arXiv subjects

S. Chatterjee

Publications and source records attributed to S. Chatterjee.

At least 19 recordsLinked to original sources

arXiv2026

Timing and statistical analysis of single-pulse search pulsar discoveries from the PALFA survey

Almost two decades after their discovery, pulsars discoverable only through their single, dispersed radio pulses, known as rotating radio transients (RRATS), remain a poorly-understood class of objects. Compared to the overall pulsar population, few have timing solutions, limiting our ability to understand the mechanisms underlying their sporadic emission. Here, we present a single-pulse analysis of twelve sources from the PALFA survey, consisting of eleven objects initially identified as RRATs and one candidate fast radio burst. We present timing solutions for five of the sources with detections at a sufficient number of epochs and spin periods for two more. For all sources, we use a Bayesian framework to fit distributions of single-pulse energies, finding support for log-normal energy distributions and pulse-to-pulse wait times that are consistent with Poisson processes. Finally, we provide updates on the previously-published candidate fast radio burst J0613+18, with new indications that it is in fact extragalactic.

astro-ph.HE↗

arXiv2026

Optical Counterparts of MeerKLASS L-band and UHF-band surveys

Context: Wide-area radio continuum surveys require reliable optical and infrared counterpart identification, but high optical source densities and extended or multi-component radio morphologies make this challenging. Aims: We present optical and infrared counterpart catalogs for MeerKLASS L-band and UHF-band on-the-fly continuum sources using KiDS DR5 and DESI Legacy Imaging Surveys DR10 (LS DR10), including counterpart probabilities, redshifts, and host-galaxy properties. Methods: We developed the Stellar-mass Enhanced Density Association (SEDA) method, an empirical framework that compares candidate densities around radio positions with those in a position-displaced control catalog. For galaxies we use positional offset, stellar mass, and redshift; quasar candidates are treated separately using offset and mid-infrared selection. A second-pass search associates multi-component radio sources with common hosts. Results: In the L-band survey, we identify 20,400 KiDS-based counterparts with $P_{\rm true}>0.5$, corresponding to 66% of L-band sources within the KiDS footprint. In the UHF-band survey, we identify 61,633 LS DR10 counterparts, corresponding to 81% of the radio sources. Spectroscopic redshifts are available for 22% and 44% of the L-band and UHF-band counterparts, respectively. The redshift distributions show low-redshift star-forming galaxies, intermediate-redshift radio galaxies, and a high-redshift tail dominated by quasars. SEDA also recovers rare radio-loud quasars, including QSO J2318-3113 at $z=6.44$ and UHF_DR1 J+111111.8+053626.6 at $z=5.24$. Conclusions: SEDA provides a data-driven route to counterpart identification for wide-area radio surveys with complex source morphologies. The catalogs enable future MeerKLASS studies of radio source populations, host-galaxy demographics, and rare high-redshift radio quasars.

astro-ph.GA↗

arXiv2026

Radio Halos in Galaxy Clusters as unveiled by the SKA telescope

Giant radio halos (RHs) are diffuse, Mpc-scale synchrotron sources observed in a growing fraction of galaxy clusters. They trace relativistic particles and magnetic fields in the intracluster medium (ICM), providing a unique window into non-thermal processes and their role in cluster evolution. RHs are primarily found in merging systems, supporting models in which turbulence generated during cluster collisions re-accelerates pre-existing electrons to the energies required for the observed radio emission. In this scenario, the occurrence, power, and spectral properties of RHs depend on the energetics of cluster mergers, with the most massive and dynamically disturbed clusters hosting the most powerful halos. Low-frequency observations are crucial to uncover ultra-steep-spectrum RHs, a key prediction of turbulent re-acceleration models, and are expected to arise from less energetic merger events. LOFAR has enabled statistical studies of large cluster samples, placing robust constraints on RH occurrence and spectral trends. In this Chapter, we model RH formation and evolution using Monte Carlo simulations calibrated on LoTSS-DR2 findings, and we present predictions for SKA-Low in the AA4 configuration. Our results show that SKA will probe an unprecedented region of cluster mass and redshift space, detecting at least $\sim 2500$ RHs up to $z \approx 0.6$, including $\gtrsim 1000$ ultra-steep-spectrum systems, and revealing halos in clusters down to $\sim 10^{14}\, M_\odot$ and out to $z \approx 1$. These surveys will provide stringent tests of turbulent re-acceleration models and significantly advance our understanding of non-thermal processes in galaxy clusters.

astro-ph.CO↗

arXiv2026

Galactic Centre Pulsars with the SKAO

The detection of a pulsar closely orbiting our Galaxy's supermassive black hole - Sagittarius~A* - is one of the ultimate prizes in pulsar astrophysics. The relativistic effects expected in such a system could far exceed those currently observable in compact binaries such as double neutron stars and pulsar white dwarfs. In addition, pulsars offer the opportunity to study the magneto-ionic properties of Earth's nearest galactic nucleus in unprecedented detail. For these reasons, and more, a multitude of pulsar searches of the Galactic Centre have been undertaken, with the outcome of just seven pulsar detections within a projected distance of 100\,pc from Sagittarius~A*. It is currently understood that a larger underlying population likely exists, but it is not until observations with the SKA have started that this population can be revealed. In this chapter, we look at important updates since the publication of the last SKAO science book and offer a focused view of observing strategies and likely outcomes with the updated SKAO design.

astro-ph.HE↗

arXiv2026

Low lying excitations in $^{150}$Pm

The low lying excitations in odd-odd $^{150}$Pm have been studied through proton induced reaction with an array of five Compton suppressed Clover HPGe and one segmented planar Ge detectors. The relative excitation functions for the observed $\gamma$ rays have been studied using singles data at two beam energies of 8~MeV and 9~MeV. 16 new $\gamma$ rays and 15 new levels have been placed in the level scheme of $^{150}$Pm based on $\gamma-\gamma$ coincidence data. The relative intensities for the observed $\gamma$ rays have been determined using total and gated projections. Tentative spin-parity assignments were made to few low lying excitations of $^{150}$Pm, using limited angular distribution data and other information. Lifetimes were estimated for two excited levels in this nucleus using using generalized centroid difference analysis, applied in the nanosecond range, with Ge detectors. Large basis shell model and projected shell model calculation were performed to interpret the experimentally observed levels. The present work indicates 1$^-$ ground state, a 2$^-$ state close to the ground state ($\sim$50~keV) and a low lying 6$^-$ isomeric state in this odd-odd nucleus along with emerging band structures developed with two quasiparticle configurations.

nucl-ex↗

arXiv2026

Evidence of the Excited X(5)-like Critical-Point Symmetry Structures in 152Sm

The positive-parity structure of 152Sm has been investigated through high-statistics {\gamma}-ray spectroscopy following the (150Nd({\alpha},2n)152Sm reaction at Elab = 26 MeV. Several collective structures built on excited 0+ states have been extended through the observation of new levels and {\gamma}-ray transitions, and spin-parity assignments have been established using directional-correlation and linear-polarization measurements. Electromagnetic transition strengths (B(E2)), deduced from measured branching ratios and known level lifetimes, reveal pronounced collectivity among the excited configurations. The resulting level scheme provides evidence for a sequence of excited collective bands extending beyond the well-known ground-state and first excited 0+ structures. The excitation energies and transition strengths are examined within the framework of the X(5) critical-point description of the first-order U(5)-SU(3) shape-phase transition. In addition to the established X(5)-like features of the low-lying spectrum, the observed systematics of the higher-lying bands are found to be consistent with excited collective structures exhibiting X(5)-like characteristics. The results provide new constraints on the realization of critical-point behavior in finite nuclei and on the evolution of collectivity in the N=90 region.

nucl-ex↗

arXiv2026

Combined LOFAR-uGMRT analysis of the diffuse radio emission in the massive clusters Abell 773 and Abell 1351

Radio halos are megaparsec-scale diffuse, non-thermal radio sources located at the centers of galaxy clusters, tracing relativistic particles and magnetic fields in the intra-cluster medium. Their origin is generally attributed to cluster mergers that generate turbulence and re-accelerate aged electrons. We study the diffuse radio emission, spectral properties, and the connection between thermal and non-thermal components in the massive galaxy clusters Abell 773 and Abell 1351 ($M_{500} \sim 7 \times 10^{14}\,M_{\odot}$), both of which are dynamically disturbed. We combine LOFAR LoTSS-DR2 observations at 144 MHz with uGMRT observations at 650 MHz, supplemented by archival XMM-Newton X-ray imaging. We confirm that both clusters host radio halos extending up to a largest linear size of $\sim 2$ Mpc. We measure an integrated spectral index $\alpha_{144}^{650} \sim -1.0$ for both clusters. The radio halo in Abell 773 resembles a classical halo and follows a sublinear radio--X-ray surface brightness relation. In contrast, Abell 1351 shows a more complex and asymmetric morphology, influenced by embedded radio sources including the brightest cluster galaxy, a tailed radio galaxy, and a ridge-like feature. These contaminating sources lead to deviations from the sublinear trend in the point-to-point radio--X-ray analysis of Abell 1351.

astro-ph.CO↗

arXiv2025

Galactic Centre Pulsars with the SKAO

The detection of a pulsar closely orbiting our Galaxy's supermassive black hole - Sagittarius A* - is one of the ultimate prizes in pulsar astrophysics. The relativistic effects expected in such a system could far exceed those currently observable in compact binaries such as double neutron stars and pulsar white dwarfs. In addition, pulsars offer the opportunity to study the magneto-ionic properties of Earth's nearest galactic nucleus in unprecedented detail. For these reasons, and more, a multitude of pulsar searches of the Galactic Centre have been undertaken, with the outcome of just seven pulsar detections within a projected distance of 100 pc from Sagittarius A*. It is currently understood that a larger underlying population likely exists, but it is not until observations with the SKA have started that this population can be revealed. In this paper, we look at important updates since the publication of the last SKAO science book and offer a focused view of observing strategies and likely outcomes with the updated SKAO design.

astro-ph.HE↗

arXiv2025

Emergent Universe Scenario in the Modified Chaplygin gas : Towards an Exact Solution and Observational Constraints

The Modified Chaplygin Gas (MCG) model is revisited as a unified framework for describing cosmic evolution. Due to the nonlinear field equations, exact solutions in cosmic time are generally unavailable; hence, a first-order approximation is employed to obtain the scale factor and flip time. The effective equation-of-state parameter evolves from a positive value in the early universe to $w_{\mathrm{eff}}\approx -1$ at late times, yielding a transition from deceleration to acceleration and approaching the $\Lambda$CDM limit. In the phantom regime, the model admits an emergent solution with a finite minimum scale factor and a late-time de~Sitter--like phase. The emergent solution is geodesically complete and free from curvature singularities, as confirmed by the regular Kretschmann scalar. CMB constraints for all considered cases remain consistent with observations within the $1\sigma$ confidence level, while the combined Hubble-$57$ and CMB analysis provides improved parameter constraints. The solutions are further verified independently using the Raychaudhuri equation, providing an additional consistency check. Overall, the results establish the MCG model as a self-consistent and observationally viable framework for cosmic evolution within general relativity.

gr-qc↗

arXiv2025

A New Evidence of Interplay Between Tetrahedral and Octahedral Symmetries and Symmetry Breaking: Exotic Rotational Bands in $^{152}$Sm

We report on an experimental evidence for a new, second tetrahedral band in $^{152}_{\;\;62}$Sm$^{}_{90}$. It was populated via fusion evaporation reaction, $^{150}{\rm Nd}(\alpha, 2n)^{152}$Sm, employing 26 MeV beam of $\alpha$ particles from K-130 cyclotron at Variable Energy Cyclotron Centre, Kolkata, India. The newly observed possible mixed parity sequence with absence of E2 and strong indication of E3 transitions is consistent with the spectroscopic criteria for a tetrahedral-symmetry rotational band that could be constructed from the allowed spin-parity assignments. This structure differs from the structure of the band previously found in the same nucleus, the new one manifesting tetrahedral symmetry not accompanied by the octahedral one. Our new experimental results are interpreted in terms of group representation theory and collective nuclear-motion theory of Bohr. We propose to generalize the notion of the tetrahedral vibrational bands and believe that our new experimental results support a number of theory predictions related to nuclear tetrahedral symmetry published earlier and bring a new light into the issue of spontaneous symmetry breaking in heavy nuclei.

nucl-ex↗

arXiv2025

GReX: An Instrument Overview and New Upper Limits on the Galactic FRB Population

We present the instrument design and initial results for the Galactic Radio Explorer (GReX), an all-sky monitor for exceptionally bright transients in the radio sky. This instrument builds on the success of STARE2 to search for fast radio bursts (FRBs) from the Milky Way and its satellites. This instrument has deployments across the globe, with wide sky coverage and searching down to $32\,\mu\text{s}$ time resolution, enabling the discovery of new super giant pulses. Presented here are the details of the hardware and software design of the instrument, performance in sensitivity and other key metrics, and experience in building a global-scale, low-cost experiment. We follow this discussion with experimental results on validation of the sensitivity via hydrogen-line measurements. We then update the rate of Galactic FRBs based on non-detection in the time since FRB 200428. Our results suggest FRB-like events are even rarer than initially implied by the detection of a MJy burst from SGR J1935+2154 in April 2020.

astro-ph.HE↗

arXiv2025

Higher-Dimensional Cosmology in the Framework of Generalized Chaplygin Gas: An Approximation Method

We present a higher-dimensional cosmological model with a generalized Chaplygin-type gas to explain the late-time acceleration of the Universe. The model admits dimensional reduction and reproduces the standard $4D$ Chaplygin cosmology for $d=0$. Using Hubble-$57$ data, we obtain observational constraints on the model parameters. Due to the highly nonlinear nature of the field equations, the model successfully describes both matter-dominated and accelerating phases of the Universe. By adopting a first-order approximation, we derive exact time-dependent solutions for the scale factors in both ordinary and extra dimensions, along with an exact expression for the flip time. The model approaches the $\Lambda$CDM scenario at large scale factors and exhibits the desired transition from deceleration to acceleration. The evolution of the deceleration parameter, effective EoS parameter, and jerk parameter is also discussed. The constrained value of the Chaplygin parameter $\alpha \ll 1$ disfavors the pure Chaplygin gas model $(\alpha = 1)$ and suggests that smaller values of $\alpha$ are favored at late times.

gr-qc↗

arXiv2025

Square Kilometre Array Science Data Challenge 3a: foreground removal for an EoR experiment

We present and analyse the results of the Science data challenge 3a (SDC3a, https://sdc3.skao.int/challenges/foregrounds), an EoR foreground-removal community-wide exercise organised by the Square Kilometre Array Observatory (SKAO). The challenge ran for 8 months, from March to October 2023. Participants were provided with realistic simulations of SKA-Low data between 106 MHz and 196 MHz, including foreground contamination from extragalactic as well as Galactic emission, instrumental and systematic effects. They were asked to deliver cylindrical power spectra of the EoR signal, cleaned from all corruptions, and the corresponding confidence levels. Here we describe the approaches taken by the 17 teams that completed the challenge, and we assess their performance using different metrics. The challenge results provide a positive outlook on the capabilities of current foreground-mitigation approaches to recover the faint EoR signal from SKA-Low observations. The median error committed in the EoR power spectrum recovery is below the true signal for seven teams, although in some cases there are some significant outliers. The smallest residual overall is $4.2_{-4.2}^{+20} \times 10^{-4}\,\rm{K}^2h^{-3}$cMpc$^{3}$ across all considered scales and frequencies. The estimation of confidence levels provided by the teams is overall less accurate, with the true error being typically under-estimated, sometimes very significantly. The most accurate error bars account for $60 \pm 20$\% of the true errors committed. The challenge results provide a means for all teams to understand and improve their performance. This challenge indicates that the comparison between independent pipelines could be a powerful tool to assess residual biases and improve error estimation.

astro-ph.IM↗

arXiv2025

Report on reproducibility in condensed matter physics

We present recommendations to improve reproducibility and replicability in condensed matter physics. This area of physics has consistently produced both fundamental insights into the workings of matter and transformative inventions. Our recommendations result from a collaboration that includes researchers from academia and government laboratories, scientific journalists, legal professionals, representatives of publishers, professional societies, and other experts. The group met in person in May 2024 at a conference at the University of Pittsburgh to discuss the growing challenges related to research reproducibility and replicability in condensed matter physics. In this report, we discuss best practices and policies at all stages of the scientific process to safeguard the value of condensed matter. We hope this report will lay the groundwork for a broader conversation to develop subfield-specific recommendations.

cond-mat.other↗

arXiv2024

The Massive and Quiescent Elliptical Host Galaxy of the Repeating Fast Radio Burst FRB20240209A

The discovery and localization of FRB20240209A by the Canadian Hydrogen Intensity Mapping Fast Radio Burst (CHIME/FRB) experiment marks the first repeating FRB localized with the CHIME/FRB Outriggers and adds to the small sample of repeating FRBs with associated host galaxies. Here we present Keck and Gemini observations of the host that reveal a redshift $z=0.1384\pm0.0004$. We perform stellar population modeling to jointly fit the optical through mid-infrared data of the host and infer a median stellar mass log$(M_*/{\rm M_{\odot}})=11.34\pm0.01$ and a mass-weighted stellar population age $\sim11$Gyr, corresponding to the most massive and oldest FRB host discovered to date. Coupled with a star formation rate $<0.36\,{\rm M_{\odot}\ yr^{-1}}$, the specific star formation rate $<10^{-11.8}\rm\ yr^{-1}$ classifies the host as quiescent. Through surface brightness profile modeling, we determine an elliptical galaxy morphology, marking the host as the first confirmed elliptical FRB host. The discovery of a quiescent early-type host galaxy within a transient class predominantly characterized by late-type star-forming hosts is reminiscent of short-duration gamma-ray bursts, Type Ia supernovae, and ultraluminous X-ray sources. Based on these shared host demographics, coupled with a large offset as demonstrated in our companion paper, we conclude that preferred progenitors for FRB20240209A include magnetars formed through merging binary neutron stars/white dwarfs or the accretion-induced collapse of a white dwarf, or a luminous X-ray binary. Together with FRB20200120E localized to a globular cluster in M81, our findings provide strong evidence that some fraction of FRBs may arise from a process distinct from the core collapse of massive stars.

astro-ph.HE↗

arXiv2024

A repeating fast radio burst source in the outskirts of a quiescent galaxy

We report the discovery of the repeating fast radio burst source FRB 20240209A using the CHIME/FRB telescope. We have detected 22 bursts from this repeater between February and July 2024, six of which were also recorded at the Outrigger station KKO. The 66-km long CHIME-KKO baseline can provide single-pulse FRB localizations along one dimension with $2^{\prime\prime}$ accuracy. The high declination of $\sim$86 degrees for this repeater allowed its detection with a rotating range of baseline vectors, enabling the combined localization region size to be constrained to $1^{\prime\prime}\times2^{\prime\prime}$. We present deep Gemini observations that, combined with the FRB localization, enabled a robust association of FRB 20240209A to the outskirts of a luminous galaxy (P(O|x) = 0.99; $L \approx 5.3 \times 10^{10}\,L_{\odot}$). FRB 20240209A has a projected physical offset of $40 \pm 5$ kpc from the center of its host galaxy, making it the FRB with the largest host galaxy offset to date. When normalized by the host galaxy size, the offset of FRB 20240209A is comparable to that of FRB 20200120E, the only FRB source known to originate in a globular cluster. We consider several explanations for the large offset, including a progenitor that was kicked from the host galaxy or in situ formation in a low-luminosity satellite galaxy of the putative host, but find the most plausible scenario to be a globular cluster origin. This, coupled with the quiescent, elliptical nature of the host as demonstrated in our companion paper, provide strong evidence for a delayed formation channel for the progenitor of the FRB source.

astro-ph.HE↗

arXiv2024

Performance study of a bakelite RPC prototype built by new technique of linseed oil coating

Resistive Plate Chamber (RPC) is one of the most commonly used detectors in high energy physics experiments for triggering and tracking because of its good efficiency ($\textgreater$~90\%) and time resolution ($\sim$~1-2~ns). Generally, bakelite which is one of the most commonly used materials as electrode plates in RPC, sometimes suffers from surface roughness issues. If the surface is not smooth, the probability of micro discharges and spurious pulses increase, which leads to the deterioration in the performance of the detector. We have developed a new method of linseed oil coating for the bakelite based detectors to avoid the surface roughness issue. The detector is characterised with Tetrafluoroethane (R134a) based gas mixture. The detector is also tested with a high rate of gamma radiation environment in the laboratory for the radiation hardness test. The detailed measurement procedure and test results are presented in this article.

physics.ins-det↗

arXiv2024

Effects of Strain Compensation on Electron Mobilities in InAs Quantum Wells Grown on InP(001)

InAs quantum wells (QWs) grown on InP substrates are interesting for their applications in devices with high spin-orbit coupling (SOC) and their potential role in creating topologically nontrivial hybrid heterostructures. These QWs rely on InGaAs cladding layers and InAlAs barrier layers to confine electrons within a thin InAs well. The highest mobility QWs are limited by interfacial roughness scattering and alloy disorder scattering in the cladding and buffer layers. Increasing QW thickness has been shown to reduce the effect of both of these scattering mechanisms. However, for current state-of-the-art devices with As-based cladding and barrier layers, the critical thickness is limited to $\leq7$ nm. In this report, we demonstrate the use of strain compensation techniques in the In$_x$Ga$_{1-x}$As cladding layers, grown on In$_{0.81}$Al$_{0.19}$As barrier layers, to extend the critical thickness well beyond this limit. We induce tensile strain in the InGaAs cladding layers by reducing the In concentration from In$_{0.81}$Ga$_{0.19}$As to In$_{0.70}$Ga$_{0.30}$As and we observe changes in both the critical thickness of the well and the maximum achievable mobility. The peak electron mobility at 2 K is $1.16\times10^6$ cm$^2/$Vs, with a carrier density of $4.2\times10^{11}$ /cm$^2$. Additionally, we study the quantum lifetime and Rashba spin splitting in the highest mobility device as these parameters are critical to determine if these structures can be used in topologically nontrivial devices.

cond-mat.mes-hall↗