The ARGO-YBJ Experiment Progresses and Future Extension

Gamma ray source detection above 30TeV is an encouraging approach for finding galactic cosmic ray origins. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100GeV. To target the goals, the ARGO-YBJ experiment has been established. Significant progresses have been made in the experiment. A large air shower detector array in an area of 1km2 is proposed to boost the sensitivity. Hybrid detection with multi-techniques will allow a good discrimination between different types of primary particles, including photons and protons, thus enable an energy spectrum measurement for individual specie. Fluorescence light detector array will extend the spectrum measurement above 100PeV where the second knee is located. An energy scale determined by balloon experiments at 10TeV will be propagated to ultra high energy cosmic ray experiments

ARGO-YBJ constraints on very high energy emission from GRBs

The ARGO-YBJ (Astrophysical Radiation Ground-based Observatory at YangBaJing) experiment is designed for very high energy $\gamma$-astronomy and cosmic ray researches. Due to the full coverage of a large area ($5600 m^2$) with resistive plate chambers at a very high altitude (4300 m a.s.l.), the ARGO-YBJ detector is used to search for transient phenomena, such as Gamma-ray bursts (GRBs). Because the ARGO-YBJ detector has a large field of view ($\sim$2 sr) and is operated with a high duty cycle ($>$90%), it is well suited for GRB surveying and can be operated in searches for high energy GRBs following alarms set by satellite-borne observations at lower energies. In this paper, the sensitivity of the ARGO-YBJ detector for GRB detection is estimated. Upper limits to fluence with 99% confidence level for 26 GRBs inside the field of view from June 2006 to January 2009 are set in the two energy ranges 10$-$100 GeV and 10 GeV$-$1 TeV.Comment: accepted for publication in Astroparticle Physic

Observation of inverse Compton emission from a long γ-ray burst.

Long-duration γ-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission1,2. Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands1-6. The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock7-9. Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C10,11. Here we report multi-frequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 × 10-6 to 1012 electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs

MAGIC very large zenith angle observations of the Crab Nebula up to 100 TeV

Aims. We measure the Crab Nebula gamma-ray spectral energy distribution in the 100 TeV energy domain and test the validity of existing leptonic emission models at these high energies.Methods. We used the novel very large zenith angle observations with the MAGIC telescope system to increase the collection area above 10 TeV. We also developed an auxiliary procedure of monitoring atmospheric transmission in order to assure proper calibration of the accumulated data. This employs recording optical images of the stellar field next to the source position, which provides a better than 10% accuracy for the transmission measurements.Results. We demonstrate that MAGIC very large zenith angle observations yield a collection area larger than a square kilometer. In only 56 h of observations, we detect the gamma-ray emission from the Crab Nebula up to 100 TeV, thus providing the highest energy measurement of this source to date with Imaging Atmospheric Cherenkov Telescopes. Comparing accumulated and archival MAGIC and Fermi/LAT data with some of the existing emission models, we find that none of them provides an accurate description of the 1 GeV to 100 TeV gamma-ray signal

Observation of a sudden cessation of a very-high-energy gamma-ray flare in PKS 1510-089 with H.E.S.S. and MAGIC in May 2016

The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complex multiwavelength behavior, and is one of only a few FSRQs detected at very high energy (VHE, E >100 GeV) -rays. VHE -ray observations with H.E.S.S. and MAGIC during late May and early June 2016 resulted in the detection of an unprecedented flare, which reveals for the first time VHE -ray intranight variability in this source. While a common variability timescale of 1.5 hr is found, there is a significant deviation near the end of the flare with a timescale of ∼ 20 min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, curvature is detected in the VHE -ray spectrum of PKS 1510-089, which is fully explained through absorption by the extragalactic background light. Optical R-band observations with ATOM reveal a counterpart of the -ray flare, even though the detailed flux evolution differs from the VHE lightcurve. Interestingly, a steep flux decrease is observed at the same time as the cessation of the VHE flare. In the high energy (HE, E >100 MeV) -ray band only a moderate flux increase is observed with Fermi-LAT, while the HE -ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the -ray spectrum indicates that the emission region is located outside of the BLR. Radio VLBI observations reveal a fast moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located ∼ 50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this correlation is indeed true, VHE rays have been produced far down the jet where turbulent plasma crosses a standing shock.Accepted manuscrip

Analysis of Cosmogenic Neutron Characteristics and the Pulses Counting Rate Using ASD, LSD, and LVD Scintillation Detectors

International audienceExperimental data obtained using three scintillation detectors are analyzed. The characteristics of cosmogenic neutrons in underground experiments their analytic dependences are considered. The behavior of background counting rate for the LVD detector for two measuring thresholds (0.5 and 5 MeV) are discussed

Characterization of the varying flux of atmospheric muons measured with the Large Volume Detector for 24 years

International audienceThe Large Volume Detector, hosted in the INFN Laboratori Nazionali del Gran Sasso, is triggered by atmospheric muons at a rate of ∼0.1  Hz. The data collected over almost a quarter of a century are used to study the muon intensity underground. The 5×107 muon series, the longest ever exploited by an underground instrument, allows for the accurate long-term monitoring of the muon intensity underground. This is relevant as a study of the background in the Gran Sasso Laboratory, which hosts a variety of long-duration, low-background detectors. We describe the procedure to select muon-like events as well as the method used to compute the exposure. We report the value of the average muon flux measured from 1994 to 2017: Iμ0=3.35±0.0005stat±0.03sys×10-4  m-2 s-1. We show that the intensity is modulated around this average value due to temperature variations in the stratosphere. We quantify such a correlation by using temperature data from the European Center for Medium-range Weather Forecasts: we find an effective temperature coefficient αT=0.94±0.01stat±0.01sys, in agreement with other measurements at the same depth. We scrutinize the spectral content of the time series of the muon intensity by means of the Lomb-Scargle analysis. This yields the evidence of a 1-year periodicity, as well as the indication of others, both shorter and longer, suggesting that the series is not a pure sinusoidal wave. Consequently, and for the first time, we characterize the observed modulation in terms of amplitude and position of the maximum and minimum on a year-by-year basis

Characterization of the varying flux of atmospheric muons measured with the Large Volume Detector for 24 years CHARACTERIZATION of the VARYING FLUX of ATMOSPHERIC ... N. YU. AGAFONOVA et al

The Large Volume Detector, hosted in the INFN Laboratori Nazionali del Gran Sasso, is triggered by atmospheric muons at a rate of 3c0.1 Hz. The data collected over almost a quarter of a century are used to study the muon intensity underground. The 5 7107 muon series, the longest ever exploited by an underground instrument, allows for the accurate long-term monitoring of the muon intensity underground. This is relevant as a study of the background in the Gran Sasso Laboratory, which hosts a variety of long-duration, low-background detectors. We describe the procedure to select muon-like events as well as the method used to compute the exposure. We report the value of the average muon flux measured from 1994 to 2017: I\u3bc0=3.35\ub10.0005stat\ub10.03sys 710-4 m-2 s-1. We show that the intensity is modulated around this average value due to temperature variations in the stratosphere. We quantify such a correlation by using temperature data from the European Center for Medium-range Weather Forecasts: we find an effective temperature coefficient \u3b1T=0.94\ub10.01stat\ub10.01sys, in agreement with other measurements at the same depth. We scrutinize the spectral content of the time series of the muon intensity by means of the Lomb-Scargle analysis. This yields the evidence of a 1-year periodicity, as well as the indication of others, both shorter and longer, suggesting that the series is not a pure sinusoidal wave. Consequently, and for the first time, we characterize the observed modulation in terms of amplitude and position of the maximum and minimum on a year-by-year basis

Exploration of the stratosphere with cosmic-ray muons detected underground

International audienceCosmic radiation is a potential additional tool for atmospheric monitoring. High-energy cosmic rays, interacting in the atmosphere, produce secondary particles, the production and propagation of which are ruled by the state of the atmosphere. Atmospheric muons carry information on the stratosphere, as its temperature modulates their intensity. Here, we present a comprehensive investigation of the 24-year series of the muon flux recorded underground with the Large Volume Detector in the Gran Sasso Laboratory in Italy. Using advanced spectral-analysis methods, we reveal, in addition to the well-known annual cycle, two significant variations with periods of about four and ten years. These two multiannual components, however, are not present in the series of the so-called effective temperature—an average parameter commonly used to describe the entire atmospheric profile in relationship to the detected muon flux—but we find them in the series of the raw temperatures in the lower-stratospheric levels. We show that the weaker multiannual cycles emerge in the temperature series thanks to the dampening of the dominant annual radiative cycle at these levels, which are affected by higher-frequency variability related to transport and wave processes. We also show that the multiannual variations are not typical only of the Gran Sasso area but are present at large scales throughout the Northern Hemisphere. The analysis of the series of the muon flux also reveals evidence of daily to monthly scale variations, especially during the highly variable winter period. Although such short-term modulations are also found in the series of the effective temperature, we show that the variations of the two series are brought to better agreement when considering only specific layers of the atmosphere depending on the event. The amplitudes of the multiannual variations are significantly larger than those expected based on the temperature modulations. Such differences may be due to acknowledged difficulties of the adopted temperature reanalysis dataset to thoroughly represent long-term variability scales, so that long-term modulations in the raw temperature series and, consequently, in the effective temperature record would result as artificially attenuated. The muon flux therefore may be envisaged as a high time-resolution integrated proxy of lower-stratospheric temperatures

MAGIC very large zenith angle observations of the Crab Nebula up to 100 TeV

Aims. We measure the Crab Nebula γ-ray spectral energy distribution in the ~100 TeV energy domain and test the validity of existing leptonic emission models at these high energies. Methods. We used the novel very large zenith angle observations with the MAGIC telescope system to increase the collection area above 10 TeV. We also developed an auxiliary procedure of monitoring atmospheric transmission in order to assure proper calibration of the accumulated data. This employs recording optical images of the stellar field next to the source position, which provides a better than 10% accuracy for the transmission measurements. Results. We demonstrate that MAGIC very large zenith angle observations yield a collection area larger than a square kilometer. In only ~ 56 h of observations, we detect the γ-ray emission from the Crab Nebula up to 100 TeV, thus providing the highest energy measurement of this source to date with Imaging Atmospheric Cherenkov Telescopes. Comparing accumulated and archival MAGIC and Fermi/LAT data with some of the existing emission models, we find that none of them provides an accurate description of the 1 GeV to 100 TeV γ-ray signal