Jeffrey L Payne

New XMM-Newton observations of supernova remnants in the Small Magellanic Cloud

Context. A complete overview of the supernova remnant (SNR) populati on is required to investigate their evolution and interacti on with the surrounding interstellar medium in the Small Magel lanic Cloud (SMC). Aims. Recent XMM-Newton observations of the SMC cover three known SNRs (DEM S5, SNR B0050 −72.8, and SNR B0058 −71.8), which are poorly studied and are X-ray faint. We used new mult i-frequency radio-continuum surveys and new optical obser vations at Hα, [S ii], and [Oiii] wavelengths, in combination with the X-ray data, to invest igate their properties and to search for new SNRs in the SMC. Methods. We used X-ray source selection criteria and found one SMC obj ect with typical SNR characteristics (HFPK 334), that was initially detected by ROSAT. We analysed the X-ray spectra a nd present multi-wavelength morphological studies of the t hr e SNRs and the new candidate. Results. Using a non-equilibrium ionisation collisional plasma mod el, we find temperatures kT around 0.18 keV for the three known remnants and 0.69 keV for the candidate. The low temperature , low surface brightness, and large extent of the three remna nts indicates relatively large ages. The emission from the new candidate ( HFPK 334) is more centrally peaked and the higher temperatur e s ggests a younger remnant. Our new radio images indicate that a pulsa r wind nebulae (PWN) is possibly associated with this object . Conclusions. The SNRs known in the SMC show a variety of morphological stru ctures that are relatively uncorrelated in the di fferent wavelength bands, probably caused by the di fferent conditions in the surrounding medium with which the re mnant interacts.Context. A complete overview of the supernova remnant (SNR) population is required to investigate their evolution and interaction with the surrounding interstellar medium in the Small Magellanic Cloud (SMC). Aims. Recent XMM-Newton observations of the SMC cover three known SNRs (DEM S5, SNR B0050−72.8, and SNR B0058−71.8), which are poorly studied and are X-ray faint. We used new multi-frequency radio-continuum surveys and new optical observations at Hα ,[ Sii], and [O iii] wavelengths, in combination with the X-ray data, to investigate their properties and to search for new SNRs in the SMC. Methods. We used X-ray source selection criteria and found one SMC object with typical SNR characteristics (HFPK 334), that was initially detected by ROSAT. We analysed the X-ray spectra and present multi-wavelength morphological studies of the three SNRs and the new candidate. Results. Using a non-equilibrium ionisation collisional plasma model, we find temperatures kT around 0.18 keV for the three known remnants and 0.69 keV for the candidate. The low temperature, low surface brightness, and large extent of the three remnants indicates relatively large ages. The emission from the new candidate (HFPK 334) is more centrally peaked and the higher temperature suggests a younger remnant. Our new radio images indicate that a pulsar wind nebulae (PWN) is possibly associated with this object. Conclusions. The SNRs known in the SMC show a variety of morphological structures that are relatively uncorrelated in the different wavelength bands, probably caused by the different conditions in the surrounding medium with which the remnant interacts.

Multifrequency study of the Large Magellanic Cloud supernova remnant (SNR) B0513-692 and new SNR candidate J051327-6911

We present a new multiwavelength study of supernova remnant (SNR) B0513−692 in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed, essentially unresolved, but unrelated radio source at its north-western edge, J051324−691049. This is identified as a likely compact H ii region based on related optical imaging and spectroscopy. We use the Australia Telescope Compact Array (ATCA) at 4790 and 8640 MHz (λ≃ 6 cm and λ≃ 3.5 cm) to determine the large-scale morphology, spectral index and polarization characteristics of B0513−692 for the first time. We detect a strongly polarized region (49 per cent) in the remnants southern edge (λ≃ 6 cm) . Interestingly, we also detect a small (∼40 arcsec) moderately bright, but distinct optical, circular shell in our Hα imagery which is adjacent to the compact H ii region and just within the borders of the north-eastern edge of B0513−692. We suggest that this is a separate new SNR candidate based on its apparently distinct character in terms of optical morphology in three imaged emission lines and indicative SNR optical spectroscopy (including enhanced optical [S ii] emission relative to Hα).

Multi-frequency study of extragalactic supernova remnants and H II regions : sculptor group Sd galaxy NGC 300

We present a multi-frequency study of supernova remnants (SNRs) and

Multifrequency study of SNR J0533-7202, a new supernova remnant in the LMC

\ion{H}{ii }

Radio planetary nebulae in the Magellanic Clouds

regions in the nearby Sculptor Group Sd galaxy NGC 300, based on new ATCA observations at the wavelengths of 13 and 20 cm, XMM-Newton observations, newly-processed ROSAT (PSPC/HRI; Read & Pietsch 2001) and VLA (20/6 cm) images of this galaxy. We have investigated the physical properties at the X-ray and radio wavelengths of the 28 optical SNRs found by Blair & Long (1997) and have expanded on the multi-wavelength work by Pannuti et al. (2000) on this same galaxy. From a total of 54 radio sources and 11 X-ray sources, we report 18 SNRs and three (3) SNR candidates (classified by spectral index alone) in NGC 300. Five of these 18 SNRs are associated with reported optical SNRs and three have X-ray counterparts. An additional 12 radio SNRs are seen in the Blair & Long (1997) [S II] images. We also investigate the luminosity function of our SNRs. Three background radio sources are confirmed and 12 other sources could represent additional background objects. Twenty two radio correlations with OB associations within NGC 300 correspond to either

The super-soft source XMMU J052016.0-692505 in the LMC: a likely white dwarf Be/X-ray binary

\ion{H}{ii }

The physical parameters of the microquasar S26 in the Sculptor Group galaxy NGC 7793

regions or SNRs making them a good tracer of SNRs near star-forming regions. Additionally, two radio sources coincide with potential globular clusters of NGC 300 reported by Kim et al. (2002).

A Chandra Observation of the Nearby Sculptor Group Sd Galaxy NGC?7793

We present a detailed study of Australia Telescope Compact Array (ATCA) observations of a newly discovered Large Magellanic Cloud (LMC) supernova remnant (SNR), SNR J0533-7202. This object follows a horseshoe morphology, with a size 37 pc x 28 pc (1-pc uncertainty in each direction). It exhibits a radio spectrum with the intrinsic synchrotron spectral index of alpha= -0.47+-0.06 between 73 and 6 cm. We report detections of regions showing moderately high fractional polarisation at 6 cm, with a peak value of 36+-6% and a mean fractional polarisation of 12+-7%. We also estimate an average rotation measure across the remnant of -591 rad m^-2. The current lack of deep X-ray observation precludes any conclusion about high-energy emission from the remnant. The association with an old stellar population favours a thermonuclear supernova origin of the remnant.

Highly absorbed X-ray binaries in the Small Magellanic Cloud

We report the extragalactic radio-continuum detection of 15 planetary nebulae (PNe) in the Magellanic Clouds (MCs) from recent Australia Telescope Compact Array+Parkes mosaic surveys. These detections were supplemented by new and high-resolution radio, optical and infrared observations which helped to resolve the true nature of the objects. Four of the PNe are located in the Small Magellanic Cloud (SMC) and 11 are located in the Large Magellanic Cloud (LMC). Based on Galactic PNe the expected radio flux densities at the distance of the LMC/SMC are up to ∼2.5 and ∼2.0 mJy at 1.4 GHz, respectively. We find that one of our new radio PNe in the SMC has a flux density of 5.1 mJy at 1.4 GHz, several times higher than expected. We suggest that the most luminous radio PN in the SMC (N S68) may represent the upper limit to radio-peak luminosity because it is approximately three times more luminous than NGC 7027, the most luminous known Galactic PN. We note that the optical diameters of these 15 Magellanic Clouds (MCs) PNe vary from very small (∼0.08 pc or 0.32 arcsec; SMP L47) to very large (∼1 pc or 4 arcsec; SMP L83). Their flux densities peak at different frequencies, suggesting that they may be in different stages of evolution. We briefly discuss mechanisms that may explain their unusually high radio-continuum flux densities. We argue that these detections may help solve the ‘missing mass problem’ in PNe whose central stars were originally 1–8 M� . We explore the possible link between ionized haloes ejected by the central stars in their late evolution and extended radio emission. Because of their higher than expected flux densities, we tentatively call this PNe (sub)sample – ‘Super PNe’.

IKT 16: a composite supernova remnant in the Small Magellanic Cloud

Aims: We report the discovery of the super-soft X-ray source XMMU J052016.0-692505 in the LMC with XMM-Newton. Methods: We analyse the EPIC spectra of XMMU J052016.0-692505 and study the likely optical counterpart LMCV2135. Results: Using an absorbed blackbody spectrum we derive a bolometric luminosity of ⪆ 1034 erg s-1 for the X-ray source at LMC distance. Assuming that the bolometric luminosity does not exceed the Eddington luminosity of a ~ 1.0 Mȯ star we derive a blackbody temperature of (25-70) eV and an LMC absorbing column density of < 6× 1021 cm-2. The likely optical counterpart of XMMU J052016.0-692505 is the LMC variable star LMCV2135 which is a MACHO and OGLE variable. The infrared and optical colors and magnitudes of this star are consistent with a hot star of likely spectral type B. The long-term MACHO light curve shows variability with a timescale of ˜ 500 and ˜ 1000 days. The optical spectra obtained at the 1.9-meter telescope of the South African Astronomical Observatory show strong Hα and Hβ emission lines (with EWH_α˜ 34 A) which indicate a B0-3e star. The radial velocities of the Hα and Hβ emission lines show a variation from ˜ 400-450 km s-1 to ˜ 5-20 km s-1 which is consistent with the systemic velocity of the LMC and an intrinsic variation most likely due to the rotation of the Be disk. We discuss LMCV2135/XMMU J052016.0-692505 as a Be/white dwarf binary system in the LMC. The super-soft X-ray spectrum of the source could be due to a stable nuclear burning white dwarf with a mass of ˜ 0.9-1.0 Mȯ.