Pulse-to-pulse intensity modulation and drifting subpulses in recycled pulsars

We report the detection of pulse-to-pulse periodic intensity modulations, in observations of recycled pulsars. Even though the detection of individual pulses was generally not possible due to their low flux density and short duration, through the accumulation of statistics over sequences of 10^5--10^6 pulses we were able to determine the presence and properties of the pulse-to-pulse intensity variations of six pulsars. In most cases we found that the modulation included a weak, broadly quasi-periodic component. For two pulsars the sensitivity was high enough to ascertain that the modulation phase apparently varies systematically across the profile, indicating that the modulation appears as drifting subpulses. We detected brighter than average individual pulses in several pulsars, with energies up to 2--7 times higher than the mean, similar to results from normal pulsars. We were sensitive to giant pulses of a rate of occurrence equal to (and in many instances much lower than) that of PSR B1937+21 at 1400 MHz (~30 times lower than at 430 MHz), but none were detected, indicating that the phenomenon is rare in recycled pulsars.Comment: 15 pages, 17 figures, accepted to A&

Astronomy using basic Mark 2 very long baseline interferometry

Two experiments were performed in April and September 1976 to determine precise positions of radio sources using conventional Mark 2 VLBI techniques. Four stations in the continental United States observed at a wavelength of 18 cm. The recording bandwidth was 2 MHz. The preliminary results using analyses of fringe rate and delay are discussed and the source positions compared with the results of other measurements

UN FORUM SERIES – the measure of … things: measurement first principles and the business and human rights assessment project

This post was contribute by Larry Catá Backer, W. Richard and Mary Eshelman Faculty Scholar Professor of Law and International Affairs at Pennsylvania State University. The 2015 United Nations Forum on Business and Human Rights will focus on “Tracking Progress and Ensuring Coherence.” The business and human rights stakeholders are increasingly focused on taking the measure of that project. An influential stakeholder, Measuring Business & Human Rights, launched a blog series on how to assess and track implementation of the UNGP

A Radio Transient 0.1 pc from Sagittarius A*

We report the discovery of a transient radio source 2.7 arcsec (0.1 pc projected distance) South of the Galactic Center massive black hole, Sagittarius A*. The source flared with a peak of at least 80 mJy in March 2004. The source was resolved by the Very Large Array into two components with a separation of ~0.7 arcsec and characteristic sizes of ~0.2 arcsec. The two components of the source faded with a power-law index of 1.1 +/- 0.1. We detect an upper limit to the proper motion of the Eastern component of ~3 x 10^3 km s^-1 relative to Sgr A*. We detect a proper motion of ~10^4 km s^-1 for the Western component relative to Sgr A*. The transient was also detected at X-ray wavelengths with the Chandra X-ray Observatory and the XMM-Newton telescope and given the designation CXOGC J174540.0-290031. The X-ray source falls in between the two radio components. The maximum luminosity of the X-ray source is ~10^36 erg s^-1, significantly sub-Eddington. The radio jet flux density predicted by the X-ray/radio correlation for X-ray binaries is orders of magnitude less than the measured flux density. We conclude that the radio transient is the result of a bipolar jet originating in a single impulsive event from the X-ray source and interacting with the dense interstellar medium of the Galactic Center.Comment: accepted in ApJ; 24 pages; 8 figure

The Spectrum and Variability of Circular Polarization in Sagittarius A* from 1.4 to 15 GHz

We report here multi-epoch, multi-frequency observations of the circular polarization in Sagittarius A*, the compact radio source in the Galactic Center. Data taken from the VLA archive indicate that the fractional circular polarization at 4.8 GHz was -0.31% with an rms scatter of 0.13% from 1981 to 1998, in spite of a factor of 2 change in the total intensity. The sign remained negative over the entire time range, indicating a stable magnetic field polarity. In the Summer of 1999 we obtained 13 epochs of VLA A-array observations at 1.4, 4.8, 8.4 and 15 GHz. In May, September and October of 1999 we obtained 11 epochs of Australia Telescope Compact Array observations at 4.8 and 8.5 GHz. In all three of the data sets, we find no evidence for linear polarization greater than 0.1% in spite of strong circular polarization detections. Both VLA and ATCA data sets support three conclusions regarding the fractional circular polarization: the average spectrum is inverted with a spectral index ~0.5 +/- 0.2; the degree of variability is roughly constant on timescales of days to years; and, the degree of variability increases with frequency. We also observed that the largest increase in fractional circular polarization was coincident with the brightest flare in total intensity. Significant variability in the total intensity and fractional circular polarization on a timescale of 1 hour was observed during this flare, indicating an upper limit to the size of 70 AU at 15 GHz. The fractional circular polarization at 15 GHz reached -1.1% and the spectral index is strongly inverted during this flare. We conclude that the spectrum has two components that match the high and low frequency total intensity components. (abridged)Comment: Accepted for publication in ApJ, 40 pages, 18 figure

S2DFS: Analysis of temporal changes of drifting subpulses

We introduce a new technique, called the Sliding Two-Dimensional Fluctuation Spectrum, used for detecting and characterising the temporal changes of drifting subpulses from radio pulsars. The method was tested using simulated data as well as archived observations made with the WSRT at wavelengths of 92 and 21 cm. The drifting subpulse phenomenon is a well known property of radio pulsars. However the properties of the temporal behaviour of drifting subpulses are not fully explored. The drifting can also be non-coherent and the presence of effects like nulling or drift rate changing can mask the drifting behaviour of the pulsar. The S2DFS is a robust method for investigating this phenomenon and by introducing it we aim to expand our knowledge of the temporal drifting subpulse properties. Our new analysis method uses horizonally collapsed fluctuation spectra obtained with the Two-Dimensional Fluctuation Spectrum method. Stacking the collapsed spectra obtained in a 256 pulse window which slides by a pulse at a time produces a map of the collapsed fluctuation spectrum. By analysing the maps one can easily determine the presence of any temporal drift changes. Simulated data showed that the technique can reveal the presence of any temporal changes in drift behaviour like mode changing or nulling. We have also analysed data of three pulsars, PSRs B0031-07, B1819-22 and B1944+17, which were selected based on the quality of the data and their known drift properties. All three sources are known to exhibit mode changes which could easily be seen in the S2DFS. The results from the analysis of the data sets used in this paper have shown that the S2DFS method is robust and complimentary to the 2DFS method in detecting and characterising the temporal changes in drifting subpulses from radio pulsars.Comment: accepted for publication in A&A, 10 pages, 7 figures, 1 tabl

A General Theory of Non-equilibrium Dynamics of Lipid-protein Fluid Membranes

We present a general and systematic theory of non-equilibrium dynamics of multi-component fluid membranes, in general, and membranes containing transmembrane proteins, in particular. Developed based on a minimal number of principles of statistical physics and designed to be a meso/macroscopic-scale effective description, the theory is formulated in terms of a set of equations of hydrodynamics and linear constitutive relations. As a particular emphasis of the theory, the equations and the constitutive relations address both the thermodynamic and the hydrodynamic consequences of the unconventional material characteristics of lipid-protein membranes and contain proposals as well as predictions which have not yet been made in already existed work on membrane hydrodynamics and which may have experimental relevance. The framework structure of the theory makes possible its applications to a range of non-equilibrium phenomena in a range of membrane systems, as discussions in the paper of a few limit cases demonstrate.Comment: 22 pages, 2 figures, minor changes and addition