ALBERT

Description: The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉VERITAS Collaboration -- VLBA 43 GHz M87 Monitoring Team -- H.E.S.S. Collaboration -- MAGIC Collaboration -- Acciari, V A -- Aliu, E -- Arlen, T -- Bautista, M -- Beilicke, M -- Benbow, W -- Bradbury, S M -- Buckley, J H -- Bugaev, V -- Butt, Y -- Byrum, K -- Cannon, A -- Celik, O -- Cesarini, A -- Chow, Y C -- Ciupik, L -- Cogan, P -- Cui, W -- Dickherber, R -- Fegan, S J -- Finley, J P -- Fortin, P -- Fortson, L -- Furniss, A -- Gall, D -- Gillanders, G H -- Grube, J -- Guenette, R -- Gyuk, G -- Hanna, D -- Holder, J -- Horan, D -- Hui, C M -- Humensky, T B -- Imran, A -- Kaaret, P -- Karlsson, N -- Kieda, D -- Kildea, J -- Konopelko, A -- Krawczynski, H -- Krennrich, F -- Lang, M J -- LeBohec, S -- Maier, G -- McCann, A -- McCutcheon, M -- Millis, J -- Moriarty, P -- Ong, R A -- Otte, A N -- Pandel, D -- Perkins, J S -- Petry, D -- Pohl, M -- Quinn, J -- Ragan, K -- Reyes, L C -- Reynolds, P T -- Roache, E -- Rose, H J -- Schroedter, M -- Sembroski, G H -- Smith, A W -- Swordy, S P -- Theiling, M -- Toner, J A -- Varlotta, A -- Vincent, S -- Wakely, S P -- Ward, J E -- Weekes, T C -- Weinstein, A -- Williams, D A -- Wissel, S -- Wood, M -- Walker, R C -- Davies, F -- Hardee, P E -- Junor, W -- Ly, C -- Aharonian, F -- Akhperjanian, A G -- Anton, G -- Barres de Almeida, U -- Bazer-Bachi, A R -- Becherini, Y -- Behera, B -- Bernlohr, K -- Bochow, A -- Boisson, C -- Bolmont, J -- Borrel, V -- Brucker, J -- Brun, F -- Brun, P -- Buhler, R -- Bulik, T -- Busching, I -- Boutelier, T -- Chadwick, P M -- Charbonnier, A -- Chaves, R C G -- Cheesebrough, A -- Chounet, L-M -- Clapson, A C -- Coignet, G -- Dalton, M -- Daniel, M K -- Davids, I D -- Degrange, B -- Deil, C -- Dickinson, H J -- Djannati-Atai, A -- Domainko, W -- Drury, L O'C -- Dubois, F -- Dubus, G -- Dyks, J -- Dyrda, M -- Egberts, K -- Emmanoulopoulos, D -- Espigat, P -- Farnier, C -- Feinstein, F -- Fiasson, A -- Forster, A -- Fontaine, G -- Fussling, M -- Gabici, S -- Gallant, Y A -- Gerard, L -- Gerbig, D -- Giebels, B -- Glicenstein, J F -- Gluck, B -- Goret, P -- Gohring, D -- Hauser, D -- Hauser, M -- Heinz, S -- Heinzelmann, G -- Henri, G -- Hermann, G -- Hinton, J A -- Hoffmann, A -- Hofmann, W -- Holleran, M -- Hoppe, S -- Horns, D -- Jacholkowska, A -- de Jager, O C -- Jahn, C -- Jung, I -- Katarzynski, K -- Katz, U -- Kaufmann, S -- Kendziorra, E -- Kerschhaggl, M -- Khangulyan, D -- Khelifi, B -- Keogh, D -- Kluzniak, W -- Kneiske, T -- Komin, Nu -- Kosack, K -- Lamanna, G -- Lenain, J-P -- Lohse, T -- Marandon, V -- Martin, J M -- Martineau-Huynh, O -- Marcowith, A -- Maurin, D -- McComb, T J L -- Medina, M C -- Moderski, R -- Moulin, E -- Naumann-Godo, M -- de Naurois, M -- Nedbal, D -- Nekrassov, D -- Nicholas, B -- Niemiec, J -- Nolan, S J -- Ohm, S -- Olive, J-F -- de Ona Wilhelmi, E -- Orford, K J -- Ostrowski, M -- Panter, M -- Paz Arribas, M -- Pedaletti, G -- Pelletier, G -- Petrucci, P-O -- Pita, S -- Puhlhofer, G -- Punch, M -- Quirrenbach, A -- Raubenheimer, B C -- Raue, M -- Rayner, S M -- Renaud, M -- Rieger, F -- Ripken, J -- Rob, L -- Rosier-Lees, S -- Rowell, G -- Rudak, B -- Rulten, C B -- Ruppel, J -- Sahakian, V -- Santangelo, A -- Schlickeiser, R -- Schock, F M -- Schroder, R -- Schwanke, U -- Schwarzburg, S -- Schwemmer, S -- Shalchi, A -- Sikora, M -- Skilton, J L -- Sol, H -- Spangler, D -- Stawarz, L -- Steenkamp, R -- Stegmann, C -- Stinzing, F -- Superina, G -- Szostek, A -- Tam, P H -- Tavernet, J-P -- Terrier, R -- Tibolla, O -- Tluczykont, M -- van Eldik, C -- Vasileiadis, G -- Venter, C -- Venter, L -- Vialle, J P -- Vincent, P -- Vivier, M -- Volk, H J -- Volpe, F -- Wagner, S J -- Ward, M -- Zdziarski, A A -- Zech, A -- Anderhub, H -- Antonelli, L A -- Antoranz, P -- Backes, M -- Baixeras, C -- Balestra, S -- Barrio, J A -- Bastieri, D -- Becerra Gonzalez, J -- Becker, J K -- Bednarek, W -- Berger, K -- Bernardini, E -- Biland, A -- Bock, R K -- Bonnoli, G -- Bordas, P -- Borla Tridon, D -- Bosch-Ramon, V -- Bose, D -- Braun, I -- Bretz, T -- Britvitch, I -- Camara, M -- Carmona, E -- Commichau, S -- Contreras, J L -- Cortina, J -- Costado, M T -- Covino, S -- Curtef, V -- Dazzi, F -- De Angelis, A -- De Cea del Pozo, E -- Delgado Mendez, C -- De los Reyes, R -- De Lotto, B -- De Maria, M -- De Sabata, F -- Dominguez, A -- Dorner, D -- Doro, M -- Elsaesser, D -- Errando, M -- Ferenc, D -- Fernandez, E -- Firpo, R -- Fonseca, M V -- Font, L -- Galante, N -- Garcia Lopez, R J -- Garczarczyk, M -- Gaug, M -- Goebel, F -- Hadasch, D -- Hayashida, M -- Herrero, A -- Hildebrand, D -- Hohne-Monch, D -- Hose, J -- Hsu, C C -- Jogler, T -- Kranich, D -- La Barbera, A -- Laille, A -- Leonardo, E -- Lindfors, E -- Lombardi, S -- Longo, F -- Lopez, M -- Lorenz, E -- Majumdar, P -- Maneva, G -- Mankuzhiyil, N -- Mannheim, K -- Maraschi, L -- Mariotti, M -- Martinez, M -- Mazin, D -- Meucci, M -- Miranda, J M -- Mirzoyan, R -- Miyamoto, H -- Moldon, J -- Moles, M -- Moralejo, A -- Nieto, D -- Nilsson, K -- Ninkovic, J -- Oya, I -- Paoletti, R -- Paredes, J M -- Pasanen, M -- Pascoli, D -- Pauss, F -- Pegna, R G -- Perez-Torres, M A -- Persic, M -- Peruzzo, L -- Prada, F -- Prandini, E -- Puchades, N -- Reichardt, I -- Rhode, W -- Ribo, M -- Rico, J -- Rissi, M -- Robert, A -- Rugamer, S -- Saggion, A -- Saito, T Y -- Salvati, M -- Sanchez-Conde, M -- Satalecka, K -- Scalzotto, V -- Scapin, V -- Schweizer, T -- Shayduk, M -- Shore, S N -- Sidro, N -- Sierpowska-Bartosik, A -- Sillanpaa, A -- Sitarek, J -- Sobczynska, D -- Spanier, F -- Stamerra, A -- Stark, L S -- Takalo, L -- Tavecchio, F -- Temnikov, P -- Tescaro, D -- Teshima, M -- Torres, D F -- Turini, N -- Vankov, H -- Wagner, R M -- Zabalza, V -- Zandanel, F -- Zanin, R -- Zapatero, J -- New York, N.Y. -- Science. 2009 Jul 24;325(5939):444-8. doi: 10.1126/science.1175406. Epub 2009 Jul 2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19574351" target="_blank"〉PubMed〈/a〉

Description: Aims. We measure the Crab Nebula γ-ray spectral energy distribution in the ~100 TeV energy domain and test the validity of existing leptonic emission models at these high energies. Methods. We used the novel very large zenith angle observations with the MAGIC telescope system to increase the collection area above 10 TeV. We also developed an auxiliary procedure of monitoring atmospheric transmission in order to assure proper calibration of the accumulated data. This employs recording optical images of the stellar field next to the source position, which provides a better than 10% accuracy for the transmission measurements. Results. We demonstrate that MAGIC very large zenith angle observations yield a collection area larger than a square kilometer. In only ~ 56 h of observations, we detect the γ-ray emission from the Crab Nebula up to 100 TeV, thus providing the highest energy measurement of this source to date with Imaging Atmospheric Cherenkov Telescopes. Comparing accumulated and archival MAGIC and Fermi/LAT data with some of the existing emission models, we find that none of them provides an accurate description of the 1 GeV to 100 TeV γ-ray signal.

Description: 1ES 1959+650 is a bright TeV high-frequency-peaked BL Lac object exhibiting interesting features like “orphan” TeV flares and broad emission in the high-energy regime that are difficult to interpret using conventional one-zone Synchrotron Self-Compton (SSC) scenarios. We report the results from the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observations in 2016 along with the multi-wavelength data from the Fermi Large Area Telescope (LAT) and Swift instruments. MAGIC observed 1ES 1959+650 with different emission levels in the very-high-energy (VHE, E 〉  100 GeV) γ-ray band during 2016. In the long-term data, the X-ray spectrum becomes harder with increasing flux and a hint of a similar trend is also visible in the VHE band. An exceptionally high VHE flux reaching ∼3 times the Crab Nebula flux was measured by MAGIC on the 13 and 14 of June, and 1 July 2016 (the highest flux observed since 2002). During these flares, the high-energy peak of the spectral energy distribution (SED) lies in the VHE domain and extends up to several TeV. The spectrum in the γ-ray (both Fermi-LAT and VHE bands) and the X-ray bands are quite hard. On 13 June and 1 July 2016, the source showed rapid variations in the VHE flux within timescales of less than an hour. A simple one-zone SSC model can describe the data during the flares requiring moderate to large values of the Doppler factors (δ ≥ 30−60). Alternatively, the high-energy peak of the SED can be explained by a purely hadronic model attributed to proton-synchrotron radiation with jet power Ljet ∼ 1046 erg s−1 and under high values of the magnetic field strength (∼100 G) and maximum proton energy (∼few EeV). Mixed lepto-hadronic models require super-Eddington values of the jet power. We conclude that it is difficult to get detectable neutrino emission from the source during the extreme VHE flaring period of 2016.

Description: The mechanisms producing fast variability of the γ-ray emission in active galactic nuclei (AGNs) are under debate. The MAGIC telescopes detected a fast, very-high-energy (VHE, E  〉  100 GeV) γ-ray flare from BL Lacertae on 2015 June 15. The flare had a maximum flux of (1.5 ± 0.3) × 10−10 photons cm−2 s−1 and halving time of 26 ± 8 min. The MAGIC observations were triggered by a high state in the optical and high-energy (HE, E  〉  100 MeV) γ-ray bands. In this paper we present the MAGIC VHE γ-ray data together with multi-wavelength data from radio, optical, X-rays, and HE γ rays from 2015 May 1 to July 31. Well-sampled multi-wavelength data allow us to study the variability in detail and compare it to the other epochs when fast, VHE γ-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays, and HE γ-rays is very similar to two other observed VHE γ-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43 GHz core. These repeating patterns indicate a connection between the three events. We also test modelling of the spectral energy distribution based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the γ-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE γ-ray flare, but all have some tension with the multi-wavelength observations.

Description: Context. PKS 1510–089 is a flat spectrum radio quasar strongly variable in the optical and GeV range. To date, very high-energy (VHE, 〉 100 GeV) emission has been observed from this source either during long high states of optical and GeV activity or during short flares. Aims. We search for low-state VHE gamma-ray emission from PKS 1510–089. We characterize and model the source in a broadband context, which would provide a baseline over which high states and flares could be better understood. Methods. PKS 1510–089 has been monitored by the MAGIC telescopes since 2012. We use daily binned Fermi-LAT flux measurements of PKS 1510–089 to characterize the GeV emission and select the observation periods of MAGIC during low state of activity. For the selected times we compute the average radio, IR, optical, UV, X-ray, and gamma-ray emission to construct a low-state spectral energy distribution of the source. The broadband emission is modeled within an external Compton scenario with a stationary emission region through which plasma and magnetic fields are flowing. We also perform the emission-model-independent calculations of the maximum absorption in the broad line region (BLR) using two different models. Results. The MAGIC telescopes collected 75 hr of data during times when the Fermi-LAT flux measured above 1 GeV was below 3  ×  10−8 cm−2 s−1, which is the threshold adopted for the definition of a low gamma-ray activity state. The data show a strongly significant (9.5σ) VHE gamma-ray emission at the level of (4.27 ± 0.61stat)  ×  10−12 cm−2 s−1 above 150 GeV, a factor of 80 lower than the highest flare observed so far from this object. Despite the lower flux, the spectral shape is consistent with earlier detections in the VHE band. The broadband emission is compatible with the external Compton scenario assuming a large emission region located beyond the BLR. For the first time the gamma-ray data allow us to place a limit on the location of the emission region during a low gamma-ray state of a FSRQ. For the used model of the BLR, the 95% confidence level on the location of the emission region allows us to place it at a distance 〉 74% of the outer radius of the BLR.

Description: Aims. In the presence of a sufficient amount of target material, γ-rays can be used as a tracer in the search for sources of Galactic cosmic rays (CRs). Here we present deep observations of the Galactic center (GC) region with the MAGIC telescopes and use them to infer the underlying CR distribution and to study the alleged PeV proton accelerator at the center of our Galaxy. Methods. We used data from ≈100 h observations of the GC region conducted with the MAGIC telescopes over five years (from 2012 to 2017). Those were collected at high zenith angles (58−70 deg), leading to a larger energy threshold, but also an increased effective collection area compared to low zenith observations. Using recently developed software tools, we derived the instrument response and background models required for extracting the diffuse emission in the region. We used existing measurements of the gas distribution in the GC region to derive the underlying distribution of CRs. We present a discussion of the associated biases and limitations of such an approach. Results. We obtain a significant detection for all four model components used to fit our data (Sgr A*, “Arc”, G0.9+0.1, and an extended component for the Galactic Ridge). We observe no significant difference between the γ-ray spectra of the immediate GC surroundings, which we model as a point source (Sgr A*) and the Galactic Ridge. The latter can be described as a power-law with index 2 and an exponential cut-off at around 20 TeV with the significance of the cut-off being only 2σ. The derived cosmic-ray profile hints to a peak at the GC position and with a measured profile index of 1.2 ± 0.3 is consistent with the 1/r radial distance scaling law, which supports the hypothesis of a CR accelerator at the GC. We argue that the measurements of this profile are presently limited by our knowledge of the gas distribution in the GC vicinity.

Description: We investigate the physical nature and origin of the gamma-ray emission from the extended source HESS J1841−055 observed at TeV and GeV energies. We observed HESS J1841−055 at TeV energies for a total effective time of 43 h with the MAGIC telescopes, in 2012 and 2013. Additionally, we analysed the GeV counterpart making use of about 10 yr of Fermi-LAT data. Using both Fermi-LAT and MAGIC, we study both the spectral and energy-dependent morphology of the source for almost four decades of energy. The origin of the gamma-ray emission from this region is investigated using multiwaveband information on sources present in this region, suggested to be associated with this unidentified gamma-ray source. We find that the extended emission at GeV–TeV energies is best described by more than one source model. We also perform the first energy-dependent analysis of the HESS J1841−055 region at GeV–TeV. We find that the emission at lower energies comes from a diffuse or extended component, while the major contribution of gamma rays above 1 TeV arises from the southern part of the source. Moreover, we find that a significant curvature is present in the combined observed spectrum of MAGIC and Fermi-LAT. The first multiwavelength spectral energy distribution of this unidentified source shows that the emission at GeV–TeV energies can be well explained with both leptonic and hadronic models. For the leptonic scenario, bremsstrahlung is the dominant emission compared to inverse Compton. On the other hand, for the hadronic model, gamma-ray resulting from the decay of neutral pions (π0) can explain the observed spectrum. The presence of dense molecular clouds overlapping with HESS J1841−055 makes both bremsstrahlung and π0-decay processes the dominant emission mechanisms for the source.