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Post Info TOPIC: Gamma Cygni


L

Posts: 131433
Date:
SNR G78.2+2.1
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Title: Discovery of TeV Gamma-ray Emission Toward Supernova Remnant SNR G78.2+2.1 
Authors: E. Aliu, S. Archambault, T. Arlen, T. Aune, M. Beilicke, W. Benbow, R. Bird, A. Bouvier, S. M. Bradbury, J. H. Buckley, V. Bugaev, K. Byrum, A. Cannon, A. Cesarini, L. Ciupik, E. Collins-Hughes, M. P. Connolly, W. Cui, R. Dickherber, C. Duke, J. Dumm, V. V. Dwarkadas, M. Errando, A. Falcone, S. Federici, Q. Feng, J. P. Finley, G. Finnegan, L. Fortson, A. Furniss, N. Galante, D. Gall, G. H. Gillanders, S. Godambe, E. V. Gotthelf, S. Griffin, J. Grube, G. Gyuk, D. Hanna, J. Holder, H. Huan, G. Hughes, T. B. Humensky, P. Kaaret, N. Karlsson, M. Kertzman, Y. Khassen, D. Kieda, H. Krawczynski, F. Krennrich, M. J. Lang, K. Lee, A. S Madhavan, G. Maier, P. Majumdar, S. McArthur, A. McCann, J. Millis, P. Moriarty, R. Mukherjee, T. Nelson, A. O'Faoláin de Bhróithe, R. A. Ong, M. Orr, et al. (36 additional authors not shown) 

We report the discovery of an unidentified, extended source of very-high-energy (VHE) gamma-ray emission, VER J2019+407, within the radio shell of the supernova remnant SNR G78.2+2.1, using 21.4 hours of data taken by the VERITAS gamma-ray observatory in 2009. These data confirm the preliminary indications of gamma-ray emission previously seen in a two-year (2007-2009) blind survey of the Cygnus region by VERITAS. VER J2019+407, which is detected at a post-trials significance of 7.5 standard deviations in the 2009 data, is localised to the northwestern rim of the remnant in a region of enhanced radio and X-ray emission. It has an intrinsic extent of 0.23° ± 0.03° (stat)+0.04°_{-0.02}°(sys) and its spectrum is well-characterised by a differential power law (dN/dE = N_0 x (E/TeV)^{-\Gamma}) with a photon index of {\Gamma} = 2.37 ± 0.14 (stat) ± 0.20 (sys) and a flux normalisation of N0 = 1.5 ± 0.2 (stat) ± 0.4(sys) x 10^-12 ph TeV^{-1} cm^{-2} s^{-1}. This yields an integral flux of 5.2 ± 0.8 (stat) ± 1.4 (sys) x 10^-12 ph cm^{-2} s^{-1} above 320 GeV, corresponding to 3.7% of the Crab Nebula flux. We consider the relationship of the TeV gamma-ray emission with the GeV gamma-ray emission seen from SNR G78.2+2.1 as well as that seen from a nearby cocoon of freshly accelerated cosmic rays. Multiple scenarios are considered as possible origins for the TeV gamma-ray emission, including hadronic particle acceleration at the supernova remnant shock. 

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L

Posts: 131433
Date:
Gamma Cygni
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Supergiant star Gamma Cygni (Sadr) lies at the centre of the Northern Cross, a famous asterism in the constellation Cygnus the Swan. The star lies at the centre of a complex of stars, dust clouds, and glowing nebulae along the plane of our Milky Way galaxy.


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Credit: Noel Carboni, Greg Parker

The field of view spans over 3 degrees and includes emission nebula IC 1318 and open star cluster NGC 6910. Left of Sadr and shaped like two wings divided by a long dark dust lane, IC 1318's popular name is the Butterfly Nebula. Above and left of Sadr, are the young, still tightly grouped stars of NGC 6910.
Distance estimates for Gamma Cyg place it at around 750 light-years while estimates for IC 1318 and NGC 6910 range from 2,000 to 5,000 light-years.

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