arXiv subjects

Varenya Upadhyaya

Publications and source records attributed to Varenya Upadhyaya.

3 recordsLinked to original sources

arXiv2025

The Role of r-Modes in Pulsar Spin-down, Pulsar Timing, and Gravitational Waves

We investigate the role of r-mode oscillations in pulsar spin-down and their implications for gravitational wave emission and pulsar timing analysis. Using a non-linear differential framework that includes r-mode contributions, we derive time-dependent solutions for rotational frequency and period evolution. These expressions are validated using observational data from the Crab pulsar with high precision. By analytically fitting braking indices and spin-down coefficients, we link measurable pulsar properties to gravitational wave signatures. Furthermore, we present closed-form expressions for neutron star compactness and tidal deformability using Lambert W and Lambert-Tsallis functions, enabling model-independent inferences from r-mode gravitational wave frequencies. Our results show that incorporating r-modes significantly improves the accuracy of spin-down models and continuous wave detectability, particularly through the inclusion of high-order frequency terms. This framework supports the modeling of timing residuals, glitch quantification, and gravitational wave constraints. Our findings have direct relevance for data analysis in ongoing and future gravitational wave observatories.

astro-ph.HE↗

arXiv2024

Tully-Fisher Relation of Late-type Galaxies at $0.6 \leq z \leq 2.5$

We present a study of the stellar and baryonic Tully-Fisher relation within the redshift range of $0.6 \leq z \leq 2.5$ utilizing observations of \sfgs. This dataset, as explored in \citet{GS23}, comprises of disk-like galaxies spanning a stellar mass range of $8.89 \leq \log(M_{star} \ [\mathrm{M_\odot}]) \leq 11.5$, baryonic mass range of $9.0 \leq \log(M_{bar} [\mathrm{M_\odot}]) \leq 11.5$, and circular velocity range of $1.65 \leq \log(V_c \ [{\rm km/s}]) \leq 2.85$. Stellar masses of these objects are estimated using spectral energy distribution fitting techniques, while gas masses are determined via scaling relations. Circular velocities are directly derived from the Rotation Curves (RCs), after meticulously correcting for beam smearing and pressure support. Our analysis confirms that our sample adheres to the fundamental mass-size relations of galaxies and reflects the evolution of velocity dispersion in galaxies, in line with previous findings. This reaffirms the reliability of our photometric and kinematic parameters (i.e., $M_{star}$ and $V_c$), thereby enabling a comprehensive examination of the Tully-Fisher relation. To attain robust results, we employed a novel orthogonal likelihood fitting technique designed to minimize intrinsic scatter around the best-fit line, as required at \hz. For the STFR, we obtained a slope of $α=3.03\pm 0.25$, an offset of $β= 3.34\pm 0.53$, and an intrinsic scatter of $ζ_{int}=0.08$ dex. Correspondingly, the BTFR yielded $α=3.21\pm 0.28$, $β=3.16\pm 0.61$, and $ζ_{int}=0.09$ dex. Our findings suggest a subtle deviation in the stellar and baryonic Tully-Fisher relation with respect to local studies, which is most-likely due to the evolutionary processes governing disk formation.

astro-ph.GA↗

arXiv2023

A test of linearity of the ratio of dark matter to baryonic matter in galaxy clusters

We search for a linearity in the ratio of dark matter to baryonic matter as a function of radius for galaxy clusters, motivated by a recent result by Lovas (arXiv:2206.11431), who has discovered such a linearity for a diverse suite of galaxies in the SPARC sample. For our analysis, we used a sample of 54 non-cool core clusters from the HIFLUGCS sample. We do not find any evidence for a linear trend in the aforementioned ratio as a function of radius for individual clusters. We then repeat this analysis for the stacked sample, which also does not show this linearity. Therefore, the linear scaling found by Lovas is not a universal property of dark matter haloes at all scales.

astro-ph.CO↗