arXiv subjects

Anirban Dutta

Publications and source records attributed to Anirban Dutta.

At least 19 recordsLinked to original sources

arXiv2026

Rubin J122659.4+090236: An Extremely Low Surface Brightness Galaxy Candidate Discovered in the Rubin LSST Early Data Preview 2

We report the serendipitous discovery of an exceptionally low surface brightness galaxy (LSBG) candidate, Rubin J122659.4+090236, in Rubin Observatory imaging of the interacting NGC 4410 system, identified in the Cosmic Treasure Chest public release. 2D Sérsic modelling of the Rubin g, r, and i images reveals a nearly round system with a shallow profile (n ~ 0.4), an effective radius of R_e ~ 6'', and central surface brightnesses of $μ_{0,g}=27.52\pm0.04$, $μ_{0,r}=27.62\pm0.07$, and $μ_{0,i}=27.04\pm0.08$ mag arcsec$^{-2}$. EAZY photo-z fitting favours an intermediate-z solution at z~0.3, while a low-redshift solution at z~0.028, consistent with the NGC 4410 system, is also permitted by a restricted EAZY fit over 0<z<0.1 without imposing a redshift prior. These alternatives imply substantially different physical interpretations, ranging from a diffuse dwarf-like system to an exceptionally extended background LSBG. This discovery demonstrates Rubin's sensitivity to extremely diffuse galaxies and highlights the potential of the LSST survey to uncover large samples of such elusive systems across wide areas, enabling systematic studies of the LSBG population and its role in galaxy evolution.

astro-ph.GA↗

arXiv2026

Can We Find the Emission Mechanism Behind the Extremely Bright GRB 230812B?

GRB 230812B is a bright long-duration GRB with a luminous, long-lived afterglow and an AstroSat/CZTI polarization measurement during the prompt phase, enabling a joint study of its prompt spectral evolution, polarization, and broadband afterglow. Time-resolved spectroscopy of the prompt emission shows that during the rising phase, the low-energy Band-function index exceeds the synchrotron line of death, favoring the presence of an additional thermal component. At later times, from $T_0+2$ s to $T_0+32$ s, the prompt spectra are consistent with predominantly non-thermal emission. Polarization analysis of the prompt emission in the $300$-$600$ keV band yields a marginal lower limit on the polarization fraction of $Π\gtrsim 50\%$ at the $1σ$ level. The long X-ray monitoring of the afterglow shows no jet break over the observed baseline. Multiwavelength afterglow modeling favors a wide jet with an inferred half-opening angle of $θ_j = 15^{+6}_{-4}$ degrees observed close to the jet axis with a viewing angle of $θ_v = 0.9^{+1.8}_{-0.6}$ degrees. The inferred circumburst density is low, $n_0 = 1.2^{+0.3}_{-0.1}\times10^{-4}\,\textrm{cm}^{-3}$, and the isotropic-equivalent kinetic energy of the jet is $E_{{\rm k}, iso} = 4.0^{+1.5}_{-0.8} \times 10^{53}$ erg. Taken together, the prompt spectral evolution favors an early phase with a thermal contribution followed by a later phase dominated by non-thermal emission. The polarization constraint in the late prompt phase is consistent with synchrotron emission, although a higher-significance polarization measurement will be required to robustly constrain the magnetic-field geometry and the relative contribution of photospheric emission.

astro-ph.HE↗

arXiv2026

Photometric and Spectroscopic Studies of Type Ic Supernovae SN 2020akf and SN 2021mxx

We present a comprehensive analysis of optical photometry and medium-resolution spectroscopy for Type Ic supernovae (SNe) SN 2020akf and SN 2021mxx. Our study covers the evolution of SN 2020akf from -5 to 109 days and SN 2021mxx from -3 to 115 days relative to their B-band maximum. Their peak quasi-bolometric luminosities are estimated at logL_bol = 42.37 +- 0.02 and 42.21 +- 0.02 erg/s, respectively. The velocities of the ejecta, derived from the Fe II 5169 A line at maximum light, are approximately 15000 km/s for SN~2020akf and about 10000 km/s for SN~2021mxx, which are consistent with those observed in other Type~Ic SNe. Using the semianalytical Arnett model, we estimate that SN 2020akf has a kinetic energy of E_k = 6.33 (+0.68)(-0.62) x 10^51 erg and an ejected mass of M_ej = 4.71 (+0.50)(-0.46) M_sun, while for SN 2021mxx, we get E_k = 0.54 (+0.08)(-0.12) x 10^51 erg and M_ej = 0.90 (+0.14)(-0.18),M_sun. The mass of Ni56 synthesized in the explosion is estimated at 0.10 +- 0.02 M_sun for SN 2020akf and 0.05 +- 0.01 M_sun for SN 2021mxx. The metallicities of the host galaxies near the SN regions are ~0.81 Z_sun for SN 2020akf and ~0.76 Z_sun for SN 2021mxx, where Z_sun indicates solar metallicity. Our detailed analysis suggests that SN 2020akf falls into the category of a transitional Type Ic SN, having spectral properties between normal and broad-line Type Ic SNe, while SN 2021mxx is a normal Type Ic SN with an extremely low value of the M_ej / E_k ratio.

astro-ph.HE↗

arXiv2026

Decadal pre-explosion activity and circumstellar interaction in a supernova

When a massive star explodes as a supernova, crucial information about its immediate environment is lost within hours. Here we report rapid optical observations from Lulin Observatory of the broad-lined Type Ic supernova SN 2026gzf, beginning 1.25 hours after Einstein Probe detected the X-ray transient EP260321a. Our data led to the discovery of the optical counterpart and showed a luminous blue first-day excess that cannot be reproduced by standard radioactive models. We find that interaction between the ejecta and $\approx 0.02$ M$_{\odot}$ of circumstellar material accounts for the early excess. Archival Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) images show variability at the explosion site over the previous $\sim 12$ years, with the source brightening by a factor of $\sim 1.5$ in the final $\sim 3$ years before explosion, providing rare evidence for pre-explosion activity in a stripped-envelope progenitor system. The precursor brightening suggests enhanced eruptive mass loss during late-stage oxygen burning before core collapse, while an additional silicon-burning episode shortly before explosion may have created the compact nearby material responsible for the X-ray shock-breakout signal. SN 2026gzf therefore offers the first view of how a stripped progenitor modifies its immediate environment shortly before death, linking long-term precursor variability, circumstellar interaction and the explosion itself.

astro-ph.HE↗

arXiv2026

From DES to KiDS: Domain adaptation for cross-survey detection of low-surface-brightness galaxies

Low-surface-brightness galaxies (LSBGs) are vital for understanding galaxy formation, but their diffuse nature makes them challenging to detect. Upcoming large-scale surveys are expected to uncover large numbers of LSBGs, requiring robust automated methods to identify them across heterogeneous datasets. As a precursor to the Legacy Survey of Space and Time (LSST) and Euclid, we explore domain adaptation techniques for cross-survey LSBG identification. Using models trained on the Dark Energy Survey (DES), we search for LSBGs in the Kilo-Degree Survey Data Release 5 (KiDS DR5). We used an ensemble consisting of one convolutional neural network (CNN) and two transformer models trained on DES cutouts and applied to KiDS DR5 imaging data. Structural parameters were estimated with galfitm, and photometric redshifts and stellar population properties were estimated through spectral energy distribution fitting with CIGALE. We identify 20,180 LSBGs and 434 ultra-diffuse galaxies (UDGs) in KiDS DR5. Their structural parameters are similar to known LSBGs from DES and the Hyper Suprime-Cam SSP Survey (HSC-SSP). The KiDS-LSBGs follow a continuous size-luminosity relation connecting classical dwarf galaxies and UDGs, and their colours are bimodal ($\sim73\%$ blue, $\sim27\%$ red). Cross-matching with spectroscopic and cluster catalogues provides redshifts for 4,913 systems, enabling a systematic characterisation of the star-forming main sequence of LSBGs. Strong environmental trends are evident, with cluster LSBGs and UDGs exhibiting redder colours and reduced star formation compared to non-cluster systems. We demonstrate that domain adaptation enables robust cross-survey LSBG identification with deep learning models, providing a scalable pathway for constructing homogeneous LSBG catalogues for the LSST and Euclid era.

astro-ph.GA↗

arXiv2026

Hubbard model at U=$\infty$: Role of single and two-boson fluctuations

We have developed a semi-analytical framework formulated in the canonical fermion representation to investigate strongly correlated electron systems. We consider the U=$\infty$ Hubbard model and used the equation of motion method to calculate the fermion self-energy which has two parts: single and two-boson exchange processes. The emergent bosons here are self-generated local charge and spin-density fluctuations which become strongly time-dependent due to extreme correlations. The computed boson spectral density is a diffusive damped mode with a long tail. The electron self-energy at $d=\infty$ is computed self-consistently. The corresponding fermionic spectral density displays a pronounced coherence peak at $ω=0$, while its frequency derivative develops a two-peak structure at finite $ω$. The resistivity shows a linear temperature dependence over a broad range, crossing over to coherent Fermi-liquid behavior at extremely low temperatures.

cond-mat.str-el↗

arXiv2026

Unveiling SN 2022eyw: A Bright Member of the Type Iax Supernova Subclass

We present comprehensive photometric and spectroscopic observations of Supernova (SN) 2022eyw, a luminous member of the Type Iax SN subclass. SN 2022eyw reached a peak absolute magnitude of $M_g = -17.80\pm0.15$ mag and exhibited a rise time of $\sim$15 days, placing it among the brighter Iax events. The bolometric light curve indicates a synthesized $^{56}$Ni mass of $0.11\pm0.01~\text{M}_{\odot}$, with an estimated ejecta mass of $0.79\pm0.09~\text{M}_{\odot}$ and kinetic energy of $0.19\times10^{51}$ erg. The spectral evolution from -8 to +110 days past maximum reveals features characteristic of bright Type Iax Supernovae, including a transition from Fe III to Fe II dominance, moderate expansion velocities, and a lack of strong C III absorption. TARDIS spectral modelling of the early-phase spectra indicates a well-mixed ejecta dominated by Fe-group elements. In addition, traces of unburnt carbon are detected, pointing to incomplete burning as expected in pure deflagration models. Late-time spectral evolution shows a blend of permitted and forbidden lines. Comparison with deflagration models suggests that SN 2022eyw originated from a partial deflagration of a Chandrasekhar-mass white dwarf, with explosion properties intermediate between the N3-def and N5-def models. These observations support pure deflagration of a CO white dwarf as a viable explosion mechanism for its luminous members.

astro-ph.HE↗

arXiv2026

Continuous dependence results for quasilinear evolution equations

We study continuous dependence of solutions to quasilinear evolution equations of parabolic-type in the framework of maximal $L^p$-regularity. For equations of the form \[ \frac{dϕ}{dt} + A(t,ϕ)ϕ= f(t,ϕ), \] we establish continuous dependence of strong solutions on initial data, and suitable approximations of the nonlinear operators $A$ and $f$. An important step for proving the main result is the fact that the maximal regularity constant of the operator $A(t,ϕ)$, with $t$ and $ϕ$ fixed, admits a uniform bound over compact subsets of the relevant Banach spaces. As an application, we consider a class of non-Newtonian fluid models with a Carreau-type viscosity and mixed boundary conditions. We show that, as the nonlinear contribution in the viscosity vanishes and the initial data converge, solutions of the non-Newtonian fluid model converge to those of the classical Navier--Stokes equations.

math.AP↗

arXiv2025

Asymptotic stability of solutions to semilinear evolution equations in Banach spaces

We prove a new linearization principle for the nonlinear stability of solutions to semilinear evolution equations of parabolic type. We assume that the set of equilibria forms a finite dimensional manifold of normally stable and normally hyperbolic equilibria. In addition, we assume that the linearized operator is the generator of an analytic semigroup (not necessarily stable). We show that if a mild solution to our evolution equation exists globally in time and remains ``close'' to the manifold of equilibria at all times, then the solution must eventually converge to an equilibrium point at an exponential rate. We apply our abstract results to the equations governing the motion of a fluid-filled heavy solid. Under general assumptions on the physical configuration and initial conditions, we show that weak solutions to the governing equations eventually converge to a steady state with an exponential rate. In particular, the fluid velocity relative to the solid converges to zero as $t\to\infty$ in $H^{2α}_p(Ω)$ for each $p\in [1,\infty)$ and $α\in [0,1)$ as well as in $H^{2}_2(Ω)$.

math.AP↗

arXiv2025

A Note on Continuous dependence of Navier-Stokes equations with oscillating force

In this paper, we examine the averaging effect of a highly oscillating external force on the solutions of the Navier-Stokes equations. We show that, as long as the force time-average decays over time, if the frequency and amplitude of the oscillating force grow, then the corresponding solutions to Navier-Stokes equations converge (in a suitable topology) to the solution of the homogeneous equations with same initial data. Our approach involves reformulating the system as an abstract evolution equation in a Banach space, and then proving continuous dependence of solutions on both initial conditions and the external forcing.

math.AP↗

arXiv2025

Effect of positronium on the $γ$-ray spectra and energy deposition in Type Ia supernovae

Type Ia supernovae (SNe Ia) are powered by the radioactive decay of isotopes such as $^{56}$Ni and $^{56}$Co, making their $γ$-ray spectra useful probes of the explosion mechanism and ejecta structure. Accurate interpretation of $γ$-ray observables, including line ratios and continuum fluxes, requires a detailed understanding of the microphysical processes that shape the spectra. One such process is positronium formation during electron-positron annihilation, which can redistribute flux from the 511 keV line into the surrounding continuum. To assess the impact of positronium on the emergent spectra, we developed a new open-source module TARDIS-HE, for time-dependent three-dimensional $γ$-ray transport, integrated into the radiative transfer code TARDIS. The code simulates $γ$-ray spectra and light curves from one-dimensional supernova ejecta models and allows for flexible incorporation of decay chains and opacity treatments. Using TARDIS-HE, we explore the effect of positronium formation by varying the positronium fraction from 0 % to 100 %, and assuming an extreme case where 75 % of positronium decays result in three-photon emission. We find that full positronium formation can reduce the 511 keV line flux by approximately 70 % and modestly enhance energy deposition by up to 2 % at around 100 days post-explosion, compared to models without positronium. These results demonstrate that while the effect is not dominant, positronium formation introduces measurable changes to $γ$-ray observables. Future observations with missions such as the Compton Spectrometer and Imager (COSI) may offer constraints on positronium formation in SNe Ia and help refine models of their radioactive energy transport.

astro-ph.HE↗

arXiv2025

Weak lensing analysis of A115, A2219 and A2261: Detection of galaxy groups and filaments around clusters

We present a weak lensing and multi-wavelength analysis of three galaxy clusters: A115, A2219, and A2261. Weak lensing is performed using shape measurements made in short 60s exposure images obtained using WIYN-ODI. Forced measurement is used to measure low Signal to Noise (SNR) sources in individual exposures. We find the weak lensing significance map recovers the galaxy clusters and most galaxy groups in the wide 40$'$ $\times$ 40$'$ field. Significant parts of the filamentary structures over this field, as indicated by the galaxy number density map, were also successfully recovered in lensing significance maps. We find the amount of structure recovery depends on both the depth and average seeing of the images. In particular, we detect a $>$ 9 Mpc long structure that contains the cluster A2219. We compare our weak lensing maps with Chandra, XMM, and LOFAR observations and find that A115 and A2219 show clear signs of ongoing mergers. In particular, we find a significant separation of hot ICM and the weak lensing contours in A115. On the other hand, while A2261 appears relaxed, based on radio and X-ray analysis, we find that it is likely interacting with a structure 700 kpc SW of the main cluster. We also successfully recovered mass structures in two regions around A2261 indicated by diffuse X-ray emission in XMM images.

astro-ph.CO↗

arXiv2025

Klein Tunneling in Uniaxial Strained Graphene under Super-Periodic Potential

In this article, we employ the transfer matrix method (TMM) to analytically explore the impact of uniaxial strain on electron scattering in graphene under locally periodic and super-periodic electrostatic potential. Our study reveals that strain significantly influences electron transmission through the merging parameter $(δ)$, which modulates the Dirac cone positions. a positive merging parameter ($δ> 0$) reduces the transmission probability by opening an energy gap at the merging point, while a negative merging parameter ($δ< 0$) enhances transmission by bringing the Dirac cones closer, facilitating electron transport at certain angles. However, the resonance peaks in super-periodic potential (SPP) are sharper for $δ< 0$, making them more pronounced but increasingly difficult to resolve as the number of barriers increases.

cond-mat.mes-hall↗

arXiv2025

Dynamic directed functional connectivity as a neural biomarker for objective motor skill assessment

Objective motor skill assessment plays a critical role in fields such as surgery, where proficiency is vital for certification and patient safety. Existing assessment methods, however, rely heavily on subjective human judgment, which introduces bias and limits reproducibility. While recent efforts have leveraged kinematic data and neural imaging to provide more objective evaluations, these approaches often overlook the dynamic neural mechanisms that differentiate expert and novice performance. This study proposes a novel method for motor skill assessment based on dynamic directed functional connectivity (dFC) as a neural biomarker. By using electroencephalography (EEG) to capture brain dynamics and employing an attention-based Long Short-Term Memory (LSTM) model for non-linear Granger causality analysis, we compute dFC among key brain regions involved in psychomotor tasks. Coupled with hierarchical task analysis (HTA), our approach enables subtask-level evaluation of motor skills, offering detailed insights into neural coordination that underpins expert proficiency. A convolutional neural network (CNN) is then used to classify skill levels, achieving greater accuracy and specificity than established performance metrics in laparoscopic surgery. This methodology provides a reliable, objective framework for assessing motor skills, contributing to the development of tailored training protocols and enhancing the certification process.

q-bio.NC↗

arXiv2025

Forced Measurement of Astronomical Sources at Low Signal to Noise

We propose a modified moment matching algorithm to avoid catastrophic failures for sources with a low signal to noise ratio (SNR). The proposed modifications include a method to eliminate non-physical negative pixel values and a forced single iteration with an initial guess derived from co-add measurements when iterative methods are unstable. We correct for all biases in measurements introduced by the method. We find that the proposed modifications allow the algorithm to avoid catastrophic failures in nearly 100\% of the cases, especially at low signal to noise ratio. Additionally, with a reasonable guess from co-add measurements, the algorithm measures the flux, centroid, size, shape and ellipticity with bias statistically consistent with zero. We show the proposed method allows us to measure sources seven times fainter than traditional methods when applied to images obtained from WIYN-ODI. We also present a scheme to find uncertainties in measurements when using the new method to measure astronomical sources.

astro-ph.IM↗

arXiv2025

Insights from the exact analytical solution of periodically driven transverse field Ising chain

We derive an exact analytical expression at stroboscopic intervals for the time-dependent wave function of a class of integrable quantum many-body systems, driven by the periodic delta-kick protocol. To investigate long-time dynamics, we use the wave function to obtain an exact analytical expression for the expectation values of the defect density, magnetization, residual energy, fidelity, and the correlation function after the $n$th drive cycle. Periodically driven integrable closed quantum systems absorb energy, and the long-time universal dynamics are described by the periodic generalized Gibbs ensemble (GGE). We demonstrate that the expectation values of all observables are divided into two parts: one highly oscillatory term that depends on the drive cycle n, and the rest of the terms are independent of it. Typically, the $n$-independent part constitutes the saturation at large n and periodic GGE. The contribution from the highly oscillatory term vanishes in large $n$. We also generalize our formalism to include square pulse and sinusoidal driving protocols.

cond-mat.str-el↗

arXiv2024

Relativistic particles in super-periodic potentials: exploring graphene and fractal systems

In this article, we employ the transfer matrix method to investigate relativistic particles in super-periodic potentials (SPPs) of arbitrary order $n \in I^{+}$. We calculate the reflection and transmission probabilities for spinless Klein particles encountering rectangular potential barriers with super-periodic repetition. It is found that spinless relativistic particles exhibit Klein tunneling and a significantly higher degree of reflection compared to their non-relativistic counterparts. Additionally, we analytically explore the behavior of experimentally realizable massless Dirac electrons as they encounter rectangular potential barriers with a super-periodic pattern in a monolayer of graphene. In this system, the transmission probability, conductance, and Fano factor are evaluated as functions of the number of barriers, the order of super-periodicity, and the angle of incidence. Our findings reveal that the transmission probability shows a series of resonances that depend on the number of barriers and the order of super-periodicity. We extend our analysis to specific cases within the Unified Cantor Potentials (UCPs)-$γ$ system ($γ$ is a scaling parameter greater than $1$), focusing on the General Cantor fractal system and the General Smith-Volterra-Cantor (GSVC) system. For the General Cantor fractal system, we calculate the tunneling probability, which reveals sharp transmission peaks and progressively thinner unit cell potentials as $G$ increases. In the GSVC system, we analyze the potential segment length and tunneling probability, observing nearly unity tunneling coefficients when $γ\approx 1$, as well as saturation behavior in transmission coefficients at higher stages $G$.

cond-mat.mes-hall↗

arXiv2024

Science with the Daksha High Energy Transients Mission

We present the science case for the proposed Daksha high energy transients mission. Daksha will comprise of two satellites covering the entire sky from 1~keV to $>1$~MeV. The primary objectives of the mission are to discover and characterize electromagnetic counterparts to gravitational wave source; and to study Gamma Ray Bursts (GRBs). Daksha is a versatile all-sky monitor that can address a wide variety of science cases. With its broadband spectral response, high sensitivity, and continuous all-sky coverage, it will discover fainter and rarer sources than any other existing or proposed mission. Daksha can make key strides in GRB research with polarization studies, prompt soft spectroscopy, and fine time-resolved spectral studies. Daksha will provide continuous monitoring of X-ray pulsars. It will detect magnetar outbursts and high energy counterparts to Fast Radio Bursts. Using Earth occultation to measure source fluxes, the two satellites together will obtain daily flux measurements of bright hard X-ray sources including active galactic nuclei, X-ray binaries, and slow transients like Novae. Correlation studies between the two satellites can be used to probe primordial black holes through lensing. Daksha will have a set of detectors continuously pointing towards the Sun, providing excellent hard X-ray monitoring data. Closer to home, the high sensitivity and time resolution of Daksha can be leveraged for the characterization of Terrestrial Gamma-ray Flashes.

astro-ph.HE↗