arXiv subjects

Reetanjali Moharana

Publications and source records attributed to Reetanjali Moharana.

At least 19 recordsLinked to original sources

arXiv2026

Hadronic Origin of Sub-PeV Gamma-Ray Emission from LHAASO J0621+3755

Very High Energy (VHE) gamma-rays in pulsars, and their surrounding halos, are interpreted to originate from the leptonic channel, electromagnetic interactions through electron inverse Compton (IC) scattering. In the hadronic scenario, TeV-PeV gamma-rays are generated from the decay of neutral pions, which are produced from cosmic rays(CR) protons interacting with the ambient medium. Recent observations of sub-PeV gamma-rays from the halo of the pulsar PSR J0622+3749 by the Large High Altitude Air Shower Observatory Kilometer-Square Array (LHAASO-KM2A) provide an opportunity to investigate the underlying emission mechanisms. Previous studies have shown that the observed emission can be consistently explained within a leptonic framework by the slow diffusion of electrons. In this work, we explore an alternative explanation based on the hadronic scenario through the proton-proton ($pp$) interaction channel, incorporating the observation of VHE gamma-rays at 7 TeV by the High-Altitude Water Cherenkov detector (HAWC). To model the observed gamma-ray spectrum, ranging from $\sim 7~\mathrm{TeV}$ up to $200~\mathrm{TeV}$, the required CR proton luminosity is found to be $η_p \sim 0.14$ of the spin-down luminosity of PSR J0622+3749. This scenario assumes that protons propagate in a one-zone superdiffusive environment, characterized by a diffusion index $α= 1.05$, within an ambient of density, $1~\mathrm{cm}^{-3}$.

astro-ph.HE↗

arXiv2025

Similar Fermi-GBM sGRBs to GW/sGRB 170817A in MeV-GeV energies

The rate of observed gravitational waves (GWs) from neutron star-neutron star (NS-NS) mergers detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) indicates the existence of more than one short gamma-ray bursts (sGRBs) similar to GW/sGRB 170817A within the total gamma-ray bursts (GRBs) recorded by satellite detectors such as BATSE, Fermi-Gamma-ray Burst Monitor (Fermi-GBM), and Swift-Burst Alert Telescope (Swift-BAT). We investigated sGRBs in the Fermi-GBM dataset based on their MeV-GeV $γ$-ray emission features, to identify sGRBs similar to sGRB 170817A. Any addition of such events can impact the rate of NS-NS CBC events observed by LIGO. SGRB 170817A exhibits two distinct emission components: a non-thermal peak and a thermal component. We adopted a multifaceted approach to identify analogous sGRBs, which involved computing the hardness ratios $HR_{1}$ and $HR_{2}$ and then clustering them via the K-means algorithm. Our further studies reveal the presence of eight such events in Fermi-GBM data, which will enable us to calculate the rate of electromagnetic (EM) counterparts associated with LIGO GW events (GW+sGRB events) across all observing runs. Giving an estimation, by the end of the $O_4$ LIGO run, there could be nearly 5 GW+sGRB events. Deviation from this number may raise concerns about our understanding of the evolution of such events over distance.

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

Time-lag in hadronic channel: to explore delayed VHE-flare of 3C 279

On 28 January 2018, the High Energy Stereoscopic System (H.E.S.S.) reported a significant very-high-energy (VHE) gamma-ray activity, occurring nearly 11 days after the high-energy (HE) gamma-ray flare observed by \textit{Fermi}-LAT from the blazar 3C 279. It has long been considered a candidate site for accelerating particles to ultra-high energies (UHE) and producing subsequent secondaries. Such an event can be crucial to explore the different phenomena of secondary production from the UHEs and viable to understand the energetics of the sources. Our study finds that the multi-wavelength flare, spanning UV, optical, X-rays, and HE gamma rays, originates from leptonic emissions, whereas the delayed VHE activity by proton synchrotron emission within the source, results from the extended duration of particle acceleration. To explain the prolonged electromagnetic emission, our model requires a magnetic field luminosity (L$'_B$) $6.1 \times 10^{43}$ erg/sec, a proton luminosity (L$'_{p}$) $1.2\times 10^{46}$ erg/sec in the jet frame.

astro-ph.HE↗

arXiv2023

Implications of photon-ALP oscillations in the extragalactic neutrino source TXS 0506+056 at sub-PeV energies

Photon-axion-like particle (ALP) oscillations result in the survival of gamma rays from distant sources above TeV energies. Studies of events observed by CAST, Fermi-LAT, and IACT have constrained the ALP parameters. We investigate the effect of photon-ALP oscillations on the gamma-ray spectra of the first extragalactic neutrino source, TXS 0506+056, for observations by Fermi-LAT and MAGIC around the IC170922-A alert. We obtain a constraint on the ALP coupling parameter $g_{aγ} < 5 \times 10^{-11}$ GeV$^{-1}$ with 95% C.L. when focusing on the ALP mass range 0.1 neV $\le$ $m_a$ $\le$ 1000 neV. Importantly, we study the implications of ALP-$γ$ oscillations on the counterpart $γ$ rays of the sub-PeV neutrinos observed from TXS 0506+056. We also show the diffuse $γ$-ray fluxes and observabilities from flat-spectrum radio quasars, high-synchrotron peaked sources, and low-intermediate-synchrotron peaked sources, assuming similar gamma-ray emissions as that from TXS 0506+056.

astro-ph.HE↗

arXiv2023

Generalized Linear Models of T$_{90}$-T$_{50}$ relation to classify GRBs

Gamma-ray bursts (GRBs) can be classified with their linearly dependent parameters alongside the standard $T_{90}$ distribution. The Generalized linear mixture model(GLM) identifies the number of linear dependencies in a two-parameter space. Classically, GRBs are classified into two classes by the presence of bimodality in the histogram of T$_{90}$. However, additional classes and sub-classes of GRBs are fascinating topics to explore. In this work, we investigate the GRBs classes in the $ T_{90} {-}T_{50}$ plane using the Generalized Linear Models(GLM) for Fermi GBM and BATSE catalogs. This study shows five linear features for the Fermi GBM catalog and four linear features for the BATSE catalog, directing towards the possibility of more than two GRB classes.

astro-ph.HE↗

arXiv2022

Proton Synchrotron, an explanation for possible extended VHE gamma-ray activity of TXS 0506+056 in 2017

TXS 0506+056, a source of the extreme energy neutrino event, IceCube-170922A, was observed on 22 September 2017. The Fermi-LAT detector reported high energy (HE) $γ$-ray flare between 100 MeV and 100 GeV starting from 15 September 2017 from this source. Several attempts to trace the very high energy (VHE) gamma-ray counterparts around the IceCube-170922A resulted in no success. Only after 28 September, the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes observed the first VHE gamma-rays from the blazar above 100 GeV. The $\sim$ 41 hr survey resulted in VHE-$γ$ ray activity till 31 October 2017. Here we propose the extended GeV $γ-$rays can be explained by taking two production channels, electron synchrotron self Compton and proton synchrotron for HE and VHE emissions, respectively. The 45 days of VHE emission from the peak of the HE-flare can be explained with $ {L_p'}{\simeq}10^{47}$ erg/sec in the jet frame and magnetic field of 2.4 G, consistent with the ${L}_{Edd}$ for a blackhole mass $5\times 10^{9} {M}_\odot$

astro-ph.HE↗

arXiv2019

Possible correlations between gamma-ray burst and its host galaxy offset

We collected the information of 304 gamma-ray bursts (GRBs) from the literature, and analyzed the correlations among the host galaxy offsets (the distance from the site of the GRB to the center of its host galaxy), $T_{\rm 90,i}$ (the duration $T_{\rm 90}$ in rest-frame), $T_{\rm R45,i}$ (the duration $T_{\rm R45}$ in rest-frame), $E_{\rm γ,iso}$ (the isotropic equivalent energy), $L_{\rm γ,iso}$ ($=E_{\rm γ,iso}/T_{\rm 90,i}$, the isotropic equivalent luminosity) and $L_{\rm pk}$ (peak luminosity). We found that $ T_{\rm 90,i}$, $ T_{\rm R45,i}$, $ E_{\rm γ,iso}$, $L_{\rm pk}$ have negative correlation with $ {\rm offset}$, which is consistent with origin of short GRBs (SGRBs) and long GRBs (LGRBs). On separate analysis, we found similar results for $\log E_{\rm γ,iso}$ - $\log {\rm (offset)}$ and $\log L_{\rm pk}$ - $\log {\rm (offset)}$ relations in case of SGRBs only, while no obvious relation for LGRBs. There is no correlations between offset and $L_{\rm γ,iso}$. We also put the special GRB 170817A {and GRB 060218A} on the plots. {The two GRBs both have low luminosity and small offset.} In the $ \log ({\rm offset})- \log T_{\rm 90,i}$ plot, we found GRB 170817A locates in between the two regions of SGRBs and LGRBs and it is the outlier in the $ {\rm offset}-E_{\rm γ, iso}$, $ {\rm offset}-L_{\rm γ, iso}$ and $ {\rm offset}-L_{\rm pk}$ plots. Together with GRB 060218A being an outlier in all plots, it indicates the speciality of GRBs 170817A and 060218A, and might imply more subgroups of the GRB samples.

astro-ph.HE↗

arXiv2017

Determine the Lorentz factor and the viewing angle of GRB 170817A

GRB 170817A is a weak short gamma-ray burst (GRB) accompanied by the gravitational wave (GW) event GW170817. It is believed, that an off beaming relativistic jet, produces this weak GRB. Here we use the $E_{\rm p,i}- E_{\rm iso}$ and $Γ- E_{\rm iso}$ relations to determine the Lorentz factor $Γ$ and the viewing angle from the edge of the jet $θ'_{\rm obs}$ of GRB 170817A. Our result shows, $Γ= 13.4 ^{+9.8}_{-5.5}$ and $θ'_{\rm obs} = 4.3^{+1.8}_{-1.5} \,^{\circ}$. This corresponds to the on-axis $E_{\rm p,i} = 415^{+361}_{-167}$ keV and $E_{\rm iso} = (2.4^{+1.6}_{-1.9}) \times 10^{47}$ ergs of the GRB, which is an intrinsically weak short GRB. Interestingly, the Doppler factor and the luminosity follow a universal relation from GRBs and blazars, which indicates they may share similar radiation mechanism.

astro-ph.HE↗

arXiv2017

Ultra-High Energy Neutrino Afterglows of nearby Long Duration Gamma-Ray Bursts

Detection of ultra-high energy (UHE, $\gtrsim 1$ PeV) neutrinos from astrophysical sources will be a major advancement in identifying and understanding the sources of UHE cosmic rays (CRs) in nature. Long duration gamma-ray burst (GRB) blast waves have been considered as potential acceleration sites of UHECRs. These CRs are expected to interact with GRB afterglow photons, which is synchrotron radiation from relativistic electrons co-accelerated with CRs in the blast wave, and naturally produce UHE neutrinos. Fluxes of these neutrinos are uncertain, however, and crucially depend on the observed afterglow modeling. We have selected a sample of 23 long duration GRBs within redshift 0.5 for which adequate electromagnetic afterglow data are available and which could produce high flux of UHE afterglow neutrinos, being nearby. We fit optical, X-ray and $γ$-ray afterglow data with an adiabatic blast wave model in a constant density interstellar medium and in a wind environment where the density of the wind decreases as inverse square of the radius from the center of the GRB. The blast wave model parameters extracted from these fits are then used for calculating UHECR acceleration and $pγ$ interactions to produce UHE neutrino fluxes from these GRBs. We have also explored the detectability of these neutrinos by currently running and upcoming large area neutrino detectors, such as the Pierre Auger Observatory, IceCube Gen-2 and KM3NeT observatories. We find that our realistic flux models from nearby GRBs will be unconstrained in foreseeable future.

astro-ph.HE↗

arXiv2017

Observational evidence for mass ejection accompanying short gamma ray bursts

The plateau in the duration distribution of long Gamma-Ray Bursts (LGRBs) provides a direct observational evidence for the Collapsar model. The plateau reflects the fact that the observed duration satisfies: $T_{90} = t_{e}-t_{b}$ where $t_{e}$ is the time that the central engine operates and $t_{b}$ is a threshold time, interpreted within the Collapsar model as the time it takes for the relativistic jet to penetrate the stellar envelope. Numerical simulation and macronova observations suggest that compact binary mergers involve mass ejection. If short-Gamma Ray Bursts (sGRBs) arise from such mergers, their jets should cross this surrounding ejecta before producing the prompt emission. Like in LGRBs, this should result in a distinct short plateau in the GRBs' duration distribution. We present a new analysis of the duration distribution for the three GRB satellites: BATSE, {\it Swift} and Fermi. We find a clear evidence for a short ($\sim 0.4$ sec) plateau in the duration distribution. This plateau is consistent with the expected jet crossing time, provided that the ejecta is of order of a few percent of solar masses.

astro-ph.HE↗

arXiv2016

Angular correlation between IceCube high-energy starting events and starburst sources

Starburst galaxies and star-forming regions in the Milkyway, with high rate of supernova activities, are candidate sources of high-energy neutrinos. Using a gamma-ray selected sample of these sources we perform statistical analysis of their angular correlation with the four-year sample of high-energy starting events (HESE), detected by the IceCube Neutrino Observatory. We find that the two samples (starburst galaxies and local star-forming regions) are correlated with cosmic neutrinos at $\sim (2-3)σ$ (pre-trial) significance level, when the full HESE sample with deposited energy $\gtrsim 20$~TeV is considered. However when we consider the HESE sample with deposited energy $\gtrsim 60$~TeV, which is almost free of atmospheric neutrino and muon backgrounds, the significance of correlation decreased drastically. We perform a similar study for Galactic sources in the 2nd Catalog of Hard {\em Fermi}-LAT Sources (2FHL, $>50$~ GeV) catalog as well, obtaining $\sim (2-3)σ$ (pre-trial) correlation, however the significance of correlation increases with higher cutoff energy in the HESE sample for this case. We also fit available gamma-ray data from these sources using a $pp$ interaction model and calculate expected neutrino fluxes. We find that the expected neutrino fluxes for most of the sources are at least an order of magnitude lower than the fluxes required to produce the HESE neutrinos from these sources. This puts the starburst sources being the origin of the IceCube HESE neutrinos in question.

astro-ph.HE↗

arXiv2016

High Energy Neutrinos from the Gravitational Wave event GW150914 possibly associated with a short Gamma-Ray Burst

High-energy neutrino (HEN) and gravitational wave (GW) can probe astrophysical sources in addition to electromagnetic observations. Multimessenger studies can reveal nature of the sources which may not be discerned from one type of signal alone. We discuss HEN emission in connection with the Advanced Laser Interferometer Gravitational-wave Observatory (ALIGO) event GW150914 which could be associated with a short gamma-ray burst (GRB) detected by the $Fermi$ Gamma-ray Burst Monitor (GBM) 0.4 s after the GW event and within localization uncertainty of the GW event. We calculate HEN flux from this short GRB, GW150914-GBM, and show that non-detection of a high-energy starting event (HESE) by the IceCube Neutrino Observatory can constrain the total isotropic-equivalent jet energy of this short burst to be less than $3\times 10^{52}$ erg.

astro-ph.HE↗

arXiv2016

Search for extragalactic astrophysical counterparts of IceCube neutrino events

Detection of 54 very high-energy (VHE) neutrinos by the IceCube Neutrino Observatory has opened a new chapter in multi-messenger astronomy. However due to large errors in measuring the directions of the neutrino shower-type events, which dominate the current event list, it is difficult to identify their astrophysical sources. We perform cross-correlation study of IceCube neutrino events with extragalactic candidate sources using X-ray and gamma-ray selected source catalogues such as Swift-BAT, 3LAC and TeV-Cat. We apply different cuts on the X-ray and gamma-ray fluxes of the sources in these catalogs, and use different source classes in order to study correlation. We use invariant statistic and Monte Carlo simulations to evaluate statistical significance of any correlation.

astro-ph.HE↗

arXiv2016

Photodisintegrated gamma rays and neutrinos from heavy nuclei in the gamma-ray burst jet of GRB 130427A

Detection of ~ 0.1-70 GeV prompt gamma-ray emission from the exceptionally bright gamma-ray burst (GRB) 130427A by the Fermi-Large Area Telescope provides an opportunity to explore the physical processes of GeV gamma-ray emission from the GRB jets. In this work we discuss interactions of Iron and Oxygen nuclei with observed keV-MeV photons in the jet of GRB 130427A in order to explain an additional, hard spectral component observed during 11.5-33 second after trigger. The photodisintegration time scale for Iron nuclei is comparable to or shorter than this duration. We find that gamma rays resulting from the Iron nuclei disintegration can account for the hard power-law component of the spectra in the 1-70 GeV range, before the gamma-gamma to electron-positron pair production with low-energy photons severely attenuates emission of higher energy photons. Electron antineutrinos from the secondary neutron decay, on the other hand, can be emitted with energies up to 2 TeV. The flux of these neutrinos is low and consistent with non-detection of GRB 130427A by the IceCube Neutrino Observatory. The required total energy in the Iron nuclei for this hadronic model for GeV emission is approximately 10 times the observed total energy released in the prompt keV-MeV emission.

astro-ph.HE↗

arXiv2015

Angular correlation of cosmic neutrinos with ultrahigh-energy cosmic rays and implications for their sources

Cosmic neutrino events detected by the IceCube Neutrino Observatory with energy $\gtrsim 30$ TeV have poor angular resolutions to reveal their origin. Ultrahigh-energy cosmic rays (UHECRs), with better angular resolutions at $>60$ EeV energies, can be used to check if the same astrophysical sources are responsible for producing both neutrinos and UHECRs. We test this hypothesis, with statistical methods which emphasize invariant quantities, by using data from the Pierre Auger Observatory, Telescope Array and past cosmic-ray experiments. We find that the arrival directions of the cosmic neutrinos are correlated with $\ge 100$ EeV UHECR arrival directions at confidence level $\approx 93\%$. The strength of the correlation decreases with decreasing UHECR energy and no correlation exists at energy $\sim 60$ EeV. A search in astrophysical databases within $3^\circ$ of the arrival directions of UHECRs with energy $\ge 100$ EeV, that are correlated with the IceCube cosmic neutrinos, resulted in 18 sources from the Swift-BAT X-ray catalog with redshift $z\le 0.06$. We also found 3 objects in the Kühr catalog of radio sources using the same criteria. The sources are dominantly Seyfert galaxies with Cygnus A being the most prominent member. We calculate the required neutrino and UHECR fluxes to produce the observed correlated events, and estimate the corresponding neutrino luminosity (25 TeV-2.2 PeV) and cosmic-ray luminosity (500 TeV-180 EeV), assuming the sources are the ones we found in the Swift-BAT and Kühr catalogs. We compare these luminosities with the X-ray luminosity of the corresponding sources and discuss possibilities of accelerating protons to $\gtrsim 100$ EeV and produce neutrinos in these sources.

astro-ph.HE↗

arXiv2014

Probing CP violation with the three years ultra-high energy neutrinos from IceCube

The IceCube collaboration has recently announced the discovery of ultra-high energy neutrino events. These neutrinos can be used to probe their production source, as well as leptonic mixing parameters. In this work, we have used the first IceCube data to constrain the leptonic CP violating phase $δ_{cp}$. For this, we have analyzed the data in the form of flux ratios. We find that the fit to $δ_{cp}$ depends on the assumptions made on the production mechanism of these astrophyscial neutrinos. Consequently, we also use this data to impose constraints on the sources of the neutrinos.

hep-ph↗

arXiv2013

Effects of Beyond Standard Model Physics on GRB Neutrinos

The nondetection of neutrinos coming from Gamma Ray Bursts (GRBs) by the IceCube experiment has raised serious questions on our understanding of GRB's and the mechanism of neutrino flux production in them. Motivated by this and the need for a precise calculation for GRB neutrino flux, here we study the effects of beyond standard model physics on the GRB neutrino flux. In the internal shock model of GRB, high energy neutrinos are expected from muon, pion and kaon decays. Using the latest best fit neutrino oscillation parameters, we compute the expected flux on earth for standard as well as non-standard oscillation scenarios. Among the non-standard scenarios, we consider neutrino decay, pseudo-dirac nature of neutrinos and presence of one eV scale light sterile neutrino. Incorporating other experimental bounds on these new physics scenarios, we show that neutrino decay scenario can significantly alter the neutrino flux on earth from the expected ones whereas the corresponding changes for pseudo-dirac and sterile neutrino cases are moderate.

astro-ph.HE↗