arXiv subjects

Surajit Paul

Publications and source records attributed to Surajit Paul.

At least 19 recordsLinked to original sources

arXiv2026

Intensity fluctuations of radio halo in galaxy cluster: Insights from power spectrum estimation

Non-thermal synchrotron emissions from radio halo allow us to study mechanisms of particle (re)acceleration, magnetic field distribution, merger history, and turbulence in the intra-cluster medium. We propose power spectrum estimation as a novel and complementary method to study galaxy clusters. We use 610 MHz observations of MACSJ0014.3-302 and MACSJ0152.5-2852 to estimate the angular power spectrum (C_l) from the central halo regions. The C_l shows excess emission only for MACSJ0014.3-302. Using simulations, we find that a halo model with power-law fluctuations, in addition to the smooth exponential radial profile, is required to explain the observed C_l. We compare the observed power-law with existing models of MHD turbulence. The method may be useful for large data from SKA, finding megahalos in other sources, or detecting faint cluster emissions beyond the visible extent.

astro-ph.CO↗

arXiv2026

The Large-Scale Structure of the Universe through the SKA lenses

The large-scale distribution of galaxies in the Universe forms an intricate, interconnected network known as the cosmic web. Cosmological simulations within the standard Lambda-CDM framework successfully reproduce this filamentary structure and predict that the nodes and filaments are filled with tenuous plasma at temperatures ranging from 10^5-10^8 K. The hottest and luminous plasma in the nodes corresponds to the intra-cluster medium, while the cooler, more tenuous, gas extends along filaments and cluster outskirts. Galaxies and galaxy groups form and flow along these filaments before accreting onto galaxy clusters (the nodes), outlining the dynamical evolution of large-scale structures. During this process, an enormous amount of energy is dissipated through complex plasma processes that can be traced by radio emitting electrons. Despite strong theoretical support for this picture, observational validation remains limited. While massive clusters have been widely detected across various wavelengths, cluster outskirts and the diffuse intergalactic medium within filaments has remained elusive due to their extremely faint emission. The advent of highly sensitive radio facilities such as LOFAR, uGMRT, and MeerKAT has recently enabled a few successful detections of emission from comparatively denser regions of the cosmic-web. These include radio megahalos, permeating the entire cluster volume, as well as bridges of radio emission connecting cluster pairs. In this chapter, we summarize current theoretical insights into the cosmic web, discuss observational strategies and recent discoveries, and highlight how the forthcoming Square Kilometre Array (SKA) is expected to transform our understanding of the cosmic web and the distribution of baryons in the Universe.

astro-ph.CO↗

arXiv2026

Probing AGN duty cycle and cluster-driven morphology in a giant episodic radio galaxy

The evolution of radio jet morphology and its energetics is significantly influenced by the environment in which the host galaxy resides. As giant radio galaxies (GRGs) often extend to the scale of entire galaxy clusters ($\sim$Mpc) and beyond, they are a suitable class of objects for studying jet--intracluster medium interactions. This paper presents a multiwavelength study of a GRG, J1007+3540, using the LOFAR Two-metre Sky Survey second data release (LoTSS DR2) at 144 MHz and the upgraded Giant Metrewave Radio Telescope (uGMRT) at 400 MHz. The source has a projected linear extension of 1.45 Mpc and is hosted by MaxBCG J151.77665+35.67813, within the WHL 100706.4+354041 cluster. At both frequencies, the source exhibits clear signatures of recurrent jet activity, a one-sided, extended, tail-like diffuse structure with a morphological break in the tail. The estimated radiative ages of the inner lobes and outer north lobe are $\sim$140 Myr and $\sim$240 Myr, respectively. In addition to the radio analysis, we performed optical--to--infrared spectral energy distribution modelling. The host galaxy is an evolved elliptical system with a stellar mass of $\log_{10}(M_\star/M_\odot) = 11.0$ and an old stellar population age of $\sim$12 Gyr. The high infrared-derived star formation rate ($\sim106~M_\odot$~yr$^{-1}$) of the source implies significant dust-obscured star formation, potentially linked to merger-driven gas inflows. J1007+3540 presents a rare combination of a restarted jet, a detached tail-like structure, and unusual spectral flattening beyond the tail break, which is very rare to report together in a GRG. This rare and remarkable system offers a unique laboratory for probing the interplay between active galactic nucleus activity, star formation, and environmental effects in cluster-surrounded GRGs.

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arXiv2026

Evidence of sloshing-driven mini-halo formation in the cool-core cluster RXCJ1558.3-1410

Radio mini-halos are perplexing features, typically hosted by X-ray cool-core galaxy clusters. Understanding the connection between thermal X-ray and non-thermal radio emission is key to uncovering their origin. Here, we present a multiwavelength study of the cool-core cluster RXCJ1558.3-1410 using archival Chandra X-ray and wideband uGMRT radio data (Bands 3, 4 and 5). Our improved analysis confirms a previously known X-ray cavity at $\sim$36 kpc south-east of the cluster centre and we report a new cavity at $\sim$42 kpc to the north-west. These cavities suggest that the AGN provides mechanical power of $\sim$$6.0 \times 10^{44}$ erg s$^{-1}$, sufficient to offset radiative cooling in the ICM. We also detect a sharp surface brightness edge at $\sim$72 kpc south-east of the centre, characterised by a temperature jump and pressure continuity, consistent with a cold front, likely caused by gas sloshing from a minor merger. Our uGMRT images reveals an interesting diffuse emission surrounding the brightest cluster galaxy (BCG), with its edge spatially coinciding with the sloshing cold front and roughly with the cooling radius. Furthermore, a low star formation rate and uniform metal abundance up to the sloshing edge are consistent with the earlier findings of suppression of star formation and metallicity homogenisation by mixing core gas through sloshing. Finally, the spatial correlation between the mini-halo and the observed X-ray features indicates that ICM sloshing, rather than AGN feedback, plays a dominant role in powering the proposed radio mini-halo emission.

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arXiv2025

Excess of diffuse gamma-ray emission detected from the galaxy cluster Abell 119 from 14-year Fermi-LAT Data

Galaxy clusters are among the most massive gravitationally bound systems in the Universe and are considered major reservoirs of high-energy cosmic rays, yet no conclusive $\gamma$-ray detection from them has been achieved. This non-detection may stem from limited sensitivity and source localization of current $\gamma$-ray instruments, as well as strong interactions of $\gamma$-rays with intervening material that restrict detectable signals to only a few nearby and dynamically active clusters. Motivated by these constraints, we selected a sample of nearby ($z<0.05$) merging clusters and analyzed 14 years of \textit{Fermi}-LAT data. In this work, we present a detailed study of Abell 119 (A119), a merging cluster with significant X-ray luminosity and complex dynamics. Using \textit{Fermipy} and \textit{Fermi} Science Tools, we modeled all potential $\gamma$-ray sources and confirmed the 4FGL point sources 4FGL J0059.3$-$0152, 4FGL J0101.0$-$0059, and 4FGL J0059.2+0006 with significant TS values.s. It further reveals, a $\sim4\sigma$ excess of diffuse $\gamma$-ray emission offset by $\sim0.25^\circ$ from the cluster center, plausibly associated with the cluster halo. An extended model provides the best fit, yielding luminosity bounds of $\sim 12.21^{+2.74}_{-3.95}\times10^{42}\,\mathrm{erg\,s^{-1}}$ and a particle spectral index of $\sim2.25^{+0.38}_{-0.13}$, consistent with earlier expectations for cluster-scale non-thermal emission. These results suggest a hadronic origin for the detected signal. Although the $\sim4\sigma$ excess is compelling, uncertainties in localization and instrumental limitations prevent a definitive detection. Nonetheless, the results highlight the potential for deeper cluster studies, and the estimated neutrino flux $E^{2}\phi_{\nu}\approx3\times10^{-10}\,\mathrm{GeV\,cm^{-2}\,s^{-1}\,sr^{-1}}$ motivates future observations with upcoming neutrino telescopes.

astro-ph.HE↗

arXiv2024

Sloshing and spiral structures breeding a putative radio mini-halo in the environment of a cool-core cluster Abell 795

Spiral structures and cold fronts in X-rays are frequently observed in cool core galaxy clusters. However, studies on radio mini-haloes associated with such spirals and their physical connections are rare. Here, we present the detection of an extended diffuse radio emission entrained in the X-ray spiral structure in a known cool core cluster Abell 795 (A795). Though the cool core is a sign of the relaxed nature of the clusters, our re-analysed 30 ks Chandra X-ray data of cluster A795 confirms the presence of an interesting log spiral structure of X-ray deficit region complemented by an X-ray excess counter spiral in the residual map, exposing its dynamical activity. Our new analysis of 150 $\&$ 325 MHz GMRT archival data of the cluster confirms the detection of a $\sim180$ kpc ultra-steep ($\alpha\sim-2.7$) diffuse radio structure which was previously reported as a candidate radio mini halo from low sensitive survey maps. This radio emission spans the entire spiral structure ($\sim186$ kpc), enclosed by two previously reported cold fronts. Furthermore, SDSS DR13 optical spectra, as well as GALEX's FUV data, show a considerably low total star formation rate of 2.52 M$_{\odot}$ yr$^{-1}$ and having no significant variation in metallicity distribution. We argued that the two-phase (hot and cold) plasma at the cluster core with differential velocity has probably caused the spiral formation and has redistributed the secondary electrons from the central BCG or the pre-accelerated electrons which have been (re-)accelerated by the sloshing turbulence to form the observed candidate radio mini-halo structure. This has been supported by a few previous studies that indicate spiral formation and sloshing turbulence may quench star formation and facilitate smooth metallicity distribution by mixing the gas in the core.

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arXiv2024

Cool-core, X-ray cavities and cold front revealed in RXCJ0352.9+1941 cluster by Chandra and GMRT observations

This paper presents a comprehensive analysis of 30 ks Chandra and 46.8 ks (13 Hr) 1.4 GHz GMRT radio data on the cool-core cluster RXCJ0352.9+1941 with an objective to investigate AGN activities at its core. This study confirms a pair of X-ray cavities at projected distances of about 10.30 kpc and 20.80 kpc, respectively, on the NW and SE of the X-ray peak. GMRT L band (1.4 GHz) data revealed a bright radio source associated with the core of this cluster hosting multiple jet-like emissions. The spatial association of the X-ray cavities with the inner pair of radio jets confirm their origin due to AGN outbursts. The 1.4 GHz radio power ${\rm 7.4 \pm 0.8 \times 10^{39} \, erg\, s^{-1}}$ is correlated with the mechanical power stored in the X-ray cavities ($\sim7.90\times 10^{44}$ erg s$^{-1}$), implying that the power injected by radio jets in the ICM is sufficient enough to offset the radiative losses. The X-shaped morphology of diffuse radio emission seems to be comprised of two pairs of orthogonal radio jets, likely formed due to a spin-flip of jets due to the merger of two systems. The X-ray surface brightness analysis of the ICM in its environment revealed two non-uniform, extended spiral-like emission structures on either side of the core, pointing towards the sloshing of gas due to a minor merger and might have resulted in a cold front at $\sim$31 arcsec (62 kpc) with a temperature jump of 1.44 keV.

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arXiv2024

Search for interacting galaxy clusters from SDSS DR-17 employing optimized friend-of-friend algorithm and multi-messenger tracers

In the theoretical framework of hierarchical structure formation, galaxy clusters evolve through continuous accretion and mergers of substructures. Cosmological simulations have revealed the best picture of the Universe as a 3-D filamentary network of dark-matter distribution called the cosmic web. Galaxy clusters are found to form at the nodes of this network and are the regions of high merging activity. Such mergers being highly energetic, contain a wealth of information about the dynamical evolution of structures in the Universe. Observational validation of this scenario needs a colossal effort to identify numerous events from all-sky surveys. Therefore, such efforts are sparse in literature and tend to focus on individual systems. In this work, we present an improved search algorithm for identifying interacting galaxy clusters and have successfully produced a comprehensive list of systems from SDSS DR-17. By proposing a set of physically motivated criteria, we classified these interacting clusters into two broad classes, 'merging' and 'pre-merging/postmerging' systems. Interestingly, as predicted by simulations, we found that most cases show cluster interaction along the prominent cosmic filaments of galaxy distribution (i.e., the proxy for DM filaments), with the most violent ones at their nodes. Moreover, we traced the imprint of interactions through multi-band signatures, such as diffuse cluster emissions in radio or X-rays. Although we could not find direct evidence of diffuse emission from connecting filaments and ridges; our catalogue of interacting clusters will ease locating such faintest emissions as data from sensitive telescopes like eROSITA or SKA, becomes accessible

astro-ph.CO↗

arXiv2023

A new enigmatic radio relic in the low mass cluster Abell 2108

We report the discovery of a radio relic in the northeastern periphery of the cluster Abell 2108 (A2108). A2108 is a part of the uGMRT LOw-MAss Galaxy Cluster Survey (GLOMACS), where our main aim is to search for diffuse radio emission signatures in very sparsely explored low-mass galaxy clusters using uGMRT band-3 (central frequency 400 MHz). We used our uGMRT band-3 data along with the existing archival band-3 uGMRT data to improve image sensitivity. Along with the previously reported southwestern relic, the discovery of the new relic makes A2108 one of the few low-mass clusters hosting double relics. The new relic spans over a region of 610 kpc $\times$ 310 kpc and, interestingly, differs considerably in size and morphology from the other relic. With XMM-Newton science archive data, we also report the tentative detection of a mildly supersonic shock of Mach number $\mathcal{M}_\mathrm{SB}=1.42$ and $\mathcal{M}_\mathrm{T} = 1.43$ from the surface brightness and temperature discontinuities, respectively near this newly found relic. Both the relics in A2108 are found to be significantly under-luminous compared to other double relic systems in the mass-luminosity plane. Though mild supersonic shocks resulting from an off-axis merger could have influenced their origin, we hypothesize that further local environments have played a crucial role in shaping their morphology.

astro-ph.HE↗

arXiv2023

Adaptive friends-of-friends algorithm for identifying gravitationally bound cosmological structures

The Universe at the present epoch is found to be a network of matter over-dense and under-dense regions. To date, this picture of the Universe is best revealed through cosmological large-volume simulations and large-scale galaxy redshift surveys, in which, the most important step is the appropriate identification of structures. So far, these structures are identified using various group finding codes, mostly based on the friends-of-friends (FoF) or spherical over-density (SO) algorithms. Although, the main purpose is to identify gravitationally bound structures, surprisingly, the mass information has hardly been used effectively by these codes. Moreover, the methods used so far either constrain the over-density or use the real unstructured geometry only. Even though these are key factors in the accurate determination of structures-mass information, hardly any attempt has been made as yet to consider these important parameters together while formulating the grouping algorithms. In this paper, we present our proposed algorithm which takes care of all the above-mentioned relevant features and ensures the bound structures by means of physical quantities, mainly mass and the total energy information. We introduced a novel concept of physically relevant arm-length for each element depending on their individual gravity leading to a distinct linking length for each unique pair of elements. This proposed algorithm is thus fundamentally new that, not only able to catch the gravitationally bound, real unstructured geometry, it does identify it roughly within a predefined physically motivated density threshold. Such a thing could not be simultaneously achieved before by any of the usual FoF or SO-based methods. We also demonstrate the unique ability of the code in the appropriate identification of structures, both from large volume cosmological simulations as well as from galaxy redshift surveys.

astro-ph.CO↗

arXiv2022

Exploring diffuse radio emission in galaxy clusters and groups with the uGMRT and the SKA

Diffuse radio emission has been detected in a considerable number of galaxy clusters and groups, revealing the presence of pervasive cosmic magnetic fields, and of relativistic particles in the large-scale structure (LSS) of the Universe. Since cluster radio emission is faint and steep spectrum, its observations are largely limited by the instrument sensitivity and frequency of observation, leading to a dearth of information, more so for lower-mass systems. The unprecedented sensitivity of recently commissioned low-frequency radio telescope arrays, aided by the development of advanced calibration and imaging techniques, have helped in achieving unparalleled image quality. At the same time, the development of sophisticated numerical simulations and the availability of supercomputing facilities have paved the way for high-resolution numerical modeling of radio emission, and the structure of the cosmic magnetic fields in LSS, leading to predictions matching the capabilities of observational facilities. In view of these rapidly-evolving scenerio in modeling and observations, in this review, we summarise the role of the new telescope arrays and the development of advanced imaging techniques and discuss the detections of various kinds of cluster radio sources. In particular, we discuss observations of the cosmic web in the form of supercluster filaments, studies of emission in poor clusters and groups of galaxies, and of ultra-steep spectrum sources. We also review the current theoretical understanding of various diffuse cluster radio sources and the associated magnetic field and polarization. As the statistics of detections improve along with our theoretical understanding, we update the source classification schemes based on their intrinsic properties. We conclude by summarising the role of the upgraded GMRT and our expectations from the upcoming Square Kilometre Array (SKA) observatories.

astro-ph.CO↗

arXiv2022

Plans for building a prototype SKA regional centre in India

In order to deliver the full science potential of the Square Kilometer Array (SKA) telescope, several SKA Regional Centres (SRCs) will be required to be constructed in different SKA member countries around the world. These SRCs will provide high performance compute and storage for the generation of advanced science data products from the basic data streams generated by the SKA Science Data Handling and Processing system, critically necessary to the success of the key science projects to be carried out by the SKA user community. They will also provide support to astronomers to enable them to carry out analysis on very large SKA datasets. Construction of such large data centres is a technical challenge for all SKA member nations. In such a situation, each country plans to construct a smaller SRC over the next few years (2022 onwards), known as a proto-SRC. In India, we propose to construct a proto-SRC which will be used for the analysis of data from SKA pathfinders and precursors with strong Indian involvement such as uGMRT, Meerkat and MWA. We describe our thinking on some aspects of the the storage, compute and network of the proto-SRC and how it will be used for data analysis as well as for carrying out various simulations related to SKA key science projects led by Indian astronomers. We also present our thoughts on how the proto-SRC plans to evaluate emerging hardware and software technologies and to also begin software development in areas of relevance to SKA data processing and analysis such as algorithm implementation, pipeline development and data visualisation software.

astro-ph.IM↗

arXiv2022

The radio source in Abell 980: A Detached-Double-Double Radio Galaxy?

It is argued that the new morphological and spectral information gleaned from the recently published LoFAR Two meter Sky Survey data release 2 (LoTSS-2 at 144 MHz) observations of the cluster Abell 980 (A980), in combination with its existing GMRT and VLA observations at higher frequencies, provide the much-needed evidence to strengthen the proposal that the cluster's radio emission comes mainly from two double radio sources, both produced by the brightest cluster galaxy (BCG) in two major episodes of jet activity. The two radio lobes left from the previous activity have become diffuse and developed an ultra-steep radio spectrum while rising buoyantly through the confining hot intra-cluster medium (ICM) and, concomitantly, the host galaxy has drifted to the cluster centre and entered a new active phase manifested by a coinciding younger double radio source. The new observational results and arguments presented here bolster the case that the old and young double radio sources in A980 conjointly represent a `double-double' radio galaxy whose two lobe-pairs have lost colinearity due to the (lateral) drift of their parent galaxy, making this system by far the most plausible case of a `Detached-Double-Double Radio Galaxy' (dDDRG).

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arXiv2022

Deciphering the ultra-steep spectrum diffuse radio sources discovered in the cool-core cluster Abell~980

Clusters of galaxies are excellent laboratories for studying recurring nuclear activity in galactic nuclei since their hot gaseous medium can vastly prolong the detectability of their radio lobes via better confinement. We report here a multi-band study of the sparsely studied galaxy cluster Abell 980, based on our analysis of {\it{Chandra}} X-ray and the GMRT (150 and 325 MHz) and EVLA (1.5 GHz) radio archival data, revealing an unusually rich phenomenology. It is shown to be a quasi-relaxed cluster with a cool core ($T\sim4.2$ keV) surrounded by a hot and extensive intracluster medium (ICM) at $T\sim6.8$ keV. The radio emission shows a rich diversity, having (i) two large diffuse sources of ultra-steep spectrum (USS), extending to opposite extremities of the ICM, each associated with an X-ray brightness discontinuity (cold front), (ii) a bright radio-double of size $\sim55$ kpc coinciding with the central BCG, and (iii) a diffuse radio source, likely a mini-halo of size $\sim110$~kpc around the BCG which possesses a huge ellipsoidal stellar halo of extent $\sim 80$~kpc. The association of cold fronts with two highly aged (~ 260 Myr) USS sources in a cool-core cluster, makes it a very rare system. These USS sources are probably radio lobes from a previous episode of jet activity in the BCG, driven buoyantly towards the outskirts of the X-ray halo, thereby creating the cold fronts. A deeper radio image of this cluster may provide a rare opportunity to verify the recently proposed alternative model which explains radio mini-haloes as the aggregate radio emission from Type I supernovae occurring in the giant stellar halo extended across the cluster core.

astro-ph.GA↗

arXiv2021

Extremely inverted peaked spectrum radio sources

We report our ongoing search for extremely inverted spectrum compact radio galaxies, for which the defining feature in the radio spectrum is not the spectral peak, but instead the slope of the spectrum (alpha) in the high-opacity (i.e., lower frequency) part of the radio spectrum. Specifically, our focus is on the spectral regime with spectral index, alpha >+2.5. The motivation for our study is, firstly, extragalactic sources with such extreme spectral index are extremely rare, because of the unavailability of right combination of sensitivity and resolution over a range of low frequencies. The second reason is more physically motivated, since alpha = +2.5 is the maximum slope theoretically possible for a standard radio source emitting synchrotron radiation. Therefore such sources could be the test-bed for some already proposed alternative scenarios for synchrotron self-absorption (SSA), like the free-free absorption (FFA) highlighting the importance of jet-ISM interaction in the radio galaxy evolution.

astro-ph.GA↗

arXiv2020

A low-frequency radio halo survey of the South Pole Telescope SZ-selected clusters with the GMRT

The presence of non-thermal electrons and large scale magnetic fields in the intra-cluster medium (ICM) is known through the detection of mega-parsec (Mpc) scale diffuse radio synchrotron emission. Although a significant amount of progress in finding new diffuse radio sources has happened in the last decade, most of the investigation has been constrained towards massive low-redshift clusters. In this work, we explore clusters with redshift $z>0.3$ in search of diffuse radio emission, at 325 MHz with the Giant Metrewave Radio Telescope (GMRT). This campaign has resulted in the discovery of 2 new radio halos (SPT-CL J0013-4906 and SPT-CL J0304-4401) along with 2 other detections (SPT-CL J2031-4037 and SPT-CL J2248-4431), previously reported (at 325 MHz) in the literature. In addition, we detect a halo candidate in 1 cluster in our sample, and upper limits for halos are placed in 8 clusters where no diffuse emission is detected. In the $P_{1.4} - L_\mathrm{X}$ plane, the detected halos follow the observed correlation, whereas the upper limits lie above the correlation line, indicating the possibility of future detection with sensitive observations.

astro-ph.HE↗

arXiv2020

uGMRT HI 21-cm absorption observations of two extremely inverted spectrum sources

We report the detection of HI 21-cm absorption in a member of the rare and recently discovered class of compact radio sources, 'Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS)'. EISERS conceivably form a special sub-class of the inverted spectrum radio galaxies since the spectral index of the optically thick part of the spectrum for these sources crosses the synchrotron self absorption limit of $α=+2.5$ (S($ν$) $\propto$ $ν^α$). We have searched for HI absorption in two EISERS using the recently upgraded Giant Metrewave Radio Telescope (uGMRT) and detected an absorption feature in one of them. The strong associated HI absorption detected against the source J1209$-$2032 ($z$=0.4040) implies an optical depth of 0.178$\pm$0.02 corresponding to an HI column density of 34.8$\pm$2.9 $\times$10$^{20}$ cm$^{-2}$, for an assumed HI spin temperature of 100 K and covering factor of 1. This is among the highest known optical depth and HI column densities found for compact radio sources of GPC/CSS type and supports the free-free absorption model for the steeply inverted radio spectrum of this source. For the other source, J1549$+$5038 ($z$ = 2.171), no HI absorption was detected in our observations.

astro-ph.GA↗

arXiv2020

Diffuse radio emission in the galaxy cluster SPT-CL J2031-4037: a steep spectrum intermediate radio halo?

The advent of sensitive low frequency radio observations has revealed a number of diffuse radio objects with peculiar properties that are challenging our understanding about the physics of the intracluster medium. Here, we report the discovery of a steep spectrum radio halo surrounding the central Brightest Cluster Galaxy (BCG) in the galaxy cluster SPT-CL J2031-4037. This cluster is morphologically disturbed yet has a weak cool core, an example of cool core/non-cool core transition system, which harbours a radio halo of $\sim 0.7$ Mpc in size. The halo emission detected at 1.7 GHz is less extended compared to that in the 325 MHz observation, and the spectral index of the part of the halo visible at 325 MHz to 1.7 GHz frequencies was found to be $-1.35 \pm 0.07$. Also, $P_{1.4\ \mathrm{GHz}}$ was found to be $0.77 \times 10^{24}$ W Hz$^{-1}$ which falls in the region where radio mini-halos, halo upper limits and ultra-steep spectrum (USS) halos are found in the $P_{1.4\ \mathrm{GHz}} - L_\mathrm{X}$ plane. Additionally, simulations presented in the paper provide support to the scenario of the steep spectrum. The diffuse radio emission found in this cluster may be a steep spectrum "intermediate" or "hybrid" radio halo which is transitioning into a mini-halo.

astro-ph.HE↗