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

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

Monitoring commercial starter culture development in presence of red grape pomace powder to produce polyphenol-enriched fresh ovine cheeses at industrial scale level

Red grape Nero d'Avola cultivar grape pomace powder (GPP) was applied during fresh ovine cheese production in order to increase polyphenol content. Before cheeses were produced, the bacteria of a freeze-dried commercial starter culture were isolated and tested in vitro against GPP. Two dominant strains, both resistant to GPP, were identified. Thestarter culture was inoculated in pasteurized ewe's milk and the curd was divided into two bulks, one added with 1% (w/w) GPP and another one GPP-free. GPP did not influence the starter culture development, since lactic acid bacteria (LAB) counts were 109 CFU/g in both cheeses at 30 d. To exclude the interference of indigenous LAB, the pasteurized milk was analyzed, and several colonies of presumptive LAB were isolated, purified and typed. Four strains were allotted into Enterococcus and Lacticaseibacillus genera. The direct comparison of the polymorphic profiles of cheese bacteria evidenced the dominance of the starter culture over milk LAB. The addition of GPP increased cheese total phenolic compounds by 0.42 g GAE/kg. Sensory evaluation indicated that GPP-enriched cheese was well appreciated by the judges, providing evidence that GPP is a suitable substrate to increase the availability of total phenolic content in fresh ovine cheese

Cladodes of Opuntia ficus-indica (L.) as source of bioactive compounds in dairy products

Recently, the interest on improving livestock products' nutraceutical profiles by sustainable feeding systems has increased. In this context, the overall quality and, in particular, the nutraceutical profile of dairy products obtained by 16 lactating Cinisara cows fed integrated in dry season with Opuntia ficus-indica cladodes, were investigated. Two homogeneous groups of cows (milk yield: 6.3 ± 1.5 kg; body weight: 213 ± 55 kg) were in succession fed with 2 different diets (CON: pasture and wheat bran; OFI: pasture, wheat bran and cladodes), according to a 2 × 2 Latin square design. The bulk milk was used to make Caciotta cheeses, analyzed at 0, 15 and 30 storage days. Milk and cheeses samples were analyzed for chemical, physical and microbiological traits. On the final products, the nutraceutical and sensorial profiles, together with the antioxidant's capacity were also determined. On milk, only the urea content in individual samples was reduced in OFI. Considering the cheeses, the integration with cladodes did not influence the starter cultures development acted with 2 strains of S. thermophilus, but caused a higher content of polyphenols and a consequent greater antioxidant capacity, together with a change in the fatty acids profile. In particular, the caprylic, capric, lauric, myristic, and palmitic fatty acids were higher, as well as the petroselinic, vaccenic, rumenic, and α-linolenic fatty acids. Differently, the oleic and the γ-linolenic fatty acids were lower. The cheeses of OFI showed better overall acceptability, and a higher yellow color, odor intensities, and butter flavor. The multivariate analysis well distinguished the cheeses belonging to the 2 groups. Further investigations should be conducted to formulate well balanced diets including cladodes for Cinisara lactating cows, but also to determine the content of other important bioactive compounds in fresh and in treated cladodes, as well as their effects on animals' welfare and their productions

A Thorough Investigation of the Microbiological, Physicochemical, and Sensory Properties of Ewe’s Yoghurt Fermented by a Selected Multi-Strain Starter Culture

This work was carried out with the aim to investigate the microbiological, physicochemical, and sensory properties of an innovative yoghurt produced from ewe’s milk. Experimental yoghurt productions were performed with a commercial freeze-dried starter preparation and a natural milk starter culture (NMSC) of Streptococcus thermophilus and Lactobacillus delbrueckii. The two yoghurts did not differ for colour parameters, showing an average value of lightness, redness, and yellowness of 94.99, −3.74, and 9.37, respectively. The yoghurt produced using the NMSC as a fermenting agent was characterised by a significantly lower fat percentage and a higher antioxidant potential than commercial starters. Microbiological analysis confirmed the safety of the final product and a level of living lactic acid bacteria of 108 CFU/g. Sensory analysis revealed some differences among yoghurts regarding unpleasant odour, homogeneity, and persistence in the mouth, but the yoghurt processed with NMSC was more appreciated. Thus, the production of ewe’s yoghurt fermented by a selected multi-strain starter culture represents an interesting strategy to enlarge the functional ovine dairy product portfolio

Pulsar studies with GRO-COMPTEL

Pulsar measurements performed by the experiment COMPTEL, aboard the Compton Gamma Ray Observatory, are described. The main results refer to the Crab and Vela pulsars whose pulse shape characteristics are given in some detail and light curves are compared with those above 50 MeV, as observed by the COS-B satellite. No other gamma-ray pulsars have been detected to date by COMPTEL, the upper limit on the pulsed signal from Geminga being compatible with indications by other experiments. © 1993

COMPTEL images locations of gamma‐ray bursts

The γ‐ray telescope COMPTEL onboard GRO has so far located 6 gamma‐ray bursts which occurred in its ∼1 sr field of view. The positions of the sources were derived by the maximum‐entropy method. Systematic and statistical uncertainties for the four strongest bursts are approximately 1° to 2° and can be reduced in future analysis

COMPTEL observations of cosmic gamma‐ray bursts

The imaging γ‐ray telescope COMPTEL on board NASA’s Compton Gamma‐Ray Observatory (GRO) has observed many cosmic gamma‐ray bursts during the early mission phase of GRO. COMPTEL records time‐resolved burst spectra over 0.1 MeV to 10 MeV energies, and, for the first time, produces direct single‐telescope gamma‐ray images (0.8–30 MeV) of cosmic gamma‐ray bursts occurring in its 1 sr field of field