Gamma-ray observations of MAXI J1820+070 during the 2018 outburst

MAXI J1820+070 is a low-mass X-ray binary with a black hole (BH) as a compact object. This binary underwent an exceptionally bright X-ray outburst from 2018 March to October, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 h of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy (HE) gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to ∼500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential HE and very-HE gamma-ray emitting region should be located at a distance from the BH ranging between 10 and 10 cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA

Constraining the Dark Matter decay lifetime with very deep observations of the Perseus cluster with the MAGIC telescopes

We present preliminary results on Dark Matter searches from observations of the Perseus galaxy cluster with the MAGIC Telescopes. MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in the Canary island of La Palma, Spain. Galaxy clusters are the largest known gravitationally bound structures in the Universe, with masses of ~10^15 Solar masses. There is strong evidence that galaxy clusters are Dark Matter dominated objects, and therefore promising targets for Dark Matter searches, particularly for decay signals. MAGIC has taken almost 300 hours of data on the Perseus Cluster between 2009 and 2015, the deepest observational campaign on any galaxy cluster performed so far in the very high energy range of the electromagnetic spectrum. We analyze here a small sample of this data and search for signs of dark matter in the mass range between 100 GeV and 20 TeV. We apply a likelihood analysis optimized for the spectral and morphological features expected in the dark matter decay signals. This is the first time that a dedicated Dark Matter optimization is applied in a MAGIC analysis, taking into account the inferred Dark Matter distribution of the source. The results with the full dataset analysis will be published soon by the MAGIC Collaboration

MWL observations of VHE blazars in 2006

In 2006 the MAGIC telescope observed the well known very high energy (VHE, > 80 GeV) blazars Mrk 421 and Mrk 501 in the course of multi-wavelength campaigns, comprising measurements in the optical, X-ray and VHE regime. MAGIC performed additional snapshot observations on Mrk 421 around the MWL campaigns and detected the source each night with high significance, establishing once more flux variability on nightly scales for this object. For certain nights, the integral flux exceeded the one of Crab significantly, whereas the truly simultaneous observations have been conducted in a rather low flux state. The MAGIC observations contemporaneous to XMM-Newton revealed clear intra-night variability. No significant correlation between the spectral index and the flux could be found for the nine days of observations. The VHE observations of Mrk 501 have been conducted during one of the lowest flux states ever measured by MAGIC for this object. The VHE and optical light curves do not show significant variability, whereas the flux in X-rays increased by about 50 %. In this contribution, the results of the MAGIC observations will be presented in detail.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200

Axion-like particle imprint in cosmological very-high-energy sources

Discoveries of very high energy (VHE) photons from distant blazars suggest that, after correction by extragalactic background light (EBL) absorption, there is a flatness or even a turn-up in their spectra at the highest energies that cannot be easily explained by the standard framework. Here, it is shown that a possible solution to this problem is achieved by assuming the existence of axion-like particles (ALPs) with masses ~1 neV. The ALP scenario is tested making use of observations of the highest redshift blazars known in the VHE energy regime, namely 3C 279, 3C 66A, PKS 1222+216 and PG 1553+113. In all cases, better fits to the observed spectra are found when including ALPs rather than considering EBL only. Interestingly, quite similar critical energies for photon/ALP conversions are also derived, independently of the source considered.Comment: 12 pages, 2 figures, 2 tables; accepted by JCAP. Replaced to match the accepted versio

Insights into the particle acceleration of a peculiar gamma -ray radio galaxy IC 310

IC 310 has recently been identified as a gamma-ray emitter based on observations at GeV energies with Fermi-LAT and at very high energies (VHE, E > 100 GeV) with the MAGIC telescopes. Despite IC 310 having been classified as a radio galaxy with the jet observed at an angle > 10 degrees, it exhibits a mixture of multiwavelength properties of a radio galaxy and a blazar, possibly making it a transitional object. On the night of 12/13th of November 2012 the MAGIC telescopes observed a series of violent outbursts from the direction of IC 310 with flux-doubling time scales faster than 5 min and a peculiar spectrum spreading over 2 orders of magnitude. Such fast variability constrains the size of the emission region to be smaller than 20% of the gravitational radius of its central black hole, challenging the shock acceleration models, commonly used in explanation of gamma-ray radiation from active galaxies. Here we will show that this emission can be associated with pulsar-like particle acceleration by the electric field across a magnetospheric gap at the base of the jet.Comment: 2014 Fermi Symposium proceedings - eConf C14102.

Measurement of the EBL through a combined likelihood analysis of gamma-ray observations of blazars with the MAGIC telescopes

The extragalactic background light (EBL) is the radiation accumulated through the history of the Universe in the wavelength range from the ultraviolet to the far infrared. Local foregrounds make the direct measurement of the diffuse EBL notoriously difficult, while robust lower limits have been obtained by adding up the contributions of all the discrete sources resolved in deep infrared and optical galaxy observations. Gamma-ray astronomy has emerged in the past few years as a powerful tool for the study of the EBL: very-high-energy (VHE) photons traversing cosmological distances can interact with EBL photons to produce e$^+$e$^-$ pairs, resulting in an energy-dependent depletion of the gamma-ray flux of distant sources that can be used to set constraints on the EBL density. The study of the EBL is one of the key scientific programs currently carried out by the MAGIC collaboration. We present here the results of the analysis of 32 VHE spectra of 12 blazars in the redshift range 0.03 - 0.94, obtained with over 300 hours of observations with the MAGIC telescopes between 2010 and 2016. A combined likelihood maximization approach is used to evaluate the density and spectrum of the EBL most consistent with the MAGIC observations. The results are compatible with state-of-the-art EBL models, and constrain the EBL density to be roughly within $\simeq 20\%$ of the nominal value in such models. The study reveals no anomalies in gamma-ray propagation in the large optical depth regime - contrary to some claims based on meta-analyses of published VHE spectra.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC 2017), Bexco, Busan, Korea (arXiv:1708.05153

Grid services for the MAGIC experiment

Exploring signals from the outer space has become an observational science under fast expansion. On the basis of its advanced technology the MAGIC telescope is the natural building block for the first large scale ground based high energy gamma-ray observatory. The low energy threshold for gamma-rays together with different background sources leads to a considerable amount of data. The analysis will be done in different institutes spread over Europe. Therefore MAGIC offers the opportunity to use the Grid technology to setup a distributed computational and data intensive analysis system with the nowadays available technology. Benefits of Grid computing for the MAGIC telescope are presented.Comment: 5 pages, 1 figures, to be published in the Proceedings of the 6th International Symposium ''Frontiers of Fundamental and Computational Physics'' (FFP6), Udine (Italy), Sep. 26-29, 200

Understanding hadronic gamma-ray emission from supernova remnants

We aim to test the plausibility of a theoretical framework in which the gamma-ray emission detected from supernova remnants may be of hadronic origin, i.e., due to the decay of neutral pions produced in nuclear collisions involving relativistic nuclei. In particular, we investigate the effects induced by magnetic field amplification on the expected particle spectra, outlining a phenomenological scenario consistent with both the underlying Physics and the larger and larger amount of observational data provided by the present generation of gamma experiments, which seem to indicate rather steep spectra for the accelerated particles. In addition, in order to study to study how pre-supernova winds might affect the expected emission in this class of sources, the time-dependent gamma-ray luminosity of a remnant with a massive progenitor is worked out. Solid points and limitations of the proposed scenario are finally discussed in a critical way.Comment: 30 pages, 5 figures; Several comments, references and a figure added. Some typos correcte