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Neutral hydrogen (H i) bubbles and shells are common in the interstellar medium (ISM). Studying their properties provides insight into the characteristics of the local ISM as well as the galaxy in which the bubbles reside. We report the detection of magnetic fields associated with superbubbles in the nearby irregular galaxy, the Small Magellanic Cloud (SMC). Using the Polarisation Sky Survey of the Universe's Magnetism (POSSUM) pilot survey, we obtain a high-density grid (⁠|$\approx 25 \, \rm sources\, deg^{-2}$|⁠) of Faraday rotation measure (RM) from polarized sources behind the SMC. This provides a sufficiently large number of RM measurements to study the magnetic properties of three of the largest H i shells previously identified in the SMC. The RM profiles as a function of distance from the shell centre show characteristic patterns at angular scales comparable to the shell size. We demonstrate that this can be explained by magnetohydrodynamic simulation models of bubbles expanding in magnetized environments. From the observations, we estimate the line-of-sight magnetic field strength at the edges of the shells is enhanced by |$\sim 1\, \rm \mu G$| with respect to their centres. This is an order of magnitude larger than the field strength in the ambient medium (⁠|$\sim 0.1\, \rm \mu G$|⁠) estimated based on the expansion velocity of the shells. This paper highlights the power of densely mapped RM grids in studying the magnetic properties of galactic substructures beyond the Milky Way. [ABSTRACT FROM AUTHOR]

We present initial results from the Polarization Sky Survey of the Universe's Magnetism (POSSUM), analysing 22 817 Faraday rotation measures (RMs) with median uncertainties of 1.2 rad m |$^{-2}$| across 1520 deg2 to study magnetized gas associated with 55 nearby galaxy groups (⁠|$z\lesssim 0.025$|⁠) with halo masses between |$10^{12.5}$| and |$10^{14.0}$| M |$_\odot$|⁠. We identify two distinct gas phases: the intragroup medium (IGrM) within 0–2 splashback radii and the warm-hot intergalactic medium (WHIM) extending from 2 to 7 splashback radii. These phases enhance the standard deviation of residual (i.e. Galactic foreground RM-subtracted) RMs by |$6.9\pm 1.8$| rad m |$^{-2}$| and |$4.2 \pm 1.2$| rad m |$^{-2}$|⁠ , respectively. Estimated magnetic field strengths are several μ G within the IGrM and 0.1–1 μ G in the WHIM. We estimate the plasma |$\beta$| in both phases, and show that magnetic pressure might be more dynamically important than in the ICM of more massive clusters or sparse cosmic web filaments. Our findings indicate that 'missing baryons' in the WHIM likely extend beyond the gravitational radii of group-mass haloes to Mpc scales, consistent with large-scale, outflow-driven 'magnetized bubbles' seen in cosmological simulations. We demonstrate that RM grids are an effective method for detecting magnetized thermal gas at galaxy group interfaces and within the cosmic web. This approach complements X-ray and Sunyaev-Zel'dovich effect methods, and when combined with fast radio burst dispersion measures, data from the full POSSUM survey – comprising approximately a million RMs – will allow direct magnetic field measurements to further our understanding of baryon circulation in these environments and the magnetized universe. [ABSTRACT FROM AUTHOR]

We present new and archival Australia Telescope Compact Array and Atacama Large Millimeter/submillimeter Array data of the Small Magellanic Cloud supernova remnant 1E 0102.2–7219 at 2100, 5500, 9000, and 108 000 MHz; as well as H  i data provided by the Australian Square Kilometre Array Pathfinder. The remnant shows a ring-like morphology with a mean radius of 6.2 pc. The 5500 MHz image reveals a bridge-like structure, seen for the first time in a radio image. This structure is also visible in both optical and X-ray images. In the 9000 MHz image, we detect a central feature that has a flux density of 4.3 mJy but rule out a pulsar wind nebula origin, due to the lack of significant polarization towards the central feature with an upper limit of 4  per cent. The mean fractional polarization for 1E 0102.2–7219 is 7 ± 1 and 12 ± 2  per cent for 5500 and 9000 MHz, respectively. The spectral index for the entire remnant is −0.61 ± 0.01. We estimate the line-of-sight magnetic field strength in the direction of 1E 0102.2–7219 of ∼44 µG with an equipartition field of |$65\pm 5\, \mu$| G. This latter model uses the minimum energy of the sum of the magnetic field and cosmic ray electrons only. We detect an H  i cloud towards this remnant at the velocity range of ∼160–180 km s−1 and a cavity-like structure at the velocity of 163.7–167.6 km s−1. We do not detect CO emission towards 1E 0102.2–7219. [ABSTRACT FROM AUTHOR]

We present a new Australian Square Kilometre Array Pathfinder (ASKAP) sample of 14 radio supernova remnants (SNR) candidates in the Large Magellanic Cloud (LMC). This new sample is a significant increase to the known number of older, larger, and low surface brightness LMC SNRs. We employ a multifrequency search for each object and found possible traces of optical and occasionally X-ray emission in several of these 14 SNR candidates. One of these 14 SNR candidates (MCSNR J0522 – 6543) has multifrequency properties that strongly indicate a bona fide SNR. We also investigate a sample of 20 previously suggested LMC SNR candidates and confirm the SNR nature of MCSNR J0506 – 6815. We detect lower surface brightness SNR candidates which were likely formed by a combination of shock waves and strong stellar winds from massive progenitors (and possibly surrounding OB stars). Some of our new SNR candidates are also found in lower density environments in which SNe type Ia explode inside a previously excavated interstellar medium. [ABSTRACT FROM AUTHOR]

We present the Australian Square Kilometre Array Pathfinder (ASKAP) observations of the Galaxy and Mass Assembly (GAMA)-23h field. The survey was carried out at 887.5 MHz and covers an ∼83 square deg field. We imaged the calibrated visibility data, taken as part of the Evolutionary Mapping of Universe Early Science Programme, using the latest version of the ASKAPSoft pipeline. The final mosaic has an angular resolution of 10 arcsec and a central rms noise of around 38 |$\mu$| Jy beam−1. The derived radio source catalogue has 39 812 entries above a peak flux density threshold of 5σ. We searched for the radio source host galaxy counterparts using the GAMA spectroscopic (with an i -band magnitude limit of 19.2 mag) and multiwavelength catalogues that are available as part of the collaboration. We identified hosts with GAMA spectroscopic redshifts for 5934 radio sources. We describe the data reduction, imaging, and source identification process, and present the source counts. Thanks to the wide area covered by our survey, we obtain very robust counts down to 0.2 mJy. ASKAP's exceptional survey speed, providing efficient, sensitive, and high-resolution mapping of large regions of the sky in conjunction with the multiwavelength data available for the GAMA23 field, allowed us to discover 63 giant radio galaxies. The data presented here demonstrate the excellent capabilities of ASKAP in the pre-SKA era. [ABSTRACT FROM AUTHOR]

We report the discovery of J0624–6948, a low-surface brightness radio ring, lying between the Galactic Plane and the large magellanic cloud (LMC). It was first detected at 888 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP), and with a diameter of ∼196 arcsec. This source has phenomenological similarities to odd radio circles (ORCs). Significant differences to the known ORCs – a flatter radio spectral index, the lack of a prominent central galaxy as a possible host, and larger apparent size – suggest that J0624–6948 may be a different type of object. We argue that the most plausible explanation for J0624–6948 is an intergalactic supernova remnant due to a star that resided in the LMC outskirts that had undergone a single-degenerate type Ia supernova, and we are seeing its remnant expand into a rarefied, intergalactic environment. We also examine if a massive star or a white dwarf binary ejected from either galaxy could be the supernova progenitor. Finally, we consider several other hypotheses for the nature of the object, including the jets of an active galactic nucleus (30Dor) or the remnant of a nearby stellar super-flare. [ABSTRACT FROM AUTHOR]

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 (Very Large Array) Galactic Plane Survey for extraction of H i absorption spectra. Analysing H i absorption spectra, 13CO emission spectra, and H i and 13CO 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 G20.4 + 0.1, G24.7 − 0.6, and G28.6 − 0.1 are 7.8 ± 0.5 kpc, 3.8 ± 0.2 kpc, and 9.6 ± 0.3 kpc, respectively. [ABSTRACT FROM AUTHOR]

We analyse RXTE/PCA X-ray spectra of the binary X-ray pulsar Her X-1/HZ Her during short high state and one binary orbit in the preceding low state, just before short high turn-on. The spectrum is well described by two continuum components (absorbed and unabsorbed). The resulting spectral parameters are modulated with orbital phase. During low state, a significant component of the flux, and its spectrum, is consistent with X-ray reflection off the face of the companion star HZ Her. This component has a significantly harder X-ray spectrum than the rest of the flux from the Her X-1 system. A second component in low state is consistent with emission from the accretion disc corona. During short high, a third strong component is present with a softer spectrum, which is associated with the neutron star and accretion disc. Due to this direct emission from the neutron star and accretion disc, the reflected emission is less clear; however, parameters and fluxes modulations during short high state indicate its presence. In low state, the hard X-ray flux (hν > 10 keV) peaks at orbital phase ϕorb ~ 0.55, which is expected from a simple model of atmospheric reflection from the companion star. The offset indicates an asymmetry in the X-ray illumination of the companion, which could be due to shadowing of the the inner face of HZ Her by the accretion disc and/or stream. [ABSTRACT FROM AUTHOR]

ABSTRACT The extremely luminous supernova 2006gy (SN 2006gy) is among the most energetic ever observed. The peak brightness was 100 times that of a typical supernova and it spent an unheard of 250 d at magnitude −19 or brighter. Efforts to describe SN 2006gy have pushed the boundaries of current supernova theory. In this work we aspire to simultaneously reproduce the photometric and spectroscopic observations of SN 2006gy using a quark nova (QN) model. This analysis considers the supernova explosion of a massive star followed days later by the QN detonation of a neutron star. We lay out a detailed model of the interaction between the supernova envelope and the QN ejecta paying special attention to a mixing region which forms at the inner edge of the supernova envelope. This model is then fitted to photometric and spectroscopic observations of SN 2006gy. This QN model naturally describes several features of SN 2006gy including the late-stage light-curve plateau, the broad Hα line and the peculiar blue Hα absorption. We find that a progenitor mass between 20 and 40 M⊙ provides ample energy to power SN 2006gy in the context of a QN. [ABSTRACT FROM AUTHOR]

ABSTRACT New radio continuum and H i line observations of the old supernova remnant CTB80 are analysed. The radio continuum emission is more extended than previously known. We analyse archival ROSAT Position Sensitive Proportional Counter images of CTB80 and find extended X-ray emission associated with CTB80 over a 1°.2 diameter region. A new H i absorption spectrum towards the core of CTB80 yields a kinematic distance of ≃1.5 kpc. An analysis of the H i channel maps confirms the inner shell discovered by Koo et al. In addition, we discover an outer slowly moving shell centred on CTB80's centre, with radius 76 arcmin and velocity 40 km s−1. The shell's size and velocity are inconsistent with a stellar wind origin, but are consistent with what is expected for a cool dense shell in the cooling (snowplough) phase of a supernova remnant. Taking into account deceleration of the shell, its age also agrees with that of CTB80 (∼60 000 yr). The resulting picture of CTB80 is that of a large old supernova remnant, with an H i shell moving out slowly behind the slow outer shock and a hot interior which is still emitting X-rays and visible in the ROSAT images. [ABSTRACT FROM AUTHOR]

ABSTRACT Three supernova remnants (SNRs) form the CTB 37 complex: CTB 37A (G348.5+0.1, associated with the TeV γ-ray source HESS J1714−385), CTB 37B (G348.7+0.3, associated with HESS J1713−381 and the magnetar CXOU J171405.7.381031) and G348.5−0.0. We use 21-cm H i absorption measurements to constrain kinematic distances to these SNRs, which have not previously been determined well. We revise the kinematic distance for CTB 37A to be in the range 6.3-9.5 kpc (previously ∼11.3 kpc) because it is beyond the near 3-kpc arm and in front of the far side of the CO cloud at −145 km s−1 towards l= 348.5. G348.5−0.0 has an H i column density (∼6.1×1021 cm−2) lower than CTB 37A (∼7.1 × 1021 cm−2). Also, G348.5−0.0 does not have the major absorption feature at −107 km s−1 that CTB 37A shows. This is caused by the near 3-kpc arm, so G348.5−0.0 is at a distance of ≤6.3 kpc. CTB 37B is at a distance of ∼13.2 kpc (previously 5-9 kpc) based on: (1) it has an absorption feature at −10 ± 5 km s−1 from the far 3-kpc arm, so CTB 37B is behind it; (2) there is absorption at −30 km s−1 but not at −26 km s−1, which yields the distance value; and (3) the H i column density towards CTB 37B (∼8.3 × 1021 cm−2) is larger than that towards CTB 37A. In summary, CTB 37A, CTB 37B and G348.5+0.0 are all at different distances and are only by chance nearby each other on the sky. In addition, we conclude that CTB 37A and 37B are not associated with the historical supernova AD 393. [ABSTRACT FROM AUTHOR]

BSTRACT Soft γ-ray repeaters (SGRs) and anomalous X-ray pulsars are believed to be magnetars, i.e. neutron stars powered by extreme magnetic fields, B∼ 1014-1015 G. The recent discovery of an SGR with low magnetic field (<7.5 × 1012 G), SGR 0418+5729, which shows bursts similar to those of SGRs, implies that a high surface dipolar magnetic field might not be necessary for magnetar-like activity. We show that the quiescent and bursting properties of SGR 0418+5729 find natural explanations in the context of low magnetic field Quark-Nova (detonative transition from a neutron star to a quark star) remnants, i.e. an old quark star surrounded by degenerate (iron-rich) Keplerian ring/debris ejected during the Quark-Nova explosion. We find that a 16 Myr old quark star surrounded by an ∼10−10 M⊙ ring, extending in radius from ∼30 to 60 km, reproduces many observed properties of SGR 0418+5729. The SGR-like burst is caused by magnetic penetration of the inner part of the ring and subsequent accretion. Radiation feedback results in months long accretion from the ring's non-degenerate atmosphere which matches well the observed decay phase. We make specific predictions (such as an accretion glitch of Δ P/ P∼−2 × 10−11 during burst and a sub-keV proton cyclotron line from the ring) that can be tested by sensitive observations. [ABSTRACT FROM AUTHOR]

The X-ray binary system 4U 1907+09 contains an accretion-powered X-ray pulsar in an eccentric orbit around a massive early-type companion star. It has been previously suggested that a trailing gas stream along with strong stellar winds could describe the orbital variations in X-ray flux. In this work, 12 yr of X-ray observations from the Rossi X-ray Timing Explorer/All-Sky Monitor are analysed. We study both the X-ray flux and column density dependence on the orbital phase. The dynamics of the wind and stream are calculated for various companion star radii, system inclinations and eccentricities; the wind and stream model is parametrized by companion star rotation, stellar wind velocity, stream width and density. These parameters are taken as inputs to compute the expected accretion luminosity which is then compared to the observed flux versus the orbital phase. The column density along the line of sight to the neutron star is calculated using the best-fitting results from the flux analysis and verifies the high extinction in the direction of 4U 1907+09. We find that the stream component of accretion contributes significantly to describing the orbital variations in X-ray flux observed in 4U 1907+09. The best-fitting free parameters of our wind and stream model such as mass-loss rate, terminal wind velocity, companion star rotation speed and interstellar extinction are found to be consistent with literature values for 4U 1907+09. The best fit to the data was found at higher values of eccentricity and lower companion star radii . [ABSTRACT FROM AUTHOR]

We suggest a revised distance to the supernova remnant (CTB 109) and its associated anomalous X-ray pulsar (AXP) 1E 2259+586 by analysing 21-cm H i-line and 12CO-line spectra of CTB 109, H ii region Sh 152 and the adjacent molecular cloud complex. CTB 109 has been established to be interacting with a large molecular cloud (recession velocity at ). The highest radial velocities of absorption features towards CTB 109 (−56 km s−1) and Sh 152 (−65 km s−1) are larger than the recombination line velocity (−50 km s−1) of Sh 152 demonstrating the velocity reversal within the Perseus Arm. The molecular cloud has cold H i column density large enough to produce H i self-absorption (HISA) and H i narrow self-absorption (HINSA) if it was at the near side of the velocity reversal. Absence of both HISA and HINSA indicates that the cloud is at the far side of the velocity reversal within the Perseus Arm, so we obtain a distance for CTB 109 of . The new distance still leads to a normal explosion energy for CTB 109/AXP 1E 2259+586. [ABSTRACT FROM AUTHOR]

We obtain new H i and 13CO images around supernova remnants Kes 69 and G21.5−0.9. By comparing H i spectra with 13CO emission spectra, we significantly revise the kinematic distance for Kes 69 to ∼5.5 kpc, which was 11.2 kpc, and refine the kinematic distance for G21.5−0.9 to ∼4.8 kpc. For Kes 69, the highest velocity of absorption is ∼86 km s−1 and a prominent H i emission feature at ∼112 km s−1 has no respective absorption. These new results suggest that Kes 69 is associated with a newly detected extended 1720-MHz OH maser at velocity of ∼85 km s−1 that originates from within the bright southern radio shell of Kes 69. For G21.5−0.9, the highest velocity of absorption is ∼67 km s−1. The H i absorption spectra of the nearby bright source PMN J1832−1035 and Kes 69 show a common absorption feature at velocity of ∼69 km s−1, which is not seen for G21.5−0.9. The resulting velocity of ∼68 km s−1 gives the best distance estimate of ∼4.8 kpc for G21.5−0.9 and associated young pulsar J1833−1034. [ABSTRACT FROM AUTHOR]

The X-ray binary system GX 301−2 consists of a neutron star in an eccentric orbit accreting from the massive early-type star Wray 977. It has previously been shown that the X-ray orbital light curve is consistent with the existence of a gas stream flowing out from Wray 977 in addition to its strong stellar wind. Here, X-ray monitoring observations by the Rossi X-ray Timing Explorer ( RXTE)/All-Sky Monitor and pointed observations by the RXTE/Proportional Counter Array over the past decade are analysed. We analyse both the flux and column density dependence on orbital phase. The wind and stream dynamics are calculated for various system inclinations, companion rotation rates and wind velocities, as well as parametrized by the stream width and density. These calculations are used as inputs to determine both the expected accretion luminosity and the column density along the line-of-sight to the neutron star. The model luminosity and column density are compared to observed flux and column density versus orbital phase, to constrain the properties of the stellar wind and the gas stream. We find that the change between bright and medium intensity levels is primarily due to decreased mass loss in the stellar wind, but the change between medium and dim intensity levels is primarily due to decreased stream density. The mass-loss rate in the stream exceeds that in the stellar wind by a factor of ∼2.5. The quality of the model fits is better for lower inclinations, favouring a higher mass for Wray 977 in its allowed range of . [ABSTRACT FROM AUTHOR]

The Cygnus Loop is one of the nearest supernova remnants (440 pc), allowing studies of spatial variations to be carried out at high physical resolution compared with other supernova remnants. Chandra Advanced CCD Imaging Spectrometer (ACIS) observations were obtained covering the bright V-shaped region on the south-west limb. This region has strong 0.2–2 keV spectral variations seen with the ROSAT Position Sensitive Proportional Counter. The nature of the spectral variations is analysed using the ACIS observations. It is found that temperature, abundance variations and column density variations all have a significant contribution to the observed spectral variations. Fits with C, N, O (O group) elements and Ne, Na, Mg, Al, Si, S, Ar (Ne group) elements varied together are better than fits with just O and Ne varied. Large spatial variations in abundances are seen, yet the Ne group to O group ratio and the Fe group (Ca, Fe, Ni) to O group ratio are nearly constant for all of the spectra. The most natural explanation is that the elements in the region are due to supernova explosion of a star of which predated the Cygnus Loop explosion. [ABSTRACT FROM AUTHOR]

ABSTRACT Hercules X-1 was observed for extended periods during its low state by the Extreme Ultraviolet Explorer (EUVE). These observations yield low-state light curves in the extreme ultraviolet (EUV) which are compared with a composite model here. The model includes reflection of soft X-rays off the companion HZ Her, including the shadowing of HZ Her by the accretion disc, and emission from the accretion disc surface. Four different geometries for the accretion disc were adopted, all derived from the RXTE All-Sky Monitor (ASM) 35-day light-curve modelling. Three were thin disc models for different system inclinations, i, and the fourth was a disc with a thick inner ring for i= 85° . With the HZ Her reflection model, with no free parameters except normalization, and a simple model for the disc emission, the models fit the data well. The disc emission accounts for about half of the EUV flux, depending on which accretion disc geometry is used. The disc geometry that best fits the EUV light curves is the disc with a thick inner ring, which is the same model that gives the best fit to the RXTE/ASM light curve. [ABSTRACT FROM AUTHOR]

Her X-1 exhibits a 35-d cycle in X-ray intensity: 'main high state-low state-short high state-low state', which is caused by a varying obscuration of the neutron star by a tilted-twisted precessing accretion disc. The 35-d X-ray light curve in Hercules X-1 has been well characterized by the Rossi X-ray Timing Explorer All-Sky Monitor (RXTE/ASM). Here, different models of the accretion disc and of the neutron star source region are constructed and applied to fit the RXTE/ ASM observations. Such detailed modelling of the shape of the 35-d light curve has not been carded out previously. The results show that a detailed model can fit the details of the light curve, and yield numerical values for the parameters of the accretion disc, its atmosphere and the inner edge of the disc. The best model here has a two-layer outer disc, a thick inner disc edge and an extended central source. [ABSTRACT FROM AUTHOR]