Excess sub-millimetre emission from GRS 1915+105

We present the first detections of the black hole X-ray binary GRS 1915+105 at sub-millimetre wavelengths. We clearly detect the source at 350 GHz on two epochs, with significant variability over the 24 hr between epochs. Quasi-simultaneous radio monitoring indicates an approximately flat spectrum from 2 - 350 GHz, although there is marginal evidence for a minimum in the spectrum between 15 - 350 GHz. The flat spectrum and correlated variability imply that the sub-mm emission arises from the same synchrotron source as the radio emission. This source is likely to be a quasi-steady partially self-absorbed jet, in which case these sub-mm observations probe significantly closer to the base of the jet than do radio observations and may be used in future as a valuable diagnostic of the disc:jet connection in this source.Comment: 5 pages, 3 figures, accepted for publication in MNRA

Cygnus X-3 in outburst : quenched radio emission, radiation losses and variable local opacity

We present multiwavelength observations of Cygnus X-3 during an extended outburst in 1994 February - March. Intensive radio monitoring at 13.3, 3.6 & 2.0 cm is complemented by observations at (sub)millimetre and infrared wavelengths, which find Cyg X-3 to be unusually bright and variable, and include the first reported detection of the source at 0.45 mm. We report the first confirmation of quenched radio emission prior to radio flaring independent of observations at Green Bank. The observations reveal evidence for wavelength-dependent radiation losses and gradually decreasing opacity in the environment of the radio jet. We find that the radiation losses are likely to be predominantly inverse Compton losses experienced by the radio-emitting electrons in the strong radiation field of a luminous companion to the compact object. We interpret the decreasing opacity during the flare sequence as resulting from a decreasing proportion of thermal electrons entrained in the jet, reflecting a decreasing density in the region of jet formation. We present, drawing in part on the work of other authors, a model based upon mass-transfer rate instability predicting gamma-ray, X-ray, infrared and radio trends during a radio flaring sequence.Comment: LaTeX, 11 pages, 6 figures. Submitted to MNRA

Comparison of VLBI, TV and traveling clock techniques for time transfer

A three part experiment was conducted to develop and compare time transfer techniques. The experiment consisted of (1) a very long baseline interferometer (VLBI), (2) a high precision portable clock time transfer system between the two sites, and (3) a television time transfer. A comparison of the VLBI and traveling clock shows each technique can perform satisfactorily at the five nsec level. There was a systematic offset of 59 nsec between the two methods, which we attributed to a difference in epochs between VLBI formatter and station clock. The VLBI method had an internal random error of one nsec at the three sigma level for a two day period. Thus, the Mark II system performed well, and VLBI shows promise of being an accurate method of time transfer. The TV system, which had technical problems during the experiment, transferred time with a random error of about 50 nsec

MERLIN observations of relativistic ejections from GRS 1915+105

We present high resolution MERLIN radio images of multiple relativistic ejections from GRS 1915+105 in 1997 October / November. The observations were made at a time of complex radio behaviour, corresponding to multiple optically-thin outbursts and several days of rapid radio flux oscillations. The radio imaging resolved four major ejection events from the system. As previously reported from earlier VLA observations of the source, we observe apparent superluminal motions resulting from intrinsically relativistic motions of the ejecta. However, our measured proper motions are significantly greater than those observed on larger angular scales with the VLA. Under the assumption of an intrinsically symmetric ejection, we can place an upper limit on the distance to GRS 1915+105 of 11.2 +/- 0.8 kpc. Solutions for the velocities unambiguously require a higher intrinsic speed by about 0.1c than that derived from the earlier VLA observations, whilst the angle to the line-of-sight is not found to be significantly different. At a distance of 11 kpc, we obtain solutions of v = 0.98 (-0.05,+0.02)c and theta = 66 +/- 2 degrees. The jet also appears to be curved on a scale which corresponds to a period of around 7 days. We observe significant evolution of the linear polarisation of the approaching component, with large rotations in position angle and a general decrease in fractional polarisation. The power input into the formation of the jet is very large, >10^38 erg/s at 11 kpc for a pair plasma. If the plasma contains a cold proton for each electron, then the mass outflow rate, >10^18 g/sec is comparable to inflow rates previously derived from X-ray spectral fits.Comment: 14 pages, 7 figures. Accepted for publication in MNRA

Simultaneous X-ray and Radio Monitoring of the Unusual Binary LSI+61 303: Measurements of the Lightcurve and High-Energy Spectrum

The binary system, LSI+61 303, is unusual both because of the dramatic, periodic, radio outbursts, and because of its possible association with the 100 MeV gamma-ray source, 2CG135+01. We have performed simultaneous radio and Rossi X-ray Timing Explorer X-ray observations at eleven intervals over the 26.5 day orbit, and in addition searched for variability on timescales ranging from milliseconds to hours. We confirm the modulation of the X-ray emission on orbital timescales originally reported by Taylor et al. (1996), and in addition we find a significant offset between the peak of the X-ray and radio flux. We argue that based on these results, the most likely X-ray emission mechanism is inverse Compton scattering of stellar photons off of electrons accelerated at the shock boundary between the relativistic wind of a young pulsar and the Be star wind. In these observations we also detected 2 -- 150 keV flux from the nearby low-redshift quasar QSO~0241+622. Comparing these measurements to previous hard X-ray and gamma-ray observations of the region containing both LSI+61 303 and QSO~0241+622, it is clear that emission from the QSO dominates.Comment: 23 pages, 6 figures, Accepted for publication in the Astrophysical Journa

Teacher Beliefs about Motivating and Teaching Students to Carry out Engineering Design Challenges: Some Initial Data

The present study examines middle school teachers’ beliefs about seven learning outcomes related to a project that involves developing and examining the effects of a set of engineering design modules constructed for use by middle school math and science teachers. Overall, the teachers involved in the intervention appear to believe they have the instructional skills, professional development, and resources to carry out the modules. Teachers from all of the schools (both intervention and comparison schools) for the most part valued the outcomes as important. Results of the study indicate that, although teachers believe they value and can obtain most of these outcomes; beliefs vary by school and other factors. One area where teachers do not seem strongly efficacious in some schools is that of fostering intrinsic motivation in their students. Teachers in one of the schools where the modules were implemented did not feel their students were capable of becoming intrinsically motivated. The implications for implementing engineering education in middle school of these beliefs and other attitudes are discussed

The substantive and practical significance of citation impact differences between institutions: Guidelines for the analysis of percentiles using effect sizes and confidence intervals

In our chapter we address the statistical analysis of percentiles: How should the citation impact of institutions be compared? In educational and psychological testing, percentiles are already used widely as a standard to evaluate an individual's test scores - intelligence tests for example - by comparing them with the percentiles of a calibrated sample. Percentiles, or percentile rank classes, are also a very suitable method for bibliometrics to normalize citations of publications in terms of the subject category and the publication year and, unlike the mean-based indicators (the relative citation rates), percentiles are scarcely affected by skewed distributions of citations. The percentile of a certain publication provides information about the citation impact this publication has achieved in comparison to other similar publications in the same subject category and publication year. Analyses of percentiles, however, have not always been presented in the most effective and meaningful way. New APA guidelines (American Psychological Association, 2010) suggest a lesser emphasis on significance tests and a greater emphasis on the substantive and practical significance of findings. Drawing on work by Cumming (2012) we show how examinations of effect sizes (e.g. Cohen's d statistic) and confidence intervals can lead to a clear understanding of citation impact differences