Time filter

Source Type

Alves M.I.R.,University Paris - Sud | Alves M.I.R.,University of Manchester | Davies R.D.,University of Manchester | Dickinson C.,University of Manchester | And 3 more authors.
Monthly Notices of the Royal Astronomical Society

We present the derivation of the free-free emission on the Galactic plane between ℓ= 20° and 44° and |b|≤ 4°, using radio recombination line (RRL) data from the Hi Parkes All Sky Survey (HIPASS). Following an upgrade of the RRL data reduction technique, which improves significantly the quality of the final RRL spectra, we have extended the analysis to three times the area covered in Alves et al. The final RRL map has an angular resolution of 14.8arcmin and a velocity resolution of 20kms -1. The electron temperature (T e) distribution of the ionized gas in the area under study at 1.4GHz is derived using the line and continuum data from the present survey. The mean T e on the Galactic plane is 6000K. The first direct measure of the free-free emission is obtained based on the derived T e distribution. Subtraction of this thermal component from the total continuum leads to the first direct measurement of the synchrotron emission at 1.4GHz. A narrow component of width 2° is identified in the latitude distribution of the synchrotron emission. We present a list of Hii regions and supernova remnants (SNRs) extracted from the present free-free and synchrotron maps, where we confirm the synchrotron nature of the SNRs G42.0-0.1 and G41.5+0.4 proposed by Kaplan et al. and the SNR G35.6-0.4 recently re-identified by Green. The latitude distribution for the RRL-derived free-free emission shows that the Wilkinson Microwave Anisotropy Probe (WMAP) maximum entropy method is too high by ~50 per cent, in agreement with other recent results. The extension of this study to the inner Galaxy region ℓ=-50° to 50° will allow a better overall comparison of the RRL result with WMAP. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source

Rubio-Herrera E.,National Autonomous University of Mexico | Rubio-Herrera E.,University of Amsterdam | Stappers B.W.,University of Manchester | Hessels J.W.T.,University of Amsterdam | And 2 more authors.
Monthly Notices of the Royal Astronomical Society

We present the results of the most sensitive and comprehensive survey yet undertaken for radio pulsars and fast transients in the Andromeda galaxy (M31) and its satellites, using the Westerbork Synthesis Radio Telescope (WSRT) at a central frequency of 328 MHz. We used the WSRT in a special configuration called 8gr8 (eight-grate) mode, which provides a large instantaneous field of view, about 5 deg2 pointing-1, with good sensitivity, long dwell times (up to 8 h pointing-1) and good spatial resolution (a few arcminutes) for locating sources. We have searched for both periodicities and single pulses in our data, aiming to detect bright, persistent radio pulsars and rotating radio transients (RRATs) of either Galactic or extragalactic origin. Our searches did not reveal any confirmed periodic signals or bright single bursts from (potentially) cosmological distances. However, we do report the detection of several singlepulse events, some repeating at the same dispersion measure, which could potentially originate from neutron stars in M31. One in particular was seen multiple times, including a burst of six pulses in 2000 s, at a dispersion measure of 54.7 pc cm-3, which potentially places the origin of this source outside our Galaxy. Our results are compared to a range of hypothetical populations of pulsars and RRATs in M31 and allow us to constrain the luminosity function of pulsars in M31. They also show that, unless the pulsar population in M31 is much dimmer than in our Galaxy, there is no need to invoke any violation of the inverse square law of the distance for pulsar fluxes. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Alves M.I.R.,University of Manchester | Davies R.D.,University of Manchester | Dickinson C.,University of Manchester | Davis R.J.,University of Manchester | And 3 more authors.
Monthly Notices of the Royal Astronomical Society

Radio recombination lines (RRLs) can be used to determine the emission measure unambiguously along the Galactic plane. We use the deep (2100 s per beam) H i Parkes Zone of Avoidance (ZOA) survey which includes three RRLs (H. 166α, H. 167α and H. 168α) within its bandwidth. The region ℓ= 36° to 44°, b=4° to +4° is chosen to include emission from the Local, Sagittarius and Scutum arms. An 8°× 8° data cube centred at (ℓ, b) = (40°, 0°) is constructed of RRL spectra with velocity and spatial resolution of 27 km s -1 and 15.5 arcmin, respectively. Well-known H ii regions are identified as well as the diffuse RRL emission on the Galactic plane. A Galactic latitude section of the integrated RRL emission across the Galactic plane delineates the brightness temperature (Tb) distribution which has a half-power width in latitude of .A value of the electron temperature Te≃ 8000 K is derived from a comparison with the Wilkinson Microwave Anisotropy Probe (WMAP) free-free maximum entropy method. The Tb distribution from the present RRL data is combined with the WMAP 5-yr data to derive the latitude distribution of the residual 'anomalous' emission on the Galactic ridge. In this paper, we demonstrate that diffuse ionized emission on the Galactic ridge can be recovered using RRLs from the ZOA survey. This method is therefore able to complement the Hα data at low Galactic latitudes, to enable an all-sky free-free template to be derived. © 2010 The Authors. Journal compilation © 2010 RAS. Source

Subrahmanyan R.,Raman Research Institute | Ekers R.D.,Australia Telescope National Facility | Saripalli L.,Raman Research Institute | Sadler E.M.,University of Sydney
Monthly Notices of the Royal Astronomical Society

We present a radio survey carried out with the Australia Telescope Compact Array. A motivation for the survey was to make a complete inventory of the diffuse emission components as a step towards a study of the cosmic evolution in radio source structure and the contribution from radio-mode feedback on galaxy evolution. The Australia Telescope Low-Brightness Survey (ATLBS) at 1388 MHz covers 8.42 deg2 of the sky in an observing mode designed to yield images with exceptional surface brightness sensitivity and low confusion. The survey was carried out in two adjacent regions on the sky centred at RA: 00h35m00s, Dec.: and RA: 00h59m17s, Dec.: (J2000.0). The ATLBS radio images, made with 0.08 mJy beam-1 rms noise and 50 arcsec beam, detect a total of 1094 sources with peak flux exceeding 0.4 mJy beam-1. The ATLBS source counts were corrected for blending, noise bias, resolution and primary beam attenuation; the normalized differential source counts are consistent with no upturn down to 0.6 mJy. The percentage integrated polarization Π0 was computed after corrections for the polarization bias in integrated polarized intensity; Π0 shows an increasing trend with decreasing flux density. Simultaneous visibility measurements made with longer baselines yielded images, with 5 arcsec beam, of compact components in sources detected in the survey. The observations provide a measurement of the complexity and diffuse emission associated with mJy and sub-mJy radio sources. 10 per cent of the ATLBS sources have more than half of their flux density in extended emission and the fractional flux in diffuse components does not appear to vary with flux density, although the percentage of sources that have complex structure increases with flux density. The observations are consistent with a transition in the nature of extended radio sources from FR-ii radio source morphology, which dominates the mJy population, to FR-i structure at sub-mJy flux density. © 2010 The Authors. Journal compilation © 2010 RAS. Source

McIntosh G.C.,University of Minnesota | Indermuehle B.,Australia Telescope National Facility
Astrophysical Journal

We report the first short term velocity centroid (VC) periodicity derived from SiO maser emission. L2 Puppis, a semi-regular AGB star, was observed using the Mopra radio telescope of the Australia Telescope National Facility in the SiO v = 1, J = 1-0 and v = 1, J = 2-1 transitions. It exhibits a 139 day period in its SiO maser VC based on a period folding analysis and a Lomb Scargle analysis. L2 Pup's SiO maser emission has an unusually large velocity range and an unusual three-peaked spectrum. To create the change in VC the entire spectrum does not shift in velocity, but changes in the relative emission of the peaks generate the variation. The changes in the VC may be due to differential illumination, an asymmetric circumstellar distribution of material, or a mixture of causes. The unusual velocity structure, similar to that observed in Orion source 1, may be due to revolution of the circumstellar material or asymmetries in the circumstellar environment. © 2013. The American Astronomical Society. All rights reserved.. Source

Discover hidden collaborations