arXiv subjects

Siddharth Savyasachi Malu

Publications and source records attributed to Siddharth Savyasachi Malu.

5 recordsLinked to original sources

arXiv2024

Bullet Cluster: Remarkable Revelations and Enduring Insights -- Part I

This study unveils new insights into the Bullet Cluster through cm-wave observations made with the Australia Telescope Compact Array, focusing on the Sunyaev-Zeldovich Effect (SZE). A novel SZE feature was discovered, distinctively offset from the X-ray brightness peak, challenging conventional associations between such phenomena. The findings, achieved through high-resolution interferometric imaging, reveal complex substructures within the SZE, including significantly displaced components uncorrelated with X-ray, optical, or lensing maps. This deviation underscores the complexity within the cluster's dynamics and suggests that detailed, high-resolution SZE imaging is crucial for understanding the physics of merging clusters. We perform several tests to ensure that one of these novel and unusual features is indeed real, and that the detection of all features in the images is robust. In addition to these displacements, we find several SZE features that are tentatively located at critical boundaries in this merging cluster - these features will be discussed in the next few papers in this series. These observations pave the way for more sophisticated analyses, combining SZE and X-ray data, to decode the evolutionary mysteries of cosmic structures like the Bullet Cluster. We note here that we are discussing only one novel and peculiar feature in the observations of the cluster done in the year 2019. Further observations have revealed more features, which we shall discuss in the next few papers in this series on the Bullet cluster.

astro-ph.CO↗

arXiv2024

A Millimeter-wave Technique for correlation and beam combination for cosmology

We discuss new techniques and ideas in mm-wave instrumentation that can be used in CMB (Cosmic Microwave background) polarization experiments. Novel techniques in antenna receiver, beam combining and detector systems have resulted in greatly improved sensitivities. We present a few promising approaches and discuss briefly plans for feasibility studies for detecting CMB polarization foregrounds and signal.

astro-ph.IM↗

arXiv2022

Accreting White Dwarfs: Effect of WD Composition on Helium Ignition During Slow Accretion

Understanding the explosion mechanism of type Ia supernova is among the most challenging issues in astrophysics. Accretion of matter on a carbon-oxygen white dwarf from a companion star is one of the most important keys in this regard. Our aim is to study the effects of WD composition on various parameters during the accretion of helium rich matter at a slow rate. We have used the computer simulation code Modules for Experiments in Stellar Astrophysics (MESA) to understand the variations in the properties such as specific heat (\textit{$C_P$}) and degeneracy parameter (\textit{$η$}). The profile of specific heat shows a discontinuity and that of the degeneracy parameter shows a dip near the ignition region. As expected, the size of WD decreases and \textit{g} increases during the accretion. However, a red-giant-like expansion is observed after the rapid ignition towards the end. Our study explains the reason behind the delay in onset of helium ignition due to the difference in carbon abundance in a CO-WD. We find that white dwarfs of the lower abundance of carbon accrete slightly longer before the onset of helium ignition.

astro-ph.SR↗

arXiv2021

Slow Accretion of Helium Rich Matter onto C-O White Dwarf: Does Composition of WD Matter?

In binary systems, the helium accretion onto carbon-oxygen (CO) white dwarfs (WDs) plays a vital role in many astrophysical scenarios, especially in supernovae type Ia. Moreover, ignition density for accretion rate $\dot{M} \lesssim 10^{-9} M_{\odot}$ $yr^{-1}$ in helium accreting CO white dwarfs decides the triggering mechanism of a supernova explosion which could be either off-centre helium flash or central carbon flash. We aim to study the accretion of helium with a slow accretion rate $5 \times 10^{-10} M_{\odot}$ $yr^{-1}$ onto relatively cool and hot white dwarfs of different abundances of carbon and oxygen. The simulation code Modules for Experiments in Stellar Astrophysics (MESA) has been used for our study. We analyze the variation in several properties like surface gravity (g), helium luminosity ($L_{He}$), and effective temperature ($T_{eff}$) during the accretion phase of the white dwarfs. We also calculate the ignition density ($ρ_{He}$) and ignition temperature ($T_{He}$) of helium burning. As expected, the size of WD decreases and g increases during the accretion. However, a red-giant-like expansion is observed after the rapid ignition towards the end. The dependence of helium accreting WD evolution on its composition has also been explored in this study. We find that white dwarfs of the lower abundance of carbon accrete slightly longer before the onset of helium ignition.

astro-ph.SR↗

arXiv2010

Broadband Fizeau Interferometers for Astrophysics

Measurements of the 2.7 K cosmic microwave background (CMB) radiation now provide the most stringent constraints on cosmological models. The power spectra of the temperature anisotropies and the $E$-mode polarization of the CMB are explained well by the inflationary paradigm. The next generation of CMB experiments aim at providing the most direct evidence for inflation through the detection of $B$-modes in the CMB polarization, presumed to have been caused by gravitational waves generated during the inflationary epoch around $10^{-34}$s. The $B$-mode polarization signals are very small ($\leq$10$^{-8}$K) compared with the temperature anisotropies ($\sim 10^{-4}$K). Systematic effects in CMB telescopes can cause leakage from temperature anisotropy into polarization. Bolometric interferometry (BI) is a novel approach to measuring this small signal with lower leakage. If BI can be made to work over wide bandwidth ($\sim20-30\%$) it can provide similar sensitivity to imagers. Subdividing the frequency passband of a Fizeau interferometer would mitigate the problem of `fringe smearing.' Furthermore, the approach should allow simultaneous measurements in image space and visibility space. For subdividing the frequency passsband (`sub-band splitting' henceforth), we write an expression for the output from every baseline at every detector in the focal plane as a sum of visibilities in different frequency sub-bands. For operating the interferometer simultaneously as an imager, we write the output as two integrals over the sky and the focal plane, with all the phase differences accounted for.}{The sub-band splitting method described here is general and can be applied to broad-band Fizeau interferometers across the electromagnetic spectrum. Applications to CMB measurements and to long-baseline optical interferometry are promising.

astro-ph.CO↗