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.
Abstract
The microquasar Cygnus X-1 displays the two typical soft and hard X-ray states of a black hole transient. During the latter, Cygnus X-1 shows a one-sided relativistic radio-jet. Recent ...detection of the system in the high energy (HE; E ≳ 60 MeV) gamma-ray range with Fermi-LAT associates this emission with the outflow. Former MAGIC observations revealed a hint of flaring activity in the very high-energy (VHE; E ≳ 100 GeV) regime during this X-ray state. We analyse ∼97 h of Cygnus X-1 data taken with the MAGIC telescopes between July 2007 and October 2014. To shed light on the correlation between hard X-ray and VHE gamma rays as previously suggested, we study each main X-ray state separately. We perform an orbital phase-folded analysis to look for variability in the VHE band. Additionally, to place this variability behaviour in a multiwavelength context, we compare our results with Fermi-LAT, AGILE, Swift-BAT, MAXI, RXTE-ASM, AMI and RATAN-600 data. We do not detect Cygnus X-1 in the VHE regime. We establish upper limits for each X-ray state, assuming a power-law distribution with photon index Γ = 3.2. For steady emission in the hard and soft X-ray states, we set integral upper limits at 95 per cent confidence level for energies above 200 GeV at 2.6 × 10−12 photons cm−2 s−1 and 1.0 × 10−11 photons cm−2 s−1, respectively. We rule out steady VHE gamma-ray emission above this energy range, at the level of the MAGIC sensitivity, originating in the interaction between the relativistic jet and the surrounding medium, while the emission above this flux level produced inside the binary still remains a valid possibility.
Context. In the last five years the Fermi Large Area Telescope (LAT) instrument detected GeV γ-ray emission from five novae. The GeV emission can be interpreted in terms of an inverse Compton process ...of electrons accelerated in a shock. In this case it is expected that protons in the same conditions can be accelerated to much higher energies. Consequently they may produce a second component in the γ-ray spectrum at TeV energies. Aims. We aim to explore the very high-energy domain to search for γ-ray emission above 50 GeV and to shed light on the acceleration process of leptons and hadrons in nova explosions. Methods. We have performed observations, with the MAGIC telescopes of the classical nova V339 Del shortly after the 2013 outburst; optical and subsequent GeV γ-ray detections triggered the MAGIC observations. We also briefly report on VHE observations of the symbiotic nova YY Her and the dwarf nova ASASSN-13ax. We complement the TeV MAGIC observations with the analysis of contemporaneous Fermi-LAT data of the sources. The TeV and GeV observations are compared in order to evaluate the acceleration parameters for leptons and hadrons. Results. No significant TeV emission was found from the studied sources. We computed upper limits on the spectrum and night-by-night flux. The combined GeV and TeV observations of V339 Del limit the ratio of proton to electron luminosities to Lp ≲ 0.15 Le.
The MAGIC stereoscopic system collected 69 hours of Crab Nebula data between October 2009 and April 2011. Analysis of this data sample using the latest improvements in the MAGIC stereoscopic software ...provided an unprecedented precision of spectral and night-by-night light curve determination at gamma rays. We derived a differential spectrum with a single instrument from 50 GeV up to almost 30 TeV with 5 bins per energy decade. At low energies, MAGIC results, combined with Fermi-LAT data, show a flat and broad Inverse Compton peak. The overall fit to the data between 1 GeV and 30 TeV is not well described by a log-parabola function. We find that a modified log-parabola function with an exponent of 2.5 instead of 2 provides a good description of the data (χred2=35/26). Using systematic uncertainties of the MAGIC and Fermi-LAT measurements we determine the position of the Inverse Compton peak to be at (53±3stat+31syst−13syst) GeV, which is the most precise estimation up to date and is dominated by the systematic effects. There is no hint of the integral flux variability on daily scales at energies above 300 GeV when systematic uncertainties are included in the flux measurement. We consider three state-of-the-art theoretical models to describe the overall spectral energy distribution of the Crab Nebula. The constant B-field model cannot satisfactorily reproduce the VHE spectral measurements presented in this work, having particular difficulty reproducing the broadness of the observed IC peak. Most probably this implies that the assumption of the homogeneity of the magnetic field inside the nebula is incorrect. On the other hand, the time-dependent 1D spectral model provides a good fit of the new VHE results when considering a 80 μG magnetic field. However, it fails to match the data when including the morphology of the nebula at lower wavelengths.
Context. The pulsar wind nebula (PWN) 3C 58 is one of the historical very high-energy (VHE; E> 100 GeV) γ-ray source candidates. It is energized by one of the highest spin-down power pulsars known ...(5% of Crab pulsar) and it has been compared with the Crab nebula because of their morphological similarities. This object was previously observed by imaging atmospheric Cherenkov telescopes (Whipple, VERITAS and MAGIC), although it was not detected, with an upper limit of 2.3% Crab unit (C.U.) at VHE. It was detected by the Fermi Large Area Telescope (LAT) with a spectrum extending beyond 100 GeV. Aims. We aim to extend the spectrum of 3C 58 beyond the energies reported by the Fermi Collaboration and probe acceleration of particles in the PWN up to energies of a few tens of TeV. Methods. We analyzed 81 h of 3C 58 data taken in the period between August 2013 and January 2014 with the MAGIC telescopes. Results. We detected VHE γ-ray emission from 3C 58 with a significance of 5.7σ and an integral flux of 0.65% C.U. above 1 TeV. According to our results, 3C 58 is the least luminous VHE γ-ray PWN ever detected at VHE and has the lowest flux at VHE to date. The differential energy spectrum between 400 GeV and 10 TeV is well described by a power-law function dφ/dE = f0(E/1 TeV)−Γ with f0 = (2.0 ± 0.4stat ± 0.6sys) × 10-13 cm-2 s-1 TeV-1 and Γ = 2.4 ± 0.2stat ± 0.2sys. The skymap is compatible with an unresolved source. Conclusions. We report the first significant detection of PWN 3C 58 at TeV energies. We compare our results with the expectations of time-dependent models in which electrons upscatter photon fields. The best representation favors a distance to the PWN of 2 kpc and far-infrared (FIR) values similar to cosmic microwave background photon fields. If we consider an unexpectedly high FIR density, the data can also be reproduced by models assuming a 3.2 kpc distance. A low magnetic field, far from equipartition, is required to explain the VHE data. Hadronic contribution from the hosting supernova remnant (SNR) requires an unrealistic energy budget given the density of the medium, disfavoring cosmic-ray acceleration in the SNR as origin of the VHE γ-ray emission.
The radio-γ-ray connection in Fermi blazars Ghirlanda, G.; Ghisellini, G.; Tavecchio, F. ...
Monthly notices of the Royal Astronomical Society,
05/2011, Letnik:
413, Številka:
2
Journal Article
The radioaI3aray connection in Fermi blazars Ghirlanda, G; Ghisellini, G; Tavecchio, F ...
Monthly notices of the Royal Astronomical Society,
05/2011, Letnik:
413, Številka:
2
Journal Article
Recenzirano
We study the correlation between the gamma -ray flux (F gamma ), averaged over the first 11 months of the Fermi survey and integrated above 100 MeV, and the radio flux density (Fr at 20 GHz) of Fermi ...sources associated with a radio counterpart in the 20-GHz Australia Telescope Compact Array (AT20G) survey. Considering the blazars detected in both bands, the correlation is highly significant and has the form F gamma proportional to F0.85+/-0.04r, similar to BL Lacertae objects and flat-spectrum radio quasars. However, only a small fraction ( similar to 1/15) of the AT20G radio sources with flat radio spectra are detected by Fermi. To understand if this correlation is real, we examine the selection effects introduced by the flux limits of both the radio and the gamma -ray surveys, and the importance of variability of the gamma -ray flux. After accounting for these effects, we find that the radio- gamma -ray flux correlation is real, but its slope is steeper than the observed one, that is, F gamma proportional to F delta r with delta in the range 1.25-1.5. The observed F gamma -Fr correlation and the fraction of radio sources detected by Fermi are reproduced assuming a long-term gamma -ray flux variability, following a lognormal probability distribution with standard deviation sigma greater than or equal to 0.5 (corresponding to F gamma varying by at least a factor of 3). Such a variability is compatible, even if not necessarily equal, with what is observed when comparing, for the sources in common, the EGRET and the Fermi
The radio-[gamma]-ray connection in Fermi blazars Ghirlanda, G; Ghisellini, G; Tavecchio, F ...
Monthly notices of the Royal Astronomical Society,
05/2011, Letnik:
413, Številka:
2
Journal Article
Recenzirano
We study the correlation between the γ-ray flux (Fγ), averaged over the first 11 months of the Fermi survey and integrated above 100 MeV, and the radio flux density (Fr at 20 GHz) of Fermi sources ...associated with a radio counterpart in the 20-GHz Australia Telescope Compact Array (AT20G) survey. Considering the blazars detected in both bands, the correlation is highly significant and has the form FγF0.85±0.04r, similar to BL Lacertae objects and flat-spectrum radio quasars. However, only a small fraction (1/15) of the AT20G radio sources with flat radio spectra are detected by Fermi. To understand if this correlation is real, we examine the selection effects introduced by the flux limits of both the radio and the γ-ray surveys, and the importance of variability of the γ-ray flux. After accounting for these effects, we find that the radio-γ-ray flux correlation is real, but its slope is steeper than the observed one, that is, FγFδr with δ in the range 1.25-1.5. The observed Fγ-Fr correlation and the fraction of radio sources detected by Fermi are reproduced assuming a long-term γ-ray flux variability, following a lognormal probability distribution with standard deviation σ≥ 0.5 (corresponding to Fγ varying by at least a factor of 3). Such a variability is compatible, even if not necessarily equal, with what is observed when comparing, for the sources in common, the EGRET and the Fermiγ-ray fluxes (even if the Fermi fluxes are averaged over 1 yr). Another indication of variability is the non-detection of 12 out of 66 EGRET blazars by Fermi, despite its higher sensitivity. We also study the strong linear correlation between the γ-ray and the radio luminosity of the 144 AT20G-Fermi associations with known redshift and show, through partial correlation analysis, that it is statistically robust. Two possible implications of these correlations are discussed: the contribution of blazars to the extragalactic γ-ray background and the prediction of blazars that might undergo extremely high states of γ-ray emission in the next few years. PUBLICATION ABSTRACT
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