-high-energy gamma-ray sky by imaging atmospheric Cherenkov telescopes (IACTs) are subject to an irreducible background from gamma-like hadron- or electron-induced air showers. The determination of this residual background is crucial for accurate spectral and spatial measurements. The Cherenkov Telescope Array (CTA) will become the next generation of IACTs. To unveil its full potential, the improved reconstruction performance of CTA needs to be coupled with a reliable background estimate across the entire field of view. This may become especially important in the case of the planned surveys of large areas of the sky. In this contribution we will present pybkgmodel, an open-source python software package developed for CTA. It aims at providing in a consistent way the various background modelling methods, based on the experience from current IACTs such as H.E.S.S, MAGIC, and VERITAS. It is designed as a toolbox allowing a user to easily choose the optimal reconstruction approach for various target regions or a combination of several algorithms. We will introduce the design of the package as well as demonstrate its functionality using data for the CTA Large-Sized Telescope prototype (LST-1).

Potential of the Cherenkov Telescope Array for studying the young nearby supernova remnants

Prokhorov D.A., Lee S.H., Nagataki S., Vink J., Ellison D.C., Ferrand G., Patnaude D.J., Roepke F.K., Seitenzahl I.R., Slane P.O., Abe K., Abe S., Acharyya A., Adam R., Aguasca-Cabot A., Agudo I., Alfaro J., Alvarez-Crespo N., Alves Batista R., Amans J.P., Amato E., Ambrosino F., Angüner E.O., Antonelli L.A., Aramo C., Arcaro C., Arrabito L., Asano K., Aschersleben J., Ashkar H., Augusto Stuani L., Baack D., Backes M., Balazs C., Balbo M., Baquero Larriva A., Barbosa Martins V., Barres de Almeida U., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Batzofin R., Baxter J., Beck G., Becker Tjus J., Beiske L., Belardinelli D., Benbow W., Bernardini E., Bernete Medrano J., Bernlöhr K., Berti A., Beshley V., Bhattacharjee P., Bhattacharyya S., Bi B., Biederbeck N., Biland A., Bissaldi E., Blanch O., Blazek J., Boisson C., Bolmont J., Bonnoli G., Bordas P., Bosnjak Z., Bradascio F., Braiding C., Bronzini E., Brose R., Brown A.M., Brun F., Brunelli G., Bulgarelli A., Burelli I., Burmistrov L., Burton M., Bylund T., Calisse P.G., Campoy-Ordaz A., Cantlay B.K., Capalbi M., Caproni A., Capuzzo-Dolcetta R., Carlile C., Caroff S., Carosi A., Carosi R., Carrasco M.S., Cascone E., Cassol F., Castrejon N., Catalani F., Cerasole D., Cerruti M., Chaty S., Chen A.W., Chernyakova M., Chiavassa A.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

Modern imaging atmospheric Cherenkov telescopes have extensively observed young nearby supernova remnants (SNRs), with ages of about 1000 years or less, in the very-high-energy (VHE) gamma-ray band. These efforts resulted in the detection of VHE emission from three young SNRs – Cassiopeia A, Tycho, and SN 1006 – and provided significant evidence for emission from the more distant Kepler’s SNR. However, many questions on the production of VHE gamma rays in these remnants remain unanswered. Using detailed physical models for Tycho’s SNR based on the CR-hydro-NEI code and physically motivated models for the other young nearby remnants, we simulated observations with the Cherenkov Telescope Array (CTA) of these gamma-ray sources. We highlight properties of these remnants accessible for investigation with future CTA observations and discuss which questions are expected to be answered.

Performance update of an event-type based analysis for the Cherenkov Telescope Array

Bernete J., Gueta O., Hassan T., Linhoff M., Maier G., Sinha A., Abe K., Abe S., Acharyya A., Adam R., Aguasca-Cabot A., Agudo I., Alfaro J., Alvarez-Crespo N., Alves Batista R., Amans J.P., Amato E., Ambrosino F., Angüner E.O., Antonelli L.A., Aramo C., Arcaro C., Arrabito L., Asano K., Aschersleben J., Ashkar H., Augusto Stuani L., Baack D., Backes M., Balazs C., Balbo M., Baquero Larriva A., Barbosa Martins V., de Almeida U.B., Barrio J.A., Bastieri D., Batista P.I., Batkovic I., Batzofin R., Baxter J., Beck G., Becker Tjus J., Beiske L., Belardinelli D., Benbow W., Bernardini E., Bernete Medrano J., Bernlöhr K., Berti A., Beshley V., Bhattacharjee P., Bhattacharyya S., Bi B., Biederbeck N., Biland A., Bissaldi E., Blanch O., Blazek J., Boisson C., Bolmont J., Bonnoli G., Bordas P., Bosnjak Z., Bradascio F., Braiding C., Bronzini E., Brose R., Brown A.M., Brun F., Brunelli G., Bulgarelli A., Burelli I., Burmistrov L., Burton M., Bylund T., Calisse P.G., Campoy-Ordaz A., Cantlay B.K., Capalbi M., Caproni A., Capuzzo-Dolcetta R., Carlile C., Caroff S., Carosi A., Carosi R., Carrasco M.S., Cascone E., Cassol F., Castrejon N., Catalani F., Cerasole D., Cerruti M., Chaty S., Chen A.W., Chernyakova M., Chiavassa A., Chudoba J., Coimbra Araujo C.H., Conforti V., Conte F.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The Cherenkov Telescope Array (CTA) will be the next-generation observatory in the field of very-high-energy (20 GeV to 300 TeV) gamma-ray astroparticle physics. The traditional approach to data analysis in this field is to apply quality cuts, optimized using Monte Carlo simulations, on the data acquired to maximize sensitivity. Subsequent steps of the analysis typically use the surviving events to calculate one set of instrument response functions (IRFs) to physically interpret the results. However, an alternative approach is the use of event types, as implemented in experiments such as the Fermi-LAT. This approach divides events into sub-samples based on their reconstruction quality, and a set of IRFs is calculated for each sub-sample. The sub-samples are then combined in a joint analysis, treating them as independent observations. In previous works we demonstrated that event types, classified using Machine Learning methods according to their expected angular reconstruction quality, have the potential to significantly improve the CTA angular and energy resolution of a point-like source analysis. Now, we validated the production of event-type wise full-enclosure IRFs, ready to be used with science tools (such as Gammapy and ctools). We will report on the impact of using such an event-type classification on CTA high-level performance, compared to the traditional procedure.

Performance of the Large-Sized Telescope prototype of the Cherenkov Telescope Array

Morcuende D., López-Coto R., Moralejo A., Nozaki S., Vuillaume T., Abe K., Abe S., Aguasca-Cabot A., Agudo I., Alvarez Crespo N., Antonelli L.A., Aramo C., Arbet-Engels A., Arcaro C., Artero M., Asano K., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Baxter J., Becerra González J., Bernardini E., Bernardos M.I., Bernete Medrano J., Berti A., Bhattacharjee P., Biederbeck N., Bigongiari C., Bissaldi E., Blanch O., Bonnoli G., Bordas P., Bulgarelli A., Burelli I., Burmistrov L., Buscemi M., Cardillo M., Caroff S., Carosi A., Carrasco M.S., Cassol F., Cauz D., Cerasole D., Ceribella G., Chai Y., Cheng K., Chiavassa A., Chikawa M., Chytka L., Cifuentes A., Contreras J.L., Cortina J., Costantini H., Dalchenko M., Dazzi F., De Angelis A., de Bony de Lavergne M., De Lotto B., De Lucia M., de Menezes R., Del Peral L., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Dellaiera M., Di Piano A., Di Pierro F., Di Pilato A., Di Tria R., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Eisenberger L., Elsässer D., Emery G., Escudero J., Fallah Ramazani V., Ferrara G., Ferrarotto F., Fiasson A., Foffano L., Freixas Coromina L., Fröse S., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Gasbarra C., Gasparrini D., Geyer D.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The next-generation ground-based gamma-ray Cherenkov Telescope Array Observatory (CTAO) will consist of imaging atmospheric Cherenkov telescopes (IACTs) of three different sizes distributed in two sites. The Large-Sized Telescopes will cover the low-energy end of the CTA energy range, starting at about 20 GeV. After its first years of operation at the CTA northern site, the Large-Sized Telescope prototype (LST-1) is in the final stage of its commissioning phase, having collected a significant amount of scientific data to date. In this contribution, we present the physics performance of the telescope using low-zenith Crab Nebula observations and Monte Carlo simulations fine-tuned accordingly. We show performance figures of merit such as the energy threshold, effective area, energy and angular resolution, and sensitivity based on the standard Hillas-parameters approach and following the source-independent and dependent analysis methods. The analysis threshold is estimated at 30 GeV. The energy resolution is around 30%, and the angular resolution is 0.3 degrees at 100 GeV. The best integral sensitivity of LST-1 is about 1.1% of the Crab Nebula flux above 250 GeV for 50 hours of observations. We also show the spectral energy distribution and light curve from Crab Nebula observations, which agree with results from other IACTs and link smoothly with Fermi-LAT when considering statistical and systematic uncertainties near the energy threshold.

Performance of joint gamma-ray observations with MAGIC and LST-1 telescopes

Di Pierro F., Berti A., de Menezes R., Jobst E., Ohtani Y., Sitarek J., Suda Y., Visentin E., Abe H., Abe K., Abe S., Abhir J., Acciari V.A., Aguasca-Cabot A., Agudo I., Alvarez Crespo N., Aniello T., Ansoldi S., Antonelli L.A., Aramo C., Arbet-Engels A., Cornelia A., Artero M., Asano K., Aubert P., Baack D., Babić A., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M.I., Bernete Medrano J., Besenrieder J., Bhattacharjee P., Biederbeck N., Bigongiari C., Biland A., Bissaldi E., Blanch O., Bonnoli G., Bordas P., Bošnjak , Bulgarelli A., Burelli I., Burmistrov L., Buscemi M., Busetto G., Campoy-Ordaz A., Cardillo M., Caroff S., Carosi A., Carosi R., Carrasco M.S., Carretero-Castrillo M., Cassol F., Castro-Tirado A.J., Cauz D., Cerasole D., Ceribella G., Chai Y., Cheng K., Chiavassa A., Chikawa M., Chilingarian A., Chytka L., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Costantini H., Covino S., D’Amico G., Dalchenko M., D’Elia V., Da Vela P., Dazzi F., De Angelis A., de Bony de Lavergne M., De Lotto B., De Lucia M., Del Peral L., Deleglise G., Delfino M., Delgado C., Delgado Mengual J., della Volpe D., Dellaiera M., Del Popolo A., Depaoli D., Di Piano A.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The prototype Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) is in commissioning phase at the Observatorio del Roque de Los Muchachos at 2200 m a.s.l. in La Palma (Canary Islands, Spain). LST-1 is a 23-m diameter telescope and is the first of four that will compose the LST part of the CTAO Northern array. The LST subarray is optimized to provide the best sensitivity for gamma rays in the 20 GeV - 200 GeV energy range. The MAGIC telescopes, which are located approximately 100 m from the LST-1, is operating as a two 17-m telescope stereoscopic system for more than 14 years. LST-1 and MAGIC routinely perform joint observations of gamma-ray sources to exploit the potential of the three-telescope system. This contribution describes the analysis pipeline and evaluates the performance of the system using Monte Carlo simulations and data on the Crab Nebula. The sensitivity achieved during joint observations with MAGIC and LST-1 is about 30% higher than that of MAGIC alone.

Observation of Active Galactic Nuclei with the Large-Sized Telescope prototype of the Cherenkov Telescope Array

Takeishi R., Álvarez Crespo N., Arbet-Engels A., Baquero Larriva A., Baxter J., Biederbeck N., Caroff S., Di Marco G., Fallah Ramazani V., Green D., Heckmann L., Láinez M., Nickel L., Nievas Rosillo M., Pons E., Priyadarshi C., Sanchez D.A., Vázquez Acosta M., Abe K., Abe S., Aguasca-Cabot A., Agudo I., Antonelli L.A., Aramo C., Arcaro C., Artero M., Asano K., Aubert P., Baktash A., Bamba A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Becerra González J., Bernardini E., Bernardos M.I., Bernete Medrano J., Berti A., Bhattacharjee P., Bigongiari C., Bissaldi E., Blanch O., Bonnoli G., Bordas P., Bulgarelli A., Burelli I., Burmistrov L., Buscemi M., Cardillo M., Carosi A., Carrasco M.S., Cassol F., Cauz D., Cerasole D., Ceribella G., Chai Y., Cheng K., Chiavassa A., Chikawa M., Chytka L., Cifuentes A., Contreras J.L., Cortina J., Costantini H., Dalchenko M., Dazzi F., De Angelis A., de Bony de Lavergne M., De Lotto B., De Lucia M., de Menezes R., Del Peral L., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Dellaiera M., Di Piano A., Di Pierro F., Di Pilato A., Di Tria R., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Eisenberger L., Elsässer D., Emery G., Escudero J., Ferrara G., Ferrarotto F., Fiasson A., Foffano L., Freixas Coromina L., Fröse S.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

Cherenkov Telescope Array (CTA) will be the next generation gamma-ray observatory. It will consist of three different sizes of telescopes, with a collective improvement of about an order of magnitude in sensitivity, compared with the current generation gamma-ray telescopes. LargeSized Telescopes (LSTs) will be the most sensitive at energies from tens of GeV up to a few TeVs, and will be the best suited to observe gamma-ray sources such as Active Galactic Nuclei (AGN). The first Large-Sized Telescope prototype (LST-1), inaugurated in 2018 and currently in commissioning phase, has accumulated more than one thousand hours of data to date. From 2020 to 2022, we have detected various gamma-ray sources, and prominent among them are several well-known AGN, like Mrk 421, Mrk 501, 1ES 1959+650, 1ES 0647+250, PG 1553+113, etc. We report on light curves and energy spectra reconstructed out of these observations down to energies of tens of GeV, which is very close to the energy threshold of LST-1.

New constraints on Lorentz invariance violation using the extraordinary flare of Mrk 421 in 2014

D’Amico G., Strišković J., Terzić T., Abe H., Abe S., Abhir J., Acciari V.A., Agudo I., Aniello T., Ansoldi S., Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres de Almeida U., Barrio J.A., Batković I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M., Bernete J., Berti A., Besenrieder J., Bigongiari C., Biland A., Blanch O., Bonnoli G., Bošnjak , Burelli I., Busetto G., Campoy-Ordaz A., Carosi A., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chilingarian A., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D’Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L., Dominis Prester D., Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Escudero J., Fariña L., Fattorini A., Foffano L., Font L., Fröse S., Fukami S., Fukazawa Y., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., Giesbrecht Paiva J.G., Giglietto N., Giordano F., Gliwny P., Godinović N., Grau R., Green D., Green J.G., Hadasch D., Hahn A., Hassan T., Heckmann L., Herrera J., Hrupec D., Hütten M., Imazawa R., Inada T., Iotov R., Ishio K.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

An extraordinary flare from blazar Mrk 421 was recorded on the night of April 24, 2014, by the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes at very high energy (VHE) from 100 GeV up to 10 TeV. Several quantum-gravity models indicate that the photon group velocity in vacuum may be energy dependent, known as in-vacuum dispersion. Violation of Lorentz Invariance (LIV) of this kind can lead to an observable effect on the time of flight of VHE photons from cosmic origin. Observations of fast and distant phenomena, such as the flare from Mrk 421, are excellent testing grounds for this hypothesis. Using an innovative binned likelihood analysis, for the first time from this source we were able to search for arrival-time delays scaling linearly or quadratically with the energy of the photon. The non-detection of energy-dependent time delays led us to set constraints on the parameter space of quantum-gravity predictions.

Multiwavelength study of GRB 201216C using the sub-TeV emission detected by MAGIC

Fukami S., Berti A., Loporchio S., Nava L., Suda Y., Noda K., Asano K., Bošnjak Ž., Longo F., Jordana-Mitjans N., Melandri A., Mundell C., Shrestha M., Steele I., Abe H., Abe S., Abhir J., Acciari V.A., Agudo I., Aniello T., Ansoldi S., Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres de Almeida U., Barrio J.A., Batković I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M., Bernete J., Besenrieder J., Bigongiari C., Biland A., Blanch O., Bonnoli G., Burelli I., Busetto G., Campoy-Ordaz A., Carosi A., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chilingarian A., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D’Amico G., D’Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L., Dominis Prester D., Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Escudero J., Fariña L., Fattorini A., Foffano L., Font L., Fröse S., Fukazawa Y., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., Giesbrecht Paiva J.G., Giglietto N., Giordano F., Gliwny P., Godinović N., Grau R., Green D., Green J.G.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

Recently, several gamma-ray bursts (GRBs) have been detected in the very-high-energy (VHE) gamma-ray energy range by ground-based gamma-ray experiments such as MAGIC, H.E.S.S., and LHASSO. For some GRBs, the VHE emission is consistent with synchrotron self-Compton (SSC) emission from high-energy electrons accelerated in the forward shock of the relativistic jet. However, more statistics are needed to further constrain the emission models. GRB 201216C is a long bright GRB detected in a broad energy range from radio to VHE. The redshift is estimated to be 1.1, making the GRB the most distant source detected in the VHE energy range. MAGIC started the observation 56 seconds after the GRB was triggered by the Swift-BAT telescope. We performed a detailed analysis and detected the signal with about 6 sigma in the first 20 minutes. MAGIC continued the observation for 2.2 hours on the same night and 4 hours on the next night. No signal was detected later than 40 minutes after the GRB trigger. We have performed modelling of the multi-wavelength emission using the MAGIC data. We analysed simultaneous optical data from Liverpool Telescope with MAGIC and included the results in the modelling. The sub-TeV emission is consistent with the single-zone SSC model in the forward shock. In this presentation, we show the final results of the MAGIC data analysis of GRB 201216C and discuss the emission mechanism of the multi-wavelength data.

Multiwavelength characterization of two flaring blazars: insight into the emission region of intermediate-synchrotron-peaked BL Lacs

Loporchio S., Bonnoli G., Cerasole D., Di Venere L., Dominis Prester D., Giordano F., Lindfors E., Manganaro M., Pavletić L., Abe H., Abe S., Abhir J., Acciari V.A., Agudo I., Aniello T., Ansoldi S., Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres de Almeida U., Barrio J.A., Batković I., Baxter J., Be-Cerra González J., Bednarek W., Bernardini E., Bernardos M., Bernete J., Berti A., Besenrieder J., Bigongiari C., Biland A., Blanch O., Bošnjak , Burelli I., Busetto G., Campoy-Ordaz A., Carosi A., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chilingarian A., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D’Amico G., D’Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Escudero J., Fariña L., Fattorini A., Foffano L., Font L., Fröse S., Fukami S., Fukazawa Y., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., GiesbrechtPaiva J.G., Giglietto N., Gliwny P., Godinović N., Grau R., Green D., Green J.G., Hadasch D., Hahn A., Hassan T., Heckmann L., Herrera J., Hrupec D., Hütten M., Imazawa R., Inada T.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The blazars B2 1811+31 and GB6 J1058+2817 were found to be in flaring state during 2020 and 2021, respectively. The high states of the sources were registered by the Fermi-LAT at energies below 100 GeV, triggering observations at higher energies with the MAGIC telescopes, in the UV/X rays with the Swift satellite and with ground-based radio and optical telescopes. The observations in the very-high-energy (VHE, 100 GeV < E < 100 TeV) gamma-ray band led to the first detection of both sources in this energy range. A long-term gamma-ray lightcurve was derived using Fermi-LAT data, identifying the time intervals in which the two sources persisted in a quiet state. Archival data collected in the radio to X-ray wavelengths showed that the two sources exhibited intermediate-synchrotron-peaked BL Lac behaviors in their low states, rather rare sources in the TeV sky. The high state of the two sources was deeply investigated thanks to the coverage provided by multi-wavelength (MWL) observational campaigns. In this contribution, we present the results of the gamma-ray observations which are included in a MWL observational campaign organized on these sources during their high-states. We discuss the flare spectral properties and temporal variability. In the high-energy gamma band, sub-daily-scale variability and strong spectral hardening give evidence for compact emission regions responsible for the radiative output at high energies during the flare.

Multi-wavelength analysis of the galactic PeVatron candidate LHAASO J2108+5157

Pirola G., Juryšek J., Balbo M., Eckert D., Tramacere A., Walter R., Abe K., Abe S., Aguasca-Cabot A., Agudo I., Alvarez Crespo N., Antonelli L.A., Aramo C., Arbet-Engels A., Arcaro C., Artero M., Asano K., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Baxter J., Becerra González J., Bernardini E., Bernardos M.I., Bernete Medrano J., Berti A., Bhattacharjee P., Biederbeck N., Bigongiari C., Bissaldi E., Blanch O., Bonnoli G., Bordas P., Bulgarelli A., Burelli I., Burmistrov L., Buscemi M., Cardillo M., Caroff S., Carosi A., Carrasco M.S., Cassol F., Cauz D., Cerasole D., Ceribella G., Chai Y., Cheng K., Chiavassa A., Chikawa M., Chytka L., Cifuentes A., Contreras J.L., Cortina J., Costantini H., Dalchenko M., Dazzi F., De Angelis A., de Bony de Lavergne M., De Lotto B., De Lucia M., de Menezes R., Del Peral L., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Dellaiera M., Di Piano A., Di Pierro F., Di Pilato A., Di Tria R., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Eisenberger L., Elsässer D., Emery G., Escudero J., Fallah Ramazani V., Ferrara G., Ferrarotto F., Fiasson A., Foffano L., Freixas Coromina L., Fröse S., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Gasbarra C., Gasparrini D.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

LHAASO J2108+5157 is a recently discovered source, detected in the Ultra-High-Energy band by the LHAASO collaboration. Two molecular clouds were identified in the direction coincident with LHAASO J2108+5157 and, from the spectra reported by LHAASO, there is no sign of an energy cutoff up to 200 TeV. This source makes a promising galactic PeVatron candidate. In 2021, the Large-Sized Telescope prototype (LST-1) of the Cherenkov Telescope Array (CTA) Observatory, collected about 50 hours of quality-selected data on LHAASO J2108+5157. Through these observations, we managed to compute stringent upper limits on the source emission in the multi-TeV band. Together with the analysis of XMM-Newton data and 12 years of Fermi-LAT data, we performed a multi-wavelength study of the source, investigating different possible scenarios of particle acceleration. In this contribution, we will present the results of the analysis, as well as the multi-wavelength modeling, and consequent interpretation of different possible scenarios of emission.

MAGIC Upper Limits on the VHE emission from Flat Spectrum Radio Quasars

Mondal H.A., Gliwny P., Principe G., Longo F., Żywucka-Hejzner N., Lindfors E., Majumdar P., Sitarek J., Abe H., Abe S., Abhir J., Acciari V.A., Agudo I., Aniello T., Ansoldi S., Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres de Almeida U., Barrio J.A., Batković I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M., Bernete J., Berti A., Besenrieder J., Bigongiari C., Biland A., Blanch O., Bonnoli G., Bošnjak , Burelli I., Busetto G., Campoy-Ordaz A., Carosi A., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chilingarian A., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D’Amico G., D’Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L., Dominis Prester D., Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Escudero J., Fariña L., Fattorini A., Foffano L., Font L., Fröse S., Fukami S., Fukazawa Y., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., Giesbrecht Paiva J.G., Giglietto N., Giordano F., Godinović N., Grau R., Green D., Green J.G., Hadasch D., Hahn A., Hassan T., Heckmann L., Herrera J., Hrupec D.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

Blazars are a class of active galactic nuclei (AGN) where the relativistic jet is pointed towards the observer. They are powerful sources of non-thermal radiation from radio to very high energy (VHE, E>100 GeV) gamma-rays. Flat Spectrum Radio Quasars (FSRQs) are a subclass of blazars where there are absorption or emission lines present in the optical spectra. The observed properties of FSRQs are strongly affected by the magnetic field in the accretion disk which changes the UV emission of Broad Line Region (BLR) and infra-red emission from the Dusty Torus. While many (774 as reported in 4FGL-DR2 catalogue [1]) FSRQs have been detected at high energies (HE; E>100 MeV), only a few (9 as of now) could be detected at VHE. In this contribution, we present observations of nine FSRQs performed by Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC)telescopes between 2008 and 2020 with a total observation time of 174 hours. We also include a few observations from the Fermi-LAT, Swift-UVOT, Swift-XRT and optical observations from Kungliga Vetenskapsakademien (KVA) for two sources CTA 102 and B2 2234+28. We also modelled the broad band emission of the sources to look for signatures of absorption in the BLR region and hence to put constraints on the location of the emission region.

MAGIC observation of BL Lacertae flaring period in 2020

Imazawa R., Strišković J., Jormanainen J., Truzzi S., Lindfors E., Dominis Prester D., Bonnoli G., Fukazawa Y., Suda Y., Abe H., Abe S., Abhir J., Acciari V.A., Agudo I., Aniello T., Ansoldi S., Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres de Almeida U., Barrio J.A., Batković I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M., Bernete J., Berti A., Besenrieder J., Bigongiari C., Biland A., Blanch O., Bošnjak , Burelli I., Busetto G., Campoy-Ordaz A., Carosi A., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chilingarian A., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D’Amico G., D’Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L., Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Escudero J., Fariña L., Fattorini A., Foffano L., Font L., Fröse S., Fukami S., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., Giesbrecht Paiva J.G., Giglietto N., Giordano F., Gliwny P., Godinović N., Grau R., Green D., Green J.G., Hadasch D., Hahn A., Hassan T., Heckmann L., Herrera J., Hrupec D.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

BL Lacertae (BL Lac) is one of the low-frequency peaked BL Lac object (LBL). Since August 2020, BL Lac has shown a historically high activity in HE (high-energy, 0.1 GeV < E < 100 GeV) gamma-ray and optical bands. The MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes performed joint observations during this flaring period with instruments operating in gamma-ray, X-ray, optical, and radio bands from August to October 2020. In the VHE (very-high-energy, E > 100 GeV) gamma-ray range, BL Lac was detected in several nights during an especially bright flare simultaneous with a HE flare. In the long-term light curves, X-ray and HE gamma-ray flux overall show correlation, but sometimes only HE gamma-ray was bright. These multi-wavelength (MWL) correlations may relate to the emission mechanisms and the origin of the observed flaring activity. In this contribution we will present some of the preliminary results on the MWL campaign of BL Lac in September 2020, with a focus on the X-ray and gamma-ray activity, based on the data collected by Swift-XRT, MAGIC and Fermi-LAT telescopes.

LST-1 observations of an enormous flare of BL Lacertae in 2021

Nozaki S., Asano K., Escudero J., Emery G., Priyadarshi C., Abe K., Abe S., Aguasca-Cabot A., Agudo I., Alvarez Crespo N., Antonelli L.A., Aramo C., Arbet-Engels A., Arcaro C., Artero M., Aubert P., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Baxter J., Becerra González J., Bernardini E., Bernardos M.I., Bernete Medrano J., Berti A., Bhattacharjee P., Biederbeck N., Bigongiari C., Bissaldi E., Blanch O., Bonnoli G., Bordas P., Bulgarelli A., Burelli I., Burmistrov L., Buscemi M., Cardillo M., Caroff S., Carosi A., Carrasco M.S., Cassol F., Cauz D., Cerasole D., Ceribella G., Chai Y., Cheng K., Chiavassa A., Chikawa M., Chytka L., Cifuentes A., Contreras J.L., Cortina J., Costantini H., Dalchenko M., Dazzi F., De Angelis A., de Bony de Lavergne M., De Lotto B., De Lucia M., de Menezes R., Del Peral L., Deleglise G., Delgado C., Delgado Mengual J., della Volpe D., Dellaiera M., Di Piano A., Di Pierro F., Di Pilato A., Di Tria R., Di Venere L., Díaz C., Dominik R.M., Dominis Prester D., Donini A., Dorner D., Doro M., Eisenberger L., Elsässer D., Fallah Ramazani V., Ferrara G., Ferrarotto F., Fiasson A., Foffano L., Freixas Coromina L., Fröse S., Fukami S., Fukazawa Y., Garcia E., Garcia López R., Gasbarra C., Gasparrini D., Geyer D.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The first prototype of LST (LST-1) for the Cherenkov Telescope Array has been in commissioning phase since 2018 and already started scientific observations with the low energy threshold around a few tens of GeV. In 2021, LST-1 observed BL Lac following the alerts based on multi-wavelength observations and detected prominent gamma-ray flares. In addition to the daily flux variability, LST-1 also detected sub-hour-scale intra-night variability reaching 3–4 times higher than the gamma-ray flux from the Crab Nebula above 100 GeV. In this proceeding, we will report the analysis results of LST-1 observations of BL Lac in 2021, especially focusing on flux variability.

Low energy performance boost through a hardware stereoscopic trigger between CTA LST-1 and MAGIC

Baxter J., Barrio J.A., Bitossi M., Donini A., Mazin D., Paoletti R., Pérez Aguilera A., Tejedor Álvarez L., Abe H., Abe K., Abe S., Abhir J., Acciari V.A., Aguasca-Cabot A., Agudo I., Alvarez Crespo N., Aniello T., Ansoldi S., Antonelli L.A., Aramo C., Arbet-Engels A., Cornelia A., Artero M., Asano K., Aubert P., Baack D., Babić A., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Batkovic I., Becerra González J., Bednarek W., Bernardini E., Bernardos M.I., Bernete Medrano J., Berti A., Besenrieder J., Bhattacharjee P., Biederbeck N., Bigongiari C., Biland A., Bissaldi E., Blanch O., Bonnoli G., Bordas P., Bošnjak , Bulgarelli A., Burelli I., Burmistrov L., Buscemi M., Busetto G., Campoy-Ordaz A., Cardillo M., Caroff S., Carosi A., Carosi R., Carrasco M.S., Carretero-Castrillo M., Cassol F., Castro-Tirado A.J., Cauz D., Cerasole D., Ceribella G., Chai Y., Cheng K., Chiavassa A., Chikawa M., Chilingarian A., Chytka L., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Costantini H., Covino S., D’Amico G., Dalchenko M., D’Elia V., Da Vela P., Dazzi F., De Angelis A., de Bony de Lavergne M., De Lotto B., De Lucia M., de Menezes R., Del Peral L., Deleglise G., Delfino M., Delgado C., Delgado Mengual J., della Volpe D., Dellaiera M., Del Popolo A., Depaoli D., Di Piano A.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The next generation facility for gamma-ray ground-based observations is the Cherenkov Telescope Array (CTA) observatory, which comprises three types of imaging atmospheric Cherenkov telescopes (IACTs). The Large-Sized Telescopes (LSTs) of CTA are the largest telescope type with a mirror dish of 23 m diameter. They cover the low energy end of the accessible gamma-ray energies for IACTs, starting from about 20 GeV up to a few TeV. The first LST prototype, known as LST-1, was officially inaugurated at the Observatorio del Roque de Los Muchachos in La Palma (Canary Islands, Spain) in 2018 and has since performed calibration observations of various known gamma-ray sources. Additionally, the site houses the MAGIC telescopes, two 17 m IACTs situated approximately 100 m away from LST-1, which have been performing stereo observations since 2009. Currently, joint observations between LST-1 and MAGIC are being carried on, and the data taken independently by the two IACT systems is analyzed by combining events via software. However, this method increases the energy threshold, as it discards all but the relatively high-energy events triggered by all three telescopes. To address this issue, we have developed a novel hardware stereo trigger system between LST-1 and MAGIC, which is capable of handling events triggered by any-two out of the three telescopes. In this contribution, we will report on the performance estimation of joint LST-1 and MAGIC observations using the hardware trigger.

Long-term study of the intermittent extreme behaviour of 1ES 2344+514

Arbet-Engels A., Mondal H.A., Fukami S., D’Ammando F., Dorner D., Chatterjee R., Majumdar P., Manganaro M., Hovatta T., Das S., Raiteri C.M., Villata M., Perri M., Verrechia F., Leto C., Filippenko A., Zheng W., Abe H., Abe S., Abhir J., Acciari V.A., Agudo I., Aniello T., Ansoldi S., Antonelli L.A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres de Almeida U., Barrio J.A., Batković I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M., Bernete J., Berti A., Besenrieder J., Bigongiari C., Biland A., Blanch O., Bonnoli G., Bošnjak , Burelli I., Busetto G., Campoy-Ordaz A., Carosi A., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chatterjee R., Chilingarian A., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D’Amico G., D’Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L., Dominis Prester D., Donini A., Doro M., Elsaesser D., Emery G., Escudero J., Fariña L., Fattorini A., Foffano L., Font L., Fröse S., Fukazawa Y., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., Giesbrecht Paiva J.G., Giglietto N., Giordano F., Gliwny P., Godinović N.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

Extreme high-frequency-peaked BL Lac objects (EHBLs) are the most energetic persistent sources in the Universe. They are characterized by a spectral energy distribution (SED) featuring a synchrotron peak energy above 1 keV. 1ES 2344+514 is a blazar known to behave as an EHBL intermittently. Until now, its EHBL nature was only reported during flares, but a coherent picture is missing as unbiased monitoring campaigns are lacking. This work presents the longest observing campaign from radio to very-high-energy (VHE) frequencies performed so far on 1ES2344+514. Using observations during 2019-2021, we carry out a systematic investigation of the intermittent EHBL phases. Together with MAGIC, the dataset also includes X-ray observations from NuSTAR, XMM-Newton, and AstroSAT, providing an unprecedented determination of the two SED components. For the first time we report a clear EHBL behaviour during a low flux activity in 1ES 2344+514. It implies a significant hardening of the electron distribution inside the jet independent of flux. We also detect a bright X-ray state characterized by an unusually soft spectra, thus violating the harder-when-brighter relation typically found in blazars. The SED study further reveals an excess in the ultraviolet data with respect to the extrapolation of the X-ray spectrum, suggesting at least two regions contributing to the synchrotron flux. Finally we investigate a gamma-ray flare not accompanied by an X-ray counterpart. This peculiar outburst is interpreted using a time-dependent model involving two emitting components.

Long term study of the blazar S5 0716+714: investigating a turbulent jet at all wavelengths

Podobnik F., Manganaro M., Jormanainen J., Lindfors E., Bonnoli G., Paoletti R., Jorstad S., Kiehlmann S., Agudo I., Elsasser D., Lorey C., Raiteri C., Villata M., Redhead A.C., Marscher A., Abe H., Abe S., Abhir J., Acciari V.A., Aniello T., Ansoldi S., Antonelli L.A., Arbet Engels A., Arcaro C., Artero M., Asano K., Baack D., Babić A., Baquero A., Barres de Almeida U., Barrio J.A., Batković I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M., Bernete J., Berti A., Besenrieder J., Bigongiari C., Biland A., Blanch O., Bošnjak , Burelli I., Busetto G., Campoy-Ordaz A., Carosi A., Carosi R., Carretero-Castrillo M., Castro-Tirado A.J., Ceribella G., Chai Y., Chilingarian A., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Covino S., D’Amico G., D’Elia V., Da Vela P., Dazzi F., De Angelis A., De Lotto B., Del Popolo A., Delfino M., Delgado J., Delgado Mendez C., Depaoli D., Di Pierro F., Di Venere L., Dominis Prester D., Donini A., Dorner D., Doro M., Elsaesser D., Emery G., Escudero J., Fariña L., Fattorini A., Foffano L., Font L., Fröse S., Fukami S., Fukazawa Y., García López R.J., Garczarczyk M., Gasparyan S., Gaug M., Giesbrecht Paiva J.G., Giglietto N., Giordano F., Gliwny P., Godinović N., Grau R., Green D., Green J.G., Hadasch D.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The blazar S5 0716+714 is an intermediate BL Lacertae object remarkable for its variability in many energy bands. It was discovered by MAGIC in the very-high-energy (VHE) gamma-ray range in 2008. Later in 2015 an impressive electric vector polarization angle (EVPA) swing was detected in connection with a multiwavelength flaring event including the VHE gamma-ray band. This generated interest in further studies of the jet of this source and its electromagnetic emission at all wavelengths. Since then, MAGIC has monitored the source in coordination with other observatories and here we present the long-term study using data from 2015 to 2022 in a MWL context. The data set also includes the extraordinary flaring activity of 2017, so far the historical maximum detected for this source in the optical and VHE gamma-ray band.

Joint searches by FACT, H.E.S.S., MAGIC and VERITAS for VHE gamma-ray emission associated with neutrinos detected by IceCube

Schüssler F., Ashkar H., Bernardini E., Berti A., Bradascio F., Buson S., Dorner D., Jin W., Kukec Mezek G., Santander M., Satalecka K., Schleicher B., Senniappanh M., Viale I., Abhir J., Baack D., Balbo M., Biland A., Brand K., Bretz T., Buss J., Eisenberger L., Elsaesser D., Günther P., Hildebrand D., Mannheim K., Noethe M., Paravac A., Rhode W., Sliusar V., Hasan S., Walter R., Aharonian F., Ait Benkhali F., Alkan A., Aschersleben J., Backes M., Baktash A., Barbosa Martins V., Barnacka A., Barnard J., Batzofin R., Becherini Y., Beck G., Berge D., Bernlöhr K., Bi B., Böttcher M., Boisson C., Bolmont J., de Bony de Lavergne M., Borowska J., Bouyahiaoui M., Breuhaus M., Brose R., Brown A., Brun F., Bruno B., Bulik T., Burger-Scheidlin C., Bylund T., Cangemi F., Caroff S., Casanova S., Cecil R., Celic J., Cerruti M., Chambery P., Chand T., Chandra S., Chen A., Chibueze J., Chibueze O., Collins T., Cotter G., Cristofari P., Damascene Mbarubucyeye J., Davids I.D., Davies J., de Jonge L., Devin J., Djannati-Ataï A., Dmytriiev A., Doroshenko V., Dreyer L., Du Plessis L., Egberts K., Einecke S., Ernenwein J.P., Fegan S., Feijen K., de Clairfontaine G.F., Fontaine G., Lott F., Füßling M., Funk S., Gabici S., Gallant Y.A., Ghafourizadeh S., Giavitto G.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

The sources of the astrophysical flux of high-energy neutrinos detected by IceCube are still largely unknown, but searches for temporal and spatial correlation between neutrinos and electromagnetic radiation are a promising approach in this endeavor. All major imaging atmospheric Cherenkov telescopes (IACTs) - FACT, H.E.S.S., MAGIC, and VERITAS - operate an active follow-up program of target-of-opportunity observations of neutrino alerts issued by IceCube. These programs use several complementary neutrino alert streams. A publicly distributed alert stream is formed by individual high-energy neutrino candidate events of potentially astrophysical origin, such as IceCube-170922A (which could be linked to the flaring blazar TXS 0506+056). A privately distributed alert stream is formed by clusters of neutrino events in time and space around either pre-selected gamma-ray sources or anywhere in the sky. Here, we present joint searches for multi-wavelength emission associated with a set of IceCube alerts, both private and public, received through mid-January 2021. We will give an overview of the programs of the participating IACTs. We will showcase the various follow-up and data analysis strategies employed in response to the different alert types and various possible counterpart scenarios. Finally, we will present results from a combined analysis of the VHE gamma-ray observations obtained across all involved instruments, as well as relevant multi-wavelength data.

Joint Observation of the Galactic Center with MAGIC and CTA-LST-1

Abe S., Berti A., Di Pierro F., López-Coto R., Moralejo A., Ohtani Y., Sitarek J., Strzys M., Suda Y., Vovk I., Abe H., Abe K., Abe S., Abhir J., Acciari V.A., Aguasca-Cabot A., Agudo I., Alvarez Crespo N., Aniello T., Ansoldi S., Antonelli L.A., Aramo C., Arbet-Engels A., Cornelia A., Artero M., Asano K., Aubert P., Baack D., Babić A., Baktash A., Bamba A., Baquero Larriva A., Baroncelli L., Barres de Almeida U., Barrio J.A., Batkovic I., Baxter J., Becerra González J., Bednarek W., Bernardini E., Bernardos M.I., Bernete Medrano J., Besenrieder J., Bhattacharjee P., Biederbeck N., Bigongiari C., Biland A., Bissaldi E., Blanch O., Bonnoli G., Bordas P., Bošnjak , Bulgarelli A., Burelli I., Burmistrov L., Buscemi M., Busetto G., Campoy-Ordaz A., Cardillo M., Caroff S., Carosi A., Carosi R., Carrasco M.S., Carretero-Castrillo M., Cassol F., Castro-Tirado A.J., Cauz D., Cerasole D., Ceribella G., Chai Y., Cheng K., Chiavassa A., Chikawa M., Chilingarian A., Chytka L., Cifuentes A., Cikota S., Colombo E., Contreras J.L., Cortina J., Costantini H., Covino S., D’Amico G., Dalchenko M., D’Elia V., Da Vela P., Dazzi F., De Angelis A., de Bony de Lavergne M., De Lotto B., De Lucia M., de Menezes R., Del Peral L., Deleglise G., Delfino M., Delgado C., Delgado Mengual J., della Volpe D., Dellaiera M.

Proceedings of Science Vol. 444 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of Science

MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs), designed to detect very-high-energy gamma rays, and is operating in stereoscopic mode since 2009 at the Observatorio del Roque de Los Muchachos in La Palma, Spain. In 2018, the prototype IACT of the Large-Sized Telescope (LST-1) for the Cherenkov Telescope Array, a next-generation ground-based gamma-ray observatory, was inaugurated at the same site, at a distance of approximately 100 meters from the MAGIC telescopes. Using joint observations between MAGIC and LST-1, we developed a dedicated analysis pipeline and established the threefold telescope system via software, achieving the highest sensitivity in the northern hemisphere. Based on this enhanced performance, MAGIC and LST-1 have been jointly and regularly observing the Galactic Center, a region of paramount importance and complexity for IACTs. In particular, the gamma-ray emission from the dynamical center of the Milky Way is under debate. Although previous measurements suggested that a supermassive black hole Sagittarius A* plays a primary role, its radiation mechanism remains unclear, mainly due to limited angular resolution and sensitivity. The enhanced sensitivity in our novel approach is thus expected to provide new insights into the question. We here present the current status of the data analysis for the Galactic Center joint MAGIC and LST-1 observations.

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