Periastron Observations of TeV Gamma-Ray Emission from a Binary System with a 50-year Period

We report on observations of the pulsar / Be star binary system PSR J2032+4127 / MT91 213 in the energy range between 100 GeV and 20 TeV with the VERITAS and MAGIC imaging atmospheric Cherenkov telescope arrays. The binary orbit has a period of approximately 50 years, with the most recent periastron occurring on 2017 November 13. Our observations span from 18 months prior to periastron to one month after. A new, point-like, gamma-ray source is detected, coincident with the location of PSR J2032+4127 / MT91 213. The gamma-ray light curve and spectrum are well-characterized over the periastron passage. The flux is variable over at least an order of magnitude, peaking at periastron, thus providing a firm association of the TeV source with the pulsar / Be star system. Observations prior to periastron show a cutoff in the spectrum at an energy around 0.5 TeV. This result adds a new member to the small population of known TeV binaries, and it identifies only the second source of this class in which the nature and properties of the compact object are firmly established. We compare the gamma-ray results with the light curve measured with the X-ray Telescope (XRT) on board the Neil Gehrels Swift Observatory and with the predictions of recent theoretical models of the system. We conclude that significant revision of the models is required to explain the details of the emission we have observed, and we discuss the relationship between the binary system and the overlapping steady extended source, TeV J2032+4130

Detection of persistent VHE gamma-ray emission from PKS 1510-089 by the MAGIC telescopes during low states between 2012 and 2017

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 (9.5¿) VHE gamma-ray emission at the level of (4.27 ± 0.61 stat ) × 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. © ESO 2018.The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO (FPA2015-69818-P, FPA2012-36668, FPA2015-68378-P, FPA2015-69210-C6-2-R, FPA2015-69210-C6-4-R, FPA2015-69210-C6-6-R, AYA2015-71042-P, AYA2016-76012-C3-1-P, ESP2015-71662-C2-2-P, CSD2009-00064), and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also supported by the Spanish Centro de Exce-lencia “Severo Ochoa” SEV-2012-0234 and SEV-2015-0548, and Unidad de Excelencia “María de Maeztu” MDM-2014-0369, by the Croatian Science Foundation (HrZZ) Project IP-2016-06-9782 and the University of Rijeka Project 13.12.1.3.02, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, the Polish National Research Centre grant UMO-2016/22/M/ST9/00382, and by the Brazilian MCTIC, CNPq and FAPERJ. IA acknowledges support from a Ramón y Cajal grant of the Ministerio de Economía, Industria, y Competitividad (MINECO) of Spain. Acquisition and reduction of the POLAMI and MAPCAT data was supported in part by MINECO through grants AYA2010-14844, AYA2013-40825-P, and AYA2016-80889-P, and by the Regional Government of Andalucía through grant P09-FQM-4784.Peer Reviewe

Deep observations of the globular cluster M15 with the MAGIC telescopes

A population of globular clusters (GCs) has been recently established by the Fermi-LAT telescope as a new class of GeV γ-ray sources. Leptons accelerated to TeV energies, in the inner magnetospheres of MSPs or in their wind regions, should produce γ-rays through the inverse Compton scattering in the dense radiation field from the huge population of stars. We have conducted deep observations of the GC M15 with the MAGIC telescopes and used 165 h in order to search for γ-ray emission. A strong upper limit on the TeV γ-ray flux < 3.2× 10^{-13} cm^{-2 s^{-1}} above 300 GeV (< 0.26{{ per cent}} of the Crab nebula flux) has been obtained. We interpret this limit as a constraint on the efficiency of the acceleration of leptons in the magnetospheres of the MSPs. We constrain the injection rate of relativistic leptons, ηe, from the MSPs magnetospheres and their surrounding. We conclude that ηe must be lower than expected from the modelling of high-energy processes in MSP inner magnetospheres. For leptons accelerated with the power-law spectrum in the MSP wind regions, ηe is constrained to be much lower than derived for the wind regions around classical pulsars. These constraints are valid for the expected range of magnetic field strengths within the GC and for the range of likely energies of leptons injected from the inner magnetospheres, provided that the leptons are not removed from the GC very efficiently due to advection process. We discuss consequences of these constraints for the models of radiation processes around millisecond pulsars. </p

A fast, very-high-energy gamma-ray flare from BL Lacertae during a period of multi-wavelength activity in June 2015

The mechanisms producing fast variability of the gamma-ray emission in active galactic nuclei (AGNs) are under debate. The MAGIC telescopes detected a fast, very-high-energy (VHE, E > 100 GeV) gamma-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) gamma-ray bands. In this paper we present the MAGIC VHE gamma-ray data together with multi-wavelength data from radio, optical, X-rays, and HE gamma 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 gamma-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays, and HE gamma-rays is very similar to two other observed VHE gamma-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 gamma-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE gamma-ray flare, but all have some tension with the multi-wavelength observations

The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies

We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsahovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25-55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ ⪆ 33) and the size of the emission region (δ-1RB≲ 3.8 × 1013cm) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux-flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.</p

Constraining dark matter lifetime with a deep gamma-ray survey of the Perseus galaxy cluster with MAGIC

Clusters of galaxies are the largest known gravitationally bound structures in the Universe, with masses around 1015 M⊙, most of it in the form of dark matter. The ground-based Imaging Atmospheric Cherenkov Telescope MAGIC made a deep survey of the Perseus cluster of galaxies using almost 400 h of data recorded between 2009 and 2017. This is the deepest observational campaign so far on a cluster of galaxies in the very high energy range. We search for gamma-ray signals from dark matter particles in the mass range between 200 GeV and 200 TeV decaying into standard model pairs. We apply an analysis optimized for the spectral and morphological features expected from dark matter decays and find no evidence of decaying dark matter. From this, we conclude that dark matter particles have a decay lifetime longer than ∼1026 s in all considered channels. Our results improve previous lower limits found by MAGIC and represent the strongest limits on decaying dark matter particles from ground-based gamma-ray instruments

A fast, very-high-energy γ -ray flare from BL Lacertae during a period of multi-wavelength activity in June 2015

166siThe 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. MAGIC and multiwavelength data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A175reservedmixedAcciari V.A.; Ansoldi S.; Antonelli L.A.; Arbet Engels A.; Baack D.; Babic A.; Banerjee B.; Bangale P.; Barres De Almeida U.; Barrio J.A.; Becerra Gonzalez J.; Bednarek W.; Bernardini E.; Berti A.; Besenrieder J.; Bhattacharyya W.; Bigongiari C.; Biland A.; Blanch O.; Bonnoli G.; Carosi R.; Ceribella G.; Cikota S.; Colak S.M.; Colin P.; Colombo E.; Contreras J.L.; Cortina J.; Covino S.; D'elia V.; Da Vela P.; Dazzi F.; De Angelis A.; De Lotto B.; Delfino M.; Delgado J.; Di Pierro F.; Do Souto Espinera E.; Dominguez A.; Dominis Prester D.; Dorner D.; Doro M.; Einecke S.; Elsaesser D.; Fallah Ramazani V.; Fattorini A.; Fernandez-Barral A.; Ferrara G.; Fidalgo D.; Foffano L.; Fonseca M.V.; Font L.; Fruck C.; Galindo D.; Gallozzi S.; Garcia Lopez R.J.; Garczarczyk M.; Gaug M.; Giammaria P.; Godinovic N.; Guberman D.; Hadasch D.; Hahn A.; Hassan T.; Herrera J.; Hoang J.; Hrupec D.; Inoue S.; Ishio K.; Iwamura Y.; Kubo H.; Kushida J.; Kuvezdic D.; Lamastra A.; Lelas D.; Leone F.; Lindfors E.; Lombardi S.; Longo F.; Lopez M.; Lopez-Oramas A.; Maggio C.; Majumdar P.; Makariev M.; Maneva G.; Manganaro M.; Mannheim K.; Maraschi L.; Mariotti M.; Martinez M.; Masuda S.; Mazin D.; Minev M.; Miranda J.M.; Mirzoyan R.; Molina E.; Moralejo A.; Moreno V.; Moretti E.; Munar-Adrover P.; Neustroev V.; Niedzwiecki A.; Nievas Rosillo M.; Nigro C.; Nilsson K.; Ninci D.; Nishijima K.; Noda K.; Nogues L.; Nothe M.; Paiano S.; Palacio J.; Paneque D.; Paoletti R.; Paredes J.M.; Pedaletti G.; Penil P.; Peresano M.; Persic M.; Prada Moroni P.G.; Prandini E.; Puljak I.; Garcia J.R.; Rhode W.; Ribo M.; Rico J.; Righi C.; Rugliancich A.; Saha L.; Saito T.; Satalecka K.; Schweizer T.; Sitarek J.; Snidaric I.; Sobczynska D.; Somero A.; Stamerra A.; Strzys M.; Suric T.; Tavecchio F.; Temnikov P.; Terzic T.; Teshima M.; Torres-Alba N.; Tsujimoto S.; Van Scherpenberg J.; Vanzo G.; Vazquez Acosta M.; Vovk I.; Will M.; Zaric D.; D'ammando F.; Hada K.; Jorstad S.; Marscher A.P.; Mobeen M.Z.; Hovatta T.; Larionov V.M.; Borman G.A.; Grishina T.S.; Kopatskaya E.N.; Morozova D.A.; Nikiforova A.A.; Lahteenmaki A.; Tornikoski M.; Agudo I.Acciari, V. A.; Ansoldi, S.; Antonelli, L. A.; Arbet Engels, A.; Baack, D.; Babic, A.; Banerjee, B.; Bangale, P.; Barres De Almeida, U.; Barrio, J. A.; Becerra Gonzalez, J.; Bednarek, W.; Bernardini, E.; Berti, A.; Besenrieder, J.; Bhattacharyya, W.; Bigongiari, C.; Biland, A.; Blanch, O.; Bonnoli, G.; Carosi, R.; Ceribella, G.; Cikota, S.; Colak, S. M.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; D'Elia, V.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Delfino, M.; Delgado, J.; Di Pierro, F.; Do Souto Espinera, E.; Dominguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Elsaesser, D.; Fallah Ramazani, V.; Fattorini, A.; Fernandez-Barral, A.; Ferrara, G.; Fidalgo, D.; Foffano, L.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; Gallozzi, S.; Garcia Lopez, R. J.; Garczarczyk, M.; Gaug, M.; Giammaria, P.; Godinovic, N.; Guberman, D.; Hadasch, D.; Hahn, A.; Hassan, T.; Herrera, J.; Hoang, J.; Hrupec, D.; Inoue, S.; Ishio, K.; Iwamura, Y.; Kubo, H.; Kushida, J.; Kuvezdic, D.; Lamastra, A.; Lelas, D.; Leone, F.; Lindfors, E.; Lombardi, S.; Longo, F.; Lopez, M.; Lopez-Oramas, A.; Maggio, C.; Majumdar, P.; Makariev, M.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Mariotti, M.; Martinez, M.; Masuda, S.; Mazin, D.; Minev, M.; Miranda, J. M.; Mirzoyan, R.; Molina, E.; Moralejo, A.; Moreno, V.; Moretti, E.; Munar-Adrover, P.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nigro, C.; Nilsson, K.; Ninci, D.; Nishijima, K.; Noda, K.; Nogues, L.; Nothe, M.; Paiano, S.; Palacio, J.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Pedaletti, G.; Penil, P.; Peresano, M.; Persic, M.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Garcia, J. R.; Rhode, W.; Ribo, M.; Rico, J.; Righi, C.; Rugliancich, A.; Saha, L.; Saito, T.; Satalecka, K.; Schweizer, T.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Somero, A.; Stamerra, A.; Strzys, M.; Suric, T.; Tavecchio, F.; Temnikov, P.; Terzic, T.; Teshima, M.; Torres-Alba, N.; Tsujimoto, S.; Van Scherpenberg, J.; Vanzo, G.; Vazquez Acosta, M.; Vovk, I.; Will, M.; Zaric, D.; D'Ammando, F.; Hada, K.; Jorstad, S.; Marscher, A. P.; Mobeen, M. Z.; Hovatta, T.; Larionov, V. M.; Borman, G. A.; Grishina, T. S.; Kopatskaya, E. N.; Morozova, D. A.; Nikiforova, A. A.; Lahteenmaki, A.; Tornikoski, M.; Agudo, I

A fast, very-high-energy γ-ray flare from BL Lacertae during a period of multi-wavelength activity in June 2015

Abstract 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 &gt; 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 &gt; 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

Study of the variable broadband emission of Markarian 501 during the most extreme Swift X-ray activity

Context. Markarian 501 (Mrk 501) is a very high-energy (VHE) gamma-ray blazar located at z = 0:034, which is regularly monitored by a wide range of multi-wavelength instruments, from radio to VHE gamma rays. During a period of almost two weeks in July 2014, the highest X-ray activity of Mrk 501 was observed in -14 years of operation of the Neil Gehrels Swift Gamma-ray Burst Observatory. Aims.We characterize the broadband variability of Mrk 501 from radio to VHE gamma rays during the most extreme X-ray activity measured in the last 14 years, and evaluate whether it can be interpreted within theoretical scenarios widely used to explain the broadband emission from blazars. Methods. The emission of Mrk 501 was measured at radio with Mets-hovi, at optical-UV with KVA and Swift/UVOT, at X-ray with Swift/XRT and Swift/BAT, at gamma ray with Fermi-LAT, and at VHE gamma rays with the FACT and MAGIC telescopes. The multi-band variability and correlations were quantified, and the broadband spectral energy distributions (SEDs) were compared with predictions from theoretical models. Results. The VHE emission of Mrk 501 was found to be elevated during the X-ray outburst, with a gamma-ray flux above 0.15 TeV varying from -0.5 to -2 times the Crab nebula flux. The X-ray and VHE emission both varied on timescales of 1 day and were found to be correlated. We measured a general increase in the fractional variability with energy, with the VHE variability being twice as large as the X-ray variability. The temporal evolution of the most prominent and variable segments of the SED, characterized on a day-by-day basis from 2014 July 16 to 2014 July 31, is described with a one-zone synchrotron self-Compton model with variations in the break energy of the electron energy distribution (EED), and with some adjustments in the magnetic field strength and spectral shape of the EED. These results suggest that the main flux variations during this extreme X-ray outburst are produced by the acceleration and the cooling of the high-energy electrons. A narrow feature at -3 TeV was observed in the VHE spectrum measured on 2014 July 19 (MJD 56857.98), which is the day with the highest X-ray flux (>0:3 keV) measured during the entire Swift mission. This feature is inconsistent with the classical analytic functions to describe the measured VHE spectra (power law, log-parabola, and log-parabola with exponential cutoff) at more than 3\u3c3. A fit with a log-parabola plus a narrow component is preferred over the fit with a single log-parabola at more than 4\u3c3, and a dedicated Monte Carlo simulation estimated the significance of this extra component to be larger than 3\u3c3. Under the assumption that this VHE spectral feature is real, we show that it can be reproduced with three distinct theoretical scenarios: (a) a pileup in the EED due to stochastic acceleration; (b) a structured jet with two-SSC emitting regions, with one region dominated by an extremely narrow EED; and (c) an emission from an IC pair cascade induced by electrons accelerated in a magnetospheric vacuum gap, in addition to the SSC emission from a more conventional region along the jet of Mrk 501