Talk at the 24th European Cosmic Ray Symposium ECRS2014, Kiel (Germany)September 1 - 5, 2014. arXiv admin note: substantial text overlap with arXiv:1407.8462
The ARGO-YBJ experiment has been in stable data taking for 5 years at the YangBaJing Cosmic Ray Observatory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm$^2$). With a duty-cycle greater than 86\% the detector collected about 5$\times $10$^{11}$ events in a wide energy range, from few hundreds GeV up to about 10 PeV. A number of open problems in cosmic ray physics has been faced exploiting different analyses. In this paper we summarize the latest results in cosmic ray physics and in gamma-ray astronomy.
The ARGO-YBJ experiment is a multipurpose detector exploiting the full-coverage approach at very high altitude. The apparatus is in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm$^2$). In this paper we report the main results in Gamma-Ray Astronomy and Cosmic Ray Physics after about 3 years of operations.
In this paper we report on the observation of the anisotropy of cosmic ray arrival direction at different angular scales with ARGO-YBJ. Evidence of new few-degree excesses throughout the sky region 195$^{\circ}\leq$ R.A. $\leq$ 315$^{\circ}$ is presented for the first time. We report also on the measurement of the light-component (p+He) spectrum of primary cosmic rays in the range 5 - 200 TeV.
The ARGO-YBJ experiment is in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm$^2$). ARGO-YBJ is facing open problems in Cosmic Ray (CR) physics in different ways. The search for CR sources is carried out by the observation of TeV gamma-ray sources both galactic and extra-galactic. The CR spectrum, composition and anisotropy are measured in a wide energy range (TeV - PeV) thus overlapping for the first time direct measurements. In this paper we summarize the current status of the experiment and describe some of the scien…
Cosmic ray antiprotons provide an important probe for the study of cosmic ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. The ARGO-YBJ experiment is observing the Moon shadow with high statistical significance at an energy threshold of a few hundred GeV. Using all the data collected until November 2009, we set two upper limits on the antip/p flux ratio: 5% at an energy of 1.4 TeV and 6% at 5 TeV with a confidence level of 90%. In the few-TeV range the ARGO-YBJ results are the lowest available, useful to constrain models for antiproton product…
The ARGO-YBJ experiment has been in stable data taking for 5 years at the YangBaJing Cosmic Ray Observatory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm^2). With a duty-cycle greater than 86% the detector collected about 5 X 10^{11} events in a wide energy range, from few hundreds GeV up to the PeV. A number of open problems in cosmic ray physics has been faced exploiting different analyses. In this paper we summarize the latest results in gamma-ray astronomy and in cosmic ray physics
The ARGO-YBJ experiment is a multipurpose detector exploiting the full coverage approach at very high altitude. The apparatus, in stable data taking since November 2007 with an energy threshold of a few hundreds of GeV and a duty-cycle of about 90 %, is located at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm2). A number of interesting results are available in Cosmic Ray Physics and in Gamma Ray Astronomy after the first 3 years of stable data taking. In this paper Gamma-Ray Astronomy results are summarized.
The measurement of proton plus helium and all-particle energy spectra in the range $20\,$ TeV to $5 \,$PeV and $80 \,$TeV to $5 \,$PeV respectively are presented. Data taken by the ARGO-YBJ detector in the 2010 year have been analyzed. The ARGO-YBJ experiment (Tibet, P. R. China) has been taking data for more than five years by means of a full-coverage array of RPC detectors. The discrimination between showers produced by light and heavy primaries has been performed by looking at the lateral particle density close to the core region. A Bayesian unfolding technique was therefore applied to the …
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, inclu…
Cosmic ray antiprotons provide an important probe for the study of cosmic-ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm$^2$), is the only experiment exploiting the full coverage approach at very high altitude presently at work. The ARGO-YBJ experiment is particularly effective in measuring the cosmic ray antimatter content via the observation of the cosmic rays Moon shadowing effect. Based on all the data recorded during the …
ARGO-YBJ is a full coverage air shower array located at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300 m a.s.l., 606 g/cm^2) recording data with a duty cycle $\geq$85% and an energy threshold of a few hundred GeV. In this paper the latest results in Gamma-Ray Astronomy are summarized.
The measurement of the anisotropies of cosmic ray arrival direction provides important informations on the propagation mechanisms and on the identification of their sources. In this paper we report the observation of anisotropy regions at different angular scales. In particular, the observation of a possible anisotropy on scales between $\sim$ 10 $^{\circ}$ and $\sim$ 30 $^{\circ}$ suggests the presence of unknown features of the magnetic fields the charged cosmic rays propagate through, as well as potential contributions of nearby sources to the total flux of cosmic rays. Evidence of new weak…
The ARGO-YBJ (Astrophysical Radiation Ground-based Observatory at YangBaJing) experiment is designed for very high energy $γ$-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 followi…
The ARGO-YBJ detector, located at high altitude in the Cosmic Ray Observatory of Yangbajing in Tibet (4300 m asl, about 600 g/cm2 of atmospheric depth) provides the opportunity to study, with unprecedented resolution, the cosmic ray physics in the primary energy region between 10^{12} and 10^{16} eV. The preliminary results of the measurement of all-particle and light-component (i.e. protons and helium) energy spectra between approximately 5 TeV and 5 PeV are reported and discussed. The study of such energy region is particularly interesting because not only it allows a better understanding of…
Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called \emph{Moon shadow}). The Moon shadow is an important tool to determine the performance of an air shower array. In fact, the displacement of the shadow center, due to the bending effect of the Geomagnetic field on the propagation of cosmic rays, allows to set the energy scale of the primary particles inducing the showers observed by the detector. The shape of the shadow permits to determine the detector point spread function. The position of the deficit at high energy allows evaluating its pointing ac…
The combined measurement of the cosmic ray (CR) energy spectrum and anisotropy in their arrival direction distribution needs the knowledge of the elemental composition of the radiation to discriminate between different origin and propagation models. Important information on the CR mass composition can be obtained studying the EAS muon content through the measurement of the CR rate at different zenith angles. In this paper we report on the observation of the anisotropy of galactic CRs at different angular scales with the ARGO-YBJ experiment. We report also on the study of the primary CR rate fo…
Measuring the anisotropy of the arrival direction distribution of cosmic rays provides important information on the propagation mechanisms and the identification of their sources. In fact, the flux of cosmic rays is thought to be dependent on the arrival direction only due to the presence of nearby cosmic ray sources or particular magnetic-field structures. Recently, the observation of unexpected excesses at TeV energy down to angular scale as narrow as $\sim10°$ raised the possibility that the problem of the origin of galactic cosmic rays may be addressed by studying the anisotropy. The ARGO-…
The flaring activity of the Crab Nebula is one of the most puzzling phenomena of the gamma ray sky. The light curves in the energy range E >100 MeV show a high flux variability on time scales ranging from hours to weeks, with sharp emission peaks superimposed to long lasting smoother modulations, whose origin is still under debate. A long term observation of the Crab Nebula at TeV energies could add useful information to understand the mechanisms responsible of this unexpected behavior. The air shower detector ARGO-YBJ monitored the Crab Nebula in the energy range 0.5-20 TeV from November 2007…
The ARGO-YBJ experiment is an extensive air shower array with full coverage RPC detectors located at Yangbajing (4300 m asl, Tibet, China). It is operated with high duty cycle (>86%) and a large field of view ($\sim$ 2sr). It continuously monitors the entire overhead sky at $γ$-ray energies above 0.1 TeV. In the talk, we will present the result of the northern sky survey (between declinations of -10$^{\circ}$ and 70$^{\circ}$) from an analysis of ~4 years of the ARGO-YBJ data (between July 2006 and February 2011). There are four known TeV sources observed with significance greater than 5 S.D..…
ARGO-YBJ, located at the YangBaJing Cosmic Ray Observatory (4300 m a.s.l., Tibet, China), is a full coverage air shower array, with an energy threshold of 300 GeV for gamma-ray astronomy. Most of the recorded events are single front showers, satisfying the trigger requirement of at least 20 particles detected in a given time window. However, in 13% of the events, two randomly arriving showers may be recorded in the same time window, and the second one, in generally smaller, does not need to satisfy the trigger condition. These events are called double front shower events. By using these small …
The ARGO--YBJ experiment has been in stable data taking for more than five years at the Yangbajing cosmic ray observatory (Tibet, P.R. China, 4300 m a.s.l.). The detector collected about $5\times10^{11}$ events in a wide energy range from few TeVs up to the PeV region. In this work we summarize the latest results in cosmic ray physics particularly focusing on the cosmic ray energy spectrum. The results of the measurement of the all-particle and proton plus helium energy spectra in the energy region between $10^{12} - 10^{16}$ eV are discussed. A precise measurement of the cosmic ray energy spe…
ARGO-YBJ preliminary results of the measurements of the all-particle and light-component (i.e. protons and helium) cosmic ray energy spectra between approximately 5 TeV and 5 PeV are reported and discussed. The resulting all-particle spectrum (measured in the energy range 100TeV - 3PeV) is in good agreement with both theoretical parametrizations and previous measurements. The light-component (i.e. p + He) has been measured with high resolution up to about 5 PeV. The preliminary result is in agreement with direct measurements and then show a clear indication of a bending below 1PeV. Improvement…
The extended gamma ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for about 4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations. The peak of the signal is found at a position consistent with the pulsar PSR J1907+0602. Parametrizing the source shape with a two-dimensional Gauss function we estimate an extension σ= 0.49 \pm 0.22 degrees, consistent with a previous measurement by the Cherenkov Array H.E.S.S.. The observed energy spectrum is dN/dE = 6.1 \pm 1.4 \times 10^-13 (E/4 TeV)^{-2…
We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100 GeV in coincidence with the prompt emission detected by satellites using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R. China, 4300 m a.s.l.), active surface (about 6700 m**2 of Resistive Plate Chambers), and large field of view (about 2 sr, limited only by the atmospheric absorption), the ARGO-YBJ air shower detector is particularly suitable for the detection of unpredictable and short duration events su…
The ARGO-YBJ experiment is a full coverage air shower detector operated at the Yangbajing International Cosmic Ray Observatory. The detector has been in stable data taking in its full configuration since November 2007 to February 2013. The high altitude and the high segmentation and spacetime resolution offer the possibility to explore the cosmic ray energy spectrum in a very wide range, from a few TeV up to the PeV region. The high segmentation allows a detailed measurement of the lateral distribution, which can be used in order to discriminate showers produced by light and heavy elements. In…
This paper reports on the measurement of the large-scale anisotropy in the distribution of cosmic-ray arrival directions using the data collected by the air shower detector ARGO-YBJ from 2008 January to 2009 December,during the minimum of solar activity between cycles 23 and 24. In this period, more than 200 billion showers were recorded with energies between 1 and 30 TeV. The observed two-dimensional distribution of cosmic rays is characterized by two wide regions of excess and deficit, respectively, both of relative intensity 0.001 with respect to a uniform flux, superimposed on smaller size…
In this work, we investigate the axion-like particle (ALP)-photon oscillation effect in the spectra of the blazar Markarian 421 (Mrk 421) using 4.5 years of the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) and Fermi Large Area Telescope (Fermi-LAT) data. These data are collected during the common operation time, which cover ten activity phases of Mrk 421. No significant ALP-photon oscillation effect is confirmed. On the other hand, not all the observations of the ten phases can be individually used to set the 95% confidence level ($\rm C.L.$) constraint on the…
Cosmic ray antiprotons provide an important probe to study the cosmic ray propagation in the interstellar space and to investigate the existence of dark matter. Acting the Earth-Moon system as a magnetic spectrometer, paths of primary antiprotons are deflected in the opposite sense with respect to those of the protons in their way to the Earth. This effect allows, in principle, the search for antiparticles in the direction opposite to the observed deficit of cosmic rays due to the Moon (the so-called `Moon shadow'). The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory (Tibe…
Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important method to determine the performance of an air shower array. In fact, the westward displacement of the shadow centre, due to the propagation of cosmic rays in the geomagnetic field, allows to calibrate the energy scale of the primary particles observed by the detector. In addition, the shape of the shadow allows a measurement of the angular resolution and the position of the deficit at high energy allows the evaluation of the pointing accuracy of the detec…
Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called \emph{Moon shadow}). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at…
The geomagnetic field causes not only the East-West effect on the primary cosmic rays but also affects the trajectories of the secondary charged particles in the shower, causing their lateral distribution to be stretched along certain directions. Thus both the density of the secondaries near the shower axis and the trigger efficiency of a detector array decrease. The effect depends on the age and on the direction of the showers, thus involving the measured azimuthal distribution. Here the non-uniformity of the azimuthal distribution of the reconstructed events in the ARGO-YBJ experiment is dee…
A sky monitoring at gamma ray energy E > 0.6 TeV has been performed by the full coverage Extensive Air Shower detector ARGO-YBJ, located in Tibet at 4300 m of altitude. We monitored 135 galactic and extragalactic gamma ray sources in the sky declination band from -10 to +70 degrees for 424 days, detecting the Crab Nebula and Mrk421 with a significance respectively of 7.0 and 8.0 standard deviations. For a set of 11 AGNs known to emit in the TeV energy range, the search has been performed in time scales of 1, 10 and 30 days in order to study possible flaring activities. Significant emissions ha…
Cosmic ray antiprotons provide an important probe for the study of cosmic-ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. Cosmic rays are hampered by the Moon, therefore a deficit of cosmic rays in its direction is expected (the so-called "Moon shadow"). The Earth-Moon system acts as a magnetic spectrometer. In fact, due to the geomagnetic field the center of the Moon shifts westward by an amount depending on the primary cosmic ray energy. Paths of primary antiprotons are therefore deflected in an opposite sense in their way to the Earth. Thi…
The measurement of cosmic ray energy spectra, in particular for individual species, is an essential approach in finding their origin. Locating the "knees" of the spectra is an important part of the approach and has yet to be achieved. Here we report a measurement of the mixed Hydrogen and Helium spectrum using the combination of the ARGO-YBJ experiment and of a prototype Cherenkov telescope for the LHAASO experiment. A knee feature at 640+/-87 TeV, with a clear steepening of the spectrum, is observed. This gives fundamental inputs to galactic cosmic ray acceleration models.
Important informations on the origin and the propagation mechanisms of cosmic rays may be provided by the measurement of the anisotropies of their arrival direction. In this paper the observation of anisotropy regions at different angular scales is reported. In particular, the observation of a possible anisotropy on scales between $\sim10^{\circ}$ and $\sim30^{\circ}$ may be a key-detection for speculations on the presence of unknown features of the magnetic fields the charged cosmic rays propagate through, as well as to potential contributions of nearby sources to the total flux of cosmic ray…
The ARGO-YBJ experiment is a full-coverage air shower detector located at the Yangbajing Cosmic Ray Observatory (Tibet, People's Republic of China, 4300 m a.s.l.). The high altitude, combined with the full-coverage technique, allows the detection of extensive air showers in a wide energy range and offer the possibility of measuring the cosmic ray proton plus helium spectrum down to the TeV region, where direct balloon/space-borne measurements are available. The detector has been in stable data taking in its full configuration from November 2007 to February 2013. In this paper the measurement o…
As one of the most active blazars, Mrk421 is an excellent candidate for the study of the physical processes within the jets of AGN. Here we report on the extensive multi-wavelength observations of Mrk 421 over 4.5 years, from 2008 August to 2013 February. This source was simultaneously monitored by several experiments at different wavelengths: ARGO-YBJ in TeV $γ$-rays, $Fermi$-LAT in GeV $γ$-rays, $Swift$-BAT in hard X-rays, $RXTE$-ASM, $MAXI$ and $Swift$-XRT in soft X-rays, $Swift$-UVOT in ultraviolet, and OVRO in radio frequencies. In particular, thanks to the ARGO-YBJ and $Fermi$ data, the …
The ARGO-YBJ air shower detector monitored the Crab Nebula gamma ray emission from 2007 November to 2013 February. The integrated signal, consisting of $\sim$3.3 $\times$ 10$^5$ events,reached the statistical significance of 21.1 standard deviations. The obtained energy spectrum in the energy range 0.3-20 TeV can be described by a power law function dN/dE = I$_0$ (E / 2 TeV)$^{-α}$, with a flux normalization I$_0$ = (5.2 $\pm$ 0.2) $\times$ 10$^{-12}$ photons cm$^{-2}$ s$^{-1}$ TeV$^{-1}$ and $α$ = 2.63 $\pm$ 0.05, corresponding to an integrated flux above 1 TeV of 1.97 $\times$ 10$^{-11}$ pho…
In 2008, the blazar Mrk421 entered in a very active phase and was one of the brightest sources in the sky at TeV energies, showing strong and frequent flaring. We searched for gamma-ray emission at energies E > 0.8 TeV during the whole 2008 with the ARGO-YBJ experiment, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, P.R. China). The observed signal is not constant and in correlation with X-ray measurements. The average emission, during the active period of the source, was about twice the Crab Nebula level, with an integral flux of (4.9$\pm 2.0$)x 10$^{-11}$ ph…
We report on a measurement of thermal neutrons, generated by the hadronic component of extensive air showers (EAS), by means of a small array of EN-detectors developed for the PRISMA project (PRImary Spectrum Measurement Array), novel devices based on a compound alloy of ZnS(Ag) and $^{6}$LiF. This array has been operated within the ARGO-YBJ experiment at the high altitude Cosmic Ray Observatory in Yangbajing (Tibet, 4300 m a.s.l.). Due to the tight correlation between the air shower hadrons and thermal neutrons, this technique can be envisaged as a simple way to estimate the number of high en…
This paper is an overview of the author's PhD thesis results. ARGO-YBJ is an extensive air shower detector located at Yangbajing (Tibet, China) at 4300 m a.s.l. It is made by a full coverage carpet plus a guard ring (total surface about 6700 m^2) of Resistive Plate Chambers grouped into 153 units called clusters. The experiment has two different operation modes. The former, the scaler mode, counts the number of events with particle multiplicity >=1, >=2, >=3, >=4 allowing to reach the lowest energy threshold of the detector (few GeVs). The latter, the shower mode, measures coordinates and arri…
The ARGO-YBJ detector, located at the Yangbajing Cosmic Ray Laboratory (4300 m a. s. l., Tibet, China), was a full coverage air shower array dedicated to gamma ray astronomy and cosmic ray studies. The wide field of view (~ 2 sr) and high duty cycle (> 86%), made ARGO-YBJ suitable to search for short and unexpected gamma ray emissions like gamma ray bursts (GRBs). Between 2007 November 6 and 2013 February 7, 156 satellite-triggered GRBs (24 of them with known redshift) occurred within the ARGO-YBJ field of view. A search for possible emission associated to these GRBs has been made in the two e…
In 2008 the blazar Markarian 421 entered a very active phase and was one of the brightest sources in the sky at TeV energies, showing frequent flaring episodes. Using the data of ARGO-YBJ, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at gamma ray energies E > 0.3 TeV during the whole year. The observed flux was variable, with the strongest flares in March and June, in correlation with X-ray enhanced activity. While during specific episodes the TeV flux could be several times larger than the Crab Nebula one, the average emissio…
The search for Gamma Ray Burst (GRB) emission in the energy range 1-100 GeV in coincidence with the satellite detection has been carried out using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) experiment. The high altitude location (4300 m a.s.l.), the large active surface ($\sim$ 6700 m$^2$ of Resistive Plate Chambers), the wide field of view ($\sim 2~$sr, limited only by the atmospheric absorption) and the high duty cycle ($>$ 86 %) make the ARGO-YBJ experiment particularly suitable to detect short and unexpected events like GRBs. With the scaler mode tec…
The sun blocks cosmic ray particles from outside the solar system, forming a detectable shadow in the sky map of cosmic rays detected by the ARGO-YBJ experiment in Tibet. Because the cosmic ray particles are positive charged, the magnetic field between the sun and the earth deflects them from straight trajectories and results in a shift of the shadow from the true location of the sun. Here we show that the shift measures the intensity of the field which is transported by the solar wind from the sun to the earth.
We report the observation of TeV gamma-rays from the Cygnus region using the ARGO-YBJ data collected from 2007 November to 2011 August. Several TeV sources are located in this region including the two bright extended MGRO J2019+37 and MGRO J2031+41. According to the Milagro data set, at 20 TeV MGRO J2019+37 is the most significant source apart from the Crab Nebula. No signal from MGRO J2019+37 is detected by the ARGO-YBJ experiment, and the derived flux upper limits at 90% confidence level for all the events above 600 GeV with medium energy of 3 TeV are lower than the Milagro flux, implying th…
The ARGO-YBJ experiment, a full coverage extensive air shower (EAS) detector located at high altitude (4300 m a.s.l.) in Tibet, China, has smoothly taken data, with very high stability, since November 2007 to the beginning of 2013. The array consisted of a carpet of about 7000 m$^2$ Resistive Plate Chambers (RPCs) operated in streamer mode and equipped with both digital and analog readout, providing the measurement of particle densities up to few particles per cm$^2$. The unique detector features (full coverage, readout granularity, wide dynamic range, etc) and location (very high altitude) al…
The ARGO-YBJ detector is an extensive air shower array that has been used to monitor the northern $γ$-ray sky at energies above 0.3 TeV from 2007 November to 2013 January. In this paper, we present the results of a sky survey in the declination band from $-10^{\circ}$ to $70^{\circ}$, using data recorded over the past five years. With an integrated sensitivity ranging from 0.24 to $\sim$1 Crab units depending on the declination, six sources have been detected with a statistical significance greater than 5 standard deviations. Several excesses are also reported as potential $γ$-ray emitters. Th…
The events recorded by ARGO-YBJ in more than five years of data collection have been analyzed to determine the diffuse gamma-ray emission in the Galactic plane at Galactic longitudes 25° < l < 100° and Galactic latitudes . The energy range covered by this analysis, from ~350 GeV to ~2 TeV, allows the connection of the region explored by Fermi with the multi-TeV measurements carried out by Milagro. Our analysis has been focused on two selected regions of the Galactic plane, i.e., 40° < l < 100° and 65° < l < 85° (the Cygnus region), where Milagro observed an excess with respect to the predictio…
This paper reports on the observation of the sidereal large-scale anisotropy of cosmic rays using data collected by the ARGO-YBJ experiment over 5 years (2008$-$2012). This analysis extends previous work limited to the period from 2008 January to 2009 December,near the minimum of solar activity between cycles 23 and 24.With the new data sample the period of solar cycle 24 from near minimum to maximum is investigated. A new method is used to improve the energy reconstruction, allowing us to cover a much wider energy range, from 4 to 520 TeV. Below 100 TeV, the anisotropy is dominated by two wid…
We report the observation of a very high energy γ-ray source, whose position is coincident with HESS J1841-055. This source has been observed for 4.5 years by the ARGO-YBJ experiment from November 2007 to July 2012. Its emission is detected with a statistical significance of 5.3 standard deviations. Parameterizing the source shape with a two-dimensional Gaussian function we estimate an extension σ=(0.40(+0.32,-0.22}) degree, consistent with the HESS measurement. The observed energy spectrum is dN/dE =(9.0-+1.6) x 10^{-13}(E/5 TeV)^{-2.32-+0.23} photons cm^{-2} s^{-1} TeV^{-1}, in the energy ra…
The hadronic interaction of cosmic rays with solar atmosphere can produce high energy gamma rays. The gamma-ray luminosity is correlated both with the flux of primary cosmic rays and the intensity of the solar magnetic field. The gamma rays below 200 GeV have been observed by $Fermi$ without any evident energy cutoff. The bright gamma-ray flux above 100 GeV has been detected only during solar minimum. The only available data in TeV range come from the HAWC observations, however outside the solar minimum. The ARGO-YBJ dataset has been used to search for sub-TeV/TeV gamma rays from the Sun durin…
ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. It is operated with a high duty cycle and a large field of view. It continuously monitors the northern sky at energies above 0.3 TeV. In this paper, we report a long-term monitoring of Mrk 421 over the period from 2007 November to 2010 February. This source was observed by the satellite-borne experiments Rossi X-ray Timing Explorer and Swift in the X-ray band. Mrk 421 was especially active in the first half of 2008. Many flares are observed in both X-ray and gamma-ray bands simultaneously. The gamm…
We report on the extensive multi-wavelength observations of the blazar Markarian 421 (Mrk 421) covering radio to gamma-rays, during the 4.5 year period of ARGO-YBJ and Fermi common operation time, from August 2008 to February 2013. In particular, thanks to the ARGO-YBJ and Fermi data, the whole energy range from 100 MeV to 10 TeV is covered without any gap. In the observation period, Mrk 421 showed both low and high activity states at all wavebands. The correlations among flux variations in different wavebands were analyzed. Seven large flares, including five X-ray flares and two GeV gamma-ray…
A correlation between the secondary cosmic ray flux and the near-earth electric field intensity, measured during thunderstorms, has been found by analyzing the data of the ARGO-YBJ experiment, a full coverage air shower array located at the Yangbajing Cosmic Ray Laboratory (4300 m a. s. l., Tibet, China). The counting rates of showers with different particle multiplicities, have been found to be strongly dependent upon the intensity and polarity of the electric field measured during the course of 15 thunderstorms. In negative electric fields (i.e. accelerating negative charges downwards), the …
The extended TeV gamma-ray source ARGO J2031+4157 (or MGRO J2031+41) is positionally consistent with the Cygnus Cocoon discovered by $Fermi$-LAT at GeV energies in the Cygnus superbubble. Reanalyzing the ARGO-YBJ data collected from November 2007 to January 2013, the angular extension and energy spectrum of ARGO J2031+4157 are evaluated. After subtracting the contribution of the overlapping TeV sources, the ARGO-YBJ excess map is fitted with a two-dimensional Gaussian function in a square region of $10^{\circ}\times 10^{\circ}$, finding a source extension $σ_{ext}$= 1$^{\circ}$.8$\pm$0$^{\circ…
The knee phenomenon of the cosmic ray spectrum, which plays an important role in studying the acceleration mechanism of cosmic rays, is still an unsolved mystery. We try to reconcile the knee spectra measured by ARGO-YBJ and Tibet-III. A simple broken power-law model fails to explain the experimental data. Therefore a modified broken power-law model with non-linear acceleration effects is adopted, which can describe the sharp knee structure. This model predicts that heavy elements dominate at the knee.
While from the energetic point of view SNRs are viable sources of Galactic CRs, the issue of whether they can accelerate protons up to PeV remains unsolved. Here we discuss particle acceleration at the forward shock of SN and discuss the possibility that the escaping particle current may excite a non-resonant instability that in turn leads to the formation of resonant modes confining particles close to the shock and increasing the maximum energy. This mechanism works throughout the expansion of the SN explosion, from the ejecta dominated (ED) to the Sedov-Taylor (ST) phase. Because of their hi…
The distribution of cosmic rays in the Galaxy at energies above few TeVs is still uncertain and this affects the expectations for the diffuse gamma flux produced by hadronic interactions of cosmic rays with the interstellar gas. We show that the TeV gamma-ray sky can provide interesting constraints. Namely, we compare the flux from the galactic plane measured by Argo-YBJ, HESS, HAWC and Milagro with the expected flux due to diffuse emission and point-like and extended sources observed by HESS showing that experimental data can already discriminate among different hyphoteses for cosmic ray dist…
Monte Carlo simulations are performed to study the correlation between the ground cosmic ray intensity and near-earth thunderstorms electric field at YBJ (4300 m a.s.l., Tibet, China). The variations of the secondary cosmic ray intensity are found to be highly dependent on the strength and polarity of the electric field. In negative fields and in positive fields greater than 600 V/cm, the total number of ground comic ray positrons and electrons increases with increasing electric field strength. And these values increase more obviously when involving a shower with lower primary energy or a high…
In recent years very important results were obtained from cosmic ray experiments about the arrival direction distribution of primaries in the TeV energy range. As most of these particles are charged nuclei, they are deflected by the magnetic field they pass through before reaching the Earth surface, the effect of the Lorentz force being inversely proportional to the particle energy. As far as the local interstellar medium is known, the gyroradius of a 10 TeV proton is expected to be only 100 a.u., small enough to make the arrival direction distribution isotropic. Since 1930s a "large scale" (9…
