arXiv subjects

Mradul Sharma

Publications and source records attributed to Mradul Sharma.

5 recordsLinked to original sources

arXiv2017

Sensitivity estimate of the MACE gamma ray telescope

The MACE (Major Atmospheric Cherenkov Experiment) is a 21 m diameter gamma-ray telescope which is presently being installed at Hanle in Ladakh, India (32^0 46^' 46^" N, 78^0 58^' 35^" E) at an altitude of 4270 m a.s.l. Once operational, it will become the highest altitude very high energy (VHE) gamma-ray telescope in the world based on Imaging Atmospheric Cherenkov Technique (IACT). In the present work, we discuss the sensitivity estimate of the MACE telescope by using a substantially large Monte Carlo simulation database at 5^0 zenith angle. The sensitivity of MACE telescope is estimated by carrying out the gamma-hadron segregation using the Random Forest method. It is estimated that the MACE telescope will have an analysis energy threshold of 38 GeV for image intensities above 50 photoelectrons. The integral sensitivity for point like sources with Crab Nebula-like spectrum above 38 GeV is ~2.7% of Crab Nebula flux at 5 sigma statistical significance level in 50 hrs of observation.

astro-ph.IM↗

arXiv2014

Gamma/hadron segregation for a ground based imaging atmospheric Cherenkov telescope using machine learning methods: Random Forest leads

A detailed case study of $γ$-hadron segregation for a ground based atmospheric Cherenkov telescope is presented. We have evaluated and compared various supervised machine learning methods such as the Random Forest method, Artificial Neural Network, Linear Discriminant method, Naive Bayes Classifiers,Support Vector Machines as well as the conventional dynamic supercut method by simulating triggering events with the Monte Carlo method and applied the results to a Cherenkov telescope. It is demonstrated that the Random Forest method is the most sensitive machine learning method for $γ$-hadron segregation.

astro-ph.IM↗

arXiv2014

Validation of a new background discrimination method for the TACTIC TeV $γ$-ray telescope with Markarian 421 data

This paper describes the validation of a new background discrimination method based on Random Forest technique by re-analysing the Markarian 421 (Mrk 421) observations performed by the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera) gamma-ray telescope. The Random Forest technique is a flexible multivariate method which combines Bagging and Random Split Selection to construct a large collection of decision trees and then combines them to construct a common classifier. Markarian 421 in a high state was observed by TACTIC during December 07, 2005 - April 30, 2006 for 202 h. Previous analysis of this data led to a detection of flaring activity from the source at Energy $ >$ 1 TeV. Within this data set, a spell of 97 h revealed strong detection of a gamma-ray signal with daily flux of > 1 Crab unit on several days. Here we re-analyze this spell as well as the data from the entire observation period with the Random Forest method. Application of this method led to an improvement in the signal detection strength by $\sim 26\%$ along with a $\sim 18\%$ increase in detected $γ$ rays compared to the conventional Dynamic Supercuts method. The resultant differential spectrum obtained is represented by a power law with an exponential cut off $Γ= -2.51 \pm 0.10$ and $E_{0} = 4.71 \pm 2.20$ TeV. Such a spectrum is consistent with previously reported results and justifies the use of Random Forest method for analyzing data from atmospheric Cherenkov telescopes.

astro-ph.HE↗

arXiv2010

High-growth-rate magnetohydrodynamic instability in differentially rotating compressible flow

The transport of angular momentum in the outward direction is the fundamental requirement for accretion to proceed in an accretion disc. This objective can be achieved if the accretion flow is turbulent. Instabilities are one of the sources for the turbulence. We study a differentially rotating compressive flow in the presence of non vanishing radial and azimuthal magnetic field and demonstrate the occurrence of a high growth rate instability. This instability operates in a region where magnetic energy density exceeds the rotational energy density.

astro-ph.GA↗

arXiv2008

Magnetohydrodynamic instability in differentially rotating compressible flow

Transport of angular momentum is one of the thrust areas of astrophysical flows. Instabilities and hence the turbulence generated by it has been invoked to understand its role in angular momentum transport in hydrodynamic and magnetohydrodynamic regime. Investigation of an unexplored region described by the parameter space $Ω_e^2 < 0$, $Ω_e$ being the epicyclic frequency, resulted in a powerful magnetohydrodynamic instability. The growth rate of this instability is rather large and is found to depend on the wavenumber.

astro-ph↗