arXiv subjects

Siddhant Manna

Publications and source records attributed to Siddhant Manna.

13 recordsLinked to original sources

arXiv2026

A MINOT-based Study of Gamma-ray emission from SPT-CL J2012-5649/Abell 3667

We present an analysis of the non-thermal properties of the merging galaxy cluster SPT-CL J2012-5649/Abell~3667 ($z = 0.0556$, $M_{500} = 7.16 \times 10^{14}\ M_\odot$) using the MINOT non-thermal emission modeling framework. The predicted hadronic gamma-ray flux from $pp$ interactions in the $1$--$300\ \mathrm{GeV}$ band is $2.82 \times 10^{-11}\ \mathrm{cm^{-2}\ s^{-1}}$ within $R_{500}$, rising to $1.15 \times 10^{-10}\ \mathrm{cm^{-2}\ s^{-1}}$ at the truncation radius ($3.7\,R_{500}$), in broad agreement with the Fermi-LAT reported flux of $1.3 \times 10^{-10}\ \mathrm{cm^{-2}\ s^{-1}}$. Approximately $76\%$ of the predicted hadronic flux originates from beyond $R_{500}$. The Inverse Compton contribution from cosmic-ray electrons is subdominant relative to the hadronic $π^0$-decay gamma-ray component by a factor of ${\sim}20$ in the $1$--$300\ \mathrm{GeV}$ energy band, and therefore does not contribute significantly to the observable signal. The best fit of the observed Fermi-LAT data is achieved with a hadronic emission assuming a proton spectrum $\propto E^{-3.5}$ and a proton energy density almost in equipartition with the thermal energy density. Even though those parameters may look extreme, they could well be explained by the particle acceleration by low Mach number accretion shocks.

astro-ph.HE↗

arXiv2026

Search for GeV gamma-ray emission from PSZ G181.06+48.47 galaxy cluster using Fermi-LAT data

We present a search for high energy gamma rays in the energy range from 1--300~GeV from the galaxy cluster PSZ2~G181.06+48.47 using 17.9~years of Fermi-LAT data. A binned likelihood analysis employing the 16-year source catalog reveals a significant $γ$-ray excess at the cluster position. Modelling the emission as a point source yields a detection with $\mathrm{TS}=19.0 (4.3 σ)$, a photon index of $Γ=3.20 \pm 0.62$, and an integrated photon flux of $(9.75\pm2.74)\times10^{-11}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$, but leaves statistically significant residual emission at the cluster center. Replacing the point-source hypothesis with a RadialGaussian spatial template significantly improves the fit, with a preferred width of $σ=0.4^{\circ}$ and an extension significance of $\mathrm{TS}_{\rm ext}=36.8 (6.0σ)$. The adopted Gaussian model yields a source detection significance of $\mathrm{TS}=55.0 (7.4σ)$, a photon index of $Γ=2.62\pm0.26$, and an integrated photon flux of $(3.22\pm0.50)\times10^{-10}\,\mathrm{ph\,cm^{-2}\,s^{-1}}$, while reducing the residual emission at the cluster position to a level consistent with zero. The cluster spectral energy distribution shows significant emission only in the lowest energy interval (1.0--3.13~GeV), while all higher-energy bins are consistent with upper limits, indicating a soft $γ$-ray spectrum with no evidence for emission above $\sim5$~GeV. These results provide strong evidence that the $γ$-ray emission associated with PSZ2~G181.06+48.47 is spatially extended on a scale of $σ\approx0.4^{\circ}$ and is more consistent with diffuse intracluster emission than with a single unresolved point source.

astro-ph.HE↗

arXiv2026

A Search for Hard X-ray/Soft $γ$-ray Emission from SPT-CL J2012-5649 (Abell 3667) Using INTEGRAL/ISGRI

We present a search for hard X-ray/soft $γ$-ray emission from the merging galaxy cluster SPT-CL J2012-5649 (Abell~3667) using archival INTEGRAL/ISGRI observations. This cluster located at $z=0.0556$ hosts prominent radio relics associated with merger-driven shocks, suggesting the presence of relativistic electrons capable of producing inverse-Compton (IC) emission in the hard X-ray to soft $γ$-ray regime. We searched for emission in the 30--300~keV energy range using the INTEGRAL Off-line scientific analysis software with a total effective exposure of 2817~s. No significant emission was detected at the cluster position in the aforementioned energy interval. The extracted ISGRI spectrum is consistent with pure background, and no physically meaningful model parameters can be constrained. From the mosaic variance maps, we derive a $3σ$ upper limit of $F_{30-300\,\mathrm{keV}} < 3.63 \times 10^{-10}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$. This limit rules out bright IC scenarios and constrains the efficiency of merger-driven particle acceleration in SPT-CL J2012-5649. Our results provide the most stringent soft $γ$-ray constraint on this system to date and highlight the need for next-generation hard X-ray missions, such as HEX-P or eXTP, to probe IC emission at theoretically predicted levels in merging clusters.

astro-ph.HE↗

arXiv2026

Search for Gamma-ray emission from Abell 119 galaxy cluster using INTEGRAL/ISGRI, COMPTEL, and DAMPE data

We present a comprehensive search for non-thermal high-energy $γ$-ray emission from the nearby merging galaxy cluster Abell~119 ($z=0.044$) using archival observations spanning over seven decades in photon energy. Our analysis combines hard X-ray data from INTEGRAL/ISGRI (30--100~keV), MeV $γ$-ray observations from COMPTEL (0.75--30~MeV), and GeV--TeV data from the DArk Matter Particle Explorer (DAMPE; 3~GeV--1~TeV). No statistically significant emission is detected at the cluster position in any energy band. In the hard X-ray regime, we derive a $3σ$ upper limit of $F_{30-100\,\mathrm{keV}} \lesssim 8.5 \times 10^{-11}$~erg~cm$^{-2}$~s$^{-1}$ from ISGRI mosaic imaging. Reanalysis of archival COMPTEL data yields 95\% confidence-level upper limits ranging from $\sim 9 \times 10^{-11}$ to $\sim 8 \times 10^{-10}$~erg~cm$^{-2}$~s$^{-1}$ across 0.75--30~MeV. In the GeV--TeV range, DAMPE constrains the differential energy flux to $\sim 10^{-12}$--$10^{-10}$~erg~cm$^{-2}$~s$^{-1}$ (95\% confidence level). These results provide independent multi-band constraints on the reported GeV excess from recent Fermi-LAT studies. While our DAMPE limits do not exclude the flux levels claimed in those analyses, the absence of confirmation across keV--MeV--GeV bands indicate that any non-thermal emission from Abell~119 remains tentative.

astro-ph.HE↗

arXiv2025

A Targeted Gamma-Ray Search of Five Prominent Galaxy Merger Systems with 17 years of Fermi-LAT Data

Galaxy mergers are among the most energetic astrophysical phenomena, driving intense star formation and potentially fueling cosmic ray acceleration, which can produce high energy $γ$-ray emission through hadronic processes. We present a targeted search for $γ$-ray emission from five prominent galaxy merger systems, NGC~3256, NGC~660, UGC~813/816, UGC~12914/12915, and VV~114 using 16.9 years of Fermi-LAT data in the 1--300~GeV energy range. Employing a binned maximum likelihood analysis, we model the emission with power-law spectra and derive spectral energy distributions (SEDs) to constrain $γ$-ray fluxes and spectral indices. Marginal detections are found for NGC~3256 (TS = 15.4, $\sim$3.51$σ$) and NGC~660 (TS = 8.16, $\sim$2.39$σ$), with photon fluxes of $(7.21 \pm 3.17) \times 10^{-11}$ and $(8.28 \pm 3.56) \times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$, respectively, suggesting merger driven star formation contributes to $γ$-ray emission. The remaining systems yield non-detections (TS $< 5$). This is the first targeted study of $γ$-ray emission from these aforementioned galaxy merger systems.

astro-ph.HE↗

arXiv2025

Search for spatial coincidences between galaxy mergers and Fermi-LAT 4FGL-DR4 sources

We present a systematic search for spatial association between a high confidence sample of 3,166 morphologically selected galaxy mergers drawn from the initial convolutional neural network (CNN) catalog of 328,151 candidate mergers and refined through SDSS cross-matching and the Fermi Large Area Telescope Fourth Source Catalog Data Release 4 (4FGL-DR4) catalog of gamma-ray sources detected by the Fermi Large Area Telescope (LAT). Using a conservative 4$σ$ positional uncertainty threshold and a Poisson based statistical framework, we identify 21 statistically significant associations with match probabilities $p < 0.05$. Among these are known classes of gamma-ray emitters such as Flat-Spectrum Radio Quasars (FSRQs), BL Lacertae objects (BLL), and radio galaxies bolstering the hypothesis that merger driven processes can fuel high energy activity. Intriguingly, five of the associated sources remain unclassified in 4FGL-DR4, hinting at a possible link between galaxy mergers and a hitherto unrecognized population of gamma-ray sources. The dominance of AGN like matches supports the scenario in which mergers trigger accretion onto central supermassive black holes, initiating AGN activity observable at gamma-ray energies. Moreover, the recurrent presence of unassociated sources among secure matches underscores the potential of merger catalogs as physically motivated priors in gamma-ray source identification efforts. This work constitutes the first dedicated effort to explore associations between gamma-ray sources and a large, morphologically selected sample of galaxy mergers catalog, opening new avenues for understanding the role of galaxy interactions in high-energy astrophysics.

astro-ph.HE↗

arXiv2025

A Stacked Analysis of GeV Gamma-Ray Emission from SPT-SZ Galaxy Clusters with 16 Years of Fermi-LAT Data

We report a statistically significant detection of cumulative $γ$-ray emission from a stacked sample of SPT-SZ selected galaxy clusters using 16.4 years of data from the Fermi Gamma-Ray Space Telescope's Large Area Telescope (LAT). By analyzing a population of clusters with individual Test Statistic (TS) values $<$ 9.0, we identify a robust cumulative signal with a TS of 75.2, which corresponds to approximately $8.4σ$ significance. In contrast, clusters with TS $<$ 4.0 yield a weaker cumulative signal of TS equal to 9.65 (2.65$σ$), consistent with background fluctuations. The derived $γ$-ray spectrum is well characterized by a power law model with a best-fit spectral index of $-2.59 \pm 0.20$ and an integrated flux of $1.67^{+1.35}_{-1.07} \times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$. The high TS values in the full sample are likely driven by AGN-dominated clusters. However, when clusters with TS between 4 and 9 are excluded, the remaining low-TS population shows a stacked signal consistent with hadronic emission.

astro-ph.HE↗

arXiv2024

Search for GeV gamma-ray emission from SPT-CL J2012-5649 with six years of DAMPE data

We search for gamma-ray emission from the galaxy cluster SPT-CL J2012-5649 in the energy range from 3 GeV to 1 TeV using the DArk Matter Particle Explorer (DAMPE) telescope. For our analysis, we use three different templates: point source, radial disk, and radial Gaussian. We do not detect a signal with significance $>3σ$ for any of these templates at any location within $R_{200}$ of the cluster center. We obtain 95\% C.L. upper limit on the energy flux ranging between $\sim 10^{-6}$ and $10^{-4} \rm{MeV~cm^{-2}~s^{-1}}$ depending on the energy range. These upper limits are consistent with a previously reported non-zero flux detected by Fermi-LAT at $6σ$ significance. This work represents the first proof of principle search for gamma-ray emission from a single galaxy cluster using DAMPE data.

astro-ph.HE↗

arXiv2024

Search for Dark Matter Annihilation to gamma-rays from SPT-SZ selected Galaxy Clusters

We search for dark matter annihilation from galaxy clusters in the energy range from 1-300 GeV using nearly 16 years of Fermi-LAT data. For this purpose, we use 350 galaxy clusters selected from the 2500 $\rm{deg^2}$ SPT-SZ survey. We model the dark matter distribution using the NFW profile for the main halo along with the Einasto profile for the substructure. The largest signal is seen for the cluster SPT-CL J2021-5257 with a significance of around $3σ$. The best-fit dark matter mass and annihilation cross-section for this cluster are equal to $(60.0 \pm 11.8)$ GeV and $\langle σv \rangle= (6.0 \pm 0.6) \times 10^{-25} \rm{cm^3 s^{-1}}$ for the $\bar{b} b$ annihilation channel. However, this central estimate is in conflict with the limits on annihilation cross-section from dwarf spheroidal galaxies, and hence cannot be attributed to dark matter annihilation. Three other clusters show significance between $2-2.5σ$, whereas all the remaining clusters show null results. The most stringent 95\% c.l. upper limit for the WIMP annihilation cross-section among all the clusters is from SPT-CL J0455-4159, viz. $\langle σv \rangle = 6.44 \times 10^{-26} \text{cm}^3 \text{s}^{-1}$ for $m_χ = 10$ GeV and $b\bar{b}$ annihilation channel.

astro-ph.CO↗

arXiv2024

Search for MeV Gamma-ray emission from TeV bright red dwarfs with COMPTEL

The SHALON atmospheric Cherenkov telescope has detected very high energy gamma-ray emission at TeV energies from eight red dwarfs, namely, V388 Cas, V547 Cas, V780 Tau, V962 Tau, V1589 Cyg, GJ 1078, GJ 3684 and GL 851.1. Consequently, these red dwarfs have been suggested as sources of ultra-high energy cosmic rays. In this work, we search for soft gamma-ray emission from these TeV bright red dwarfs between 0.75-30 MeV using archival data from the COMPTEL gamma-ray imaging telescope, as a follow-up to a similar search for GeV gamma-ray emission using the Fermi-LAT telescope. Although, prima-facie, we detect non-zero photon flux from three red dwarfs with high significance, these signals can attributed to contamination from nearby sources such as Crab and Cygnus, which are within the angular resolution of COMPTEL, and have been previously detected as very bright point sources at MeV energies. Therefore, we could not detect any statistically significant signal ($>3σ$) from any of these eight red dwarfs from 0.75-30 MeV. We then report the 95% confidence level upper limits on the differential photon flux (at 30 MeV), integral photon flux and integral energy flux for all of the eight red dwarfs. The integral energy flux limits range between $10^{-11}-10^{-10} \rm{ergs/cm^2/s}$.

astro-ph.HE↗

arXiv2024

A test for the redshift dependence of $σ_8$ using $fσ_8$ measurements

We search for a redshift dependence of $σ_8^0$ using 23 growth rate measurements from redshift space distortions and peculiar velocity measurements as a consistency check of $Λ$CDM. For this purpose we use the dataset from arXiv:1806.10822 consisting of 22 measurements, which has been vetted for internal consistencies. Eighteen of these measurements have been obtained from the Gold-2017 sample, collated from multiple redshift space distortion surveys between 2009 and 2016, whereas the remaining four have been obtained from the eBOSS DR14 quasar survey. We also added one additional data point from the BOSS DR12 CMASS galaxy sample. We find that for this dataset the $σ_8^0$ values are consistent between the low redshift and high redshift samples using three different redshift cuts. This implies that the growth rate measurements are consistent with a constant $σ_8^0$ in accord with $Λ$CDM, assuming there are no uncontrolled systematics in this dataset.

astro-ph.CO↗

arXiv2024

A pilot search for MeV gamma-ray emission from five galaxy clusters using archival COMPTEL data

We search for MeV gamma-ray emission between 0.75-30 MeV from five galaxy clusters, viz. Coma, VIRGO, SPT-CL J2012-5649, Bullet, and El Gordo, using archival data from the COMPTEL telescope. For this purpose we use three search templates: point source, radial disk and radial Gaussian. We do not detect any signals from Coma, SPT-CL J2012-5649, Bullet and El Gordo clusters with the 95\% c.l. photon energy flux limit $\sim 10^{-10} ~\rm{erg /cm^2/s} $. For VIRGO, we detect a non-zero signal between 0.92 to 1.63 MeV having marginal significance of about $2.5σ$, with the observed energy flux $ \sim 10^{-9}~\rm{ergs/cm^2/s}$. However, we do not confirm the previously reported evidence in literature for a gamma-ray line from Coma and VIRGO clusters between 5-7 MeV.

astro-ph.HE↗

arXiv2023

Search for GeV Gamma-Ray Emission from SPT-SZ selected Galaxy Clusters with 15 years of Fermi-LAT data

Galaxy clusters could produce gamma-rays from inverse Compton scattering of cosmic ray electrons or hadronic interactions of cosmic ray protons with the intracluster medium. It is still an open question on whether gamma-ray emission ($>$ GeV energies) has been detected from galaxy clusters. We carry out a systematic search for gamma-ray mission based on 300 galaxy clusters selected from the 2500 deg.$^2$ SPT-SZ survey after sorting them in descending order of $M_{500}/z^2$, using about 15 years of Fermi-LAT data in the energy range between 1-300 GeV. We were able to detect gamma-ray emission with significance of about $6.1σ$ from one cluster, viz SPT-CL J2012-5649. The estimated photon energy flux from this cluster is approximately equal to $1.3 \times 10^{-6}$ MeV cm$^{-2}$ s$^{-1}$. The gamma-ray signal is observed between $1-10$ GeV with the best-fit spectral index equal to $-3.61 \pm 0.33$. However, since there are six radio galaxies spatially coincident with SPT-CL J2012-5649 within the Fermi-LAT PSF, we cannot rule out the possibility this signal could be caused by some of these radio galaxies. Six other SPT-SZ clusters show evidence for gamma-ray emission with significance between $3-5σ$. None of the remaining clusters show statistically significant evidence for gamma-ray emission.

astro-ph.HE↗