Studio dello spettro VHE della sorgente PKS 1424+240 ed implicazioni sulla propagazione dei raggi gamma da distanze cosmologiche

Attraverso il confronto tra gli indici spettrali nei domini HE e VHE dello spettro del blazar PKS 1424+240 si determina un limite superiore al redshift dello stesso. Tale valore risulta essere compatibile con le piu' recenti misure sperimentali, suggerendo che PKS 1424+240 appartenga ad una nuova classe di blazar con emissione ad energie estremamente alte.ope

MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT081 for the first time: a deep multiwavelength study

https://pos.sissa.it/395/815/pdfPublished versio

Studio dello spettro VHE della sorgente PKS 1424+240 ed implicazioni sulla propagazione dei raggi gamma da distanze cosmologiche

Attraverso il confronto tra gli indici spettrali nei domini HE e VHE dello spettro del blazar PKS 1424+240 si determina un limite superiore al redshift dello stesso. Tale valore risulta essere compatibile con le piu' recenti misure sperimentali, suggerendo che PKS 1424+240 appartenga ad una nuova classe di blazar con emissione ad energie estremamente alte

MAGIC detection of Geminga: an Inverse Compton tail?

We report the detection of pulsed emission from the Geminga pulsar (PSR J0633+1746) with the MAGIC Telescopes. After the Crab and Vela pulsars, Geminga is the third one detected in the very high energy domain, and its estimated age of ~340 ky makes it the oldest one. The spectrum derived by MAGIC extends from ~15 GeV to 75 GeV and can be well modeled with a simple, soft power-law function. For energies below 40 GeV it overlaps with Fermi-LAT measurements. Joint fits to MAGIC and Fermi-LAT data disfavour the existence of a sub-exponential cut-off in this energy range. Our results are discussed in the framework of the outer gap accelerator model. Such power-law emission can be interpreted as the transition from curvature radiation to inverse Compton (IC) scattering of charges accelerated in the northern outer gap. The IC component is expected to continue towards higher energies. The model fails to fit the overall shape of the spectrum, indicating that a major review is required. The MAGIC Telescopes are two IACTs on the Canary Island of La Palma. In recent years they have significantly improved their performance below 100 GeV with the introduction of a novel trigger system, the Sum-Trigger-II, which halves the energy threshold of the system.ISSN:1824-803

Deep observations of the globular cluster M15 with the MAGIC telescopes

Abstract 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 < 3.2×10−13cm−2s−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

The blazar TXS 0506+056 associated with a high-energy neutrino: insights into extragalactic jets and cosmic ray acceleration

International audienceA neutrino with energy ∼290 TeV, IceCube-170922A, was detected in coincidence with the BL Lac object TXS 0506+056 during enhanced gamma-ray activity, with chance coincidence being rejected at ∼3σ level. We monitored the object in the very-high-energy (VHE) band with the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes for ∼41 hr from 1.3 to 40.4 days after the neutrino detection. Day-timescale variability is clearly resolved. We interpret the quasi-simultaneous neutrino and broadband electromagnetic observations with a novel one-zone lepto-hadronic model, based on interactions of electrons and protons co-accelerated in the jet with external photons originating from a slow-moving plasma sheath surrounding the faster jet spine. We can reproduce the multiwavelength spectra of TXS 0506+056 with neutrino rate and energy compatible with IceCube-170922A, and with plausible values for the jet power of . The steep spectrum observed by MAGIC is concordant with internal γγ absorption above ∼100 GeV entailed by photohadronic production of a ∼290 TeV neutrino, corroborating a genuine connection between the multi-messenger signals. In contrast to previous predictions of predominantly hadronic emission from neutrino sources, the gamma-rays can be mostly ascribed to inverse Compton upscattering of external photons by accelerated electrons. The X-ray and VHE bands provide crucial constraints on the emission from both accelerated electrons and protons. We infer that the maximum energy of protons in the jet comoving frame can be in the range ∼1014 – 1018 eV

Intensity interferometry with the MAGIC telescopes

Due to their large mirror size, fast response to single photons, sensitivity and telescope baselines in the order of 100 m, Imaging Atmospheric Cherenkov Telescopes are ideally suited to perform intensity interferometry observations. In 2019 a test readout setup was installed in the two 17-m diameter MAGIC telescopes to allow performing interferometry measurements with them. The first on-sky measurements were able to detect correlated intensity fluctuations consistent with the stellar diameters of three different stars: Adhara (n CMa), Benetnasch ([ UMa) and Mirzam (V CMa). After the upgrade of the setup in 2021, MAGIC is now equipped with a high-duty-cycle intensity interferometer, already in operation. A technical description of the interferometer and first performance results obtained by measuring several known stellar diameter are presented

Extreme blazars under the eyes of MAGIC

Extreme high-frequency-peaked BL Lac objects (EHBLs) are the most energetic persistent sources in the universe. This contribution reports on long-term observing campaigns of tens of EHBLs that have been organized by the MAGIC collaboration to enlarge their population at VHE and understand the origin of their extreme properties. EHBLs are characterized by a spectral energy distribution (SED) featuring a synchrotron peak energy above 1 keV. Several EHBLs display a hard spectral index at very high energies (VHE; E > 100 GeV), suggesting a gamma-ray SED component peaking significantly above 1 TeV. Such extreme properties are challenging current standard emission and acceleration mechanisms. Recent studies have also unveiled intriguing disparities in the temporal characteristics of EHBLs. Some sources seem to display a persistent EHBL behaviour, while others belong to the EHBL family only temporarily. Here, we present recent results of the first hard-TeV EHBL catalog. The MAGIC observations are accompanied by an extensive multiwavelength coverage to obtain an optimal determination of the SED. This allow us to investigate leptonic and hadronic scenarios for the emission. We also present the recent detection of the EHBL RX J0812.0+0237 in the VHE band by MAGIC. Finally, we discuss a broad multiwavelength campaign on the BL Lac type object 1ES 2344+514, which showed intermittent EHBL characteristics in August 2016