The EGRET observations have been used to obtain upper limits for the efficiency eta of conversion of MSP spin-down power into hard gamma rays. These expectations have been reinforced by recent discoveries of a substantial number of radio MSPs in several clusters for example, 11 have been found in 47 Tucanae (Manchester et al.). Model predictions of the total number of pulsars range in the hundreds for some clusters. However, a large number of MSPs are expected in globular cluster cores where the formation rate of accreting binary systems is high. To date, no high-energy emission has been detected from an individual MSP. Several theoretical models suggest that MSPs may be sources of high-energy gamma radiation emitted either as primary radiation from the pulsar magnetosphere or as secondary radiation generated by conversion into photons of a substantial part of the relativistic e(+/-) pair wind expected to flow from the pulsar. The observations were done as part of an all-sky survey by the energetic Gamma Ray Experiment Telescope ( EGRET) on the Compton Gamma Ray Observatory ( CGRO) during Phase I of the CGRO mission (1991 June to 1992 November). We report upper limits to the high-energy gamma-ray emission from the millisecond pulsars (MSPs) in a number of globular clusters. Measurements made during that month and in the subsequent sky survey phase have verified that the instrument time resolution, angular resolution, and gamma ray detection efficiency are all within nominal limits.ĮGRET upper limits to the high-energy gamma-ray emission from the millisecond pulsars in nearby globular clusters The EGRET instrument was activated on April 15, and the first month of operations was devoted to verification of the instrument performance. On April 5, 1991, the Space Shuttle Atlantis carried the Compton Gamma Ray Observatory ( CGRO) into orbit, deploying the satellite on April 7. Performance of the EGRET astronomical gamma ray telescope Processing of the data can not occur until a complete exposure has been accumulated for each covering. The column headings are defined as follows: 'Coverings' = number of observations to cover the error circle 'SubPtg' = total number of sub-pointings to observe all of the coverings 'Rec'd' = number of individual sub-pointings received to date 'CompFlds' = number of individual coverings for which the requested complete exposure has been received. This project was awarded ROSAT observing time for four unidentified EGRET sources, summarized in the table. As a result, each pointing is broken into one or more sub-pointings of various exposure times. The scheduling of ROSAT observations is carried out to maximize the efficiency of the total schedule. Hence, a number (>4) of ROSAT pointings must be obtained for each EGRET source to cover the field. Each ROSAT field is about 30 deg in diameter. Each error circle is a degree or larger in diameter. The critical items in the project are the individual ROSAT observations that are used to cover the 99% error circle of the unidentified EGRET source. This project was awarded funding from the CGRO program to support ROSAT and ground-based observations of unidentified sources from data obtained by the EGRET instrument on the Compton Gamma-Ray Observatory.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |