arXiv subjects

Sanya Gupta

Publications and source records attributed to Sanya Gupta.

3 recordsLinked to original sources

arXiv2025

The MDW Hα Sky Survey: Data Release 1

The Mittelman-di Cicco-Walker (MDW) H$α$ Sky Survey is an autonomously-operated all-sky narrow-band (3nm) H$α$ imaging survey. The survey was founded by amateur astronomers and the northern sky (Decl. $\geq$ 0$^\circ$) is presented here in its second stage of refinement for academic use. Each 3.6$\times$3.6 sq. deg MDW field has 12 20-minute individual exposures with a pixel scale of 3.6", a typical PSF of 6", and a stack point source depth of 16-17 magnitudes. The northern MDW Survey Data Release 1 (DR1) includes: calibrated and raw mean and individual images, star-removed mean fields, and point source catalogs for all images matched to Data Release 1 of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) and the INT Galactic Plane Survey (IGAPS). Our initial study of H$α$ filament widths finds a typical FWHM of 30-45" in the Lyra region. The matched catalogs (with a median match distance of ~0.5"), combined with our distinctive narrow-band photometry, are used to identify H$α$ variable and excess sources. These initial studies highlight some of the many scientific uses of the MDW H$α$ survey.

astro-ph.IM↗

arXiv2025

The Role of Electric Dominance for Particle Injection in Relativistic Reconnection

Magnetic reconnection in relativistic plasmas -- where the magnetization $σ\gg1$ -- is regarded as an efficient particle accelerator, capable of explaining the most dramatic astrophysical flares. We employ two-dimensional (2D) particle-in-cell simulations of relativistic pair-plasma reconnection with vanishing guide field and outflow boundaries to quantify the impact of the energy gain occurring in regions of electric dominance ($E>B$) for the early stages of particle acceleration (i.e., the ``injection'' stage). We calculate the mean fractional contribution $ζ(ε^\ast,ε_{\rm T}$) by $E>B$ fields to particle energization up to the injection threshold energy, $ε^\ast=σ/4$; here, $ε_{\rm T}$ is the particle energy at time $T$. We find that $ζ$ monotonically increases with $σ$ and $ε_{\rm T}$; for $σ\gtrsim 50$ and $ε_{\rm T}/σ\gtrsim 8$, we find that $\gtrsim 80\%$ of the energy gain obtained before reaching $ε^\ast=σ/4$ occurs in $E>B$ regions. We find that $ζ$ is independent of simulation box size $L_x$, as long as $ε_{\rm T}$ is normalized to the maximum particle energy, which scales as $ε_{\rm max}\propto L_{\rm x}^{1/2}$ in 2D. The distribution of energy gains $ε_χ$ acquired in $E>B$ regions can be modeled as $dN/dε_χ\proptoε_χ^{-0.35}\exp[-(ε_χ/0.06\,σ)^{0.5}]$. Our results help assess the role of electric dominance in relativistic reconnection with vanishing guide fields, which may be realized in the magnetospheres of black holes and neutron stars.

astro-ph.HE↗

arXiv2023

Comptonization by Reconnection Plasmoids in Black Hole Coronae III: Dependence on the Guide Field in Pair Plasma

We perform two-dimensional particle-in-cell simulations of magnetic reconnection for various strengths of the guide field (perpendicular to the reversing field), in magnetically-dominated electron-positron plasmas. Magnetic reconnection under such conditions could operate in accretion disk coronae around black holes. There, it has been suggested that the trans-relativistic bulk motions of reconnection plasmoids containing inverse-Compton-cooled electrons could Compton-upscatter soft photons to produce the observed non-thermal hard X-rays. Our simulations are performed for magnetizations $3 \leq σ\leq 40$ (defined as the ratio of enthalpy density of the reversing field to plasma enthalpy density) and guide field strengths $0 \leq B_{\rm g}/B_0 \leq 1$ (normalized to the reversing field strength $B_0$). We find that the mean bulk energy of the reconnected plasma depends only weakly on the flow magnetization but strongly on the guide field strength -- with $B_{\rm g}/B_0 = 1$ yielding a mean bulk energy twice smaller than $B_{\rm g}/B_0 = 0$. Similarly, the dispersion of bulk motions around the mean -- a signature of stochasticity in the plasmoid chain's motions -- is weakly dependent on magnetization (for $σ\gtrsim 10$) but strongly dependent on the guide field strength -- dropping by more than a factor of two from $B_{\rm g}/B_0 = 0$ to $B_{\rm g}/B_0 = 1$. In short, reconnection in strong guide fields ($B_{\rm g}/B_0 \sim 1$) leads to slower and more ordered plasmoid bulk motions than its weak guide field ($B_{\rm g}/B_0 \sim 0$) counterpart.

astro-ph.HE↗