arXiv subjects

M. Sharma

Publications and source records attributed to M. Sharma.

At least 19 recordsLinked to original sources

arXiv2025

An energetic absorption outflow in QSO J1402+2330: Analysis of DESI observations

Context. Quasar outflows play a significant role in the active galactic nucleus (AGN) feedback, impacting the interstellar medium and potentially influencing galaxy evolution. Characterizing these outflows is essential for understanding AGN-driven processes. Aims. We aim to analyze the physical properties of the mini-broad absorption line outflow in quasar J1402+2330 using data from the Dark Energy Spectroscopic Instrument (DESI) survey. We seek to measure the outflows location, energetics, and potential impact on AGN feedback processes. Methods. In the spectrum of J1402+2330, we identify multiple ionic absorption lines, including ground and excited states. We measure the ionic column densities and then use photoionization models to determine the total hydrogen column density and ionization parameter of the outflow. We utilized the population ratio of the excited state to the ground state of N iii and S iv to determine the electron number density. Results. The derived electron number density, combined with the ionization parameter, indicates an outflow distance of approximately 2200 pc from the central source. Having a mass outflow rate of more than one thousand solar masses per year and a kinetic energy output exceeding 5 percent of the Eddington luminosity, this outflow can significantly contribute to AGN feedback. Conclusions. Our findings suggest the absorption outflow in J1402+2330 plays a potentially significant role in AGN feedback processes. This study highlights the value of DESI data in exploring AGN feedback mechanisms.

astro-ph.GA↗

arXiv2025

The ultraviolet luminosity function of star-forming galaxies between redshifts of 0.4 and 0.6

We combine ultraviolet imaging of the 13H survey field, taken with the XMM-Newton Optical Monitor telescope (XMM-OM) and the Neil Gehrels Swift Observatory Ultraviolet and Optical Telescope (UVOT) in the UVM2 band, to measure rest-frame ultraviolet 1500A luminosity functions of star-forming galaxies with redshifts between 0.4 and 0.6. In total the UVM2 imaging covers a sky area of 641 square arcmin, and we detect 273 galaxies in the UVM2 image with 0.4<z<0.6. The luminosity function is fit by a Schechter function with best-fit values for the faint end slope alpha = -1.8 +0.4 -0.3 and characteristic absolute magnitude M* = -19.1 +0.3 -0.4. In common with XMM-OM based studies at higher redshifts, our best-fitting value for M* is fainter than previous measurements. We argue that the purging of active galactic nuclei from the sample, facilitated by the co-spatial X-ray survey carried out with XMM-Newton is important for the determination of M*. At the brightest absolute magnitudes (M1500<-18.5) the average UV colour of our galaxies is consistent with that of minimal-extinction local analogues, but the average UV colour is redder for galaxies at fainter absolute magnitudes, suggesting that higher levels of dust attenuation enter the sample at absolute magnitudes somewhat fainter than M*.

astro-ph.GA↗

arXiv2024

Very High-energy Gamma-Ray Episodic Activity of Radio Galaxy NGC 1275 in 2022-2023 Measured with MACE

The radio galaxy NGC 1275, located at the central region of Perseus cluster, is a well-known very high-energy (VHE) gamma-ray emitter. The Major Atmospheric Cherenkov Experiment Telescope has detected two distinct episodes of VHE (E > 80 GeV) gamma-ray emission from NGC 1275 during 2022 December and 2023 January. The second outburst, observed on 2023 January 10, was the more intense of the two, with flux reaching 58$\%$ of the Crab Nebula flux above 80 GeV. The differential energy spectrum measured between 80 GeV and 1.5 TeV can be described by a power law with a spectral index of $\Gamma = - 2.90 \pm 0.16_{stat}$ for both flaring events. The broadband spectral energy distribution derived from these flares, along with quasisimultaneous low-energy counterparts, suggests that the observed gamma-ray emission can be explained using a homogeneous single-zone synchrotron self-Compton model. The physical parameters derived from this model for both flaring states are similar. The intermediate state observed between two flaring episodes is explained by a lower Doppler factor or magnetic field, which subsequently returned to its previous value during the high-activity state observed on 2023 January 10.

astro-ph.HE↗

arXiv2023

On the Dust properties of the UV galaxies in the redshift range $z \sim 0.6-1.2$

Far-infrared observations from the \textit{Herschel Space Observatory} are used to estimate the infrared (IR) properties of ultraviolet-selected galaxies. We stack the PACS (100, 160 $\mu \mathrm{m}$) and SPIRE (250, 350 and 500$\mu \mathrm{m}$) maps of the Chandra deep field south (CDFS) on a source list of galaxies selected in the rest-frame ultraviolet (UV) in a redshift range of $0.6-1.2$. This source list is created using observations from the XMM-OM telescope survey in the CDFS using the UVW1 (2910 {\AA}) filter. The stacked data are binned according to the UV luminosity function of these sources, and the average photometry of the UV-selected galaxies is estimated. By fitting modified black bodies and IR model templates to the stacked photometry, average dust temperatures and total IR luminosity are determined. The luminosity-weighted average temperatures are consistent with a weak trend of increasing temperature with redshift found by previous studies. Infrared excess, unobscured, and obscured star formation rate (SFR) values are obtained from the UV and IR luminosities. We see a trend in which dust attenuation increases as UV luminosity decreases. It remains constant as a function of IR luminosities at fixed redshift across the luminosity range of our sources. In comparison to local luminous infrared galaxies with similar SFRs, the higher redshift star-forming galaxies in the sample show a lesser degree of dust attenuation. Finally, the inferred dust attenuation is used to correct the unobscured SFR density in the redshift range $0.6-1.2$. The dust-corrected SFR density is consistent with measurements from IR-selected samples at similar redshifts.

astro-ph.GA↗

arXiv2022

On the bright-end of the UV luminosity functions of galaxies at $z \sim 0.6-1.2$

We derive the Ultra-Violet (UV) luminosity function (LF) of star-forming galaxies in the redshift range $z = 0.6 - 1.2$, in the rest-frame far-UV ($1500$ \r{A}) wavelength. For this work, we are in particular interested in the bright end of the UV LF in this redshift range. Data from the XMM-Newton Optical Monitor (XMM-OM), near-ultraviolet ($2410-3565$ \r{A}) observations over 1.5 sq. deg of the COSMOS field are employed for this purpose. We compile a source-list of $879$ sources with $UVW1_\mathrm{AB}$ in the range $\sim 21-24$ mags from the wide-area UVW1 image of the COSMOS field in the two bins $0.6 \leq z \leq 0.8$ and $0.8 \leq z \leq 1.2$. The $M_{1500}$ for these sources lies in the interval $[-19.10,-22.50]$. We use the maximum likelihood to fit a Schechter function model to the un-binned data to estimate the parameters (faint-end slope, characteristic magnitude, and normalisation) of the Schechter function. We find the shape of the LF to be consistent with the Schechter model, and the parameters are in fair agreement with other studies conducted using direct measurements of the $1500$\r{A} flux. We see a brightening of the characteristic magnitude as we move from lower ($0.7$) to higher ($1.0$) redshift. The measures for luminosity density are within the error margins of past studies. We examine the brightest sources in our sample for the AGN contribution. These sources are characterised by their spectral energy distributions, integrated infrared luminosities, and morphologies. We also explore their overlap with the brightest IR galaxies in a similar redshift range.

astro-ph.GA↗

arXiv2022

Coaxial tungsten hot plate-based cathode source for Cesium plasma production confined in MPD device

A Multi-dipole line cusp configured Plasma Device (MPD) having six electromagnets with embedded Vacoflux-50 as a core material and a hot filament-based cathode for Argon plasma production has been characterized by changing the pole magnetic field values. For the next step ahead, a new tungsten ionizer plasma source for contact ionization cesium plasma has been designed, fabricated, and constructed and thus plasma produced will be confined in MPD. An electron bombardment heating scheme at high voltage is adopted for heating of 6.5cm diameter tungsten plate. This article describes the detailed analysis of the design, fabrication, operation, and characterization of temperature distribution over the tungsten hot plate using the Infrared camera of the tungsten ionizer. The tungsten plate has sufficient temperature for the production of Cesium ions/plasma.

physics.plasm-ph↗

arXiv2022

Galaxy luminosity functions at redshifts 0.6 to 1.2 in the Chandra Deep Field South

We present the rest-frame Ultra-Violet (UV) galaxy luminosity function (LF) and luminosity density (LD) measurements in the far-UV (150 nm) wavelength, in the redshift range z = 0.6 - 1.2. The UV LF is derived using XMM-Newton Optical Monitor (XMM-OM), ultraviolet (160 - 400 nm) observations of the Chandra Deep Field South, over an area of 396 sq. arcmin. Using the deep UV imaging of the CDFS, we identified more than 2500 galaxies in our sample with faint UVW1(AB) limit 24.5 mag. This sample along with various other catalogues containing redshift information, is used to calculate the binned representation of the galaxy UV LF in the two redshift bins 0.6 - 0.8 and 0.8 - 1.2, having a wide range of 150 nm rest-frame UV magnitudes, reaching 1 - 1.5 magnitudes fainter than previous studies at similar redshifts. The binned LF is described well by the Schechter function form. Using maximum-likelihood the Schechter function is fitted to the unbinned data to obtain the best-fit values of the the UV galaxy LF parameters. We find that characteristic magnitude brightens by 0.8 mag from z = 0.7 to z = 1, implying an increase in the star formation activity between these redshifts, as reported by past studies. Our estimate of the faint-end slope -1.10+0.19-0.18 is on the shallower side compared with previous studies at z = 0.7, whereas a value of -1.56+0.19-0.18 estimated for z = 1.0, agrees with previous results given the uncertainties.

astro-ph.GA↗

arXiv2021

The ultraviolet luminosity function of star-forming galaxies between redshifts of 0.6 and 1.2

We use ultraviolet imaging taken with the XMM-Newton Optical Monitor telescope (XMM-OM), covering 280 square arcminutes in the UVW1 band (effective wavelength 2910 Angstroms) to measure rest-frame ultraviolet (1500 Angstrom) luminosity functions of galaxies with redshifts z between 0.6 and 1.2. The XMM-OM data are supplemented by a large body of optical and infrared imaging to provide photometric redshifts. The XMM-OM data have a significantly narrower point-spread-function (resulting in less source confusion) and simpler K-correction than the GALEX data previously employed in this redshift range. Ultraviolet-bright active galactic nuclei are excluded to ensure that the luminosity functions relate directly to the star-forming galaxy population. Binned luminosity functions and parametric Schechter-function fits are derived in two redshift intervals: 0.6<z<0.8 and 0.8<z<1.2. We find that the luminosity function evolves such that the characteristic absolute magnitude M* is brighter for 0.8<z<1.2 than for 0.6<z<0.8.

astro-ph.GA↗

arXiv2019

An Advanced Conceptual Diagnostic Healthcare Framework for Diabetes and Cardiovascular Disorders

The data mining along with emerging computing techniques have astonishingly influenced the healthcare industry. Researchers have used different Data Mining and Internet of Things (IoT) for enrooting a programmed solution for diabetes and heart patients. However, still, more advanced and united solution is needed that can offer a therapeutic opinion to individual diabetic and cardio patients. Therefore, here, a smart data mining and IoT (SMDIoT) based advanced healthcare system for proficient diabetes and cardiovascular diseases have been proposed. The hybridization of data mining and IoT with other emerging computing techniques is supposed to give an effective and economical solution to diabetes and cardio patients. SMDIoT hybridized the ideas of data mining, Internet of Things, chatbots, contextual entity search (CES), bio-sensors, semantic analysis and granular computing (GC). The bio-sensors of the proposed system assist in getting the current and precise status of the concerned patients so that in case of an emergency, the needful medical assistance can be provided. The novelty lies in the hybrid framework and the adequate support of chatbots, granular computing, context entity search and semantic analysis. The practical implementation of this system is very challenging and costly. However, it appears to be more operative and economical solution for diabetes and cardio patients.

cs.CY↗

arXiv2018

Experimental observation of drift wave turbulence in an inhomogeneous six-pole cusp magnetic field of MPD

This paper presents a detailed study on the controlled experimental observation of drift wave instabilities in an inhomogeneous Six pole cusp magnetic field generated by an in-house developed Multi-pole line cusp magnetic field device (MPD) [Patel et al. Rev. Sci. Instrum., 44, 726 (2018)]. The device is composed of six axially symmetric cusps and non-cusp (in between two consecutive magnets) regions. The observed instability has been investigated in one of these non-cusp regions by controlling the radial plasma density gradient with changing pole magnetic field which is a unique feature of this device. It has been observed that the frequency of the instability changes explicitly with the density gradient. Moreover the scale length of plasma parameters, frequency spectrum, cross-correlation function, and fluctuation level of plasma densities has been measured in order to identify the instability. The cross field drift velocity due to fluctuation in plasma parameters have been measured from the wave number- frequency S (kz, {\omega}) spectrum and verified with the theoretical values obtained from density scale length formula. Further from the S (kz, {\omega}) spectrum it has been found that the drift velocity alternates the sign in the consecutive non-cusp regions.

physics.plasm-ph↗

arXiv2018

Characterization of Argon Plasma in a variable Multi-pole line Cusp Magnetic Field Configuration

This paper demonstrates a detailed characterization of argon plasma in a variable multi-pole line cusp magnetic field (VMMF). The VMMF has been produced by placing six electromagnets (with embedded profiled vacoflux-50 core) over a large cylindrical volume (1 m axial length and 40 cm diameter). The magnetic field have been measured by hall probe method and compared with simulated magnetic field by performing simulation using FEMM tools. Results from magnetic field simulation indicate that the rate of change of pole magnetic field (maximum magnetic field) with respect to magnet current for vacoflux-50 core is high (7.53 G/A) as compared to the simple air core electromagnet (2.15 G/A). The area of the nearly field free region (null region) in the chamber volume can be controlled without changing a number of pole magnets. From the experimental results, it has been observed that in this field configuration the confinement of the primary electrons increases and leak width of plasma decreases with increasing the magnetic field. Thus the mean density, particle confinement time and the stability of the plasma increase with increasing magnetic field. In addition to this, it has been found that the radial uniformity of the plasma density explicitly depends on the VMMF. It is also shown that the VMMF controls the scavenging of confined primary electrons and confinement of primary electron increased with magnetic field which helps to boost up the plasma density.

physics.plasm-ph↗

arXiv2017

A new multi line-cusp magnetic field plasma device (MPD) with variable magnetic field for fundamental plasma studies

One of the fundamental problems is the understanding of physics of electrostatic and electromagnetic fluctuations in multi-scale plasma turbulence. Especially so, in continuously connected plasma regions with varying degree of magnetization. Examples range from multiscale plasmas in Magnetron-like devices to astrophysical plasmas confined by magnetic dipole structures, solar wind driven collision-less and weakly collisional plasmas around Earth, to mention a few. Such plasmas are dominated by both electron scale and ion scale physics as well as finite beta effects. To investigate such processes in laboratory experiments requires excellent control of continuously connected regions of nearly zero plasma beta with finite beta regions as well as the gradient length scales of mean density and temperatures. To address some of these phenomena at laboratory scale, a new multi-line cusp configured plasma device (MPD) consisting of electromagnets with core material has been constructed with a capability to experimentally control the relative volume fractions of magnetized to unmagntized plasma volume as well as accurate control on the gradient length scales of mean density and temperature profiles. The hot tungsten cathode produced Argon plasma in the MPD has been characterised using single Langmuir probes. Argon plasma has been produced in the device over a wide range of pressure 5 x 10-5 mBar to 1 x 10-3 mBar, achieving plasma density range from 109 to 1011cm-3 and temperature in the range 1eV to 8eV.

physics.plasm-ph↗

arXiv2013

A Hash based Approach for Secure Keyless Steganography in Lossless RGB Images

This paper proposes an improved steganography approach for hiding text messages in lossless RGB images. The objective of this work is to increase the security level and to improve the storage capacity with compression techniques. The security level is increased by randomly distributing the text message over the entire image instead of clustering within specific image portions. Storage capacity is increased by utilizing all the color channels for storing information and providing the source text message compression. The degradation of the images can be minimized by changing only one least significant bit per color channel for hiding the message, incurring a very little change in the original image. Using steganography alone with simple LSB has a potential problem that the secret message is easily detectable from the histogram analysis method. To improve the security as well as the image embedding capacity indirectly, a compression based scheme is introduced. Various tests have been done to check the storage capacity and message distribution. These testes show the superiority of the proposed approach with respect to other existing approaches.

cs.CR↗

arXiv2012

Galactic winds driven by cosmic-ray streaming

Galactic winds are observed in many spiral galaxies with sizes from dwarfs up to the Milky Way, and they sometimes carry a mass in excess of that of newly formed stars by up to a factor of ten. Multiple driving processes of such winds have been proposed, including thermal pressure due to supernova-heating, UV radiation pressure on dust grains, or cosmic ray (CR) pressure. We here study wind formation due to CR physics using a numerical model that accounts for CR acceleration by supernovae, CR thermalization, and advective CR transport. In addition, we introduce a novel implementation of CR streaming relative to the rest frame of the gas. We find that CR streaming drives powerful and sustained winds in galaxies with virial masses M_200 < 10^{11} Msun. In dwarf galaxies (M_200 ~ 10^9 Msun) the winds reach a mass loading factor of ~5, expel ~60 per cent of the initial baryonic mass contained inside the halo's virial radius and suppress the star formation rate by a factor of ~5. In dwarfs, the winds are spherically symmetric while in larger galaxies the outflows transition to bi-conical morphologies that are aligned with the disc's angular momentum axis. We show that damping of Alfven waves excited by streaming CRs provides a means of heating the outflows to temperatures that scale with the square of the escape speed. In larger haloes (M_200 > 10^{11} Msun), CR streaming is able to drive fountain flows that excite turbulence. For halo masses M_200 > 10^{10} Msun, we predict an observable level of H-alpha and X-ray emission from the heated halo gas. We conclude that CR-driven winds should be crucial in suppressing and regulating the first epoch of galaxy formation, expelling a large fraction of baryons, and - by extension - aid in shaping the faint end of the galaxy luminosity function. They should then also be responsible for much of the metal enrichment of the intergalactic medium.

astro-ph.CO↗

arXiv2012

TeV Gamma-ray Observations of Markarian 421 using TACTIC during 2009-10

We have observed the blazar Markarian 421 with the TACTIC $\gamma$-ray telescope at Mt. Abu, India, from 22 November 2009 to 16 May 2010 for 265 hours. Detailed analysis of the data so recorded revealed presence of a TeV $\gamma$-ray signal with a statistical significance of 12.12$\sigma$ at $E_{\gamma}\geq$ 1 TeV. We have estimated the time averaged differential energy spectrum of the source in the energy range 1.0 - 16.44 TeV. The spectrum fits well with the power law function of the form ($dF/dE=f_0 E^{-\Gamma}$) with $f_0=(1.39\pm0.239)\times 10^{-11}cm^{-2}s^{-1}TeV^{-1}$ and $\Gamma=2.31\pm0.14$.

astro-ph.HE↗

arXiv2009

Search for TeV $γ$ -rays from H1426+428 during 2004-07 with the TACTIC telescope

The BL Lac object H1426+428 ($z\equiv 0.129$) is an established source of TeV $γ$-rays and detections of these photons from this object also have important implications for estimating the Extragalactic Background Light (EBL) in addition to the understanding of the particle acceleration and $γ$-ray production mechanisms in the AGN jets. We have observed this source for about 244h in 2004, 2006 and 2007 with the TACTIC $γ$-ray telescope located at Mt. Abu, India. Detailed analysis of these data do not indicate the presence of any statistically significant TeV $γ$-ray signal from the source direction. Accordingly, we have placed an upper limit of $\leq1.18\times10^{-12}$ $photons$ $cm^{-2}$ $s^{-1}$ on the integrated $γ$-ray flux at 3$σ$ significance level.

astro-ph.CO↗

arXiv2008

Very High Energy gamma-ray observations of Mrk 501 using TACTIC imaging gamma-ray telescope during 2005-06

In this paper we report on the Markarian 501 results obtained during our TeV $γ$-ray observations from March 11 to May 12, 2005 and February 28 to May 7, 2006 for 112.5 hours with the TACTIC $γ$-ray telescope. During 2005 observations for 45.7 hours, the source was found to be in a low state and we have placed an upper limit of 4.62 $\times$ 10$^{-12}$ photons cm$^{-2}$ s$^{-1}$ at 3$σ$ level on the integrated TeV $γ$-ray flux above 1 TeV from the source direction. However, during the 2006 observations for 66.8h, detailed data analysis revealed the presence of a TeV $γ$-ray signal from the source with a statistical significance of 7.5$σ$ above $E_γ\geq$ 1 TeV. The time averaged differential energy spectrum of the source in the energy range 1-11 TeV is found to match well with the power law function of the form ($dΦ/dE=f_0 E^{-Γ}$) with $f_0=(1.66\pm0.52)\times 10^{-11}cm^{-2}s^{-1}TeV^{-1}$ and $Γ=2.80\pm0.27$.

astro-ph↗

arXiv2008

Neutron Beam Effects on Spin Exchange Polarized He-3

We have observed depolarization effects when high intensity cold neutron beams are incident on alkali-metal-spin-exchange polarized He-3 cells used as neutron spin filters. This was first observed as a reduction of the maximum attainable He-3 polarization and was attributed to a decrease of alkali-metal polarization, which led us to directly measure alkali-metal polarization and spin relaxation over a range of neutron fluxes at LANSCE and ILL. The data reveal a new alkali-metal spin-relaxation mechanism that approximately scales as the square root of the neutron capture-flux density incident on the cell. This is consistent with an effect proportional to the recombination-limited ion concentration, but is much larger than expected from earlier work.

nucl-ex↗