Size of the Vela Pulsar's Emission Region at 18 cm Wavelength

We present measurements of the linear diameter of the emission region of the Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a function of pulse phase from the distribution of visibility on the Mopra-Tidbinbilla baseline. As we demonstrate, in the presence of strong scintillation, finite size of the emission region produces a characteristic W-shaped signature in the projection of the visibility distribution onto the real axis. This modification involves heightened probability density near the mean amplitude, decreased probability to either side, and a return to the zero-size distribution beyond. We observe this signature with high statistical significance, as compared with the best-fitting zero-size model, in many regions of pulse phase. We find that the equivalent full width at half maximum of the pulsar's emission region decreases from more than 400 km early in the pulse to near zero at the peak of the pulse, and then increases again to approximately 800 km near the trailing edge. We discuss possible systematic effects, and compare our work with previous results

The Multi-Component Nature of the Vela Pulsar Nonthermal X-ray Spectrum

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, both in the spectrum and the light curve, that the emission in the RXTE band is a blend of two separate non-thermal components. The spectrum of the harder component connects smoothly with the OSSE, COMPTEL and EGRET spectrum 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.Comment: 12 pages, 3 figures, accepted for publication in Astrophysical Journa

Digital History, Digital Sources, Digital Display: The Her Hat Was in the Ring Project on U.S. Women Who Ran for Political Office Before 1920

In the second half of the nineteenth century and through the first two decades of the twentieth century thousands of women ran for political office on local, state, and national levels throughout the U.S. Due to the principle of federalism, each state decided on voting and electoral rights in their jurisdiction. Thus, prior to 1920 voting rights for women were unevenly applied from state to state. In most women could vote at all. In some states and localities they could vote only for a few offices, such as school board representatives, county officers, and state office holders. In a very few states and territories, where they had been given complete suffrage rights, women could cast ballots for candidates on all levels. Women took up the challenge to run for public office both when they could not vote (relying solely on male voters), and when they finally gained partial or complete suffrage. We estimate that approximately 4,000 women ran in almost 6,000 campaigns by 1920. Currently, our database contains information for 2,300 women, who ran in over 3,000 campaigns. Using traditional and digital resources the Her Hat Was in the Ring project identifies these women candidates providing biographical information for each woman, information about her campaign(s), party affiliation, photographs when available, lists of selected resources, and other aggregate data, via a freely-available, web-based content management system

Digital History, Digital Sources, Digital Display: The Her Hat Was in the Ring Project on U.S. Women Who Ran for Political Office Before 1920

In the second half of the nineteenth century and through the first two decades of the twentieth century thousands of women ran for political office on local, state, and national levels throughout the U.S. Due to the principle of federalism, each state decided on voting and electoral rights in their jurisdiction. Thus, prior to 1920 voting rights for women were unevenly applied from state to state. In most women could vote at all. In some states and localities they could vote only for a few offices, such as school board representatives, county officers, and state office holders. In a very few states and territories, where they had been given complete suffrage rights, women could cast ballots for candidates on all levels. Women took up the challenge to run for public office both when they could not vote (relying solely on male voters), and when they finally gained partial or complete suffrage. We estimate that approximately 4,000 women ran in almost 6,000 campaigns by 1920. Currently, our database contains information for 2,300 women, who ran in over 3,000 campaigns. Using traditional and digital resources the Her Hat Was in the Ring project identifies these women candidates providing biographical information for each woman, information about her campaign(s), party affiliation, photographs when available, lists of selected resources, and other aggregate data, via a freely-available, web-based content management system

The Preservation Challenge: A Guide to Conserving Library Materials (Book Review)

published or submitted for publicatio

Finding agriculture among biodiversity: metadata in practice

The breadth of biodiversity literature available through the Biodiversity Heritage Library (BHL) is potentially of great use to agricultural research. It provides access to literature drawn from across the world, and its archives document the Earth as it was one hundred years ago and more. However, this strength of BHL is also its weakness: the breadth of coverage of BHL can complicate finding relevant literature. In this short paper, we will explore the practical issues arising from attempting to filter out relevant legacy literature to support agricultural research

Quasar Proper Motions and Low-Frequency Gravitational Waves

We report observational upper limits on the mass-energy of the cosmological gravitational-wave background, from limits on proper motions of quasars. Gravitational waves with periods longer than the time span of observations produce a simple pattern of apparent proper motions over the sky, composed primarily of second-order transverse vector spherical harmonics. A fit of such harmonics to measured motions yields a 95%-confidence limit on the mass-energy of gravitational waves with frequencies <2e-9 Hz, of <0.11/h*h times the closure density of the universe.Comment: 15 pages, 1 figure. Also available at http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/index.htm

Noise in the Cross-Power Spectrum of the Vela Pulsar

We compare the noise in interferometric measurements of the Vela pulsar from ground- and space-based antennas with theoretical predictions. The noise depends on both the flux density and the interferometric phase of the source. Because the Vela pulsar is bright and scintillating, these comparisons extend into both the low and high signal-to-noise regimes. Furthermore, our diversity of baselines explores the full range of variation in interferometric phase. We find excellent agreement between theoretical expectations and our estimates of noise among samples within the characteristic scintillation scales. Namely, the noise is drawn from an elliptical Gaussian distribution in the complex plane, centered on the signal. The major axis, aligned with the signal phase, varies quadratically with the signal, while the minor axis, at quadrature, varies with the same linear coefficients. For weak signal, the noise approaches a circular Gaussian distribution. Both the variance and covariance of the noise are also affected by artifacts of digitization and correlation. In particular, we show that gating introduces correlations between nearby spectral channels

VLBA Imaging of the OH Maser in IIIZw35

We present a parsec-scale image of the OH maser in the nucleus of the active galaxy IIIZw35, made using the Very Long Baseline Array at a wavelength of 18 cm. We detected two distinct components, with a projected separation of 50 pc (for D=110 Mpc) and a separation in Doppler velocity of 70 km/s, which contain 50% of the total maser flux. Velocity gradients within these components could indicate rotation of clouds with binding mass densities of ~7000 solar masses per cubic parsec, or total masses of more than 500,000 solar masses. Emission in the 1665-MHz OH line is roughly coincident in position with that in the 1667-MHz line, although the lines peak at different Doppler velocities. We detected no 18 cm continuum emission; our upper limit implies a peak apparent optical depth greater than 3.4, assuming the maser is an unsaturated amplifier of continuum radiation.Comment: 10 pages, 3 figure