Spatial Variation in Microcystin concentrations in Nebraska Reservoirs

The purpose of this study was to see if there were spatial differences in microcystin concentrations within reservoirs and examine whether more than one sample needs to be collected to more accurately represent water quality conditions. The Nebraska Department of Environmental Quality (NDEQ) collects water samples from beach or shoreline areas where sampling is simple and people are more likely to be in direct contact with the water. I hypothesized that Microcystis concentrations would vary spatially in local reservoirs and that beach sampling may not accurately represent toxin conditions for the entire reservoir. This is significant at the time of sampling. For example, if prevailing winds blow towards the sampling site, toxin producing cyanobacteria may accumulate along the shoreline and give a false-positive reading and vice versa

Spatial Variation in Microcystin concentrations in Nebraska Reservoirs

The purpose of this study was to see if there were spatial differences in microcystin concentrations within reservoirs and examine whether more than one sample needs to be collected to more accurately represent water quality conditions. The Nebraska Department of Environmental Quality (NDEQ) collects water samples from beach or shoreline areas where sampling is simple and people are more likely to be in direct contact with the water. I hypothesized that Microcystis concentrations would vary spatially in local reservoirs and that beach sampling may not accurately represent toxin conditions for the entire reservoir. This is significant at the time of sampling. For example, if prevailing winds blow towards the sampling site, toxin producing cyanobacteria may accumulate along the shoreline and give a false-positive reading and vice versa

Spatial Variation in Microcystin concentrations in Nebraska Reservoirs

The purpose of this study was to see if there were spatial differences in microcystin concentrations within reservoirs and examine whether more than one sample needs to be collected to more accurately represent water quality conditions. The Nebraska Department of Environmental Quality (NDEQ) collects water samples from beach or shoreline areas where sampling is simple and people are more likely to be in direct contact with the water. I hypothesized that Microcystis concentrations would vary spatially in local reservoirs and that beach sampling may not accurately represent toxin conditions for the entire reservoir. This is significant at the time of sampling. For example, if prevailing winds blow towards the sampling site, toxin producing cyanobacteria may accumulate along the shoreline and give a false-positive reading and vice versa

COMPTEL observations of the quasar PKS 0528+134 during the first 3.5 years of the CGRO mission

The COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy range 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have been analyzed. During the first two years PKS 0528+134 was most significantly detected at energies above 3 MeV. During the last year there is only evidence for the quasar at energies below 3 MeV indicating a spectral change. The time-averaged COMPTEL energy spectrum between 0.75 MeV and 30 MeV is well represented by a power-law shape. Spectra collected from different observational periods reveal different power-law shapes: a hard state during flaring observations reported by EGRET, and a soft state otherwise. The combined simultaneous EGRET and COMPTEL spectra indicate these two spectral states as well. During low intensisty gamma-ray phases no spectral break is obvious from the combined COMPTEL and EGRET measurements. For the gamma-ray flaring phases however, the combined COMPTEL and EGRET data require a spectral bending at MeV-energies. By fitting broken power-law functions the best-fit values for the break in photon index range between 0.6 and 1.7, and for the break energy between ~5 MeV and ~20 MeV. Because the flux values measured by COMPTEL below 3 MeV in both states are roughly equal, the observations would be consistent with an additional spectral component showing up during gamma-ray flaring phases of PKS 0528+134. Such a component could be introduced by e.g. a high-energy electron-positron population with a low-energy cutoff in their bulk Lorentz factor distribution. The multiwavelength spectrum of PKS 0528+134 for gamma-ray flaring phases shows that the major energy release across the entire electro-magnetic spectrum is measured at MeV-energies.Comment: 10 pages, 8 postscript figures, latex, to appear in: A&A 328, 33 (1997

SPI Measurements of the Diffuse Galactic Hard X-ray Continuum

INTEGRAL Spectrometer SPI data from the first year of the Galactic Centre Deep Exposure has been analysed for the diffuse continuum from the Galactic ridge. A new catalogue of sources from the INTEGRAL Imager IBIS has been used to account for their contribution to the celestial signal. Apparently diffuse emission is detected at a level ~10% of the total source flux. A comparison of the spectrum of diffuse emission with that from an analysis of IBIS data alone shows that they are consistent. The question of the contribution of unresolved sources to this ridge emission is still open.Comment: Proceedings of the 5th INTEGRAL Workshop, Munich 16-20 February 2004. ESA SP-552. Reference to Terrier et al. (2004) updated to include astro-ph versio

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

COMPTEL Observations of AGN at MeV-Energies

The COMPTEL experiment aboard CGRO, exploring the previously unknown sky at MeV-energies, has so far detected 10 Active Galactic Nuclei (AGN): 9 blazars and the radio galaxy Centaurus A. No Seyfert galaxy has been found yet. With these results COMPTEL has opened the field of extragalactic Gamma-ray astronomy in the MeV-band.Comment: 4 pages, 2 figures including 1 color plot, to appear in the Proceedings of the 3rd INTEGRAL Workshop "The Extreme Universe", held in Taormina, Italy, 14-18 September 199