arXiv subjects

M. D. Filipović

Publications and source records attributed to M. D. Filipović.

At least 37 records · Page 2Linked to original sources

arXiv2025

Study of a giant Large Magellanic Cloud Supernova Remnant, Veliki (J0450.4-7050)

We present a high-resolution radio-continuum view and a multi-frequency analysis of the Large Magellanic Cloud (LMC) Supernova Remnant (SNR) J0450.4-7050, which we give the nickname Veliki. These high-resolution observations reveal a larger extent than previously measured, making J0450.4-7050 one of the largest SNRs that we know of. Additionally, we observe a higher than expected radio surface brightness and an unusually flat spectral index ($α= -0.26 \pm 0.02$), with little spectral variation over the remnant. We observe a bright H$α$ shell indicating significant cooling over the remnant, but also an excess of [Oiii] on the eastern shock front. We investigate several theoretical scenarios to explain the emission and radio evolution of J0450.4-7050 in the context of the LMC environment, and determine that this is most likely an older, predominantly radiative, SNR with a higher shock compression ratio, which gives a flatter non-thermal spectrum, in combination with a thermal (bremsstrahlung) emission contribution.

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arXiv2025

ASKAP-EMU radio continuum detection of planetary nebula NGC 5189: the "Infinity" nebula

We report the radio continuum detection of well known Galactic Planetary Nebula (PN) NGC 5189, observed at 943 MHz during the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey. Two detections of NGC 5189 have been made during the survey, of better resolution than previous radio surveys. Both measurements of the integrated flux density are consistent with each other, at $S_{\rm 943\,MHz} = 0.33\pm0.03$ Jy, and the spectral luminosity is $L_{\rm{943\,MHz}}$ = 8.89 $\times$ 10$^{13}$ W m$^{-2}$ Hz$^{-1}$. Using available flux density measurements for radio-detections of NGC 5189, we calculate a radio surface brightness at 1 GHz and measure $Σ_{\rm 1~GHz}$ = 6.0 $\times$ 10$^{-21}$ W m$^{-2}$ Hz$^{-1}$ sr$^{-1}$, which is in the expected range for Galactic PNe. We measure an apparent size of 3.4${'}$ $\times$ 2.2${'}$ corresponding to physical diameters of 1.48 pc $\times$ 0.96 pc, and combine available radio observations of NGC 5189 to estimate a spectral index of $α$ = 0.12 $\pm$ 0.05. Hence, we agree with previous findings that NGC 5189 is a thermal (free-free) emitting nebula. Additional measurements of the optical depth ($τ= 0.00246$) and electron density ($N_{e} = 138~cm^{-3}$) support our findings that NGC 5189 is optically thin at 943 MHz. Furthermore, the radio contours from the ASKAP-EMU image have been overlaid onto a Hubble Space Telescope (HST) Wide Field Camera 3 image, demonstrating that the radio morphology closely traces the optical. Notably, the contour alignment for the innermost region highlights the two envelopes of gas previously reported to be low-ionisation structures, which is considered a defining feature of post common-envelope PNe that surround a central Wolf-Rayet star.

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arXiv2025

Multipole Analysis and Application to Supernova Remnant X-ray Images

We develop a multipole analysis method for images with a circular boundary, then apply it to supernova remnant (SNR) images. The morphology of SNR images is related to several factors, including the inhomogeneities of the supernova ejecta and of the circumstellar medium in which the ejecta and shock wave travel. The current multipole method corrects some errors in a previously presented method, and applies the new analysis to test for differences in X-ray image morphology between Type Ia and core-collapse type SNRs. We find there is no clear difference between the two SNR types in morphology as measured by multipole moments.

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arXiv2025

The Evolutionary Map of the Universe: A new radio atlas for the southern hemisphere sky

We present the Evolutionary Map of the Universe (EMU) survey conducted with the Australian Square Kilometre Array Pathfinder (ASKAP). EMU aims to deliver the touchstone radio atlas of the southern hemisphere. We introduce EMU and review its science drivers and key science goals, updated and tailored to the current ASKAP five-year survey plan. The development of the survey strategy and planned sky coverage is presented, along with the operational aspects of the survey and associated data analysis, together with a selection of diagnostics demonstrating the imaging quality and data characteristics. We give a general description of the value-added data pipeline and data products before concluding with a discussion of links to other surveys and projects and an outline of EMU's legacy value.

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arXiv2025

Study of tau neutrinos and non-unitary neutrino mixing with the first six detection units of KM3NeT/ORCA

Oscillations of atmospheric muon and electron neutrinos produce tau neutrinos with energies in the GeV range, which can be observed by the ORCA detector of the KM3NeT neutrino telescope in the Mediterranean Sea. First measurements with ORCA6, an early subarray corresponding to about 5$\%$ of the final detector, are presented. A sample of 5828 neutrino candidates has been selected from the analysed exposure of 433 kton-years. The $ν_τ$ normalisation, defined as the ratio between the number of observed and expected tau neutrino events, is measured to be $S_τ= 0.48^{+0.5}_{-0.33}$. This translates into a $ν_τ$ charged-current cross section measurement of $σ_τ^{\text{meas}} = (2.5 ^{+2.6}_{-1.8}) \times 10^{-38}$ cm$^{2}$ nucleon$^{-1}$ at the median $ν_τ$ energy of 20.3 GeV. The result is consistent with the measurements of other experiments. In addition, the current limit on the non-unitarity parameter affecting the $τ$-row of the neutrino mixing matrix was improved, with $α_{33}>$ 0.95 at the 95$\%$ confidence level.

hep-ex↗

arXiv2025

gSeaGen code by KM3NeT: an efficient tool to propagate muons simulated with CORSIKA

The KM3NeT Collaboration has tackled a common challenge faced by the astroparticle physics community, namely adapting the experiment-specific simulation software to work with the CORSIKA air shower simulation output. The proposed solution is an extension of the open source code gSeaGen, which allows the transport of muons generated by CORSIKA to a detector of any size at an arbitrary depth. The gSeaGen code was not only extended in terms of functionality but also underwent a thorough redesign of the muon propagation routine, resulting in a more accurate and efficient simulation. This paper presents the capabilities of the new gSeaGen code as well as prospects for further developments.

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arXiv2025

ASKAP and VLASS search for a radio-continuum counterpart of ultra-high-energy neutrino event KM3-230213A

We present the results of an Australian Square Kilometre Array Pathfinder (ASKAP) 944 MHz and Very Large Array Sky Survey (VLASS) 3~GHz search for a radio-continuum counterpart of the recent ultra-high-energy (UHE) neutrino event, KM3-230213A. Using (ASKAP), we catalog 1052 radio sources within the 1.5$^\circ$ radius search area (68% certainty region) around the particle's calculated origin, 10 of which we classify as blazar candidates based on their radio spectra. The most prominent radio source in the search area is the nearby spiral galaxy UGCA 127 (nicknamed Phaedra, From Greek: $ϕαiδρα$, a Cretan princess of Greek Mythology, derived from Phaidros, Greek: $ϕαιδρoς$, meaning 'bright'.). Its non-thermal radio spectrum classifies it as a non-blazar active galactic nucleus (AGN). We also present an extended radio source, WISEA J061715.89-075455.4 (nicknamed Hebe, From Greek: $Hβη$, the Greek goddess of youth.), located only ~7' from the geometric center of the search area, with a very unusual highly polarized compact component. Finally, we present a strong radio source, EMU J062248-072246 (nicknamed Narcissus, From Greek $Nαρκισσoζ$ was a self-absorbed hunter from Thespiae in Boeotia.), which has a maximum self-absorption spectral slope of +2.5 at low frequencies, and exhibits ~25% flux density variability over the ~5-year VLASS 3~GHz survey.

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arXiv2025

Probing invisible neutrino decay with the first six detection units of KM3NeT/ORCA

In the era of precision measurements of neutrino oscillation parameters, it is necessary for experiments to disentangle discrepancies that may indicate physics beyond the Standard Model in the neutrino sector. KM3NeT/ORCA is a water Cherenkov neutrino detector under construction and anchored at the bottom of the Mediterranean Sea. The detector is designed to study the oscillations of atmospheric neutrinos and determine the neutrino mass ordering. This paper focuses on the initial configuration of ORCA, referred to as ORCA6, which comprises six out of the foreseen 115 detection units of photosensors. A high-purity neutrino sample was extracted during 2020 and 2021, corresponding to an exposure of 433 kton-years. This sample is analysed following a binned log-likelihood approach to search for invisible neutrino decay, in a three-flavour neutrino oscillation scenario, where the third neutrino mass state $ν_3$ decays into an invisible state, e.g. a sterile neutrino. The resulting best fit of the invisible neutrino decay parameter is $α_3 = 0.92^{+1.08}_{-0.57}\times 10^{-4}~\mathrm{eV^2}$, corresponding to a scenario with $θ_{23}$ in the second octant and normal neutrino mass ordering. The results are consistent with the Standard Model, within a $2.1\,σ$ interval.

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arXiv2025

First Searches for Dark Matter with the KM3NeT Neutrino Telescopes

Indirect dark matter detection methods are used to observe the products of dark matter annihilations or decays originating from astrophysical objects where large amounts of dark matter are thought to accumulate. With neutrino telescopes, an excess of neutrinos is searched for in nearby dark matter reservoirs, such as the Sun and the Galactic Centre, which could potentially produce a sizeable flux of Standard Model particles. The KM3NeT infrastructure, currently under construction, comprises the ARCA and ORCA undersea Čerenkov neutrino detectors located at two different sites in the Mediterranean Sea, offshore of Italy and France, respectively. The two detector configurations are optimised for the detection of neutrinos of different energies, enabling the search for dark matter particles with masses ranging from a few GeV/c$^2$ to hundreds of TeV/c$^2$. In this work, searches for dark matter annihilations in the Galactic Centre and the Sun with data samples taken with the first configurations of both detectors are presented. No significant excess over the expected background was found in either of the two analyses. Limits on the velocity-averaged self-annihilation cross section of dark matter particles are computed for five different primary annihilation channels in the Galactic Centre. For the Sun, limits on the spin-dependent and spin-independent scattering cross sections of dark matter with nucleons are given for three annihilation channels.

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arXiv2025

ASKAP EMU Radio Detection of the Reflection Nebula VdB-80 in the Monoceros Crossbones Filamentary Structure

We present a new radio detection from the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey associated with the reflection nebula (RN) VdB-80. The radio detection is determined to be a previously unidentified HII region, now named Lagotis. The RN is located towards Monoceros, centred in the molecular cloud feature known as the `Crossbones'. The 944 MHz EMU image shows a roughly semicircular HII region with an integrated flux density of 30.2$\pm$0.3 mJy. The HII region is also seen at 1.4 GHz by NVSS, yielding an estimated spectral index of 0.65$\pm$0.51, consistent with thermal radio emission. Gaia DR3 and 2MASS data give a distance to the stars associated with the HII region of $\sim$960 pc. This implies a size of 0.76$\times$0.68($\pm$0.09) pc for the HII region. We derive an HII region electron density of the bright radio feature to be 26 cm$^{-3}$, requiring a Lyman-alpha photon flux of $10^{45.6}$ s$^{-1}$, which is consistent with the expected Lyman flux of HD 46060, the B2II type star which is the likely ionising star of the region. The derived distance to this region implies that the Crossbones feature is a superposition of two filamentary clouds, with Lagotis embedded in the far cloud.

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arXiv2025

Search for non-standard neutrino interactions with the first six detection units of KM3NeT/ORCA

KM3NeT/ORCA is an underwater neutrino telescope under construction in the Mediterranean Sea. Its primary scientific goal is to measure the atmospheric neutrino oscillation parameters and to determine the neutrino mass ordering. ORCA can constrain the oscillation parameters $Δm^{2}_{31}$ and $θ_{23}$ by reconstructing the arrival direction and energy of multi-GeV neutrinos crossing the Earth. Searches for deviations from the Standard Model of particle physics in the forward scattering of neutrinos inside Earth matter, produced by Non-Standard Interactions, can be conducted by investigating distortions of the standard oscillation pattern of neutrinos of all flavours. This work reports on the results of the search for non-standard neutrino interactions using the first six detection units of ORCA and 433 kton-years of exposure. No significant deviation from standard interactions was found in a sample of 5828 events reconstructed in the 1 GeV$-$1 TeV energy range. The flavour structure of the non-standard coupling was constrained at 90\% confidence level to be $|\varepsilon_{μτ} | \leq 5.4 \times 10^{-3}$, $|\varepsilon_{eτ} | \leq 7.4 \times 10^{-2}$, $|\varepsilon_{eμ} | \leq 5.6 \times 10^{-2}$ and $-0.015 \leq \varepsilon_{ττ} - \varepsilon_{μμ} \leq 0.017$. The results are comparable to the current most stringent limits placed on the parameters by other experiments.

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arXiv2024

PSR J1631-4722: The Discovery of a Young and Energetic Pulsar in the Supernova Remnant G336.7+0.5

Detecting a pulsar associated with a supernova remnant (SNR) and/or pulsar wind nebula (PWN) is crucial for unraveling its formation history and pulsar wind dynamics, yet the association with a radio pulsar is observed only in a small fraction of known SNRs and PWNe. In this paper, we report the discovery of a young pulsar J1631$-$4722, associated with the Galactic SNR G336.7$+$0.5 using Murriyang, CSIRO's Parkes radio telescope. It is also potentially associated with a PWN revealed by the Rapid ASKAP (Australian Square Kilometre Array Pathfinder) Continuum Survey (RACS). This 118 ms pulsar has a high dispersion measure of 873 $\mathrm{pc\,cm^{-3}}$ and a rotation measure of $-$1004 $\mathrm{rad\,m^{-2}}$. Because of such a high DM, at frequencies below 2 GHz, the pulse profile is significantly scattered, making it effectively undetectable in previous pulsar surveys at $\sim$1.4 GHz. Follow-up observations yield a period derivative of $\dot{P} = 3.6 \times 10^{-15}$, implying a characteristic age, $τ_{c} = 33\,$kyr, and spin-down luminosity, $\dot{E} = 1.3\times10^{36}\,$erg$\,s^{-1}$. PSR$\,$J1631$-$4722, with its high spin-down luminosity and potential link to a PWN, stands out as a promising source of the high-energy $γ$-ray emission observed in the region.

astro-ph.HE↗

arXiv2024

Investigating Unusual H$α$ Features towards the Scutum Supershell

We investigate the unusual H$α$ features found towards the Scutum Supershell via recent arc-minute and arc-second resolution imaging. These multi-degree features resemble a long central spine ending in a bow-shock morphology. We performed a multi-wavelength study in [SII] optical, radio continuum, infrared continuum, HI, CO, X-ray and gamma-ray emissions. Interestingly, we found the Galactic worm GW16.9$-$3.8 HI feature appears within the Scutum Supershell, and likely influences the spine morphology. Furthermore, the rightmost edge of the bow-shock H$α$ emission overlaps with [S II] line emission, 4.85 GHz radio, and both 60$μ$m and 100$μ$m infrared continuum emissions, suggesting some potential for excitation by shock heating. We estimated the photo-ionisation from O-type and B-type stars in the region (including those from the OB associations Ser OB1B, Ser OB2 and Sct OB3) and found that this mechanism could supply the excitation to account for the observed H$α$ luminosity of the spine and bow-shock of $\sim$1e36 - 2e36 erg/s (d/2.5 kpc)$^2$. Recent MHD simulations by Drozdov et al. (2022) demonstrate the potential for supernova events to drive outflow and bow-shock types of features of the same energetic nature and physical scale as the H$α$ emission we observe here. While this clearly requires many supernova events over time, we speculate that one contributing event could have come from the presumably energetic supernova (hypernova) birth of the magnetar tentatively identified in the X-ray binary LS 5039.

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arXiv2024

Measurement of neutrino oscillation parameters with the first six detection units of KM3NeT/ORCA

KM3NeT/ORCA is a water Cherenkov neutrino detector under construction and anchored at the bottom of the Mediterranean Sea. The detector is designed to study oscillations of atmospheric neutrinos and determine the neutrino mass ordering. This paper focuses on an initial configuration of ORCA, referred to as ORCA6, which comprises six out of the foreseen 115 detection units of photo-sensors. A high-purity neutrino sample was extracted, corresponding to an exposure of 433 kton-years. The sample of 5828 neutrino candidates is analysed following a binned log-likelihood method in the reconstructed energy and cosine of the zenith angle. The atmospheric oscillation parameters are measured to be $\sin^2θ_{23}= 0.51^{+0.04}_{-0.05}$, and $ Δm^2_{31} = 2.18^{+0.25}_{-0.35}\times 10^{-3}~\mathrm{eV^2} \cup \{-2.25,-1.76\}\times 10^{-3}~\mathrm{eV^2}$ at 68\% CL. The inverted neutrino mass ordering hypothesis is disfavoured with a p-value of 0.25.

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arXiv2024

New radio continuum study of the Large Magellanic Cloud Supernova Remnant N49

We present new Australia Telescope Compact Array (ATCA) radio observations toward N49, one of the brightest extragalactic Supernova remnants (SNRs) located in the Large Magellanic Cloud. Our new and archival ATCA radio observations were analysed along with $Chandra$ X-ray data. These observations show a prominent `bullet' shaped feature beyond the southwestern boundary of the SNR. Both X-ray morphology and radio polarisation analysis support a physical connection of this feature to the SNR. The 'bullet' feature's apparent velocity is estimated at $\sim$1300 km s$^{-1}$, based on its distance ($\sim$10 pc) from the remnant's geometric centre and estimated age ($\sim$7600 yrs). we estimated the radio spectral index, $α= -0.55 \pm 0.03$ which is typical of middle-age SNRs. Polarisation maps created for N49 show low to moderate levels of mean fractional polarisation estimated at 7$\pm$1% and 10$\pm$1% for 5.5 and 9 GHz, respectively. These values are noticeably larger than found in previous studies. Moreover, the mean value for the Faraday rotation of SNR N49 from combining CABB data is 212$\pm$65 rad m$^{-2}$ and the maximum value of RM is 591$\pm$103 rad m$^{-2}$.

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arXiv2024

The TRAPUM Small Magellanic Cloud pulsar survey with MeerKAT: I. Discovery of seven new pulsars and two Pulsar Wind Nebula associations

The sensitivity of the MeerKAT radio interferometer is an opportunity to probe deeper into the population of rare and faint extragalactic pulsars. The TRAPUM (TRAnsients and PUlsars with MeerKAT) collaboration has conducted a radio-domain search for accelerated pulsars and transients in the Small Magellanic Cloud (SMC). This partially targeted survey, performed at L-band (856-1712 MHz) with the core array of the MeerKAT telescope in 2-h integrations, is twice as sensitive as the latest SMC radio pulsar survey. We report the discovery of seven new SMC pulsars, doubling this galaxy's radio pulsar population and increasing the total extragalactic population by nearly a quarter. We also carried out a search for accelerated millisecond pulsars in the SMC Globular Cluster NGC 121 using the full array of MeerKAT. This improved the previous upper limit on pulsed radio emission from this cluster by a factor of six. Our discoveries reveal the first radio pulsar-PWN systems in the SMC, with only one such system previously known outside our galaxy (the "Crab pulsar twin" in the Large Magellanic Cloud, PSR J0540$-$6919). We associate the 59 ms pulsar discovery PSR J0040$-$7337, now the fastest spinning radio pulsar in the SMC, with the bow-shock Pulsar Wind Nebula (PWN) of Supernova Remnant DEM S5. We also present a new young pulsar with a 79 ms period, PSR J0048$-$7317, in a PWN recently discovered in a MeerKAT radio continuum image. Using the multi-beam capability of MeerKAT, we localised our pulsar discoveries, and two previous Murriyang discoveries, to a positional uncertainty of a few arcseconds.

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arXiv2024

Searches for neutrino counterparts of gravitational waves from the LIGO/Virgo third observing run with KM3NeT

The KM3NeT neutrino telescope is currently being deployed at two different sites in the Mediterranean Sea. First searches for astrophysical neutrinos have been performed using data taken with the partial detector configuration already in operation. The paper presents the results of two independent searches for neutrinos from compact binary mergers detected during the third observing run of the LIGO and Virgo gravitational wave interferometers. The first search looks for a global increase in the detector counting rates that could be associated with inverse beta decay events generated by MeV-scale electron anti-neutrinos. The second one focuses on upgoing track-like events mainly induced by muon (anti-)neutrinos in the GeV--TeV energy range. Both searches yield no significant excess for the sources in the gravitational wave catalogs. For each source, upper limits on the neutrino flux and on the total energy emitted in neutrinos in the respective energy ranges have been set. Stacking analyses of binary black hole mergers and neutron star-black hole mergers have also been performed to constrain the characteristic neutrino emission from these categories.

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arXiv2024

Self-supervised contrastive learning of radio data for source detection, classification and peculiar object discovery

New advancements in radio data post-processing are underway within the SKA precursor community, aiming to facilitate the extraction of scientific results from survey images through a semi-automated approach. Several of these developments leverage deep learning (DL) methodologies for diverse tasks, including source detection, object or morphology classification, and anomaly detection. Despite substantial progress, the full potential of these methods often remains untapped due to challenges associated with training large supervised models, particularly in the presence of small and class-unbalanced labelled datasets. Self-supervised learning has recently established itself as a powerful methodology to deal with some of the aforementioned challenges, by directly learning a lower-dimensional representation from large samples of unlabelled data. The resulting model and data representation can then be used for data inspection and various downstream tasks if a small subset of labelled data is available. In this work, we explored contrastive learning methods to learn suitable radio data representation from unlabelled images taken from the ASKAP EMU and SARAO MeerKAT GPS surveys. We evaluated trained models and the obtained data representation over smaller labelled datasets, also taken from different radio surveys, in selected analysis tasks: source detection and classification, and search for objects with peculiar morphology. For all explored downstream tasks, we reported and discussed the benefits brought by self-supervised foundational models built on radio data.

astro-ph.IM↗