Search for extended γ-ray emission around AGN with MAGIC telescopes

TeV photons coming from a distant extragalactic source are not able to propagate over large distances because they interact with the extragalactic background light photons producing pairs e+e−. These pairs, in turn, interact with the cosmic microwave background via inverse-compton producing a secondary γ-ray emission at lower energies. Extragalactic magnetic fields alter the trajectories of the electron pairs hence the secondary emission can be extended around the TeV sources. This process can be used to constrain the magnetic fields in the inter-galactic medium. We present the study of the emission profile of the blazar Markarian 421 yielding upper limit on the halo flux of the order of 1.5% Crab units in the energy range 300–1300 GeV

The UHECR-FR0 Radio Galaxy Connection: A Multi-Messenger Study of Energy Spectra/Composition Emission and Intergalactic Magnetic Field Propagation

This study investigates low luminosity Fanaroff-Riley Type 0 (FR0) radio galaxies as a potentially significant source of ultra-high energy cosmic rays (UHECRs). Due to their much higher prevalence in the local universe compared to more powerful radio galaxies (about five times more than FR-1s), FR0s may provide a substantial fraction of the total UHECR energy density. To determine the nucleon composition and energy spectrum of UHECRs emitted by FR0 sources, simulation results from CRPropa3 are fit to Pierre Auger Observatory data. The resulting emission spectral indices, rigidity cutoffs, and nucleon fractions are compared to recent Auger results. The FR0 simulations include the approximately isotropic distribution of FR0 galaxies and various intergalactic magnetic field configurations (including random and structured fields) and predict the fluxes of secondary photons and neutrinos produced during UHECR propagation through cosmic photon backgrounds. This comprehensive simulation allows for investigating the properties of the FR0 sources using observational multi-messenger data.Comment: PoS 444 (38th ICRC) 151

INFN Camera demonstrator for the Cherenkov Telescope Array

The Cherenkov Telescope Array is a world-wide project for a new generation of ground-based Cherenkov telescopes of the Imaging class with the aim of exploring the highest energy region of the electromagnetic spectrum. With two planned arrays, one for each hemisphere, it will guarantee a good sky coverage in the energy range from a few tens of GeV to hundreds of TeV, with improved angular resolution and a sensitivity in the TeV energy region better by one order of magnitude than the currently operating arrays. In order to cover this wide energy range, three different telescope types are envisaged, with different mirror sizes and focal plane features. In particular, for the highest energies a possible design is a dual-mirror Schwarzschild-Couder optical scheme, with a compact focal plane. A silicon photomultiplier (SiPM) based camera is being proposed as a solution to match the dimensions of the pixel (angular size of ~ 0.17 degrees). INFN is developing a camera demonstrator made by 9 Photo Sensor Modules (PSMs, 64 pixels each, with total coverage 1/4 of the focal plane) equipped with FBK (Fondazione Bruno Kessler, Italy) Near UltraViolet High Fill factor SiPMs and Front-End Electronics (FEE) based on a Target 7 ASIC, a 16 channels fast sampler (up to 2GS/s) with deep buffer, self-trigger and on-demand digitization capabilities specifically developed for this purpose. The pixel dimensions of $6\times6$ mm$^2$ lead to a very compact design with challenging problems of thermal dissipation. A modular structure, made by copper frames hosting one PSM and the corresponding FEE, has been conceived, with a water cooling system to keep the required working temperature. The actual design, the adopted technical solutions and the achieved results for this demonstrator are presented and discussed.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

Quasi-periodic modulation observed in the gamma-ray blazar PG 1553+113 and the MAGIC campaign 2015-2017

A gamma-ray nearly-periodic oscillation was observed from the well-known GeV/TeV BL Lac object PG 1553+113 by the Fermi Large Area Telescope (LAT). The quasi-periodicity in the gamma-ray flux (E>100 MeV and E>1 GeV), reported for the first time in an active galactic nucleus, is significant with a 100 GeV) gamma rays and will cover the next maximum of activity, expected between the end of 2016 and beginning of 2017. The MWL data collected during this campaign, coupled with the gamma-ray ones form MAGIC, will be the key to determine the nature of the periodicity to disentangle the processes driving the periodic modulation from flaring activity typical in blazar objects

The disease associated Tau35 fragment has an increased propensity to aggregate compared to full-length Tau

Tau35 is a truncated form of tau found in human brain in a subset of tauopathies. Tau35 expression in mice recapitulates key features of human disease, including progressive increase in tau phosphorylation, along with cognitive and motor dysfunction. The appearance of aggregated tau suggests that Tau35 may have structural properties distinct from those of other tau species that could account for its pathological role in disease. To address this hypothesis, we performed a structural characterization of monomeric and aggregated Tau35 and compared the results to those of two longer isoforms, 2N3R and 2N4R tau. We used small angle X-ray scattering to show that Tau35, 2N3R and 2N4R tau all behave as disordered monomeric species but Tau35 exhibits higher rigidity. In the presence of the poly-anion heparin, Tau35 increases thioflavin T fluorescence significantly faster and to a greater extent than full-length tau, demonstrating a higher propensity to aggregate. By using atomic force microscopy, circular dichroism, transmission electron microscopy and X-ray fiber diffraction, we provide evidence that Tau35 aggregation is mechanistically and morphologically similar to previously reported tau fibrils but they are more densely packed. These data increase our understanding of the aggregation inducing properties of clinically relevant tau fragments and their potentially damaging role in the pathogenesis of human tauopathies

Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010

Context. Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy distribution (SED). Aims. The goal is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk 421. These mechanisms may also apply to more distant blazars that cannot be studied with the same level of detail. Methods. A flare occurring in March 2010 was observed for 13 consecutive days (from MJD 55 265 to MJD 55 277) with unprecedented wavelength coverage from radio to very high energy (VHE; E> 100 GeV) γ-rays with MAGIC, VERITAS, Whipple, Fermi-LAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We modeled the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigated the physical parameters, and evaluated whether the observed broadband SED variability can be associated with variations in the relativistic particle population. Results. The activity of Mrk 421 initially was high and then slowly decreased during the 13-day period. The flux variability was remarkable at the X-ray and VHE bands, but it was minor or not significant at the other bands. The variability in optical polarization was also minor. These observations revealed an almost linear correlation between the X-ray flux at the 2–10 keV band and the VHE γ-ray flux above 200 GeV, consistent with the γ-rays being produced by inverse-Compton scattering in the Klein-Nishina regime in the framework of SSC models. The one-zone SSC model can describe the SED of each day for the 13 consecutive days reasonably well, which once more shows the success of this standard theoretical scenario to describe the SEDs of VHE BL Lacs such as Mrk 421. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission, while the other smaller zone, which is spatially separated from the first, contributes to the daily variable emission occurring at X-rays and VHE γ-rays. The second blob is assumed to have a smaller volume and a narrow electron energy distribution with 3 × 104<γ< 6 × 105, where γ is the Lorentz factor of the electrons. Such a two-zone scenario would naturally lead to the correlated variability at the X-ray and VHE bands without variability at the optical/UV band, as well as to shorter timescales for the variability at the X-ray and VHE bands with respect to the variability at the other bands. Conclusions. Both the one-zone and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly with the underlying particle population. This shows that the particle acceleration and cooling mechanism that produces the radiating particles might be the main mechanism responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement with the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by varying the parameters related to the emitting region itself (δ, B and R), in addition to the parameters related to the particle population.Fil: Aleksic, J.. IFAE; EspañaFil: Ansoldi, S.. Università di Udine; ItaliaFil: Antonelli, L. A.. INAF National Institute for Astrophysics; ItaliaFil: Antoranz, P.. Università di Siena; ItaliaFil: Babic, A.. University of Rijeka; CroaciaFil: Bangale, P.. Max-Planck-Institut für Physik; AlemaniaFil: Barres de Almeida, U.. Max-Planck-Institut für Physik; AlemaniaFil: Barrio, J. A.. Universidad Complutense de Madrid; EspañaFil: Becerra Gonzalez, J.. Inst. de Astrofísica de Canarias; EspañaFil: Bednarek, W.. University of Łódź,; PoloniaFil: Bernardini, E.. Deutsches Elektronen-Synchrotron (DESY); AlemaniaFil: Biasuzzi, B.. Università di Udine; ItaliaFil: Biland, A.. ETH Zurich; SuizaFil: Blanch, O.. IFAE; EspañaFil: Boller, A.. ETH Zurich; SuizaFil: Bonnefoy, S.. Universidad Complutense de Madrid; EspañaFil: Bonnoli, G.. INAF National Institute for Astrophysics ; ItaliaFil: Borracci, F.. Max-Planck-Institut für Physik; AlemaniaFil: Bretz, T.. Universität Würzburg ; AlemaniaFil: Carmona, E.. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas ; EspañaFil: Carosi, A.. INAF National Institute for Astrophysics; ItaliaFil: Colin, P.. Max-Planck-Institut für Physik; AlemaniaFil: Colombo, E.. Inst. de Astrofísica de Canarias; EspañaFil: Contreras, J. L.. Universidad Complutense; EspañaFil: Cortina, J.. IFAE; EspañaFil: Covino, S.. INAF National Institute for Astrophysics; ItaliaFil: Da Vela, P.. Università di Siena; ItaliaFil: Dazzi, F.. Max-Planck-Institut für Physik; AlemaniaFil: Pichel, Ana Carolina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Rovero, Adrian Carlos. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: The Veritas Collaboration.Fil: The MAGIC Collaboration

Multiwavelength observations of Mrk 501 in 2008

Context. Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100 GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the γ-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available γ-ray instrumentation was easier toperform. Aims: Our goal is to characterize the source γ-ray emission in detail, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. Methods: We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE γ-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign. Results: Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy and a tentative correlation between the X-ray and VHE fluxes. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. Conclusions: The one-zone SSC model can adequately describe the broadband spectral energy distribution of the source during the two months covered by the MW campaign. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during such a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity.Fil: Aleksic, J.. IFAE; EspañaFil: Ansoldi, S.. Università di Udine; ItaliaFil: Antonelli, L. A.. INAF National Institute for Astrophysics; ItaliaFil: Antoranz, P.. Università di Siena; ItaliaFil: Babic, A.. University of Rijeka ; Croacia. University of Split; CroaciaFil: Bangale, P.. Max-Planck-Institut für Physik; AlemaniaFil: Barres de Almeida, U.. Max-Planck-Institut für Physik; AlemaniaFil: Barrio, J. A.. Universidad Complutense de Madrid; EspañaFil: Becerra Gonzalez, J.. Inst. de Astrofísica de Canarias; EspañaFil: Bednarek, W.. University of Lodz; PoloniaFil: Berger, K.. Inst. de Astrofísica de Canarias; EspañaFil: Bernardini, E.. Deutsches Elektronen-Synchrotron (DESY); AlemaniaFil: Biland, A.. ETH Zurich; SuizaFil: Blanch, O.. IFAE; EspañaFil: Bock, R. K.. Max-Planck-Institut für Physik; AlemaniaFil: Bonnefoy, S.. Universidad Complutense de Madrid; EspañaFil: Bonnoli, G.. INAF National Institute for Astrophysics; ItaliaFil: Borracci, F.. Max-Planck-Institut für Physik; AlemaniaFil: Bretz, T.. Universität Würzburg; Alemania. Now at École polytechnique fédérale de Lausanne (EPFL); SuizaFil: Carmona, E.. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas; EspañaFil: Carosi, A.. INAF National Institute for Astrophysics; ItaliaFil: Carreto Fidalgo, D.. Universität Würzburg; AlemaniaFil: Colin, P.. Max-Planck-Institut für Physik; AlemaniaFil: Colombo, E.. Inst. de Astrofísica de Canarias; EspañaFil: Contreras, J. L.. Universidad Complutense de Madrid; EspañaFil: Cortina, J.. IFAE; EspañaFil: Covino, S.. INAF National Institute for Astrophysics; ItaliaFil: Da Vela, P.. Università di Siena; ItaliaFil: Dazzi, F.. Università di Udine; ItaliaFil: Pichel, Ana Carolina. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: The MAGIC collaboration.Fil: The VERITAS collaboration

Detection of very high energy gamma-ray emission from the gravitationally-lensed blazar QSO B0218+357 with the MAGIC telescopes

Context. QSO B0218+357 is a gravitationally lensed blazar located at a redshift of 0.944. The gravitational lensing splits the emitted radiation into two components, spatially indistinguishable by gamma-ray instruments, but separated by a 10-12 day delay. In July 2014, QSO B0218+357 experienced a violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes. Aims. The spectral energy distribution of QSO B0218+357 can give information on the energetics of z ~ 1 very high energy gamma- ray sources. Moreover the gamma-ray emission can also be used as a probe of the extragalactic background light at z ~ 1. Methods. MAGIC performed observations of QSO B0218+357 during the expected arrival time of the delayed component of the emission. The MAGIC and Fermi-LAT observations were accompanied by quasi-simultaneous optical data from the KVA telescope and X-ray observations by Swift-XRT. We construct a multiwavelength spectral energy distribution of QSO B0218+357 and use it to model the source. The GeV and sub-TeV data, obtained by Fermi-LAT and MAGIC, are used to set constraints on the extragalactic background light. Results. Very high energy gamma-ray emission was detected from the direction of QSO B0218+357 by the MAGIC telescopes during the expected time of arrival of the trailing component of the flare, making it the farthest very high energy gamma-ray sources detected to date. The observed emission spans the energy range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy distribution of QSO B0218+357 is consistent with current extragalactic background light models. The broad band emission can be modeled in the framework of a two zone external Compton scenario, where the GeV emission comes from an emission region in the jet, located outside the broad line region.Comment: 11 pages, 6 figures, accepted for publication in A&

A search for spectral hysteresis and energy-dependent time lags from X-ray and TeV gamma-ray observations of Mrk 421

Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three "target-of-opportunity" (ToO) observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering X-ray and optical/ultraviolet bands) and VERITAS (covering TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi-LAT) and a number of radio and optical facilities. Although neither rapid flares nor significant X-ray/TeV correlation are detected, these observations reveal subtle changes in the X-ray spectrum of the source over the course of a few days. We search the simultaneous X-ray and TeV data for spectral hysteresis patterns and time delays, which could provide insight into the emission mechanisms and the source properties (e.g. the radius of the emitting region, the strength of the magnetic field, and related timescales). The observed broadband spectra are consistent with a one-zone synchrotron self-Compton model. We find that the power spectral density distribution at $\gtrsim 4\times 10^{-4}$ Hz from the X-ray data can be described by a power-law model with an index value between 1.2 and 1.8, and do not find evidence for a steepening of the power spectral index (often associated with a characteristic length scale) compared to the previously reported values at lower frequencies.Comment: 45 pages, 15 figure