Ιανουάριος 2016

Post date: Jan 12, 2016 8:13:19 AM

08/01/2016, 16:30

Μαρία Πετροπούλου

Title: "Correlated neutrino and photon emission during γ-ray flares from the blazar Mrk 421: predictions for IceCube"

Abstract: Blazars, being highly variable sources across the electromagnetic spectrum, may serve as promising targets for high-energy neutrino detection, especially during periods of flaring activity. Using as a testbed the nearby blazar Mrk 421, we present a detailed hadronic model of its emission during a 13-day flaring period. We calculate the expected muon neutrino event rate observed by IceCube at energies >1PeV, and compare it with that expected from a longer, yet non-flaring, period of emisison. After applying the derived correlation between the >1PeV neutrino and 0.1-300 GeV emission to the long-term Fermi/LAT light curve of Mrk 421, we calculate the expected number of muon neutrino events above 1 PeV within 5 years of full IceCube detector livetime and discuss the implications of the results.

15/01/2016, 16:00

Γιώργος Βασιλόπουλος

Title: "The X-ray dust scattered rings of the black hole low mass binary V404 Cyg"

Abstract: We report on the first detection of X-ray dust scattered rings from the Galactic low mass X-ray binary V404 Cyg. The observation of the system with Swift/XRT on June 30 2015 revealed the presence of five concentric ring-like structures centred at the position of V404 Cyg. Follow-up Swift/XRT observations allowed a time-dependent study of the X-ray rings. Assuming that these are the result of small-angle, single X-ray scattering by dust grains along the line of sight, we find that their angular size scales as θ ~ t^1/2 in agreement with theoretical predictions. The dust grains are concentrated in five dust layers located at about 2.12, 2.05, 1.63, 1.50 and 1.18 kpc from the observer. These coincide roughly with locations of enhanced extinction as determined by infrared photometry. Assuming that the grain size distribution is described by a generalized Mathis-Rumpl-Nordsieck model, we find that the power-law index of the most distant cloud is q~4.4, while q ~ 3.5-3.7 in all other clouds. We constrain at a 3σ level the maximum grain size

of the intermediate dust layers in the range 0.16-0.20μm and set a lower limit of ~0.2μm in the other clouds. Hints of an exponential cutoff at the angular intensity profile of the outermost X-ray ring suggest that the smallest grains have sizes 0.01μm < a_min < 0.03μm. Based on the relative ratios of dust column densities we find the highest dust concentration at ~1.6~kpc. Our results indicate a gradient in the dust properties within 1 kpc from V404 Cyg.

22/01/2016, 16:30

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