Moharana, Reetanjali

Cosmic ray (CR) anisotropy of several scales have been observed over the last decade by a number of experiments located in the Northern and Southern hemispheres. The GRAPES-3 experiment, located at 11.4◦ N can observe a significant portion of both the hemispheres and covers about 56% of the sky at TeV energies. Several small-scale anisotropic features, with a strength of ∼ 10−4 − 10−3, have been observed using four years of GRAPES-3 data collected within a period of 2013-2016, by using the method of time-scrambling. Two striking hot-spot regions have been observed with a significance of more than 4σ. These structures are consistent with the observations reported by Milagro, ARGO-YBJ and HAWC. These structures, their characteristic features and a comparison of results from other experiments are described in this work.

The GRAPES-3 is an extensive air shower array located in Ooty (11.4◦ N, 76.7◦ E), designed to study cosmic rays and gamma rays at TeV-PeV energies. The compact array of scintillator detectors coupled with a mid-latitude location and shower front curvature corrections enable an angular resolution of ∼0.5 degrees above 50 TeV energies, as verified using the Moon shadow method. Furthermore, GRAPES-3 is equipped with a large area (560 m2) muon telescope (called G3MT) to determine the muon content of the recorded air showers. Since large muon content is a defining feature of cosmic ray initiated air showers, G3MT is useful in estimating the muon content and rejecting the overwhelming cosmic ray background. Using both the features of good angular resolution and gamma-hadron separation using the muon content, a search for very high energy (E > 50 TeV) gamma rays from the Crab Nebula is under progress. We have used ten years (2013-2022) of air shower data for this analysis. The detailed methodology, current status, and future plans for detecting point gamma ray sources will be discussed.

The GRAPES-3 extensive air shower consisting of a dense scintillator array and a 560 m2 area tracking muon detector is designed to study the cosmic ray energy spectrum and composition over the knee region. Another muon telescope similar to the existing one is under construction and one of its module is already operational. Since the muon content is a sensitive parameter of the cosmic ray primary composition, with the doubling of the area of the expanded muon detector, the mass separation of the different primary cosmic rays is expected to be improved at low energy when the muon density is low. In this paper we present our simulation studies of the sensitivity of the expanded muon telescope to the primary composition over 10-100 TeV by studying muon multiplicity distributions (MMDs) . We used CORSIKA for shower simulation and GEANT-4 for simulating the detector response.

An orphan very-high-energy gamma-ray flare from 3C 279 was reported on 28 January 2018, however, it was not accompanied by a Fermi-LAT flare. This VHE orphan flare was reported by the High Energy Stereoscopic System (H.E.S.S) telescope Eleven days after the Fermi-LAT flare. Distinct mechanisms from regular gamma-ray flares must produce orphan flares. A coherent explanation for this phenomenon, the proton synchrotron, and electron synchrotron with External Compton(EC) have been put forth.

The GRAPES-3 experiment consists of a densely packed array of 400 plastic scintillator detectors and a large area (560 m2) muon telescope. It measures cosmic rays in an energy range of several TeV to over 10 PeV with a trigger efficiency of more than 90% for proton primaries above 40 TeV, providing a substantial overlap with space based direct experiments. The scintillator array records the particle density and arrival time of the shower secondaries, which were used to estimate the shower parameters. The muon telescope is dedicated to recording the muon component in the shower. The observed muon multiplicity distributions (MMDs) were used for precise measurements of the average nuclear composition for proton, helium, nitrogen, aluminium, and iron primaries, independent of making assumptions about the primary composition. In the present work, Gold’s unfolding algorithm was used to extract the nuclear composition and obtain the proton energy spectrum with the help of simulation based on QGSJET-II-04/FLUKA hadronic interaction models. Details of the analysis and results for the extracted composition and proton energy spectrum below the Knee will be presented.

Compared to satellites and balloon-borne experiments, ground based air shower detectors enjoy larger fields-of-view and higher effective areas, making them ideal for studies of gamma rays above TeV energies. The Gamma Ray Astronomy at PeV EnergieS Phase-3 (GRAPES-3) experiment is an extensive air shower (EAS) array located in Ooty, India, with ∼400 densely packed scintillator detectors accompanied by a 560 m2 muon telescope. With the recent improvement in the angular resolution and an effective background rejection efficiency, the GRAPES-3 experiment has an excellent ability to study gamma-ray sources in the ultra-high energy (UHE) regime. In this work, we will present the acceptance of the GRAPES-3 towards gamma-ray-initiated showers, studied using CORSIKA simulated data.

The GRAPES-3 experiment consists of a large area (560m2) muon telescope consisting of 3712 proportional counters of each dimension of 6m × 0.1m × 0.1m. A similar muon telescope next to the existing one is under construction. The new muon telescope is designed to have a 70% larger field of view (2.3 sr to 3.9 sr) as compared to the existing one. One of the 16 modules of the new muon telescope has been made operational. The energy threshold is 0.5 GeV for vertically incident muons. In this paper, we present our GEANT-4 simulation results of muon energy deposition and angular distributions using the new muon telescope of GRAPES-3, as well as the results of the muon module rate for incoming muons with GRAPES-3 data.

The first Gravitational Wave was discovered on September 14, 2015, by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO), and since then, we have observed 93 such events significantly. With these 93 events, we have studied the classification based on their parameters using Generalized Linear Models (GLM) and Gaussian Mixture Models (GMM). GMM is a mixture of the weighted sum of different Gaussian distributions that describe the number of classes in the data. GLM is a statistical modeling technique identifying various relationships between a response variable and predictor variables. These relationships can be normal, linear, logistic, Poisson, exponential, etc.

We present the measurement of the cosmic ray proton spectrum from 50 TeV to 1.3 PeV using 7.81×106 extensive air shower events recorded by the ground-based GRAPES-3 experiment between 1 January 2014 and 26 October 2015 with a live time of 460 day. Our measurements provide an overlap with direct observations by satellite and balloon-based experiments. The electromagnetic and muon components in the shower were measured by a dense array of plastic scintillator detectors and a tracking muon telescope, respectively. The relative composition of the proton primary from the air shower data containing all primary particles was extracted using the multiplicity distribution of muons which is a sensitive observable for mass composition. The observed proton spectrum suggests a spectral hardening at ∼166 TeV and disfavors a single power law description of the spectrum up to the Knee energy (∼3 PeV).

Gamma-ray bursts (GRBs) can be studied with their linearly dependent parameters alongside the standard distribution. The generalized linear model (GLM) identifies the number of linear dependences in a two-parameter space. Classically, GRBs are classified into two classes by the presence of bimodality in the histogram of. However, additional classes and different features of GRBs are fascinating topics to explore. In this work, we investigate GRB features in the plane using the GLM for three major catalogues: Swift, the Fermi Gamma-ray Burst Monitor (GBM), and the Burst And Transient Source Experiment (BATSE). This study shows five linear features for the Fermi GBM catalogue and four linear features for the BATSE catalogue, directing us towards the possibility of non-Gaussianity in the light curves of GRBs.