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&

Calibration of Low-Frequency, Wide-Field Radio Interferometers Using Delay/Delay-Rate Filtering

We present a filtering technique that can be applied to individual baselines of wide-bandwidth, wide-field interferometric data to geometrically select regions on the celestial sphere that contain primary calibration sources. The technique relies on the Fourier transformation of wide-band frequency spectra from a given baseline to obtain one-dimensional "delay images", and then the transformation of a time-series of delay images to obtain two-dimensional "delay/delay-rate images." Source selection is possible in these images given appropriate combinations of baseline, bandwidth, integration time and source location. Strong and persistent radio frequency interference (RFI) limits the effectiveness of this source selection owing to the removal of data by RFI excision algorithms. A one-dimensional, complex CLEAN algorithm has been developed to compensate for RFI-excision effects. This approach allows CLEANed, source-isolated data to be used to isolate bandpass and primary beam gain functions. These techniques are applied to data from the Precision Array for Probing the Epoch of Reionization (PAPER) as a demonstration of their value in calibrating a new generation of low-frequency radio interferometers with wide relative bandwidths and large fields-of-view.Comment: 17 pages, 6 figures, 2009AJ....138..219

Strategies to increase the 4-year graduation rate of engineering students at XXX university

San Jos© State University (SJSU) has implemented several strategies to increase its graduation and retention rates. One of these strategies was block scheduling. Incoming freshmen students in the College of Engineering were put into at least two classes with the same students so that they formed a learning community. This effort began in Fall 2015 and the first four-year graduates received their degrees in 2019. Overall, the percent of engineering students graduating in four years has increased from 7.3% for Fall 2013 freshmen to 17.4% for Fall 2015 freshmen, our first cohort in this project. We surveyed all the engineering students scheduled to graduate either in Spring or Summer 2019 and asked them about their experiences at SJSU. This paper will discuss the results of a survey of the engineering students who graduated in four years and what helped them graduate in a timely manner. In addition, we will analyze the differences in four-year completion rates among different groups of students

Detection of Circular Polarization in the Galactic Center Black Hole Candidate Sagittarius A*

We report here the detection of circular polarization in the Galactic Center black hole candidate, Sagittarius A*. The detection was made at 4.8 GHz and 8.4 GHz with the Very Large Array. We find that the fractional circular polarization at 4.8 GHz is $m_c=-0.36 \pm 0.05$ and that the spectral index of the circular polarization is $\alpha=-0.6 \pm 0.3$ ($m_c \propto \nu^{\alpha}$). The systematic error in $m_c$ is less than 0.04% at both frequencies. In light of our recent lower limits on the linear polarization in Sgr A*, this detection is difficult to interpret with standard models. We consider briefly whether scattering mechanisms could produce the observed polarization. Detailed modeling of the source and the scattering medium is necessary. We propose a simple model in which low energy electrons reduce linear polarization through Faraday depolarization and convert linear polarization into circular polarization. Circular polarization may represent a significant new parameter for studying the obscured centimeter wavelength radio source in Sgr A*.Comment: ApJL accepted, 11 pages including 1 figur

A New Class of Pulsars

In 1939, seven years after the discovery of the neutron, nuclear physicists constructed the first models of a "neutron star." Stable results were found with masses comparable to the Sun's radii of about 10 km. Binary pulsars, pulsars with millisecond periods and pulsars in globular clusters are distinguished by their evolutionary histories, and are providing tools for fundamental tests of physics