arXiv subjects

D. McConnell

Publications and source records attributed to D. McConnell.

43 records · Page 3Linked to original sources

arXiv2005

Polarized Diffuse Emission at 2.3 GHz in a High Galactic Latitude Area

Polarized diffuse emission observations at 2.3 GHz in a high Galactic latitude area are presented. The 2\degr X 2\degr field, centred in (α=5^h,δ=-49\degr), is located in the region observed by the BOOMERanG experiment. Our observations has been carried out with the Parkes Radio telescope and represent the highest frequency detection done to date in low emission areas. Because of a weaker Faraday rotation action, the high frequency allows an estimate of the Galactic synchrotron contamination of the Cosmic Microwave Background Polarization (CMBP) that is more reliable than that done at 1.4 GHz. We find that the angular power spectra of the E- and B-modes have slopes of β_E = -1.46 +/- 0.14 and β_B = -1.87 +/- 0.22, indicating a flattening with respect to 1.4 GHz. Extrapolated up to 32 GHz, the E-mode spectrum is about 3 orders of magnitude lower than that of the CMBP, allowing a clean detection even at this frequency. The best improvement concerns the B-mode, for which our single-dish observations provide the first estimate of the contamination on angular scales close to the CMBP peak (about 2 degrees). We find that the CMBP B-mode should be stronger than synchrotron contamination at 90 GHz for models with T/S > 0.01. This low level could move down to 60-70 GHz the optimal window for CMBP measures.

astro-ph↗

arXiv2003

The radio luminosity distribution of pulsars in 47 Tucanae

We have used the Australia Telescope Compact Array to seek the integrated radio flux from all the pulsars in the core of the globular cluster 47 Tucanae. We have detected an extended region of radio emission and have calibrated its flux against the flux distribution of the known pulsars in the cluster. We find the total 20-cm radio flux from the cluster's pulsars to be S = 2.0 +/- 0.3 mJy. This implies the lower limit to the radio luminosity distribution to be L_1400 = 0.4 mJy kpc^2 and the size of the observable pulsar population to be N < 30.

astro-ph↗

arXiv2003

The Vela Pulsar's Radio Nebula

We have discovered that the radio nebula surrounding the Vela pulsar covers a much wider extent than previously reported, with two lobes to the North and South of the pulsar. Indications of this object have been reported previously, but its symmetric morphology around the pulsar and other details had not been identified as they were hidden due to poor sensitivity to low spatial frequencies. The structure is highly polarised and the polarisation vectors, once corrected for Faraday rotation, reveal symmetry with respect to the spin axis of the pulsar. The X-ray emission found by Chandra lies at the centre of this structure, in a region which has no detectable excess of radio emission. We estimate total fluxes and regional fluxes from the Northern and Southern lobes, plus the X-ray region at four radio frequencies; 1.4, 2.4, 5 and 8.5 GHz. We present the corresponding images in both the total and polarised intensities, as well as those showing the derotated linear polarisation vectors.

astro-ph↗

arXiv2002

The 2000 Periastron Passage of PSR B1259-63

We report here on a sequence of 28 observations of the binary pulsar system PSR B1259-63/SS2883 at four radio frequencies made with the Australia Telescope Compact Array around the time of the 2000 periastron passage. Observations made on 2000 Sep 1 show that the pulsar's apparent rotation measure (RM) reached a maximum of $-14800 \pm 1800$ rad m$^{-2}$, some 700 times the value measured away from periastron, and is the largest astrophysical RM measured. This value, combined with the dispersion measure implies a magnetic field in the Be star's wind of 6 mG. We find that the light curve of the unpulsed emission is similar to that obtained during the 1997 periastron but that differences in detail imply that the emission disc of the Be star is thicker and/or of higher density. The behaviour of the light curve at late times is best modelled by the adiabatic expansion of a synchrotron bubble formed in the pulsar/disc interaction. The expansion rate of the bubble $\sim 12$ km s$^{-1}$ is surprisingly low but the derived magnetic field of 1.6 G close to that expected.

astro-ph↗

arXiv1999

Radio sources near the core of globular cluster 47 Tucanae

We present ATCA radio images of the globular cluster 47 Tucanae made at 1.4 and 1.7 GHz and provide an analysis of the radio sources detected within 5 arcmin of the cluster centre. 11 sources are detected, most of which are clustered about the core of 47 Tuc. Both of the pulsars in 47 Tuc whose positions are known can be identified with sources in the 1.4 GHz image. The source distribution has a characteristic radius of ~100 arcsec, larger than the 23 arcsec radius of the cluster core. We compare source positions with the positions of nine X-ray sources and find no correspondence.

astro-ph↗

arXiv1999

A Coordinated Radio Afterglow Program

We describe a ground-based effort to find and study afterglows at centimeter and millimeter wavelengths. We have observed all well-localized gamma-ray bursts in the Northern and Southern sky since BeppoSAX first started providing rapid positions in early 1997. Of the 23 GRBs for which X-ray afterglows have been detected, 10 have optical afterglows and 9 have radio afterglows. A growing number of GRBs have both X-ray and radio afterglows but lack a corresponding optical afterglow.

astro-ph↗

arXiv1999

Optical and Radio Observations of the Afterglow from GRB990510: Evidence for a Jet

We present multi-color optical and two-frequency radio observations of the bright SAX event, GRB 990510. The well-sampled optical decay, together with the radio observations are inconsistent with simple spherical afterglow models. The achromatic optical steepening and the decay of the radio afterglow both occuring at $t \sim 1$ day are evidence for hydrodynamical evolution of the source, and can be most easily interpreted by models where the GRB ejecta are collimated in a jet. Employing a simple jet model to interpret the observations, we derive a jet opening angle of $θ_o = 0.08$, reducing the isotropic gamma-ray emission of $2.9 \times 10^{53}$ erg by a factor $\sim 300$. If the jet interpretation is correct, we conclude that GRB observations to-date are consistent with an energy for the central source of $E \lsim 10^{52}$ erg.

astro-ph↗