Browsing by Author "Fermi/LAT Collaboration"
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Item Calorimetric neutrino expectations from bright blazar flares(Proceedings of Science, 2019-07-24) Kreter, Michael; Kadler, Matthias; Krauß, Felicia; Buson, Sara; Ojha, Roopesh; Mannheim, Karl; Wilms, Jörn; Böttcher, Markus; Fermi/LAT CollaborationBlazar jets are extreme environments, in which relativistic proton interactions with an ultraviolet photon field could give rise to photopion production. High-confidence associations of individual high-energy neutrinos with blazar flares could be achieved via spatially and temporally coincident detections. In 2017, the track-like, extremely high-energy neutrino event IC 170922A was found to coincide with increased γ-ray emission from the blazar TXS 0506+056, leading to the identification of the most promising neutrino source candidate so far. We test the chance coincidence of such events by calculating the expected number of neutrinos that can be detected by IceCube, based on a broadband parametrization of bright short-term blazar flares that were observed in the past 8 years by Fermi/LAT. We find that the integrated keV-to-GeV fluence of most individual blazar flares is far too small to yield a substantial Poisson probability for the detection of one or more neutrinos with IceCube. In contrast to such short-term flares that usually last only a few days or less, TXS0506+056 did show a major outburst that lasted several months, giving rise to a much higher fluence than most short blazar flares. We show, based on the calorimetric argumentation presented in this work, that the association of the IC 170922A neutrino with TXS 0506+056 is energetically plausible at a significance level of about 3.5 sigma. We further discuss strategies to search for more significant associations in future data unblindings of IceCube and KM3NeT.Item Search for high-redshift blazars with Fermi/LAT(Proceedings of Science, 2019-07-24) Kreter, Michael; Kadler, Matthias; Krauß, Felicia; Buson, Sara; Ojha, Roopesh; Wilms, Jörn; Böttcher, Markus; Fermi/LAT CollaborationHigh-redshift blazars (z ≥ 2.5) are one of the most powerful classes of γ-ray sources in the Universe. These objects possess the highest jet powers and luminosities and have black-hole masses often in excess of 10⁹ solar masses. In addition, high-redshift blazars are important cosmological probes and serve as test objects for blazar evolution models. Due to their large distance, their high-energy emission peaks are often downshifted to energies below the GeV range, which makes them difficult to study with Fermi/LAT and only the very brightest objects are detectable. Hence, only a small number of high-redshift blazars could be detected with Fermi/LAT so far. In this work, we present a strategy to increase the detection statistics at redshift z ≥ 2.5 via a search for flaring events in high-redshift γ-ray blazars whose long-term flux is just below the sensitivity limit of Fermi/LAT. Seven previously GeV undetected high-redshift blazars have been identified from their bright monthly outburst periods, while more detections are expected in the future.Item Swift Follow-up of the Gamma-ray Detection of 4C +50.11(2014-02-11) Krauss, Felicia; Carpenter, Bryce; Ojha, Roopesh; Kadler, Matthias; Fermi/LAT Collaboration; Wilms, JoernItem Swift Follow-up of the Gamma-ray Flare in PKS 2142-75(2014-06-07) Krauss, F.; Ciprini, S.; Ojha, R.; Kadler, M.; Fermi/LAT Collaboration