Stars of extragalactic origin in the solar neighborhood

We computed the spatial velocities and the galactic orbital elements using Hipparcos data for 77 nearest main-sequence F-G-stars with published the iron, magnesium, and europium abundances determined from high dispersion spectra and with the ages estimated from theoretical isochrones. A comparison with the orbital elements of the globular clusters that are known was accreted by our Galaxy in the past reveals stars of extragalactic origin. We show that the relative elemental abundance ratios of r- and \alpha- elements in all the accreted stars differ sharply from those in the stars that are genetically associated with the Galaxy. According to current theoretical models, europium is produced mainly in low mass Type II supernovae (SNe II), while magnesium is synthesized in larger amounts in high mass SN II progenitors. Since all the old accreted stars of our sample exhibit a significant Eu overabundance relative to Mg, we conclude that the maximum masses of the SNII progenitors outside the Galaxy were much lower than those inside it are. On the other hand, only a small number of young accreted stars exhibit low negative ratios $[Eu/Mg] < 0$. The delay of primordial star formation burst and the explosions of high mass SNe II in a relatively small part of extragalactic space can explain this situation. We provide evidence that the interstellar medium was weakly mixed at the early evolutionary stages of the Galaxy formed from a single proto-galactic cloud and that the maximum mass of the SN II progenitors increased in it with time simultaneously with the increase in mean metallicity.Comment: Accepted for 2004, Astronomy Letters, Vol. 30, No. 3, P.148-158 15 pages, 3 figure

The Spectrum and Morphology of the Fermi Bubbles

The Fermi bubbles are two large structures in the gamma-ray sky extending to 55 deg above and below the Galactic center. We analyze 50 months of Fermi Large Area Telescope data between 100 MeV and 500 GeV above 10 deg in Galactic latitude to derive the spectrum and morphology of the Fermi bubbles. We thoroughly explore the systematic uncertainties that arise when modeling the Galactic diffuse emission through two separate approaches. The gamma-ray spectrum is well described by either a log parabola or a power law with an exponential cutoff. We exclude a simple power law with more than 7 sigma significance. The power law with an exponential cutoff has an index of 1.90+/-0.2 and a cutoff energy of 110+/- 50 GeV. We find that the gamma-ray luminosity of the bubbles is 4.4(+)2.4(-0.9 ) 10(exp 37) erg s-1. We confirm a significant enhancement of gamma-ray emission in the south-eastern part of the bubbles, but we do not find significant evidence for a jet. No significant variation of the spectrum across the bubbles is detected. The width of the boundary of the bubbles is estimated to be 3.4(+)3.7(-)2.6 deg. Both inverse Compton (IC) models and hadronic models including IC emission from secondary leptons t the gamma-ray data well. In the IC scenario, the synchrotron emission from the same population of electrons can also explain the WMAP and Planck microwave haze with a magnetic field between 5 and 20 micro-G

Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT

Pulsars are rapidly-rotating, highly-magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently, only seven were observed to pulse in gamma rays and these were all discovered at other wavelengths. The Fermi Large Area Telescope makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics and the energetics of pulsar wind nebulae and supernova remnants.Comment: Corresponding authors: Michael Dormody, Paul S. Ray, Pablo M. Saz Parkinson, Marcus Ziegle

Gamma-ray burst investigation via polarimetry and spectroscopy (GRIPS)

59The primary scientific goal of the GRIPS mission is to revolutionize our understanding of the early universe using gamma-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of gamma-ray energies (200 keV-50 MeV) and of polarimetry (200-1000 keV). The gamma-ray sensitivity to nuclear absorption features enables the measurement of column densities as high as 10(28)cm (-aEuro parts per thousand 2). Secondary goals achievable by this mission include direct measurements of all types of supernova interiors through gamma-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact stars, interstellar shocks, and clusters of galaxies.nonenoneGreiner J.; Iyudin A.; Kanbach G.; Zoglauer A.; Diehl R.; Ryde F.; Hartmann D.; v. Kienlin A.; McBreen S.; Ajello M.; Bagoly Z.; Balasz L. G.; Barbiellini G.; Bellazini R.; Bezrukov L.; Bisikalo D. V.; Bisnovaty-Kogan G.; Boggs S.; Bykov A.; Cherepashuk A. M.; Chernenko A.; Collmar W.; DiCocco G.; Droege W.; Gierlik M.; Hanlon L.; Horvath I.; Hudec R.; Kiener J.; Labanti C.; Langer N.; Larsson S.; Lichti G.; Lipunov V. M.; Lubsandorgiev B. K.; Majczyna A.; Mannheim K.; Marcinkowski R.; Marisaldi M.; McBreen B.; Meszaros A.; Orlando E; Panasyuk M. I.; Pearce M.; Pian E.; Poleschuk R. V.; Pollo A.; Pozanenko A.; Savaglio S.; Shustov B.; Strong A.; Svertilov S.; Tatischeff V.; Uvarov J.; Varshalovich D. A.; Wunderer C. B.; Wrochna G.; Zabrodskij A. G.; Zeleny L. M.Greiner, J.; Iyudin, A.; Kanbach, G.; Zoglauer, A.; Diehl, R.; Ryde, F.; Hartmann, D.; v. Kienlin, A.; Mcbreen, S.; Ajello, M.; Bagoly, Z.; Balasz, L. G.; Barbiellini, G.; Bellazini, R.; Bezrukov, L.; Bisikalo, D. V.; Bisnovaty-Kogan, G.; Boggs, S.; Bykov, A.; Cherepashuk, A. M.; Chernenko, A.; Collmar, W.; Dicocco, G.; Droege, W.; Gierlik, M.; Hanlon, L.; Horvath, I.; Hudec, R.; Kiener, J.; Labanti, C.; Langer, N.; Larsson, S.; Lichti, G.; Lipunov, V. M.; Lubsandorgiev, B. K.; Majczyna, A.; Mannheim, K.; Marcinkowski, R.; Marisaldi, M.; Mcbreen, B.; Meszaros, A.; Orlando, E; Panasyuk, M. I.; Pearce, M.; Pian, E.; Poleschuk, R. V.; Pollo, A.; Pozanenko, A.; Savaglio, S.; Shustov, B.; Strong, A.; Svertilov, S.; Tatischeff, V.; Uvarov, J.; Varshalovich, D. A.; Wunderer, C. B.; Wrochna, G.; Zabrodskij, A. G.; Zeleny, L. M