arXiv subjects

S. Ranasinghe

Publications and source records attributed to S. Ranasinghe.

12 recordsLinked to original sources

arXiv2026

CHANG-ES XL: Magnetic Field Structures in the Disk and Halo of NGC 891

We present new Karl G. Jansky Very Large Array S-band (2-4 GHz) observations of the edge-on spiral galaxy NGC 891, complemented by C-band data, to investigate the structure of its radio continuum halo. Using rotation measure synthesis we detected an extended polarized halo, with most spatially extended polarized emission confined to Faraday depths within +/- 150 rad m-2. We identified a localized region in the north-east side of the galaxy that shows an enhancement in polarized intensity (not in percentage polarization). By combining the radio data with H-alpha and diffuse X-ray maps, we discuss a possible origin for this structure: a superbubble powered by clustered supernovae. Across the disk and halo, the percentage polarization decreases toward the midplane but shows a mild wavelength dependence, despite the edge-on orientation of NGC 891. This behavior implies that the depolarization cannot be dominated by small-scale Faraday rotation within the disk. Instead, it is possible that most of the observed polarized emission arises on the Earth-facing side of the galaxy. Our peak rotation measure (RM) map shows a smooth transition along the major axis, consistent with a large scale axisymmetric magnetic field. Using H-alpha and UV data, we analyzed the distribution of H II regions and found that they are parts of different spiral arms. We also identified a faint, isolated H II region at a galactocentric radius of 16.9 kpc, with both H-alpha and far-UV counterparts, indicating star formation outside the thin disk.

astro-ph.GA↗

arXiv2026

Multipole Functions for Image Analysis II: Equal Area Weighting and Application to Supernova Remnant Images

New basis functions for 2 dimensional (2D) image analysis with a circular boundary (referred to as multipole analysis) are derived which are equal-area weighted. We present open access Python code hosted by GitHub, with which users can apply the multipole analysis to images. The new multipole analysis is applied to a set of 28 supernova remnants (SNRs) which are selected to have both radio and X-ray images, and have been identified as Type Ia or Type CC. Each pair of SNR images (radio and X-ray) was convolved to the same spatial resolution prior to analysis. The resulting multipole radial powers and angular powers, from order 0 to 5, for a given SNR are different for different multipoles and for a given multipole are different between X-ray and radio images. The X-ray radial powers (for orders >0) are larger on average than the radio radial powers (more radial structure in X-rays than radio). The angular powers are smaller than the radial powers on average (more radial structure than angular structure). Comparing Type Ia and Type CC populations, the radial powers (for orders >0) are on average larger for Type CC than Type Ia for X-ray and radio images, with larger difference for X-ray images. The angular powers (for orders >0) are similar between Type Ia and Type CC for both radio and X-ray images.

astro-ph.IM↗

arXiv2025

Multi-frequency radio-continuum study of the LMC SNR N206 (Goat's Eye) and its "zig-zag" PWN

We present new radio-continuum observations of the Large Magellanic Cloud (LMC) supernova remnant (SNR) N206, which we give the name "Goat's Eye". Goat's Eye contains an interior radio structure that is likely a pulsar wind nebula (PWN), which we analyse in further detail. We use new radio observations from the Australia Telescope Compact Array (ATCA) telescope, as well as several archival radio observations, to calculate spectral indices, and find a steep spectral index for the whole SNR ($\alpha = -0.60\pm0.02$), and a flatter spectral index for the PWN ($\alpha = -0.16\pm0.03$). We also measure the polarisation and magnetic field properties of the PWN. Previously reported as a linear structure, the new observations show an unusual "zig-zag"-like structure, visible in radio-continuum total intensity, linear polarisation, and magnetic field orientations. The origin of this zig-zag structure is unclear, but we propose some origin scenarios that will require further observations to differentiate between.

astro-ph.HE↗

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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arXiv2023

A Statistical Analysis of Galactic Radio Supernova Remnants

We present an revised table of 390 Galactic radio supernova remnants (SNRs) and their basic parameters. Statistical analyses are performed on SNR diameters, ages, spectral indices, Galactic heights and spherical symmetries. Furthermore, the accuracy of distances estimated using the $\Sigma$-D relation is examined. The arithmetic mean of the Galactic SNR diameters is $30.5$ pc with standard error $1.7$ pc and standard deviation $25.4$ pc. The geometric mean and geometric standard deviation factor of Galactic SNR diameters is $21.9$ pc and $2.4$, respectively. We estimate ages of 97 SNRs and find that the supernova (SN) birth rate to be lower than, but within $2\sigma$ of currently accepted values for SN birth rate. The mean spectral index of shell-type SNRs is $-0.51 \pm 0.01$ and no correlations are found between spectral indices and the SNR parameters of molecular cloud (MC) association, SN type, diameter, Galactic height and surface brightness. The Galactic height distribution of SNRs is best described by an exponential distribution with a scale height of $48 \pm 4$ pc. The spherical symmetry measured by the ovality of radio SNRs is not correlated to any other SNR parameters considered here or to explosion type.

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arXiv2022

Distances, Radial Distribution and Total Number of Galactic Supernova Remnants

We present a table of 215 SNRs with distances. New distances are found to SNR G$51.26+0.11$ of $6.6 \pm 1.7$ kpc using HI absorption spectra, and to 5 other SNRs using maser/molecular cloud associations. We recalculate the distances and errors to all SNRs using a consistent rotation curve and provide errors where they were not previously estimated. This results in a significant distance revisions for 20 SNRs. Because of observational constraints and selection effects, there to be is an apparent deficit of observed number of Galactic supernova remnants (SNRs). To investigate this, we employ two methods. The first method applies correction factors for the selection effects to derive the radial density distribution. The second method compares functional forms for the SNR surface density and selection function against the data to find which functions are consistent with the data. The total number of SNRs in the Galaxy is $\sim3500$ (Method 1) or in the range $\sim2400$ to $\sim5600$ (Method 2). We conclude that the current observed number of SNRs is not yet complete enough to give a well-determined total SNR number or radial density function.

astro-ph.HE↗

arXiv2021

Search for and Identification of Young Compact Galactic Supernova Remnants Using THOR

Young Supernova remnants (SNRs) with smaller angular sizes are likely missing from existing radio SNR catalogues, caused by observational constraints and selection effects. In order to find new compact radio SNR candidates, we searched the high angular resolution (25") THOR radio survey of the first quadrant of the galaxy. We selected sources with non-thermal radio spectra. HI absorption spectra and channel maps were used to identify which sources are galactic and to estimate their distances. Two new compact SNRs were found: G31.299$-$0.493 and G18.760$-$0.072, of which the latter was a previously suggested SNR candidate. The distances to these SNRs are 5.0 $\pm$ 0.3 kpc and 4.7 $\pm$ 0.2 kpc, respectively. Based on the SN rate in the galaxy or on the statistics of known SNRs, we estimate that there are 15$-$20 not yet detected compact SNRs in the galaxy and that the THOR survey area should contain three or four. Our detection of two SNRs (half the expected number) is consistent with the THOR sensitivity limit compared with the distribution of integrated flux densities of SNRs.

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arXiv2019

Distance and Evolutionary States of Supernova Remnant G18.9-1.1 and Candidate G28.6+0.0

HI spectra of the supernova remnant G18.9-1.1 and the supernova remnant candidate G28.6+0.0 are analyzed. We compared the spectra to $^{13}$CO emission spectra and to spectra of HII regions in the area to determine kinematic distances. G18.9-1.1 is at 2.1$\pm$0.4 kpc and G28.6+0.0 is at 9.0$\pm$0.3 kpc from the Sun. Using published X-ray spectra of G18.9-1.1, we apply supernova remnant models for shocked-ISM temperature and emission measure. We find that G18.9-1.1 has a low, but not atypical, explosion energy of $\simeq$3$\times$10$^{50}$ erg and is in a low density region of the ISM, $\simeq$0.1 cm$^{-3}$. It has age $\simeq$3700 yr if the ejecta mass is 1.4 M$_{\odot}$, typical of Type Ia SNe, or $\simeq$4700 yr if the ejecta mass is 5 M$_{\odot}$ typical of core-collapse SN. The candidate G28.6+0.0 does not have reported X-ray emission, so we apply a basic Sedov model. The Sedov age is $\simeq$600 yr if the ISM density is 1 cm$^{-3}$ but could be as old as $\simeq$6000 yr if the ISM density is as high as 100 cm$^{-3}$.

astro-ph.HE↗

arXiv2018

Evolutionary Models for 15 Galactic Supernova Remnants with New Distances

Recent studies using 21 cm HI line and $^{13}$CO line observations in the inner part of the Galaxy have resulted in new distances for 30 Galactic supernova remnants (SNRs). 15 of those remnants have observed X-ray spectra, for which shocked-gas temperatures and emission measures are measured. Here we apply spherically symmetric SNR evolution models to these 15 remnants to obtain estimates for ages, explosion energies, circum-stellar medium densities and profiles (uniform or wind-type).From the distribution of ages we obtain a supernova birth rate and estimate incompleteness. The energies and densities can be well fit with log-normal distributions. The distribution of explosion energies is very similar to that of SNRs in the Large Magellanic Cloud (LMC), suggesting SN explosions in the LMC and in the Galaxy are very similar. The density distribution has higher mean density for Galactic SNRs than for LMC SNRs, by a factor $\sim$2.5.

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arXiv2017

Distances to Supernova Remnants G$20.4+0.1$, G$24.7-0.6$ and G$28.6-0.1$ and New Molecular Cloud Associations

Accurate distances to supernova remnants (SNRs) are crucial in determining their size, age, luminosity and evolutionary state. To determine distances, we chose three SNRs from the VLA Galactic Plane Survey (VGPS) for extraction of HI absorption spectra. Analysing HI absorption spectra, $^{13}$CO emission spectra, and HI and $^{13}$CO channel maps, kinematic velocities (or their limits) to the three SNRs were calculated. The three SNRs are probably associated with molecular clouds and the new distance to G$20.4+0.1$, G$24.7-0.6$ and G$28.6-0.1$ are $7.8 \pm0.5$ kpc, $3.8\pm 0.2 $ kpc and $ 9.6 \pm 0.3 $ kpc, respectively.

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arXiv2017

New Distances to Four Supernova Remnants

Distances are found for four supernova remnants without previous distance measurements. H I spectra and H I channel maps are used to determine the maximum velocity of H I absorption for the four supernova remnants (SNRs). We examined $^{13}$CO emission spectra and channel maps to look for possible molecular gas associated with each SNR, but did not find any. The resulting distances for the SNRs are $3.5 \pm 0.2$ kpc (G24.7+0.6), $4.7 \pm 0.3$ kpc (G29.6+0.1), $4.1 \pm 0.5$ kpc (G41.5+0.4) and $4.5 \pm 0 .4 - 9.0 \pm 0.4$ kpc (G57.2+0.8).

astro-ph.GA↗

arXiv2013

X-ray and Radio Observations of the gamma Cygni Supernova Remnant G78.2+2.1

We analyse \textit{ROSAT} and \textit{Chandra} ACIS X-ray observations and HI absorption spectra of the $γ$ Cygni supernova remnant (G78.2+2.1, DR4). The \textit{ROSAT} All-Sky-Survey image shows G78.2+2.1 has an adjacent limb-brightened shell north of it. A new \textit{ROSAT} mosaic shows details of the X-ray emission over the entire face of G78.2+2.1. We also create \textit{Chandra} mosaics which cover much of the northern rim and central regions of G78.2+2.1. HI absorption spectra result in association of G78.2+2.1 with the $γ$ Cygni nebula, with distance 1.7 to 2.6 kpc. Chandra spectra for G78.2+2.1 give an X-ray temperature of 0.6-1.2 keV (90% error), and that a Sedov model has age of 6800-10000 yr. A compact power-law X-ray source in G78.2+2.1 is consistent with the same distance as G78.2+2.1. The northern X-ray shell is identified with a B3 star at distance of 980 pc and is proposed as a stellar wind bubble.

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