arXiv subjects

Sovan Chakraborty

Publications and source records attributed to Sovan Chakraborty.

At least 19 recordsLinked to original sources

arXiv2026

Reconstructing the Auger UHECR Dipole: A Hybrid Analysis of 4LAC AGNs and Nearby Starburst Galaxies

The large-scale dipole anisotropy observed by the Pierre Auger Observatory above $8$~EeV provides important clues about the origin of ultra-high-energy cosmic rays (UHECRs). In this work, we investigate whether gamma-ray active galactic nuclei (AGNs) from the Fermi-LAT Fourth AGN Catalog (4LAC) can explain the observed dipole and examine the contribution of nearby starburst galaxies (SBGs). Incorporating source fluxes, redshift distributions, GZK attenuation, and a mixed-composition framework, we demonstrate that single-source populations of AGNs and SBGs alone fail to reproduce the observed Auger dipole. To resolve this, we construct a hybrid AGN+SBG model. The best-fit solution for the $8$--$16$~EeV interval requires a $23$\% AGN contribution and $45$\% SBG contribution, which gives a dipole amplitude of $5.03$\% while maintaining the dipole direction of ($104.1^\circ$, $-25.1^\circ$) with angular separation of $7.10^\circ$. In the other energy intervals also, we find that the nearby SBGs increasingly dominate the anisotropic component while AGNs provide a subdominant contribution alongside a quasi-isotropic background.

astro-ph.HE↗

arXiv2026

Neutrino mass ordering from the next Galactic supernova at DUNE, HK, and JUNO

The next Galactic core-collapse supernova (CCSN) will offer a unique opportunity to determine the neutrino mass ordering. We focus on two observables: the electron neutrino ($\nu_e$) neutronization burst and the rise-time of the electron antineutrino ($\bar{\nu}_e$) flux during the accretion phase. The neutronization burst, a sharp $\nu_e$ peak within $\sim 20$-$30$ ms, provides a clean and robust signature of mass ordering through its appearance or disappearance. During the accretion phase, the faster rise of heavy lepton flavor neutrinos ($\nu_x$) leads to a distinct faster rise-time behavior of the oscillated $\bar{\nu}_e$ signal, resulting in mass ordering discrimination. Using realistic CCSN simulations for multiple progenitor masses, we compute event rates and perform a statistical analysis for a Galactic ($10$~kpc) CCSN event at DUNE, Hyper-Kamiokande (HK), and JUNO detectors. The neutronization burst remains largely independent of SN hydrodynamic simulation models, with DUNE and HK achieving $\gtrsim 6\sigma$ and $\gtrsim 4\sigma$ sensitivity for normal (NO) to inverted ordering (IO) discrimination, respectively. However, the rise-time observable is prone to progenitor degeneracies. To mitigate this cumulative and ratio-based observables constructed at characteristic timescales ($20$ ms & $100$ ms) are used. The resulting confidence levels from the rise-time analysis to discriminate IO/NO in HK and JUNO are $\sim 5\sigma$ and $\sim 3\sigma$, respectively. Our results highlight the complementarity of detectors and observables, and demonstrate that combining neutronization burst and accretion phase information will be crucial for a definitive determination of the neutrino mass ordering in the next Galactic supernova.

hep-ph↗

arXiv2025

High-energy Neutrino Predictions for T Coronae Borealis: Probing Particle Acceleration in Novae

The MAGIC detection of near-TeV gamma rays from the 2021 RS Oph ($2.45$ kpc) outburst has established recurrent novae as TeV particle accelerators. However, the origin of this emission (hadronic vs leptonic) remains unclear due to the lack of coincident neutrinos detected by IceCube. The upcoming outburst of the much closer T Coronae Borealis (T CrB, $\sim0.887$ kpc) offers a unique opportunity to detect these rare nova neutrinos. Here we present the first comparative analysis of the hadronic secondary fluxes expected from the upcoming T CrB outburst and evaluate their detectability across major observatories, considering two proton-acceleration mechanisms: (i) an external shock (ES) at $\sim10^{13}$ cm, and (ii) magnetic reconnection (MR), near the white dwarf surface at $\sim10^{9}$ cm. While the benchmark ES model predicts a gamma-ray flux detectable by current facilities, its corresponding neutrino flux largely remains undetectable. In contrast, the MR scenario generates a robust neutrino flux within the reach of IceCube and KM3NeT. Importantly, as the MR-produced gamma-rays are absorbed, the escaping MR neutrinos will arrive hours before any ES-origin signals. This distinct temporal separation can create a powerful phenomenological signature to disentangle the nova acceleration physics.

astro-ph.HE↗

arXiv2025

A White Paper on The Multi-Messenger Science Landscape in India

The multi-messenger science using different observational windows to the Universe such as Gravitational Waves (GWs), Electromagnetic Waves (EMs), Cosmic Rays (CRs), and Neutrinos offer an opportunity to study from the scale of a neutron star to cosmological scales over a large cosmic time. At the smallest scales, we can explore the structure of the neutron star and the different energetics involved in the transition of a pre-merger neutron star to a post-merger neutron star. This will open up a window to study the properties of matter in extreme conditions and a guaranteed discovery space. On the other hand, at the largest cosmological scales, multi-messenger observations allow us to study the long-standing problems in physical cosmology related to the Hubble constant, dark matter, and dark energy by mapping the expansion history of the Universe using GW sources. Moreover, the multi-messenger studies of astrophysical systems such as white dwarfs, neutron stars, and black holes of different masses, all the way up to a high redshift Universe, will bring insightful understanding into the physical processes associated with them that are inaccessible otherwise. This white paper discusses the key cases in the domain of multi-messenger astronomy and the role of observatories in India which can explore uncharted territories and open discovery spaces in different branches of physics ranging from nuclear physics to astrophysics.

astro-ph.HE↗

arXiv2024

Exploring velocity dispersion anisotropy in a dark matter dominated ultra-diffuse galaxy with modified gravity models

The kinematics of the ultra-diffuse galaxy (UDG) NGC1052-DF44 is primarily influenced by the presence of dark matter (DM). In this paper, we conduct a contrasting kinematic study of DF44 within the alternative modified gravity framework. In comparison to NFW DM, we test three alternative gravity models viz Milgromian dynamics (MOND), characterized by a known acceleration scale, a generic $f(R)$ model, assuming an expansion of the Ricci scalar, and a quantum gravity-inspired Renormalization Group correction to General Relativity (RGGR), which involves the running of the gravitational coupling parameter $G$ with the Universe's energy scale. For each gravity model, we evaluate the velocity dispersion (VD) of the galaxy beyond the conventional radial isotropic assumption and extend to two anisotropy scenarios, i.e., constant and Osipkov-Merritt. Our results show that all three gravity models can provide consistent fits to the observed VD of DF44; however, only MOND and RGGR remain competitive with NFW DM. Interestingly, the constant anisotropy scenario in all the models is also found to be competitive with the complete isotropic assumption.

astro-ph.CO↗

arXiv2024

Phenomenology of renormalization group improved gravity from the kinematics of SPARC galaxies

Renormalization Group correction to General Relativity (RGGR) proposes a logarithmic running of the gravitational coupling $\left(G\right)$, resulting in a modified description of gravity. This has the potential to explain the observed kinematics of the galaxies, including the missing-mass problem. We, for the first time, based on the galaxy morphological types, investigate the dynamics of a diverse collection of galaxies present in the Spitzer Photometry for Accurate Rotation Curve (SPARC) catalog. We phenomenologically constrain the RGGR model parameter $\left(\barν\right)$ along with the mass-to-light ratio for a sample of 100 SPARC galaxies, selected from four different morphological types, viz. early, spiral, late, and starburst. Our statistical analysis finds RGGR to fit the observed galaxy kinematics consistently. The constrained RGGR model parameter also supports the claim that it has a near-linear dependence on the galactic baryonic mass. From our morphology study, we find that the parameter $\barν$ decreases from the early-type to the starburst galaxies. Finally, the renormalization group improved gravity is tested against the two established empirical relations for the SPARC catalog, viz., the Radial Acceleration Relation (RAR) and the Baryonic Tully Fisher relation (BTFR), both are found to be satisfied consistently.

gr-qc↗

arXiv2024

The Amaterasu particle: constraining the superheavy dark matter origin of UHECRs

Amaterasu, the second most energetic ($244$ EeV) cosmic ray particle has been recently detected by the Telescope Array (TA) surface detector. The origin of the TA Amaterasu event is puzzling, as its arrival direction points back to a void in the local Universe, lacking conventional astrophysical ultra-high-energy (UHE) cosmic ray sources. Hence, we explore the possibility if this TA Amaterasu event could have originated from the decay of superheavy dark matter (SHDM) in the Milky Way. Such an origin also opens up multi-messenger detection channels in both UHE gamma-rays and UHE neutrinos. In this present work, using the TA Amaterasu event and the multi-messenger limits/sensitivities from various UHE telescopes, we place stringent constraints on the lifetime and mass of the SHDM. We find that the non-detection of the corresponding gamma-rays at the Pierre Auger Observatory (PAO) and the TA is in severe tension with the SHDM parameter space required to explain the TA Amaterasu event. Additionally, we extend the multi-messenger analysis to the future UHE gamma-ray and UHE neutrino telescopes such as PAO upgrade, GRAND 200k and IceCube-Gen2. We find that the bounds from the future neutrino telescopes will be able to compete with the present UHECR bounds. However, compared to the existing UHE gamma-ray bounds, the future PAO upgrade and the GRAND 200k gamma-ray detectors will improve the bounds on SHDM lifetime by at least one order of magnitude.

hep-ph↗

arXiv2024

Gamma-rays and Neutrinos from Giant Molecular Cloud Populations in the Galactic Plane

The recent IceCube detection of significant neutrino flux from the inner Galactic plane has provided us valuable insights on the spectrum of cosmic rays in our Galaxy. This flux can be produced either by a population of Galactic point sources or by diffused emission from cosmic ray interactions with the interstellar medium or by a mixture of both. In this work, we compute diffused gamma-ray and neutrino fluxes produced by a population of giant molecular clouds (GMCs) in our Galaxy, assuming different parametrizations of the Galactic diffused cosmic ray distribution. In particular, we take into account two main cases: (I) constant cosmic ray luminosity in our Galaxy, and (II) space-dependent cosmic ray luminosity, based on the supernovae distribution in our Galaxy. For Case-I, we found that the neutrino flux from GMCs is a factor of $\sim 10$ below compared to $π^0$ and KRA$_γ$ best-fitted models of IceCube observations at $10^5$ GeV. Instead, for Case-II the model can explain up to $\sim 90 \%$ of the neutrino flux at that energy. Moreover, for this last scenario IceCube detector could be able to detect neutrino events from the Galactic centre regions. We then calculated gamma-ray and neutrino fluxes from individual GMCs and noticed that several current and future Cherenkov telescopes and neutrino observatories have the right sensitivities to study these objects. In particular, very neutrino-bright region such as Aquila Rift is favourable for detection by the IceCube-Gen2 observatory.

astro-ph.HE↗

arXiv2024

A relook at the GZK Neutrino-Photon Connection: Impact of Extra-galactic Radio Background & UHECR properties

Ultra-high energy cosmic rays (UHECRs) beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off provide us with a unique opportunity to understand the universe at extreme energies. Secondary GZK photons and GZK neutrinos associated with the same interaction are indeed interconnected and render access to multi-messenger analysis of UHECRs. The GZK photon flux is heavily attenuated due to the interaction with Cosmic Microwave Background (CMB) and the Extra-galactic Radio Background (ERB). The present estimate of the ERB comprising of several model uncertainties together with the ARCADE2 radio results in large propagation uncertainties in the GZK photon flux. On the other hand, the weakly interacting GZK neutrino flux is unaffected by these propagation effects. In this work, we make an updated estimate of the GZK photon and GZK neutrino fluxes considering a wide variation of both the production and propagation properties of the UHECR like, the spectral index, the cut-off energy of the primary spectrum, the distribution of sources and the uncertainties in the ERB estimation. We explore the detection prospects of the GZK fluxes with various present and upcoming UHECR and UHE neutrino detectors such as Auger, TA, GRAND, ANITA, ARA, IceCube and IceCube-Gen2. The predicted fluxes are found to be beyond the reach of the current detectors. In future, proposed IceCube-Gen2, Auger upgrade and GRAND experiments will have the sensitivity to the predicted GZK photon and GZK neutrino fluxes. Such detection can put constraints on the UHECR source properties and the propagation effects due to the ERB. We also propose an indirect limit on the GZK photon flux using the neutrino-photon connection for any future detection of GZK neutrinos by the IceCube-Gen2 detector. We find this limit to be consistent with our GZK flux predictions.

astro-ph.HE↗

arXiv2023

Gamma-rays and neutrinos from supernovae of Type Ib/c with late time emission

Observations of some supernovae (SNe), such as SN 2014C, in the X-ray and radio wavebands revealed a rebrightening over a timescale of about a year since their detection. Such a discovery hints towards the evolution of a hydrogen-poor SN of Type Ib/c into a hydrogen-rich SN of Type IIn, the late time activity being attributed to the interaction of the SN ejecta with a dense hydrogen-rich circumstellar medium (CSM) far away from the stellar core. We compute the neutrino and gamma-ray emission from these SNe, considering interactions between the shock accelerated protons and the non-relativistic CSM protons. Assuming three CSM models inspired by recent electromagnetic observations, we explore the dependence of the expected multi-messenger signals on the CSM characteristics. The detection prospects of existing and upcoming gamma-ray (Fermi-LAT and Cerenkov Telescope Array) and neutrino (IceCube and IceCube-Gen2) telescopes are also outlines. Our findings are in agreement with the non-detection of neutrinos and gamma-rays from past SNe exhibiting late time emission. Nevertheless, the detection prospects of SNe with late time emission in gamma-rays and neutrinos with the Cerenkov Telescope Array and IceCube-Gen2 (Fermi-LAT and IceCube) are promising and could potentially provide new insight into the CSM properties, if the SN burst should occur within $10$ Mpc ($4$ Mpc).

astro-ph.HE↗

arXiv2023

Velocity dispersion of dark matter deficient ultra-diffuse galaxies: A case for modified gravity

The line of sight velocity dispersion of the ultra-diffuse galaxies (UDGs) NGC1052-DF2 and NGC1052-DF4 have been reasonably explained only with the baryonic matter, without requiring any dark matter contribution. The comparable ratio between the baryonic and halo mass also ascertain the above claim for the two dark matter deficit galaxies. This paves the way for analyzing alternative gravity theories such as the $f(R)$ gravity and the Renormalization Group correction to General Relativity (RGGR). The analysis of the line of sight velocity dispersion shows that the choice of $f(R)$ gravity models such as Taylor expanded $f(R)$ about $R=0$ or a simple power law model of choice $R^n$ is consistent with the observational data. Similar statistical analysis is done for the RGGR and is also found to be a viable explanation for the observed velocity dispersion. We perform a global fit of the model parameters together with both the UDGs. The coupling parameters of the theories are considered as the global ones, and local variables such as the scale parameters are considered to be dependent on the individual galaxy.

gr-qc↗

arXiv2023

Probing LHAASO Galactic PeVatrons through gamma-ray and neutrino correspondence

Recently, Large High Altitude Air Shower Observatory (LHAASO) has detected several Galactic point sources of ultra high energy (UHE; $E_γ> 100$ TeV) gamma-rays. These gamma-rays are possibly created in leptonic or hadronic interactions of cosmic rays (CRs) of PeV energies. In the hadronic channel ($p-p$ interaction), the gamma-rays are accompanied by neutrinos. The detection of neutrinos is therefore crucial in understanding CR acceleration in such objects. To estimate the neutrino flux, we adopt the two LHAASO sources (J2226+6057, J1908+0621) found to be spatially associated with the Supernova remnants (SNR G106.3+2.7, SNR G40.5-0.5). For these two sources, the detected TeV-PeV gamma-ray spectra are found to be unusually hard (with spectral index $\sim$ 1.8). We develop a model of gamma-ray and neutrino emission based on the above two prototypes. The neutrino fluxes from these two sources are found to be below the IceCube sensitivity, but are detectable in upcoming IceCube-Gen2 and KM3NeT experiments. We further estimate the neutrino fluxes from similar other 10 LHAASO PeVatron sources and most of them are found to be detectable in IceCube-Gen2 and KM3NeT. Finally, we explore our model parameters, in particular the spectral power law index and estimate the future potential of the neutrino detectors to probe CR acceleration in such Galactic sources.

astro-ph.HE↗

arXiv2022

Supernova fast flavor conversions in 1+1D : Influence of mu-tau neutrinos

In the dense supernova environment, neutrinos can undergo fast flavor conversions which depend on the large neutrino-neutrino interaction strength. It has been recently shown that both their presence and outcome can be affected when passing from the commonly used three neutrino species approach to the more general one with six species. Here, we build up on a previous work performed on this topic and perform a numerical simulation of flavor evolution in both space and time, assuming six neutrino species. We find that the results presented in our previous work remain qualitatively the same even for flavor evolution in space and time. This emphasizes the need for going beyond the simplistic approximation with three species when studying fast flavor conversions.

hep-ph↗

arXiv2022

Inelastic charged current interaction of supernova neutrinos in two-phase liquid xenon dark matter detectors

It has been known that neutrinos from supernova (SN) bursts can give rise to nuclear recoil (NR) signals arising from coherent elastic neutrino-nucleus scattering (CE$ν$NS) interaction, a neutral current (NC) process, of the neutrinos with xenon nuclei in future large (multi-ton scale) liquid xenon (LXe) detectors employed for dark matter search, depending on the SN progenitor mass and distance to the SN. In this paper, we show that the same detectors will also be sensitive to inelastic charged current (CC) interactions of the SN electron neutrinos ($ν_e$CC) with the xenon nuclei. Such interactions, while creating an electron in the final state, also leave the post-interaction target nucleus in an excited state, the subsequent deexcitation of which produces, among other particles, gamma rays and neutrons. The electron and deexcitation gamma rays will give ``electron recoil" (ER) type signals, while the deexcitation neutrons produce, through their multiple scattering on the xenon nuclei, further xenon nuclear recoils that will also give NR signals (in addition to those produced through the CE$ν$NS interactions). We discuss the observable scintillation and ionization signals associated with SN neutrino induced CE$ν$NS and $ν_e$CC events in a generic LXe detector and argue that upcoming sufficiently large LXe detectors should be able to detect both these types of events due to neutrinos from reasonably close by SN bursts. We also note that since the total CC induced ER and NR signals receive contributions predominantly from $ν_e$CC interactions while the CE$ν$NS contribution comes from NC interactions of {\emph all the six species of neutrinos}, identification of the $ν_e$CC and CE$ν$NS origin events may offer the possibility of extracting useful information about the distribution of the total SN explosion energy going into different neutrino flavors.

hep-ph↗

arXiv2022

High energy particles from young supernovae: gamma-ray and neutrino connections

Young core-collapse supernovae (YSNe) are factories of high-energy neutrinos and gamma-rays as the shock accelerated protons efficiently interact with the protons in the dense circumstellar medium. We explore the detection prospects of secondary particles from YSNe of Type IIn, II-P, IIb/II-L, and Ib/c. Type IIn YSNe are found to produce the largest flux of neutrinos and gamma-rays, followed by II-P YSNe. Fermi-LAT and the Cherenkov Telescope Array (IceCube-Gen2) have the potential to detect Type IIn YSNe up to $10$~Mpc ($4$~Mpc), with the remaining YSNe Types being detectable closer to Earth. We also find that YSNe may dominate the diffuse neutrino background, especially between $10$~TeV and $10^3$~TeV, while they do not constitute a dominant component to the isotropic gamma-ray background observed by Fermi-LAT. At the same time, the IceCube high-energy starting events and Fermi-LAT data already allow us to exclude a large fraction of the model parameter space of YSNe otherwise inferred from multi-wavelength electromagnetic observations of these transients.

astro-ph.HE↗

arXiv2022

Simulation of Nuclear Recoils due to Supernova Neutrino-induced Neutrons in Liquid Xenon Detectors

Neutrinos from supernova (SN) bursts can give rise to detectable number of nuclear recoil (NR) events through the coherent elastic neutrino-nucleus scattering (CE$ν$NS) process in large scale liquid xenon detectors designed for direct dark matter search, depending on the SN progenitor mass and distance. Here we show that in addition to the direct NR events due to CE$ν$NS process, the SN neutrinos can give rise to additional nuclear recoils due to the elastic scattering of neutrons produced through inelastic interaction of the neutrinos with the xenon nuclei. We find that the contribution of the supernova neutrino-induced neutrons ($ν$I$n$) can significantly modify the total xenon NR spectrum at large recoil energies compared to that expected from the CE$ν$NS process alone. Moreover, for recoil energies $\gtrsim20$ keV, dominant contribution is obtained from the ($ν$I$n$) events. We numerically calculate the observable S1 and S2 signals due to both CE$ν$NS and $ν$I$n$ processes for a typical liquid xenon based detector, accounting for the multiple scattering effects of the neutrons in the case of $ν$I$n$, and find that sufficiently large signal events, those with S1$\gtrsim$50 photo-electrons (PE) and S2$\gtrsim$2300 PE, come mainly from the $ν$I$n$ scatterings.

astro-ph.HE↗

arXiv2020

Fast flavor conversions in supernovae: the rise of mu-tau neutrinos

Neutrinos in a core-collapse supernova can undergo fast flavor conversions with a possible impact on the explosion mechanism and nucleosynthesis. We perform the first non-linear simulations of fast conversions in the presence of three neutrino flavors. The recent supernova simulations with muon production call for such an analysis, as they relax the standard $ν_{μ,τ}=\barν_{μ,τ}$ (two-flavor) assumption. Our results show the significance of muon and tau lepton number angular distributions, together with the traditional electron lepton number ones. Indeed, our three-flavor results are potentially very different from two-flavor ones. These results strengthen the need to further investigate the occurrence of fast conversions in supernova simulation data, including the degeneracy breaking of mu and tau neutrinos.

hep-ph↗

arXiv2020

Three flavor neutrino conversions in supernovae: Slow $\&$ Fast instabilities

Self induced neutrino flavor conversions in the dense regions of stellar core collapse are almost exclusively studied in the standard two flavor scenario. Linear stability analysis has been successfully used to understand these flavor conversions. This is the first linearized study of $\textit{three flavor}$ fast instabilities. The `fast' conversions are fascinating distinctions of the dense neutrino systems. In the fast modes the collective oscillation dynamics are independent of the neutrino mass, growing at the scale of the large neutrino-neutrino interaction strength ($10^5$ km$^{-1}$) of the dense core. This is extremely fast, in comparison to the usual `slow' collective modes driven by much smaller vacuum oscillation frequencies ($10^0$ km$^{-1}$). The three flavor analysis shows distinctive characteristics for both the slow and the fast conversions. The slow oscillation results are in qualitative agreement with the existing nonlinear three flavor studies. For the fast modes, addition of the third flavor opens up possibilities of influencing the growth rates of flavor instabilities when compared to a two flavor scenario.

hep-ph↗