Energetic proton spectra in the 11 June 1991 solar flare

The June 11, 1991 gamma-ray flare seen by the Compton Gamma-ray Observatory (CGRO) displays several features that make it a dynamic and rich event. It is a member of a class of long duration gamma-ray events with both 2.223 MeV and greater than 8 MeV emission for hours after the impulsive phase. It also contains an inter-phase between the impulsive and extended phases that presents a challenge to the standard gamma-ray line (GRL) flare picture. This phase has strong 2.223 MeV emission and relatively weak 4.44 MeV emission indicative of a very hard parent proton spectrum. However, this would indicate emission greater than 8 MeV, which is absent from this period. We present the application of new spectroscopy techniques to this phase of the flare in order to present a reasonable explanation for this seemly inconsistent picture

Gamma ray measurements of the 1991 November 15 solar flare

The 1991 November 15 X1.5 flare was a well observed solar event. Comprehensive data from ground-based observatories and spacecraft provide the basis for a contextual interpretation of gamma-ray spectra from the Compton Gamma Ray Observatory (CGRO). In particular, spectral, spatial, and temporal data at several energies are necessary to understand the particle dynamics and the acceleration mechanism(s) within this flare. X-ray images, radio, Ca XIX data and magnetograms provide morphological information on the acceleration region [4,5], while gamma-ray spectral data provide information on the parent ion spectrum. Furthermore, time profiles in hard X-rays and gamma-rays provide valuable information on temporal characteristics of the energetic particles. We report the results of our analysis of the evolution of this flare as a function of energy (∼25 keV–2.5 MeV) and time. These results, together with other high energy data (e.g. from experiments on Yohkoh, Ulysses, and PVO) may assist in identifying and understanding the acceleration mechanism(s) taking place in this event

Methodology for fitting and updating predictive accident models with trend [forthcoming]

Reliable predictive accident models (PAMs) have a variety of important uses in traffic safety research and practice. They are used to help identify sites in need of remedial treatment, in the design of transport schemes to assess safety implications, and to estimate the effectiveness of remedial treatments. The PAMs currently in use in the UK are now quite old; the data used in their development was gathered up to 30 years ago. Many changes have occurred over that period in road and vehicle design, in road safety campaigns and legislation, and the national accident rate has fallen substantially. It seems unlikely that these aging models can be relied upon to provide accurate and reliable predictions of accident frequencies on the roads today. This paper addresses a number of methodological issues that arise in seeking practical and efficient ways to update PAMs. Models for accidents on rural single carriageway roads have been chosen to illustrate these issues, including the choice of distributional assumption for overdispersion, the choice of goodness of fit measures, questions of independence between observations in different years, and between links on the same scheme, the estimation of trends in the models, the uncertainty of predictions, as well as considerations about the most efficient and convenient ways to fit the required models, given the considerable advances that have been seen in statistical computing software in recent years

Scientific objectives and first results from COMPTEL

The imaging Compton telescope (COMPTEL) is the first imaging telescope in space to explore the MeV gamma ray range. At present it is performing a complete sky survey. In later phases of the mission, selected celestial objects will be studied in more detail. Targets of special interest in the COMPTEL energy range are radio pulsars, X-ray binaries, novae, supernova remnants, molecular clouds, and the interstellar medium within the Milky Way, as well as the nuclei of active galaxies, supernovae, and the diffuse cosmic background radiation in extragalactic space. The first four months of operation demonstrated that COMPTEL basically performs as expected. The Crab is clearly seen at its proper position in the first images of the anticenter region of the Galaxy. The Crab pulsar lightcurve was measured with unprecedented accuracy. The quasar 3C273 was seen for the first time at MeV-energies. Several cosmic bursts within the COMPTEL field of view could be located to an accuracy of about 1 degree. On June 9, 11, and 15, 1991 COMPTEL observed gamma ray (continuum and line) emission from three solar flares. Neutrons were also detected from the June 9 flare. At the present state of analysis, COMPTEL achieves the prelaunch predictions of its sensitivity within a factor of 2. Based on the present performance of COMPTEL, the team is confident that COMPTEL will fulfill its primary mission of surveying and exploring the MeV sky

Gauge Theory for the Rate Equations: Electrodynamics on a Network

Systems of coupled rate equations are ubiquitous in many areas of science, for example in the description of electronic transport through quantum dots and molecules. They can be understood as a continuity equation expressing the conservation of probability. It is shown that this conservation law can be implemented by constructing a gauge theory akin to classical electrodynamics on the network of possible states described by the rate equations. The properties of this gauge theory are analyzed. It turns out that the network is maximally connected with respect to the electromagnetic fields even if the allowed transitions form a sparse network. It is found that the numbers of degrees of freedom of the electric and magnetic fields are equal. The results shed light on the structure of classical abelian gauge theory beyond the particular motivation in terms of rate equations.Comment: 4 pages, 2 figures included, v2: minor revision, as publishe

Data analysis of the COMPTEL instrument on the NASA gamma ray observatory

The Compton imaging telescope (COMPTEL) on the Gamma Ray Observatory (GRO) is a wide field of view instrument. The coincidence measurement technique in two scintillation detector layers requires specific analysis methods. Straightforward event projection into the sky is impossible. Therefore, detector events are analyzed in a multi-dimensional dataspace using a gamma ray sky hypothesis convolved with the point spread function of the instrument in this dataspace. Background suppression and analysis techniques have important implications on the gamma ray source results for this background limited telescope. The COMPTEL collaboration applies a software system of analysis utilities, organized around a database management system. The use of this system for the assistance of guest investigators at the various collaboration sites and external sites is foreseen and allows different detail levels of cooperation with the COMPTEL institutes, dependent on the type of data to be studied

Neutron induced background in the COMPTEL detector on the Gamma Ray Observatory

Interactions of neutrons in a prototype of the Compton imaging telescope (COMPTEL) gamma ray detector for the Gamma Ray Observatory were studied to determine COMPTEL's sensitivity as a neutron telescope and to estimate the gamma ray background resulting from neutron interactions. The IUCF provided a pulsed neutron beam at five different energies between 18 and 120 MeV. These measurements showed that the gamma ray background from neutron interactions is greater than previously expected. It was thought that most such events would be due to interactions in the upper detector modules of COMPTEL and could be distinguished by pulse shape discrimination. Rather, the bulk of the gamma ray background appears to be due to interactions in passive material, primarily aluminum, surrounding the D1 modules. In a considerable fraction of these interactions, two or more gamma rays are produced simultaneously, with one interacting in the D1 module and the other interacting in the module of the lower (D2) detector. If the neutron interacts near the D1 module, the D1 D2 time of flight cannot distinguish such an event from a true gamma ray event. In order to assess the significance of this background, the flux of neutrons in orbit has been estimated based on observed events with neutron pulse shape signature in D1. The strength of this neutron induced background is estimated. This is compared with the rate expected from the isotropic cosmic gamma ray flux

COMPTEL: Instrument description and performance

The imaging Compton telescope (COMPTEL) is one of the four gamma ray detectors aboard the Compton Gamma Ray Observatory (GRO). COMPTEL is sensitive to gamma rays from 800 keV to 30 MeV with a field of view of approximately 1 sr. Its angular resolution ranges between 1 and 2 degrees depending on the energy and incidence angle. The energy resolution of better than 10 percent FWHM enables COMPTEL to provide spectral resolution in the regime of astrophysical nuclear lines. The effective area varies typically from 10 to 50 cm(exp 2) depending on the energy and event selections made. In its telescope mode, COMPTEL is able to study a wide variety of objects, pointlike as well as extended in space. With 0.125 msec timing resolution, pulsed emission can be studied. In the single detector mode, COMPTEL uses two of its detectors to study the temporal spectral evolution of strong gamma ray bursts or transients

COMPTEL gamma-ray observations of the C4 solar flare on 20 January 2000

The “Pre-SMM” (Vestrand and Miller 1998) picture of gamma-ray line (GRL) flares was that they are relatively rare events. This picture was quickly put in question with the launch of the Solar Maximum Mission (SMM). Over 100 GRL flares were seen with sizes ranging from very large GOES class events (X12) down to moderately small events (M2). It was argued by some (Bai 1986) that this was still consistent with the idea that GRL events are rare. Others, however, argued the opposite (Vestrand 1988; Cliver, Crosby and Dennis 1994), stating that the lower end of this distribution was just a function of SMM’s sensitivity. They stated that the launch of the Compton Gamma-ray Observatory (CGRO) would in fact continue this distribution to show even smaller GRL flares. In response to a BACODINE cosmic gamma-ray burst alert, COMPtonTELescope on the CGRO recorded gamma rays above 1 MeV from the C4 flare at 0221 UT 20 January 2000. This event, though at the limits of COMPTEL’s sensitivity, clearly shows a nuclear line excess above the continuum. Using new spectroscopy techniques we were able to resolve individual lines. This has allowed us to make a basic comparison of this event with the GRL flare distribution from SMM and also compare this flare with a well-observed large GRL flare seen by OSSE