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FERMI LAT observations of LS I +61°303: first detection of an orbital modulation in GeV gamma rays

FERMI LAT observations of LS I +61°303: first detection of an orbital modulation in GeV gamma rays
FERMI LAT observations of LS I +61°303: first detection of an orbital modulation in GeV gamma rays
This Letter presents the first results from the observations of LS I +61º303 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 ± 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 ± 0.03(stat) ± 0.07(syst) 10-6 ph cm-2 s-1, with a cutoff at 6.3 ± 1.1(stat) ± 0.4(syst) GeV and photon index ? = 2.21 ± 0.04(stat) ± 0.06(syst). There is no significant spectral change with orbital phase. The phase of maximum emission, close to periastron, hints at inverse Compton scattering as the main radiation mechanism. However, previous very high-energy gamma ray (>100 GeV, VHE) observations by MAGIC and VERITAS show peak emission close to apastron. This and the energy cutoff seen with Fermi suggest the link between HE and VHE gamma rays is nontrivial.
binaries: close, gamma rays: observations, stars: variables, x-rays: binaries, X-rays: LS I +61?303
2041-8205
L123-L128
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Conrad, J.
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Corbel, S.
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Corbet, R.
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Cutini, S.
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Dermer, C.D.
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de Angelis, A.
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de Luca, A.
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de Palma, F.
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Digel, S.W.
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Dormody, M.
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do Couto e Silva, E.
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Drell, P.S.
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Dubois, R.
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Dubus, G.
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Dumora, D.
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Farnier, C.
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Favuzzi, C.
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Fegan, S.J.
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Frailis, M.
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Fukazawa, Y.
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Funk, S.
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Fusco, P.
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Gargano, F.
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Gasparrini, D.
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Gehrels, N.
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Germani, S.
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Giebels, B.
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Giglietto, N.
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Giordano, F.
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Glanzman, T.
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Godfrey, G.
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Grondin, M.-H.
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Grove, J.E.
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Guillemot, L.
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Guiriec, S.
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Hanabata, Y.
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Harding, A.K.
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Hayashida, M.
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Hays, E.
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Hill, A.B.
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Hughes, R.E.
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Jóhannesson, G.
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Johnson, A.S.
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Kamae, T.
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Katagiri, H.
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Kataoka, J.
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Kawai, N.
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Kerr, M.
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Knödlseder, J.
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Kocian, M.L.
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Kuehn, F.
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Kuss, M.
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Lande, J.
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Larsson, S.
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Latronico, L.
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Longo, F.
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Loparco, F.
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Lott, B.
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Lovellette, M.N.
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Lubrano, P.
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Madejski, G.M.
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Makeev, A.
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Marelli, M.
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Mazziotta, M.N.
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McEnery, J.E.
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Meurer, C.
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Michelson, P.F.
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Mitthumsiri, W.
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Mizuno, T.
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Monte, C.
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Monzani, M.E.
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Morselli, A.
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Moskalenko, I.V.
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Murgia, S.
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Nolan, P.L.
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Nuss, E.
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Ohsugi, T.
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Okumura, A.
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Omodei, N.
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Orlando, E.
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Ormes, J.F.
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Paneque, D.
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Panetta, J.H.
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Parent, D.
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Pelassa, V.
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Pepe, M.
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Pesce-Rollins, M.
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Piron, F.
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Porter, T.A.
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Rainò, S.
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Rando, R.
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Ray, P.S.
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Razzano, M.
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Rea, N.
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Reimer, A.
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Reimer, O.
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Reposeur, T.
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Ritz, S.
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Rochester, L.S.
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Rodriguez, A.Y.
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Romani, R.W.
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Ryde, F.
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Sadrozinski, H.F.-W.
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Sanchez, D.
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Sander, A.
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Saz Parkinson, P.M.
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Scargle, J.D.
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Sgrò, C.
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Shaw, M.S.
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Sierpowska-Bartosik, A.
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Siskind, E.J.
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Smith, D.A.
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Smith, P.D.
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Spandre, G.
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Spinelli, P.
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Striani, E.
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Strickman, M.S.
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Suson, D.J.
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Tajima, H.
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Takahashi, H.
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Takahashi, T.
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Tanaka, T.
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Thayer, J.B.
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Thompson, D.J.
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Tibaldo, L.
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Torres, D.F.
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Tosti, G.
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Tramacere, A.
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Uchiyama, Y.
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Usher, T.L.
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Vasileiou, V.
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Vilchez, N.
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Vitale, V.
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Waite, A.P.
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Wang, P.
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Winer, B.L.
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Wood, K.S.
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Ylinen, T.
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Ziegler, M.
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Abdo, A.A., Ackermann, M., Ajello, M., Atwood, W.B., Axelsson, M., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Baughman, B.M., Bechtol, K., Bellazzini, R., Berenji, B., Blandford, R., Bloom, E.D., Bonamente, E., Borgland, A.W., Bregeon, J., Brez, A., Brigida, M., Bruel, P., Burnett, T.H., Caliandro, G.A., Cameron, R.A., Caraveo, P.A., Casandjian, J.M., Cavazzuti, E., Cecchi, C., Çelik, Ö., Charles, E., Chaty, S., Chekhtman, A., Cheung, C.C., Chiang, J., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L.R., Conrad, J., Corbel, S., Corbet, R., Cutini, S., Dermer, C.D., de Angelis, A., de Luca, A., de Palma, F., Digel, S.W., Dormody, M., do Couto e Silva, E., Drell, P.S., Dubois, R., Dubus, G., Dumora, D., Farnier, C., Favuzzi, C., Fegan, S.J., Focke, W.B., Frailis, M., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Germani, S., Giebels, B., Giglietto, N., Giordano, F., Glanzman, T., Godfrey, G., Grenier, I.A., Grondin, M.-H., Grove, J.E., Guillemot, L., Guiriec, S., Hanabata, Y., Harding, A.K., Hayashida, M., Hays, E., Hill, A.B., Hughes, R.E., Jóhannesson, G., Johnson, A.S., Johnson, R.P., Johnson, T.J., Johnson, W.N., Kamae, T., Katagiri, H., Kataoka, J., Kawai, N., Kerr, M., Knödlseder, J., Kocian, M.L., Kuehn, F., Kuss, M., Lande, J., Larsson, S., Latronico, L., Longo, F., Loparco, F., Lott, B., Lovellette, M.N., Lubrano, P., Madejski, G.M., Makeev, A., Marelli, M., Mazziotta, M.N., McEnery, J.E., Meurer, C., Michelson, P.F., Mitthumsiri, W., Mizuno, T., Monte, C., Monzani, M.E., Morselli, A., Moskalenko, I.V., Murgia, S., Nolan, P.L., Nuss, E., Ohsugi, T., Okumura, A., Omodei, N., Orlando, E., Ormes, J.F., Paneque, D., Panetta, J.H., Parent, D., Pelassa, V., Pepe, M., Pesce-Rollins, M., Piron, F., Porter, T.A., Rainò, S., Rando, R., Ray, P.S., Razzano, M., Rea, N., Reimer, A., Reimer, O., Reposeur, T., Ritz, S., Rochester, L.S., Rodriguez, A.Y., Romani, R.W., Ryde, F., Sadrozinski, H.F.-W., Sanchez, D., Sander, A., Saz Parkinson, P.M., Scargle, J.D., Sgrò, C., Shaw, M.S., Sierpowska-Bartosik, A., Siskind, E.J., Smith, D.A., Smith, P.D., Spandre, G., Spinelli, P., Striani, E., Strickman, M.S., Suson, D.J., Tajima, H., Takahashi, H., Takahashi, T., Tanaka, T., Thayer, J.B., Thayer, J.G., Thompson, D.J., Tibaldo, L., Torres, D.F., Tosti, G., Tramacere, A., Uchiyama, Y., Usher, T.L., Vasileiou, V., Vilchez, N., Vitale, V., Waite, A.P., Wang, P., Winer, B.L., Wood, K.S., Ylinen, T. and Ziegler, M. (2009) FERMI LAT observations of LS I +61°303: first detection of an orbital modulation in GeV gamma rays. The Astrophysical Journal Letters, 701 (2), L123-L128. (doi:10.1088/0004-637X/701/2/L123).

Record type: Article

Abstract

This Letter presents the first results from the observations of LS I +61º303 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 ± 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 ± 0.03(stat) ± 0.07(syst) 10-6 ph cm-2 s-1, with a cutoff at 6.3 ± 1.1(stat) ± 0.4(syst) GeV and photon index ? = 2.21 ± 0.04(stat) ± 0.06(syst). There is no significant spectral change with orbital phase. The phase of maximum emission, close to periastron, hints at inverse Compton scattering as the main radiation mechanism. However, previous very high-energy gamma ray (>100 GeV, VHE) observations by MAGIC and VERITAS show peak emission close to apastron. This and the energy cutoff seen with Fermi suggest the link between HE and VHE gamma rays is nontrivial.

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Published date: 20 August 2009
Keywords: binaries: close, gamma rays: observations, stars: variables, x-rays: binaries, X-rays: LS I +61?303
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 336984
URI: http://eprints.soton.ac.uk/id/eprint/336984
ISSN: 2041-8205
PURE UUID: 3fd5dc69-377b-40c8-a3a6-fc7b2cda738b
ORCID for A.B. Hill: ORCID iD orcid.org/0000-0003-3470-4834

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Date deposited: 13 Apr 2012 15:31
Last modified: 15 Mar 2024 03:17

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Contributors

Author: A.A. Abdo
Author: M. Ackermann
Author: M. Ajello
Author: W.B. Atwood
Author: M. Axelsson
Author: L. Baldini
Author: J. Ballet
Author: G. Barbiellini
Author: D. Bastieri
Author: B.M. Baughman
Author: K. Bechtol
Author: R. Bellazzini
Author: B. Berenji
Author: R. Blandford
Author: E.D. Bloom
Author: E. Bonamente
Author: A.W. Borgland
Author: J. Bregeon
Author: A. Brez
Author: M. Brigida
Author: P. Bruel
Author: T.H. Burnett
Author: G.A. Caliandro
Author: R.A. Cameron
Author: P.A. Caraveo
Author: J.M. Casandjian
Author: E. Cavazzuti
Author: C. Cecchi
Author: Ö. Çelik
Author: E. Charles
Author: S. Chaty
Author: A. Chekhtman
Author: C.C. Cheung
Author: J. Chiang
Author: S. Ciprini
Author: R. Claus
Author: J. Cohen-Tanugi
Author: L.R. Cominsky
Author: J. Conrad
Author: S. Corbel
Author: R. Corbet
Author: S. Cutini
Author: C.D. Dermer
Author: A. de Angelis
Author: A. de Luca
Author: F. de Palma
Author: S.W. Digel
Author: M. Dormody
Author: E. do Couto e Silva
Author: P.S. Drell
Author: R. Dubois
Author: G. Dubus
Author: D. Dumora
Author: C. Farnier
Author: C. Favuzzi
Author: S.J. Fegan
Author: W.B. Focke
Author: M. Frailis
Author: Y. Fukazawa
Author: S. Funk
Author: P. Fusco
Author: F. Gargano
Author: D. Gasparrini
Author: N. Gehrels
Author: S. Germani
Author: B. Giebels
Author: N. Giglietto
Author: F. Giordano
Author: T. Glanzman
Author: G. Godfrey
Author: I.A. Grenier
Author: M.-H. Grondin
Author: J.E. Grove
Author: L. Guillemot
Author: S. Guiriec
Author: Y. Hanabata
Author: A.K. Harding
Author: M. Hayashida
Author: E. Hays
Author: A.B. Hill ORCID iD
Author: R.E. Hughes
Author: G. Jóhannesson
Author: A.S. Johnson
Author: R.P. Johnson
Author: T.J. Johnson
Author: W.N. Johnson
Author: T. Kamae
Author: H. Katagiri
Author: J. Kataoka
Author: N. Kawai
Author: M. Kerr
Author: J. Knödlseder
Author: M.L. Kocian
Author: F. Kuehn
Author: M. Kuss
Author: J. Lande
Author: S. Larsson
Author: L. Latronico
Author: F. Longo
Author: F. Loparco
Author: B. Lott
Author: M.N. Lovellette
Author: P. Lubrano
Author: G.M. Madejski
Author: A. Makeev
Author: M. Marelli
Author: M.N. Mazziotta
Author: J.E. McEnery
Author: C. Meurer
Author: P.F. Michelson
Author: W. Mitthumsiri
Author: T. Mizuno
Author: C. Monte
Author: M.E. Monzani
Author: A. Morselli
Author: I.V. Moskalenko
Author: S. Murgia
Author: P.L. Nolan
Author: E. Nuss
Author: T. Ohsugi
Author: A. Okumura
Author: N. Omodei
Author: E. Orlando
Author: J.F. Ormes
Author: D. Paneque
Author: J.H. Panetta
Author: D. Parent
Author: V. Pelassa
Author: M. Pepe
Author: M. Pesce-Rollins
Author: F. Piron
Author: T.A. Porter
Author: S. Rainò
Author: R. Rando
Author: P.S. Ray
Author: M. Razzano
Author: N. Rea
Author: A. Reimer
Author: O. Reimer
Author: T. Reposeur
Author: S. Ritz
Author: L.S. Rochester
Author: A.Y. Rodriguez
Author: R.W. Romani
Author: F. Ryde
Author: H.F.-W. Sadrozinski
Author: D. Sanchez
Author: A. Sander
Author: P.M. Saz Parkinson
Author: J.D. Scargle
Author: C. Sgrò
Author: M.S. Shaw
Author: A. Sierpowska-Bartosik
Author: E.J. Siskind
Author: D.A. Smith
Author: P.D. Smith
Author: G. Spandre
Author: P. Spinelli
Author: E. Striani
Author: M.S. Strickman
Author: D.J. Suson
Author: H. Tajima
Author: H. Takahashi
Author: T. Takahashi
Author: T. Tanaka
Author: J.B. Thayer
Author: J.G. Thayer
Author: D.J. Thompson
Author: L. Tibaldo
Author: D.F. Torres
Author: G. Tosti
Author: A. Tramacere
Author: Y. Uchiyama
Author: T.L. Usher
Author: V. Vasileiou
Author: N. Vilchez
Author: V. Vitale
Author: A.P. Waite
Author: P. Wang
Author: B.L. Winer
Author: K.S. Wood
Author: T. Ylinen
Author: M. Ziegler

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