A study of super-luminous stars with the Fermi Large Area Telescope

The $\gamma$-ray emission from stars is induced by the interaction of cosmic rays with stellar atmospheres and photon fields. This emission is expected to come in two components: a stellar disk emission, where $\gamma$-rays are mainly produced in atmospheric showers generated by hadronic cosmic rays, and an extended halo emission, where the high density of soft photons in the surroundings of stars create a suitable environment for $\gamma$-ray production via inverse Compton (IC) scattering by cosmic-ray electrons. Besides the Sun, no other disk or halo from single stars has ever been detected in $\gamma$-rays. However, by assuming a cosmic-ray spectrum similar to that observed on Earth, the predicted $\gamma$-ray emission of super-luminous stars, like e.g. Betelgeuse and Rigel, could be high enough to be detected by the Fermi Large Area Telescope (LAT) after its first decade of operations. In this work, we use 12 years of Fermi-LAT observations along with IC models to study 9 super-luminous nearby stars, both individually and via stacking analysis. Our results show no significant $\gamma$-ray emission, but allow us to restrict the stellar $\gamma$-ray fluxes to be on average $<3.3 \times 10^{-11}$ ph cm$^{-2}$ s$^{-1}$ at a 3$\sigma$ confidence level, which translates to an average local density of electrons in the surroundings of our targets to be less than twice of that observed for the Solar System.Comment: 8 pages, 4 figure

Beginning a journey across the universe: the discovery of extragalactic neutrino factories

Neutrinos are the most elusive particles in the Universe, capable of traveling nearly unimpeded across it. Despite the vast amount of data collected, a long standing and unsolved issue is still the association of high-energy neutrinos with the astrophysical sources that originate them. Amongst the candidate sources of neutrinos there are blazars, a class of extragalactic sources powered by supermassive black holes that feed highly relativistic jets, pointed towards the Earth. Previous studies appear controversial, with several efforts claiming a tentative link between high-energy neutrino events and individual blazars, and others putting into question such relation. In this work we show that blazars are unambiguously associated with high-energy astrophysical neutrinos at unprecedented level of confidence, i.e. chance probability of 6 x 10^{-7}. Our statistical analysis provides the observational evidence that blazars are astrophysical neutrino factories and hence, extragalactic cosmic-ray accelerators.Comment: Published in ApJ

Optical characterization of WISE selected blazar candidates

Context. Over the last decade more than five thousand γ-ray sources have been detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. Given the positional uncertainty of the telescope, nearly 30% of these sources remain without an obvious counterpart at lower energies. This has motivated the release of new catalogs of γ-ray counterpart candidates and several follow up campaigns in the last decade. Aims. Recently, two new catalogs of blazar candidates were released. These are the improved and expanded version of the WISE Blazar-Like Radio-Loud Sources (WIBRaLS2) catalog and the Kernel Density Estimation selected candidate BL Lacs (KDEBLLACS) catalog, both selecting blazar-like sources based on their infrared colors from the Wide-field Infrared Survey Explorer (WISE). In this work we characterize these two catalogs, clarifying the true nature of their sources based on their optical spectra from SDSS data release 15, thus testing their efficiency in selecting true blazars. Methods. We first selected all WIBRaLS2 and KDEBLLACS sources with available optical spectra in the footprint of Sloan Digital Sky Survey data release 15. We then analyzed these spectra to verify the nature of each selected candidate and to measure the fraction of the catalogs composed by spectroscopically confirmed blazars. Finally, we evaluated the impact of selection effects, especially those related to optical colors of WIBRaLS2/KDEBLLACS sources and their optical magnitude distributions. Results. We found that at least ∼30% of each catalog is made up of confirmed blazars, with quasars being the major contaminants in the case of WIBRaLS2 (≈58%) and normal galaxies in the case of KDEBLLACS (≈38.2%). The spectral analysis also allowed us to identify the nature of 11 blazar candidates of uncertain type (BCUs) from the Fermi-LAT fourth Point Source Catalog (4FGL) and to find 25 new BL Lac objects.Fil: de Menezes, Raniere. Universidade Do Sao Paulo. Instituto Astronomia, Geofísica E Ciencias Atmosfericas. Departamento de Astronomia; Brasil. Università degli Studi di Torino; ItaliaFil: Peña Herazo, Harold A.. Instituto Nacional de Astrofísica; México. Università di Torino; Italia. Istituto Nazionale Di Fisica Nucleare.; Italia. Osservatorio Astrofisico di Torino; ItaliaFil: Marchesini, Ezequiel Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Istituto Nazionale Di Fisica Nucleare.; Italia. Università di Torino; ItaliaFil: D´Abrusco, Raffaele. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Masetti, Nicola. Osservatorio di Astrofisica e Scienza dello Spazio; Italia. Universidad Andrés Bello; ChileFil: Nemmen, Rodrigo. Universidade Do Sao Paulo. Instituto Astronomia, Geofísica E Ciencias Atmosfericas. Departamento de Astronomia; BrasilFil: Massaro, Francesco. Università di Torino; Italia. Istituto Nazionale Di Fisica Nucleare.; Italia. Osservatorio Astrofisico di Torino; Italia. Consorzio Interuniversitario per la Fisica Spaziale ; ItaliaFil: Ricci, Federica. Pontificia Universidad Católica de Chile; ChileFil: Landoni, Marco. Osservatorio Astronomico di Brera; ItaliaFil: Paggi, Alessandro. Università di Torino; ItaliaFil: Smith, Howard A.. Harvard-Smithsonian Center for Astrophysics; Estados Unido

Optical spectroscopic observations of gamma-ray blazar candidates, X: results from the 2018–2019 SOAR and OAN-SPM observations of blazar candidates of uncertain type

The fourth Fermi Large Area Telescope Source Catalog (4FGL) lists over 5000 γ-ray sources with statistical significance above 4 σ. About 23% of the sources listed in this catalog are unidentified/unassociated γ-ray sources while ∼26% of the sources are classified as blazar candidates of uncertain type (BCUs), lacking optical spectroscopic information. To probe the blazar nature of candidate counterparts of UGSs and BCUs, we started our optical spectroscopic follow up campaign in 2012, which up to date account for more than 350 observed sources. In this paper, the tenth of our campaign, we report on the spectroscopic observations of 37 sources, mostly BCUs, whose observations were carried out predominantly at the Observatorio Astronómico Nacional San Pedro Mártir and the Southern Astrophysical Research Observatory between August 2018 and September 2019. We confirm the BL Lac nature of 27 sources and the flat spectrum radio quasar nature of three sources. The remaining ones are classified as six BL Lacs galaxy-dominated and one normal galaxy. We were also able to measure the redshifts for 20 sources, including 10 BL Lacs. As in previous analyses, the largest fraction of BCUs revealed to be BL Lac objects.Fil: de Menezes, Raniere. Universidade de Sao Paulo; Brasil. Università di Torino; ItaliaFil: Amaya Almazán, R. A.. Instituto Nacional de Astrofisica Optica y Electronica; MéxicoFil: Marchesini, Ezequiel Joaquín. Università di Torino; Italia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Peña Herazo, H. A.. Istituto Nazionale di Astrofisica; Italia. Università di Torino; ItaliaFil: Massaro, F.. Istituto Nazionale di Astrofisica; Italia. Università di Torino; ItaliaFil: Chavushyan, V.. Instituto Nacional de Astrofisica Optica y Electronica; MéxicoFil: Paggi, A.. Istituto Nazionale di Astrofisica; ItaliaFil: Landoni, M.. Osservatorio Astronomico Di Brera; ItaliaFil: Masetti, N.. Inaf Istituto Di Astrofisica Spaziale E Fisica Cosmica, Bologna; Italia. Universidad Andrés Bello; ChileFil: Ricci, F.. Universidad Católica de Chile; ChileFil: D'Abrusco, R.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: La Franca, F.. Università Degli Studi Roma Tre; ItaliaFil: Smith, Howard A.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Milisavljevic, D.. College Of Science; ItaliaFil: Tosti, G.. Università di Perugia; ItaliaFil: Jiménez Bailón, E.. Universidad Nacional Autónoma de México; MéxicoFil: Cheung, C. C.. Spece Sciences División. Naval Research Laboratory; Estados Unido

The Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems co-located with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to $\leq 11$ known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall, >235 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot E$ decreases to its observed minimum near $10^{33}$ erg s$^{-1}$, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties and fit results to guide and be compared with modeling results.Comment: 142 pages. Accepted by the Astrophysical Journal Supplemen