The On-orbit Calibrations for the Fermi Large Area Telescope

The Large Area Telescope (LAT) on--board the Fermi Gamma ray Space Telescope began its on--orbit operations on June 23, 2008. Calibrations, defined in a generic sense, correspond to synchronization of trigger signals, optimization of delays for latching data, determination of detector thresholds, gains and responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA), measurements of live time, of absolute time, and internal and spacecraft boresight alignments. Here we describe on orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector. Instrument response functions will be described in a separate publication. This paper demonstrates the stability of calibrations and describes minor changes observed since launch. These results have been used to calibrate the LAT datasets to be publicly released in August 2009.Comment: 60 pages, 34 figures, submitted to Astroparticle Physic

The spectral energy distribution of fermi bright blazars

We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν-log ν Fν representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, αro, and optical to X-ray, αox, spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (νSpeak) is positioned between 1012.5 and 1014.5 Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10 13 and 1017 Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked (HBL) BL Lacs are detected in the LBAS sample, only less than 13% of known bright FSRQs and LBL BL Lacs are included. This suggests that the latter sources, as a class, may be much fainter γ-ray emitters than LBAS blazars, and could in fact radiate close to the expectations of simple SSC models. We categorized all our sources according to a new physical classification scheme based on the generally accepted paradigm for Active Galactic Nuclei and on the results of this SED study. Since the LAT detector is more sensitive to flat spectrum γ-ray sources, the correlation between νSpeak and γ-ray spectral index strongly favors the detection of high energy peaked blazars, thus explaining the Fermi overabundance of this type of sources compared to radio and EGRET samples. This selection effect is similar to that experienced in the soft X-ray band where HBL BL Lacs are the dominant type of blazars. © 2010 The American Astronomical Society

Insights into the high-energy γ-ray emission of Markarian 501 from extensive multifrequency observations in the Fermi era

We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size ≲0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (≃1044 erg s-1) constitutes only a small fraction (∼10-3) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude. © 2011. The American Astronomical Society

Spatial genetic structure in wild cardoon, the ancestor of cultivated globe artichoke: Limited gene flow, fragmentation and population history

Nuclear and chloroplast markers and phenotypic characters were integrated to analyse the population genetic structure of wild cardoon, Cynara cardunculus var. sylvestris, the ancestor of cultivated globe artichoke, Cynara cardunculus var. scolymus on the island of Sardinia, Italy. The spatial scale ranged from a few metres to ∼200 km. Wild cardoon appears to be genetically fragmented, with significant genetic divergence at various scales, indicating that gene flow is insufficient to counterbalance the effects of genetic drift or founder effects. Divergence between populations was higher for chloroplast (40%) than for nuclear markers (15%), suggesting that gene flow via seed was lower than via pollen. Two main genetic groups were detected; these correlated with differences in flowering time, capitula size, glossiness, and anthocyanin pigmentation. A complex population structure of wild cardoon emerged over small spatial scales, likely resulting from the interplay between gene dispersal, colonisation history and selective forces. Indeed, Sardinia appears to be a ‘hybrid zone’ of different gene pools. The island has unique diverse germplasm that has originated from hybridisation among different gene pools. The sampling of seeds from a few plants but from many sites is suggested as the best strategy to harvest the genetic diversity of wild cardoon.Peer Revie

Storia della Camera del Lavoro di Cagliari nel Novecento

Il volume collettaneo Storia della Camera del Lavoro di Cagliari nel Novecento, curato da Giannarita Mele e Claudio Natoli, è apparso per Carocci Editore nel 2007, nel quadro delle iniziative scientifiche e culturali collegate al centenario della CGIL. Frutto di una collaborazione scientifica fra il Dipartimento di Studi Storici, Geografici ed Artistici dell’Università di Cagliari, la Camera del Lavoro di Cagliari e l’Archivio di Stato di Cagliari, il volume ricostruisce, su una solida base archivistica e documentaria, la storia del movimento sindacale a Cagliari, o meglio della Camera del Lavoro, dalla sua nascita nel 1907 e per tutto il secolo XX, analizzando le forme organizzative, la cultura e le lotte per l’emancipazione e i diritti dei lavoratori e delle lavoratrici nel più ampio contesto provinciale di Cagliari e sullo sfondo dei differenti avvenimenti che hanno caratterizzato il “secolo breve” anche in Sardegna. La prima parte del volume, dopo una riflessione sulla storia di Cagliari e delle sue trasformazioni dal 1906 al 2006 (Giangiacomo Ortu), comprende una serie di saggi dedicati al movimento sindacale nell’età liberale, dalla nascita della Camera del Lavoro di Cagliari nel 1907 (Claudio Natoli) e dallo sviluppo del movimento operaio in età giolittiana (Giovanni Murgia), alle trasformazioni durante la guerra e il primo dopoguerra (Maria Luisa Di Felice), fino ad un’analisi delle condizioni dei lavoratori nel sud Sardegna durante il regime fascista (Maria Luisa Plaisant). La seconda parte del volume comprende una serie di saggi dedicati alle varie fasi della storia della istituzione camerale nell’immediato secondo dopoguerra e nell’Italia repubblicana, dalla sua ricostituzione nel 1944 (Giannarita Mele), ai difficili anni ’50 e ’60 (Giorgio Caredda), fino agli inizi del 21° secolo. In particolare sono stati esaminati il ruolo svolto dalla Camera del Lavoro di coordinamento e direzione del movimento dei lavoratori e delle lavoratrici nelle diverse categorie dell’industria (Lidia Sedda), del settore primario e di quello terziario (Barbara Manca), della scuola e dell’Università (Alessandra Secci), nonché il suo ruolo di contrattazione territoriale nella città e nella “programmazione negoziata” (Emanuela Usai). La terza parte del volume riguarda un saggio sulla Manifattura Tabacchi di Cagliari, emblema delle lotte operaie delle donne di cui vengono ricostruiti, a partire dagli archivi della stessa Manifattura, i rapporti di lavoro e la loro organizzazione negli organismi sindacali aziendali (Angela Ambu e Anna Cherchi). Infine un’utile rassegna sulle fonti del movimento dei lavoratori in Sardegna conservate presso l’Archivio di Stato di Cagliari (Angela Multinu)