Blazar spectral variability as explained by a twisted inhomogeneous jet

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the observed emitting knots or jet regions have also been suggested as an explanation of flaring events and can also explain specific properties of blazar emission, such as intra-day variability, quasi-periodicity and the delay of radio flux variations relative to optical changes. Such a geometric interpretation, however, is not universally accepted because alternative explanations based on changes in physical conditions-such as the size and speed of the emitting zone, the magnetic field, the number of emitting particles and their energy distribution-can explain snapshots of the spectral behaviour of blazars in many cases. Here we report the results of optical-to-radio-wavelength monitoring of the blazar CTA 102 and show that the observed long-term trends of the flux and spectral variability are best explained by an inhomogeneous, curved jet that undergoes changes in orientation over time. We propose that magnetohydrodynamic instabilities or rotation of the twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the extreme optical outburst of 2016-2017 (brightness increase of six magnitudes) occurred when the corresponding emitting region had a small viewing angle. The agreement between observations and theoretical predictions can be seen as further validation of the relativistic beaming theory.

Imaging soft x-rays using a microchannel plate

The GOLDHELOX Project is a student run project to construct a robotic solar telescope that will be used to take images of the sun in the soft X-ray region (171–181Å) of the spectrum. The optical system uses a microchannel plate (MCP) detector. We tested the MCP to familiarize ourselves with and verify that MCP's can be used to image soft X-rays. Soft X-rays were created by a Manson source attached to a proportional counter to determine the amount of emitted X-rays detected by the MCP. The voltages on the MCP were varied to observe responses of varying voltage differences. Most of the observations were visible observations along with images made by a 35 mm camera with a telephoto lens. We found the 1000 V difference to produce the strongest and clearest images.

NASA G-133 "GoldHelox": A Project Update

NASA G-133, also known as the "GoldHelox Project", is a fully autonomous, soft X-ray, solar telescope designed for use on board the space shuttle. Conceived, designed and built by students at Brigham Young University, it will image the sun with a spatial resolution of 2.5 arc-seconds with a temporal resolution of one second. The instrument will image X-rays with wavelengths between 171Å and 181Å coming from highly ionized Fe lines in the sun's corona. Data will consist of several hundred high resolution photographs that will help in understanding the initial phases of solar flares, and the relationship between solar flares and the physics of the coronal-chromospheric transition region. This paper briefly outlines the project's goals, gives a brief overview of the construction and operation of the instrument and addresses the unique aspects of running a predominantly undergraduate research project. It summarizes the lessons learned to date, and the current project status.

Goldhelox: a soft x-ray solar telescope

The Goldhelox Project is the construction and use of a near-normal incidence soft x-ray robotic solar telescope by undergraduate students at Brigham Young University. Once it is completed and tested, it will be deployed from a Get-Away-Special (GAS) canister in the bay of a space shuttle. It will image the sun at a wavelength of 171-181Å with a time resolution of 1 sec and a spatial resolution of 2.5 arcsec. The observational bandpass was chosen to image x-rays from highly ionized coronal Fe lines. The data will be an aid in better understanding the beginning phases of solar flares and how flaring relates to the physics of the corona-chromosphere transition region. Goldhelox is tentatively scheduled to fly on a space shuttle sometime in 1995 or 1996. This paper outlines the project goals, basic instrument design, and the unique aspects of making this an undergraduate endeavor.

The effects of topical and oral slow-release nitroglycerin on anterior myocardial infarction size assessed by precordial ST segment mapping

The effect of slow-release nitroglycerin and nitroglycerin ointment in reducing anterior myocardial infarction size was assessed in 18 patients by means of epicardial mapping. The sum of all ST elevations (sigma ST), the number of leads with ST elevations greater than 1 mm (NST), the sum of the ST segment elevations of those leads with ST elevations greater than 1 mm (sigma STmm) and the average ST segment elevations (ST) were evaluated. No statistically significant difference between the two forms of nitroglycerin and placebo was found over a 72-h period. These data suggest that no benefit in terms of reduction in myocardial infarction size, assessed by epicardial mapping, is obtained from therapy with oral slow release nitroglycerin and nitroglycerin ointment.