FERMI LAT OBSERVATIONS OF LS I+61\ub0303: FIRST DETECTION OF AN ORBITAL MODULATION IN GeV GAMMA RAYS
- Abdo, Aa
- Ackermann, M
- Ajello, M
- Atwood, Wb
- Axelsson, M
- Baldini, L
- Ballet, J
- Barbiellini, G
- Bastieri, Denis
- Baughman, Bm
- Bechtol, K
- Bellazzini, R
- Berenji, B
- Blandford, R
- Bloom, Ed
- Bonamente, E
- Borgland, Aw
- Bregeon, J
- Brez, A
- Brigida, M
- Bruel, P
- Burnett, Th
- Caliandro, Ga
- Cameron, Ra
- Caraveo, Pa
- Casandjian, Jm
- Cavazzuti, E
- Cecchi, C
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- Charles, E
- Chaty, S
- Chekhtman, A
- Cheung, Cc
- Chiang, J
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- Claus, R
- COHEN TANUGI, J
- Cominsky, Lr
- Conrad, J
- Corbel, S
- Corbet, R
- Cutini, S
- Dermer, Cd
- DE ANGELIS, A
- DE LUCA, A
- DE PALMA, F
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- Dormody, M
- Silva, Ede
- Drell, Ps
- Dubois, R
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- Dumora, D
- Farnier, C
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- Fukazawa, Y
- Funk, S
- Fusco, P
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- Gasparrini, D
- Gehrels, N
- Germani, S
- Giebels, B
- Giglietto, N
- Giordano, F
- Glanzman, T
- Godfrey, G
- Grenier, Ia
- Grondin, Mh
- Grove, Je
- Guillemot, L
- Guiriec, S
- Hanabata, Y
- Harding, Ak
- Hayashida, M
- Hays, E
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- Hughes, Re
- Johannesson, G
- Johnson, As
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- Johnson, Tj
- Johnson, Wn
- Kamae, T
- Katagiri, H
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- Kawai, N
- Kerr, M
- Knodlseder, J
- Kocian, Ml
- Kuehn, F
- Kuss, M
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- Larsson, S
- Latronico, L
- Longo, F
- Loparco, F
- Lott, B
- Lovellette, Mn
- Lubrano, P
- Madejski, Gm
- Makeev, A
- Marelli, M
- Mazziotta, Mn
- Mcenery, Je
- Meurer, C
- Michelson, Pf
- Mitthumsiri, W
- Mizuno, T
- Monte, C
- Monzani, Me
- Morselli, A
- Moskalenko, Iv
- Murgia, S
- Nolan, Pl
- Nuss, E
- Ohsugi, T
- Okumura, A
- Omodei, N
- Orlando, E
- Ormes, Jf
- Paneque, D
- Panetta, Jh
- Parent, D
- Pelassa, V
- Pepe, M
- PESCE ROLLINS, M
- Piron, F
- Porter, Ta
- Raino, S
- Rando, Riccardo
- Ray, Ps
- Razzano, M
- Rea, N
- Reimer, A
- Reimer, O
- Reposeur, T
- Ritz, S
- Rochester, Ls
- Rodriguez, Ay
- Romani, Rw
- Ryde, F
- Sadrozinski, Hfw
- Sanchez, D
- Sander, A
- Parkinson, Pms
- Scargle, Jd
- Sgro, C
- Shaw, Ms
- SIERPOWSKA BARTOSIK, A
- Siskind, Ej
- Smith, Da
- Smith, Pd
- Spandre, G
- Spinelli, P
- Striani, E
- Strickman, Ms
- Suson, Dj
- Tajima, H
- Takahashi, H
- Takahashi, T
- Tanaka, T
- Thayer, Jb
- Thayer, Jg
- Thompson, Dj
- Tibaldo, Luigi
- Torres, Df
- Tosti, G
- Tramacere, A
- Uchiyama, Y
- Usher, Tl
- Vasileiou, V
- Vilchez, N
- Vitale, V
- Waite, Ap
- Wang, P
- Winer, Bl
- Wood, Ks
- Ylinen, T
- Ziegler, M.
DOIAbstract
This Letter presents the first results from the observations of LS I +61\ub0303 using Large Area Telescope data from the Fermi Gamma-Ray Space Telescope between 2008 August and 2009 March. Our results indicate variability that is consistent with the binary period, with the emission being modulated at 26.6 \ub1 0.5 days. This constitutes the first detection of orbital periodicity in high-energy gamma rays (20 MeV-100 GeV, HE). The light curve is characterized by a broad peak after periastron, as well as a smaller peak just before apastron. The spectrum is best represented by a power law with an exponential cutoff, yielding an overall flux above 100 MeV of 0.82 \ub1 0.03(stat) \ub1 0.07(syst) 10\u20136 ph cm\u20132 s\u20131, with a cutoff at ...
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