Showing papers by "Richard Dodson published in 2002"
TL;DR: In this paper, four relaxation timescales are found, which are believed to be due to the variable coupling between the crust and the interior fluid, one is very short, about 60 s; the others have been previously reported and are 0.56, 3.33, and 19.1 days in length.
Abstract: Pulsars are rotating neutron stars, sweeping the emission regions from the magnetic poles across our line of sight. Isolated neutron stars lose angular momentum through dipole radiation and (possibly) particle winds; hence, they slow down extremely steadily, making them among the most reliable timing sources available. However, it is well known that younger pulsars can suffer glitches, when they suddenly deviate from their stable rotation period. On 2000 January 16 (MJD 51,559), the rate of pulsation from the Vela pulsar (B0833-45) showed such a fractional period change of 3.1 × 10-6, the largest recorded for this pulsar. The glitch was detected and reported by the Hobart radio telescope. The speedy announcement allowed the X-ray telescope, Chandra, and others to make Target-of-Opportunity observations. The data placed an upper limit of 40 s for the transition time from the original to the new period. Four relaxation timescales are found, which are believed to be due to the variable coupling between the crust and the interior fluid. One is very short, about 60 s; the others have been previously reported and are 0.56, 3.33, and 19.1 days in length.
131 citations
TL;DR: In this article, the Rossi X-Ray Timing Explorer (RXTE) was used to detect a double-peaked, pulsed emission at 2-30 keV.
Abstract: We report on our analysis of a 274 ks observation of the Vela pulsar with the Rossi X-Ray Timing Explorer (RXTE). The double-peaked, pulsed emission at 2-30 keV, which we had previously detected during a 93 ks observation, is confirmed with much-improved statistics. There is now clear evidence, in both the spectrum and the light curve, that the emission in the RXTE band is a blend of two separate nonthermal components. The spectrum of the harder component connects smoothly with the OSSE, COMPTEL, and EGRET spectra, and the peaks in the light curve are in phase coincidence with those of the high-energy light curve. The spectrum of the softer component is consistent with an extrapolation to the pulsed optical flux, and the second RXTE pulse is in phase coincidence with the second optical peak. In addition, we see a peak in the 2-8 keV RXTE pulse profile at the radio phase.
72 citations
TL;DR: In this article, images from VLBI Space Observatory Programme (VSOP) observations of 14 compact extragalactic southern hemisphere radio sources were presented, including a description of the observations, the data reduction techniques, and the parameters of the resulting images and model fits.
Abstract: We present images from VLBI Space Observatory Programme (VSOP) observations of 14 compact extragalactic southern hemisphere radio sources, including a description of the observations, the data reduction techniques, and the parameters of the resulting images and model fits. These images provide the highest resolution information to date for many of these objects. Comparisons are made between VSOP and previous ground-based VLBI results, including images from data extracted from the geodetic VLBI archive at the United States Naval Observatory. From the VSOP data, we find that the two radio galaxies observed have lower peak brightness temperatures than the 12 quasars. Also, these data show (1) no evidence for obvious differences between the brightness temperature distributions of gamma-ray-loud and gamma-ray-quiet radio-loud active galactic nuclei and (2) no evidence for obvious correlations between brightness temperature and spectral index, radio polarization, flux density, or month timescale modulation index. These results are consistent with previous work by Lister, Tingay, & Preston, who found that the only observable significantly correlated with VSOP-derived brightness temperature is intraday variability, which is strongly correlated with many relativistic beaming indicators. For one source, PKS 1127-145, we undertake a detailed investigation of the milliarcsecond-scale component positions as a function of time, taking data from the literature and the current work, to estimate proper motions. As a result, we suggest that two components previously reported as stationary, C1 and C2, have apparent transverse speeds of (9.1 ± 3.8) and (5.3 ± 2.3) h-1c, respectively. We also make the first investigation of the apparent motion in the nearest GHz-peaked spectrum radio galaxy, PKS 1718-649, finding an upper limit on the apparent separation speed of 0.08c. Comparison of geodetic VLBI and VSOP data show no significant detection of component motion in PKS 0208-512, (2.4 ± 3.1) h-1c, and only a tentative detection in PKS 0537-441, (2.8 ± 2.2) h-1c. A significant detection of component motion is found in PKS 1610-771, solely from the geodetic VLBI data, (9.4 ± 3.5) h-1c.
51 citations
TL;DR: The first detection of pulsed X-ray emission from the young, energetic radio and γ-ray pulsar PSR B1706-44 using data obtained with the High Resolution Camera on board the Chandra X-Ray Observatory was reported in this paper.
Abstract: We report the first detection of pulsed X-ray emission from the young, energetic radio and γ-ray pulsar PSR B1706-44. We find a periodic signal at a frequency of f = 9.7588088 ± 0.0000026 Hz (at epoch 51585.34104 MJD), consistent with the radio ephemeris, using data obtained with the High Resolution Camera on board the Chandra X-Ray Observatory. The probability that this detection is a chance occurrence is 3.5 × 10-5 as judged by the Rayleigh test. The folded light curve has a broad, single-peaked profile with a pulsed fraction of 23% ± 6%. This result is consistent with a ROSAT PSPC upper limit of less than 18% after allowing for the ability of Chandra to resolve the pulsar from a surrounding synchrotron nebula. We also fitted Chandra spectroscopic data on PSR B1706-44, which require at least two components, e.g., a blackbody of T∞ = 1.66 × 106 K and a power law of Γ = 2.0 ± 0.5. The blackbody radius at the nominal 2.5 kpc distance is only R∞ = 3.6 ± 0.9 km, indicating either a hot region on a cooler surface or the need for a realistic atmosphere model that would allow a lower temperature and larger area. Because the power-law and blackbody spectra each contribute more than 23% of the observed flux, it is not possible to decide which component is responsible for the modulation in the spectrally unresolved light curve.
47 citations
TL;DR: In this paper, the first detection of pulsed X-ray emission from the young, energetic radio and Gamma-ray pulsar PSR B1706-44 was reported, with a frequency of f = 9.7588088 +/- 0.0000026 Hz (at epoch 51585.34104 MJD).
Abstract: We report the first detection of pulsed X-ray emission from the young, energetic radio and Gamma-ray pulsar PSR B1706-44. We find a periodic signal at a frequency of f = 9.7588088 +/- 0.0000026 Hz (at epoch 51585.34104 MJD), consistent with the radio ephemeris, using data obtained with the High Resolution Camera on-board the Chandra X-ray Observatory}. The probability that this detection is a chance occurrence is 3.5E-5 as judged by the Rayleigh test. The folded light curve has a broad, single-peaked profile with a pulsed fraction of 23% +/- 6%. This result is consistent the ROSAT PSPC upper limit of < 18% after allowing for the ability of Chandra to resolve the pulsar from a surrounding synchrotron nebula. We also fitted Chandra spectroscopic data on PSR B1706-44, which require at least two components, e.g., a blackbody of temperature T(infinity) between 1.51E6 K and 1.83E6 K and a power-law of Gamma = 2.0 +/- 0.5. The blackbody radius at the nominal 2.5 kpc distance is only R(infinity) = 3.6 +/- 0.9 km, indicating either a hot region on a cooler surface, or the need for a realistic atmosphere model that would allow a lower temperature and larger area. Because the power-law and blackbody spectra each contribute more than 23% of the observed flux, it is not possible to decide which component is responsible for the modulation in the spectrally unresolved light curve.
41 citations
TL;DR: In this paper, the Australia Telescope Compact Array (ATCA) was used to make a sensitive (5σ≃ 100 mJy) search for maser emission from the 4765-MHz 2 Π 1 / 2 F = 1 → 0 transition of OH.
Abstract: We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5σ≃ 100 mJy) search for maser emission from the 4765-MHz 2 Π 1 / 2 F = 1 → 0 transition of OH. 55 star formation regions were searched and maser emission with a peak flux density in excess of 100 mJy was detected toward 14 sites, with 10 of these being new discoveries. In addition we observed the 4750-MHz 2 Π 1 / 2 F = 1 → 1 transition towards a sample of star formation regions known to contain 1720-MHz OH masers, detecting marginal maser emission from G348.550-0.979. If confirmed this would be only the second maser discovered from this transition. The occurrence of 4765-MHz OH maser emission accompanying 1720-MHz OH masers in a small number of well-studied star formation regions has led to a general perception in the literature that the two transitions favour similar physical conditions. Our search has found that the presence of the excited-state 6035-MHz OH transition is a much better predictor of 4765-MHz OH maser emission from the same region than 1720-MHz OH maser emission is. Combining our results with those of previous high-resolution observations of other OH transitions we have examined the published theoretical models of OH masers and find that none of them predicts any conditions in which the 1665-, 6035- and 4765-MHz transitions are inverted simultaneously.
29 citations
TL;DR: In this article, the authors used the Australia Telescope Compact Array (ATCA) to make a sensitive search for maser emission from the 4765-MHz $^2\Pi_{1/2}$ F=1$\to$0 transition of OH.
Abstract: We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5-$\sigma$ $\simeq$ 100 mJy) search for maser emission from the 4765-MHz $^2\Pi_{1/2}$ F=1$\to$0 transition of OH. Fifty five star formation regions were searched and maser emission with a peak flux density in excess of 100 mJy was detected toward fourteen sites, with ten of these being new discoveries. In addition we observed the 4750-MHz $^2\Pi_{1/2}$ F=1$\to$1 transition towards a sample of star formation regions known to contain 1720-MHz OH masers, detecting marginal maser emission from G348.550-0.979. If confirmed this would be only the second maser discovered from this transition. The occurrence of 4765-MHz OH maser emission accompanying 1720-MHz OH masers in a small number of well studied star formation regions has lead to a general perception in the literature that the two transitions favour similar physical conditions. Our search has found that the presence of the excited-state 6035-MHz OH transition is a much better predictor of 4765-MHz OH maser emission from the same region than is 1720-MHz OH maser emission. Combining our results with those of previous high resolution observations of other OH transitions we have examined the published theoretical models of OH masers and find that none of them predict any conditions in which the 1665-, 6035- and 4765-MHz transitions are simultaneously inverted.
Erratum abstract:
Dodson & Ellingsen (2002) included several observations with significant pointing errors, invalidating the upper limits found in these directions. These have now been reobserved or recalculated. A new table of upper limits has been generated, and two more masers that would have been seen have been found.
26 citations
TL;DR: The association of G343.1-2.3 and PSR B1706-44 has been controversial from its first proposal as discussed by the authors, but the association is still likely.
Abstract: The association of G343.1-2.3 and PSR B1706-44 has been controversial from its first proposal. In this paper we address the difficulties, and argue that the association is still likely. New evidence comes from images of G343.1-2.3 obtained using the Australia Telescope Compact Array (ATCA), and of the pulsar obtained using the Chandra X-ray observatory. Mosaicking was required to cover the full extent of G343.1-2.3, and we present the polarization images from this experiment. Also an X-ray pulsar wind nebula has been found in the archived Chandra observations, with the correct morphology to support the association. The ATCA observations confirm the much larger extent of the supernova remnant, which now encompasses the pulsar. The X-ray morphology points back toward the centre of the supernova remnant, indicating the direction of the proper motion, and that the pulsar and supernova remnant are associated.
20 citations
TL;DR: In this article, an observational program using the ATCA to monitor the intraday variability (IDV) of a sample of sources at 4.8 and 8.6 GHz is presented.
Abstract: We are undertaking an observational program using the ATCA to monitor the intraday variability (IDV) of a sample of sources at 4.8 and 8.6 GHz. The sources were selected to include the known strong southern IDV sources plus a number of sources whose IDV was recently discovered. The present monitoring program will extend over a full year in order to search for any annual cycle that may be present in the long-term IDV characteristics of these sources. In this paper we discuss the observing strategy and data analysis, and present the first results from our observations.
18 citations
TL;DR: The association of G343.1-2.3 and PSR 1706-44 has been controversial from its first proposal as discussed by the authors, but it is still likely to be confirmed.
Abstract: The association of G343.1-2.3 and PSR 1706-44 has been controversial from its first proposal. In this paper we address the difficulties, and argue that the association is still likely. New evidence comes from images of G343.1-2.3 obtained using the Australia Telescope Compact Array (ATCA), and the pulsar obtained using the CHANDRA X-ray observatory. Mosaicing was required to cover the full extent of G343.1-2.3, and we present the polarisation images from this experiment. Also an X-ray pulsar wind nebula has been found in the archived CHANDRA observations, with the correct morphology to support the association. The ATCA observations confirm the much larger extent of the SNR, which now encompasses the pulsar. The X-ray morphology points back toward the centre of the SNR, indicating the direction of the proper motion, and that the PSR and SNR are associated.
16 citations
TL;DR: In this paper, the rate of pulsation from the Vela pulsar (B0833-45) showed such a fractional period change of {\rm $3.1\times 10^{-6}$}, the largest recorded for this pulsar.
Abstract: Pulsars are rotating neutron stars, sweeping the emission regions from the magnetic poles across our line of sight. Isolated neutron stars lose angular momentum through dipole radiation and (possibly) particle winds, hence they slow down extremely steadily, making them amongst the most reliable timing sources available. However, it is well known that younger pulsars can suffer glitches, when they suddenly deviate from their stable rotation period. On 2000 January 16 (MJD 51559) the rate of pulsation from the Vela pulsar (B0833-45) showed such a fractional period change of {\rm $3.1\times 10^{-6}$}, the largest recorded for this pulsar. The glitch was detected and reported by the Hobart radio telescope. The speedy announcement allowed the X-ray telescope, Chandra, and others, to make Target of Opportunity observations. The data placed an upper limit of 40 seconds for the transition time from the original to the new period. Four relaxation timescales are found, which are believed to be due to the variable coupling between the crust and the interior fluid. One is very short, about 60 seconds; the others have been previously reported and are 0.56, 3.33 and 19.1 days in length.
01 Jan 2002
TL;DR: In this paper, four relaxation timescales are found, which are believed to be due to the transfer of inertia through the internal structure of the Vela pulsar (B0833-45) and are 0.56, 3.33 and 19.1 days in length.
Abstract: Pulsars are rotating neutron stars, sweeping the emission regions from the magnetic poles across our line of sight. Isolated neutron stars lose angular momentum through dipole radiation and (possibly) particle winds, hence they slow down extremely steadily, making them amongst the most reliable timing sources available. However, it is well known that younger pulsars can suffer glitches, when they suddenly deviate from their stable rotation period. On 2000 January 16 (MJD 51559) the rate of pulsation from the Vela pulsar (B0833-45) showed such a fractional period change of 3.1 x 10^{-6}, the largest recorded for this pulsar. The glitch was detected and reported by the Hobart radio telescope. The speedy announcement allowed the X-ray telescope, Chandra, and others, to make Target of Opportunity observations. The data placed an upper limit of 40 seconds for the transition time from the orginal to the new period. Four relaxation timescales are found, which are believed to be due to the transfer of inertia through the internal structure. One is very short, about 60 seconds; the others have been previously reported and are 0.56, 3.33 and 19.1 days in length.
Posted Content•
TL;DR: The 14-metre radio telescope at Mt. Pleasant Observatory, Tasmania, Australia, has been used to monitor the Vela pulsar for the last 21 years and revealed a particularly short-term decay component (Dodson, McCulloch, & Lewis 2002).
Abstract: Two daily pulsar monitoring programs are progressing at the Mount Pleasant Observatory, Hobart, Tasmania, Australia. A new system involving the 26-metre radio telescope monitors 10 young pulsars daily and is focussed on near-real-time glitch finding. This will allow Target of Opportunity observations to measure post-glitch heating of the neutron star surface (Helfand, Gotthelf, & Halpern 2000).
The 14-metre continues its 21st year of daily monitoring of the Vela pulsar with a recent comprehensive frontend upgrade. This is prior to an upgrade of the backend equipment currently in progress. The 14-metre observed the most recent glitch of the Vela pulsar in January 2000 to the highest time resolution of any glitch and revealed a particularly short-term decay component (Dodson, McCulloch, & Lewis 2002). This decay component will provide constraints to the nature of the coupling of the stellar crust to the liquid interior.
01 Jan 2002
TL;DR: The association of G343.1-2.3 and PSR 1706-44 with the Australia Telescope Compact Array (ATCA) has been investigated in this article, where the ATCA observations confirm the much larger extent of the SNR, which now encompasses the pulsar.
Abstract: The association of G343.1-2.3 and PSR 1706-44 has been controversial from its first proposal. In this paper we present new evidence from images made by with the Australia Telescope Compact Array (ATCA), MRT and Mt. Pleasant. To cover the full extent of G343.1-2.3 with ATCA mosaicing was required, and we present the polarisation images from this experiment. The ATCA observations confirms the much larger extent of the SNR, which now encompasses the pulsar.