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- Abeysekara, A. U., et al.
(författare)
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VERITAS and Fermi-LAT Observations of TeV Gamma-Ray Sources Discovered by HAWC in the 2HWC Catalog
- 2018
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing. - 0004-637X .- 1538-4357. ; 866:1
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Tidskriftsartikel (refereegranskat)abstract
- The High Altitude Water Cherenkov (HAWC) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100 GeV) gamma-ray sources based on 507 days of observation. Among these, 19 sources are not associated with previously known teraelectronvolt (TeV) gamma-ray sources. We have studied 14 of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1 TeV-30 TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected 14 new HAWC sources from our analysis of Fermi-LAT data for energies higher than 10 GeV. During the search, we detected gigaelectronvolt (GeV) gamma-ray emission coincident with a known TeV pulsar wind nebula, SNR G54.1+0.3 (VER J1930+188), and a 2HWC source, 2HWC J1930+188. The fluxes for isolated, steady sources in the 2HWC catalog are generally in good agreement with those measured by imaging atmospheric Cherenkov telescopes. However, the VERITAS fluxes for SNR G54.1+0.3, DA 495, and TeV J2032+4130 are lower than those measured by HAWC, and several new HAWC sources are not detected by VERITAS. This is likely due to a change in spectral shape, source extension, or the influence of diffuse emission in the source region.
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- Aartsen, M. G., et al.
(författare)
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Multiwavelength follow-up of a rare IceCube neutrino multiplet
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 607
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Tidskriftsartikel (refereegranskat)abstract
- On February 17, 2016, the IceCube real-time neutrino search identified, for the first time, three muon neutrino candidates arriving within 100 s of one another, consistent with coming from the same point in the sky. Such a triplet is expected once every 13.7 years as a random coincidence of background events. However, considering the lifetime of the follow-up program the probability of detecting at least one triplet from atmospheric background is 32%. Follow-up observatories were notified in order to search for an electromagnetic counterpart. Observations were obtained by Swift's X-ray telescope, by ASAS-SN, LCO and MASTER at optical wavelengths, and by VERITAS in the very-high-energy gamma-ray regime. Moreover, the Swift BAT serendipitously observed the location 100 s after the first neutrino was detected, and data from the Fermi LAT and HAWC observatory were analyzed. We present details of the neutrino triplet and the follow-up observations. No likely electromagnetic counterpart was detected, and we discuss the implications of these constraints on candidate neutrino sources such as gamma-ray bursts, core-collapse supernovae and active galactic nucleus flares. This study illustrates the potential of and challenges for future follow-up campaigns.
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- Pardo Jimenez, Raul, 1988, et al.
(författare)
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GPU powered ROSA analyzer
- 2013
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Ingår i: 42nd Annual International Conference on Parallel Processing, ICPP 2013; Lyon; France; 1 October 2013 through 4 October 2013. - 0190-3918. - 9780769551173 ; , s. 901-908
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Konferensbidrag (refereegranskat)abstract
- In this work we present the first version of ROSAA, Rosa Analyzer, using a GPU architecture. ROSA is a Markovian Process Algebra [11] able to capture pure non-determinism, probabilities and timed actions; Over it, a tool has been developed for getting closer to a fully automatic process of analyzing the behaviour of a system specified as a process of ROSA, so that, ROSAA [10] is able to automatically generate the part of the Labeled Transition System (occasionally the whole one), LTS in the sequel, in which we could be interested, but, since this is a very computationally expensive task, a GPU powered version of ROSAA which includes parallel processing capabilities, has been created to better deal with such generating process. As the conventional GPU processing loads are mainly focused on data parallelization over quite similar types of data, this work means a quite novel use of these kind of architectures, moreover the authors do not know any other formal model tool running over GPUs. ROSAA running starts with the Syntactic analysis so generating a layered structure suitable to, afterwards, apply the Operational Semantics transition rules in the easiest way. Since from each specification/state more than one rule could be applied, this is the key point at which GPU should provide its benefits, i.e., allowing to generate all the new states reachable in a singlesemantics- step from a given one, at the same time through a simultaneous launching of a set of threads over the GPU platform. Although this establishes a step forward to the practical usefulness of such type of tools, the state-explosion problem arises indeed, so we are aware that reducing the size of the LTS will be sooner or later required, in this line the authors are working on an heuristics to properly prune an enough number of branches of the LTS, so making the task of generating it, more tractable.
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