Australia Telescope National Facility

About: Australia Telescope National Facility is a facility organization based out in Sydney, New South Wales, Australia. It is known for research contribution in the topics: Galaxy & Pulsar. The organization has 699 authors who have published 2774 publications receiving 151507 citations. The organization is also known as: ATNF.

A Search for Pulsars in Quiescent Soft X-Ray Transients. I.

Abstract: We have carried out a deep search at 1.4 GHz for radio pulsed emission from six soft X-ray transient sources observed during their X-ray quiescent phase. The commonly accepted model for the formation of millisecond radio pulsars predicts the presence of a rapidly rotating, weakly magnetized neutron star in the core of these systems. The sudden drop in accretion rate associated with the end of an X-ray outburst causes the Alfven surface to move outside the light cylinder, allowing the pulsar emission process to operate. No pulsed signal was detected from the sources in our sample. We discuss several mechanisms that could hamper the detection and suggest that free-free absorption from material ejected from the system by the pulsar radiation pressure could explain our null result.

Non-circular motions and the cusp-core discrepancy in dwarf galaxies

Abstract: Context. The cusp-core discrepancy is one of the major problems in astrophysics. It results from comparing the observed mass distribution of galaxies with the predictions of cold dark matter simulations. The latter predict a cuspy density profile in the inner parts of galaxies, whereas observations of dwarf and low surface brightness galaxies show a constant-density core. Aims. We want to determine the shape of the dark matter potential in the nuclear regions of a sample of six nearby irregular dwarf galaxies. Methods. In order to quantify the amount of non-circular motions that could potentially affect a mass decomposition, we first perform a harmonic decomposition of the H i Hermite velocity fields of all sample galaxies. We then decompose the H i rotation curves into different mass components by fitting NFW and pseudo-isothermal halo models to the H i rotation curves using a χ 2 minimisation. We model the minimum-disc, the minimum-disc + gas, and the maximum-disc cases. Results. The non-circular motions are in all cases studied here of the order of only a few km s −1 (generally corresponding to less than 25% of the local rotation velocity), which means that they do not significantly affect the rotation curves. The observed rotation curves can better be described by the cored pseudo-isothermal halo than by the NFW halo. The slopes of the dark matter density profiles confirm this result and are in good agreement with previous studies. The quality of the fits can often be improved when including baryons, which suggests that they contribute significantly to the inner part of the density profile of dwarf galaxies.

Dressing a Naked Quasar: Star Formation and Active Galactic Nucleus Feedback in HE 0450-2958

Abstract: We present Australia Telescope Compact Array radio continuum observations of the quasar/galaxy system HE 0450-2958. An asymmetric triple linear morphology is observed, with the central radio component coincident with the quasar core and a second radio component associated with a companion galaxy at a projected distance of 7 kpc from the quasar. The system obeys the far-infrared to radio continuum correlation, implying that the radio emission is energetically dominated by star formation activity. However, there is undoubtedly some contribution to the overall radio emission from a low-luminosity active galactic nucleus (AGN) core and a pair of radio lobes. Long-baseline radio interferometric observations of the quasar core place a 3 ? upper limit of 0.6 mJy at 1400 MHz on the AGN contribution to the quasar's radio emission: less than 30% of the total. The remaining 70% of the radio emission from the quasar is associated with star formation activity and provides the first direct evidence of the quasar's host galaxy. A reanlaysis of the Very Large Telescope (VLT) spectroscopic data shows extended emission-line regions aligned with the radio axis and extended on scales of ~20 kpc. This is interpreted as evidence for jet-cloud interactions, similar to those observed in radio galaxies and Seyferts. The emission lines in the companion galaxy are consistent with radiative shocks, and its spatial association with the eastern radio lobe implies that large-scale jet-induced star formation has played a role in this galaxy's evolution.

A single fast radio burst localized to a massive galaxy at cosmological distance

Abstract: Fast Radio Bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Non-repeating FRB observations have had insufficient positional accuracy to localize them to an individual host galaxy. We report the interferometric localization of the single pulse FRB 180924 to a position 4 kpc from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web.

Polarization profiles of southern pulsars at 3.1 GHz

Abstract: We present polarization profiles for 48 southern pulsars observed with the new 10-cm receiver at the Parkes telescope. We have exploited the low system temperature and high bandwidth of the receiver to obtain profiles which have good signal-to-noise for most of our sample at this relatively high frequency. Although, as expected, a number of profiles are less linearly polarized at 3.1 GHz than at lower frequencies, we identify some pulsars and particular components of profiles in other pulsars which have increased linear polarization at this frequency. We discuss the dependence of linear polarization with frequency in the context of a model in which emission consists of the superposition of two, orthogonally polarized modes. We show that a simple model, in which the orthogonal modes have different spectral indices, can explain many of the observed properties of the frequency evolution of both the linear polarization and the total power, such as the high degree of linear polarization seen at all frequencies in some high spin-down, young pulsars. Nearly all the position angle profiles show deviations from the rotating vector model; this appears to be a general feature of high-frequency polarization observations.