Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory

Data from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius $A$. Also the events detected simultaneously by the surface and fluorescence detectors (the `hybrid' data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction.Comment: Matches published versio

Mouse Chromosome 11

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46996/1/335_2004_Article_BF00648429.pd

Observation of a sudden cessation of a very-high-energy gamma-ray flare in PKS 1510-089 with H.E.S.S. and MAGIC in May 2016

The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complex multiwavelength behavior, and is one of only a few FSRQs detected at very high energy (VHE, E >100 GeV) -rays. VHE -ray observations with H.E.S.S. and MAGIC during late May and early June 2016 resulted in the detection of an unprecedented flare, which reveals for the first time VHE -ray intranight variability in this source. While a common variability timescale of 1.5 hr is found, there is a significant deviation near the end of the flare with a timescale of ∼ 20 min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, curvature is detected in the VHE -ray spectrum of PKS 1510-089, which is fully explained through absorption by the extragalactic background light. Optical R-band observations with ATOM reveal a counterpart of the -ray flare, even though the detailed flux evolution differs from the VHE lightcurve. Interestingly, a steep flux decrease is observed at the same time as the cessation of the VHE flare. In the high energy (HE, E >100 MeV) -ray band only a moderate flux increase is observed with Fermi-LAT, while the HE -ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the -ray spectrum indicates that the emission region is located outside of the BLR. Radio VLBI observations reveal a fast moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located ∼ 50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this correlation is indeed true, VHE rays have been produced far down the jet where turbulent plasma crosses a standing shock.Accepted manuscrip

Effects of forest disturbance and regeneration on net precipitation and soil water dynamics in tropical montane rain forest on Mount Kilimanjaro, Tanzania

© Cambridge University Press 2010. The montane rain forest belt on Mt. Kilimanjaro forms an important water source for northern Tanzania that is threatened by both logging and fire. The aim of this study was to investigate consequences of forest fragmentation on various aspects of the water cycle. Soil properties, rainfall, throughfall, and soil water suction were analyzed for mature forest, secondary forest patches, and large clearings. A total of 10 plots located on the south-western slopes of the mountain between 2100 and 2300 m.a.s.l. were monitored from May 2000 until June 2002. Annual rainfall amounts ranged from 2000–2600 mm and showed high spatial and inter-annual variability. Rainfall interception ranged from 3% to 9% of incident rainfall in clearings to a maximum of 32% in forests. In general, soils under mature forest were wettest and showed only minor moisture fluctuations through the year. Soils of secondary forest sites were driest and soil water suction exhibited the largest fluctuations. The difference between the two forest types may reflect a combination of differences in interception, evaporation from the forest floor, and transpiration, because ventilation and radiation penetration can be expected to be enhanced in fragmented secondary forest. In clearings the higher throughfall and presumably lower transpiration rates led to moister conditions compared to adjacent secondary forest sites. Top-soil sand contents of the Andisols differed between sites, with disturbed sites having higher sand contents and consequently lower water contents at similar soil water suctions than did mature forest sites. […]