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The GRAPES-3 is a near-equatorial extensive air shower experiment, located in Ooty, India at an altitude of 2200 m above mean sea level. It consists of a dense array of 400 scintillator detectors of 1 m$^{2}$ area each with 8 m inter separation. The array triggers showers induced by cosmic ray and gamma ray primaries in the TeV-PeV energy range. An associated muon telescope of 560 m$^2$ area is designed to record muons above 1 GeV energy in the triggered showers. Additionally, it is designed to trigger on individual muons, providing measurement of muon flux with a statistics of $\sim$4$\times$10$^{9}$ muons per day and an average angular resolution of 4$^{\circ}$. In this paper, we summarize the recent results obtained using air shower data on cosmic ray energy spectrum and composition below the Knee, cosmic ray anisotropy, angular resolution, gamma ray source searches and thunderstorm phenomena using the muon flux data.

The GRAPES-3 extensive air shower (EAS) array located at Ooty is equipped with 400 plastic scintillator detectors spread over an area of 25000 m$^2$ and a muon telescope of area 560 m$^2$ built with 3,712 proportional counters. One of its principal objectives is to measure the primary cosmic ray energy spectrum in the TeV-PeV energy region. The response of the photo-multiplier tubes (PMTs) used in the plastic scintillator detectors becomes nonlinear at densities $>$ 50 particles per m$^2$ in large EAS. We describe a technique to correct for the nonlinearity of these PMTs, thereby extending the dynamic range of the detector for observed particle densities up to 5000 particles per m$^2$. The details of the technique will be presented.

A diffuse gamma-ray emission at $\sim$100 TeV can be expected as a result of the interactions of ultra-high-energy cosmic rays (UHECRs) with the cosmic microwave background (CMB) during their propagation. This radiation carries the information on the distribution of energetic sources and hence the cosmological evolution of the universe. The GRAPES-3 is an extensive air shower (EAS) array, located at Ooty in southern India. It consists of 400 plastic scintillators (each 1 m$^2$) and a large area (560 m$^2$) muon telescope. The muon telescope has the ability to differentiate the gamma-rays from charged cosmic rays through their muon content. We report on the study of isotropic diffuse gamma-ray flux from GRAPES-3 over 10-300 TeV.

The GRAPES-3 experiment located in Ooty consists of an array of 400 plastic scintillator detectors spread over an area of 25000𝑚 2 and a large area (560 𝑚 2 ) muon telescope. Every day, the array records about 3 million showers induced by the interaction of primary cosmic rays in the atmosphere. One of the primary objectives of the experiment is to measure the energy spectrum and composition of the cosmic rays in the TeV-PeV energy range. However, some of the detected showers have cores outside the array. This fraction increases with energy due to the higher lateral spread of shower particles at higher energies. Identifying these events is thus crucial for accurate measurement of the cosmic ray energy spectrum. This work will describe simple cut based as well as machine learning based strategies for identifying and excluding such events and their impact on the cosmic ray energy spectrum as measured by the Bayesian unfolding technique.

The Gamma Ray Astronomy at PeV EnergieS phase-3 (GRAPES-3) experiment is located at Ooty in India (11.4$^{\circ}$ N, 76.7$^{\circ}$ E and 2200 m above m.s.l.). It consists of a densely packed array of 400 plastic scintillator detectors and a large area muon telescope (560 m$^{2}$). It measures cosmic rays from several TeV to over 10 PeV energies providing a substantial overlap with direct experiments while covering the knee region. Shower parameters are reconstructed by fitting the observed particle densities with the NKG lateral distribution function (LDF). For this analysis, the QGSJET-II-04 hadronic interaction model is used to generate the air shower simulation data for proton, helium, nitrogen, aluminium, and iron primaries. Precise measurements of the average nuclear composition are obtained by fitting muon multiplicity distributions (MMDs) for all simulated primaries with the MMDs measured by the muon telescope. Details of the analysis and preliminary results for the extracted composition and elemental energy spectrum for proton and helium from a few tens of TeV to a few PeV will be presented.

The deflection of cosmic rays (CRs) in the interstellar magnetic field results in an almost isotropic flux as observed on Earth. However, an anisotropy has been observed at the level of ∼ 10^{-4} − 10^{-3}. The GRAPES-3 experiment located at Ooty, India consists of an array of 400 plastic scintillator detectors. It measures the particle densities and their relative arrival times in extensive air showers produced by the CRs. This information collected is then reconstructed to obtain the energy and direction of the primary CRs. The near-equatorial location of GRAPES-3 provides an opportunity to study this anisotropy in both hemispheres of the celestial sphere in the TeV-PeV energy range. However, detector and atmospheric effects that induce a few per cent change in the primary CR flux are challenges to be addressed. This work describes the use of the time scrambling method to address some these systematics and observe anisotropy.

The Moon acts as a shield against the cosmic rays, preventing them from reaching the earth, which gives rise to a deficit in the flux along the direction of the Moon. The observed deficit can be used for obtaining the absolute calibration of the angular resolution and to verify the pointing accuracy of the array. GRAPES-3 is an extensive air shower experiment located at Ooty, India consisting of a dense array of scintillator detectors. It records $\sim$$10^9$ showers per year with a median energy of 10 TeV. With the precise determination of the arrival time of shower particles and an accurate correction for the shower front curvature, a major improvement in the angular resolution of the array has been achieved. This was done by the array division methods including the left-right and even-odd methods. Here, we present a verification of the angular resolution estimates and the pointing accuracy by observing shadow of the Moon in the cosmic ray flux.

The GRAPES-3 is a high-altitude, near-equator extensive air shower array at Ooty, India which is designed to observe cosmic and gamma-rays in TeV-PeV energy range. It consists of a dense array of 400 scintillator detectors operating in conjunction with a 560 $m^2$ area muon telescope. Due to recent improvements in the measurements of shower arrival time and corrections for shower front curvature based on shower size and age, the angular resolution of the array has been significantly improved. By leveraging the resultant improved angular resolution and an efficient rejection of the cosmic ray background using the muon content of the shower, a search for gamma-rays above 30 TeV from the Crab Nebula has been performed. The results will be presented during the conference.

The GRAPES-3 experiment reported the measurement of 1.3 GV potential across one of the massive thunderclouds recorded on 1 December 2014 by making use of the muon imaging technique. This measurement is ten times larger than the maximum potential reported previously by balloon and rocket sounding measurements, verifying the almost a century old prediction by C.T.R. Wilson. These measurements rely on the precise estimate of the change in the angular muon flux caused by the acceleration of muons during their passage through the charged layers of thunderstorms. The electric potential is estimated with the help of Monte Carlo simulations by using CORSIKA and other in-house tools. A study of the thunderstorms events recorded since April 2011 displays an asymmetry in their azimuthal distribution which can be understood to be caused by the ratio of $\mu^+$/$\mu^-$.

The large area 560\,m$^2$ directional muon telescope at Gamma Ray Astronomy at PeV Energies phase -3 (GRAPES-3) experiment in Ooty, India was designed primarily to study the extensive air showers (EAS) and made operational in year 1998. It has turned out to be an unique instrument to make fascinating study of exotic phenomenon by introduction of a new parallel data acquisition system (DAQ) in year 2000 to measure the muon directional flux. The recent discoveries of transient weakening of Earth’s magnetic shield probed by a Cosmic Ray Burst and measurement of the electrical properties of a thundercloud through muon imaging has demonstrated the capabilities of this instrument. The design of new triggerless muon data acquisition system (TM-DAQ) using Field-programmable gate array (FPGA) would enhance the present capabilities and open a new window on several physics fronts such as, a) precise measurement of the muon flux for thunderstorm studies, b) study of large angle EAS using the muon component, c) search for exotic particles characterized by early or delayed arrivals. We present here the key salient features of the TM-DAQ along with initial observations.

The large area muon telescope of GRAPES-3 has been operating continuously for more than two decades with a DAQ which has several limitations. At present, this DAQ is in the process of being upgraded with a FPGA based system. The new DAQ system is designed to be triggerless and capable of recording every hit from the 3712 proportional counters along with a time-stamp (10 ns accuracy) which has significantly expanded the physics horizon of the experiment. This triggerless feature allows the detection of muons beyond the nominal zenith range of the current system ($\theta$$

A large area (560 m^2) muon telescope in the GRAPES-3 experiment at Ooty, India records muon intensity at high cutoff rigidities (Rc) varies from 14–32 GV along 169 independent directions spanning a field of view of 2.3 sr. The threshold energy of the recorded muons is sec(theta) GeV along a direction with a zenith angle (theta) and with the average angular accuracy of∼4 degrees. The directional capabilities of the muon telescope are exploited for studying the effect of atmospheric pressure on the muon flux as a function of Rc. It is observed that the barometric coefficient relationship with logarithmic Rc can be well described by a second order polynomial function with a high Spearman Rank correlation coefficient of 0.99

The GRAPES-3 experiment is designed to perform precision studies of gamma-ray sources in the TeV-PeV energy region. It consists of 400 plastic scintillator detectors spanning an effective area of 25000 m^2 and a large area (560 m^2) muon telescope which records ∼4 x 10^9 muons every day. With the recent installation of an improved triggerless data acquisition (DAQ) system, the information related to every muon is recorded with a timing resolution of 10 ns. The angular resolution and pointing accuracy of the upgraded muon telescope has been validated by characterizing the shadow of the moon among recorded muons. Here, the details of the analysis and results, as well as the simulation studies to account for the deflection of the particles in the Earth’s magnetic field will be presented.

Following the GRAPES-3 discovery of a transient weakening of Earth's magnetic shield through observation of a cosmic ray burst on 22 June 2015, we have been involved in an effort to search for more such events in 20 years of archived data. An important step in analyzing the data is to simulate the cosmic ray trajectories in the geomagnetic field influenced by the interplanetary magnetic field during a geomagnetic storm. The simulation of 22 June 2015 burst required over two months of running time on the 1280 core GRAPES-3 computer cluster in Ooty. We have developed a fast, efficient technique which has allowed us to simulate the 22 June 2015 event in a fraction of a second with the same resolution as the earlier computational-intensive method. This has laid the foundation for quick analysis of a large number of such events in archival data, and of future events virtually in real-time. Details of this method will be presented during the conference.

The GRAPES-3 experiment, a high-density extensive air shower (EAS) array located at Ooty, India is designed for high precision measurements of cosmic ray energy spectrum and nuclear composition in energy range of 10^13 - 10^16 eV . It consists of tightly packed 1 m 2 area 400 plastic scintillation detectors covering an effective area of 25,000 m^2. The trigger rate and particle density measured by EAS array shows strong correlation with the atmospheric parameters such as the pressure and temperature. By employing linear regression, and Fast Fourier Transform techniques, the pressure and temperature coefficients for the dependence of trigger rate and particle density, respectively were obtained. Thereafter, by applying corrections for these effects the contribution of atmospheric effects was largely eliminated in the EAS data. These corrections are expected to result in a better measurement of EAS parameters which will be presented during the conference.