First detection of GeV emission from an ultraluminous infrared galaxy: Arp 220 as seen with the Fermi Large Area Telescope

Cosmic rays (CRs) in starburst galaxies produce high energy gamma-rays by colliding with the dense interstellar medium (ISM). Arp 220 is the nearest ultra luminous infrared galaxy (ULIRG) that has star-formation at extreme levels, so it has long been predicted to emit high-energy gamma-rays. However, no evidence of gamma-ray emission was found despite intense efforts of search. Here we report the discovery of high-energy gamma-ray emission above 200 MeV from Arp 220 at a confidence level of $\sim 6.3 \sigma$ using 7.5 years of \textsl {Fermi} Large Area Telescope observations. The gamma-ray emission shows no significant variability over the observation period and it is consistent with the quasi-linear scaling relation between the gamma-ray luminosity and total infrared luminosity for star-forming galaxies, suggesting that these gamma-rays arise from CR interactions. As the high density medium of Arp 220 makes it an ideal CR calorimeter, the gamma-ray luminosity can be used to measure the efficiency of powering CRs by supernova (SN) remnants given a known supernova rate in Arp 220. We find that this efficiency is about $4.2\pm2.6\%$ for CRs above 1 GeV.Comment: Accepted by ApJL, 6 pages, 3 figure

Grey Critical Chain Project Scheduling Technique and Its Application

Based on the idea of Grey System and interval number coefficient notation, a Grey Critical Chain scheduling approach is studied. According to Grey system theory, the time of project or task completion can be considered as the object that extension is definite but intension is uncertain, which is coincident with the character of the project management. The Grey Critical Chain Scheduling Technique mainly aims at the single project time management, but the management idea can also be applied to the other knowledge areas of the project management. In this Technique, we improve the selection method of the buffer time in the Critical Chain, in order to obtain reasonable Feeding Buffer time and Project Buffer time. In this paper, we will use an example to discuss the Grey Critical Chain Scheduling Technique, compare Grey Critical Chain with Program Evaluation and Review Technique, Critical Chain and Fuzzy Critical Chain, analyze the advantages, disadvantages and applicable scope of their own. Key words: Critical Chain, Grey System, Interval Number, Schedule Management, Project Management Résumé: Sur la base de l’idée de Système Gris et la notation du coefficient de nombre d’intervalle, l’approche de pragrammtion d’une Chaîne Critique Grise est étudiée. Selon la théorie du Système Gris, le temps du projet ou de la tâche peut être considéré comme l’objet dont l’extention est définitive mais l’intention est incertaine, qui est conforme au caractère du management de projet. La Technique de Programmation de la Chaîne Critique Grise vise essentiellement le management du temps du projet simple, mais l’idée de management peut aussi être appliquée dans d’autres domaines du management de projet. Avec cette technique, nous améliorons la méthode de sélection du temps d’amortissement dans la Chaîne Critique afin d’obtenir le temps d’amortissement de l’alimentation raisonnable et le temps d’amortissement de projet. Dans l’article présent, nous allons utiliser un exemple pour discuter la Technique de Programmation de la Chaîne Critique Grise, comparer la Chaîne Critique Grise avec l’Evaluation du Programme et la Technique de révision, la Chaîne Critique et la Chaîne Critique Floue, et analyser leurs avantages, désavantages et champ d’application. Mots-Clés: Chaîne Critique, Système Gris, nombre d’intervalle, management de programme, management de proje