We report on the Fermi-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the gamma-ray sky and the first example of a radio-quiet gamma-ray pulsar. The observations cover one year, from the launch of the Fermi satellite through 2009 June 15. A data sample of over 60,000 photons enabled us to build a timing solution based solely on gamma-rays. Timing analysis shows two prominent peaks, separated by Delta phi = 0.497 +/- 0.004 in phase, which narrow with increasing energy. Pulsed gamma-rays are observed beyond 18 GeV, precluding emission below 2.7 stellar radii because of magnetic absorption. The phase-averaged spectrum was fitted with a power law with exponential cutoff of spectral index Gamma = (1.30 +/- 0.01 +/- 0.04), cutoff energy E(0) = (2.46 +/- 0.04 +/- 0.17) GeV, and an integral photon flux above 0.1 GeV of (4.14 +/- 0.02 +/- 0.32) x 10(-6) cm(-2) s(-1). The first uncertainties are statistical and the second ones are systematic. The phase-resolved spectroscopy shows a clear evolution of the spectral parameters, with the spectral index reaching a minimum value just before the leading peak and the cutoff energy having maxima around the peaks. The phase-resolved spectroscopy reveals that pulsar emission is present at all rotational phases. The spectral shape, broad pulse profile, and maximum photon energy favor the outer magnetospheric emission scenarios.
Fermi-LAT observations of the Geminga pulsar / Abdo, Aa; Ackermann, M; Ajello, M; Baldini, L; Ballet, J; Barbiellini, G; Bastier, D; Baughman, Bm; Bechtol, K; Bellazzini, R; Berenji, B; Bignami, Gf; Blandford, Rd; Bloom, Ed; Bonamente, E; Borgland, Aw; Bregeon, J; Brez, A; Brigida, M; Brueli, P; Burnett, Th; Caliandro, Ga; Cameron, Ra; Caraveo, Pa; Casandjian, Jm; Cecchi, C; Celik, O; Charles, E; Chekhtman, A; Cheung, Cc; Chiang, J; Ciprini, S; Claus, R; Cohen Tanugi, J; Conrad, J; Dermer, Cd; de Palma, F; Dormody, M; Silva, Ede; Drell, Ps; Dubois, R; Dumora, D; Edmonds, Y; Farnier, C; Favuzzi, Cecilia; Fegan, Sj; Focke, Wb; Fortin, P; Frailis, M; Furazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Germani, S; Giavitto, G; Giglietto, Nicola; Giordano, F; Glanzman, T; Godfrey, G; Grenier, Ia; Grondin, Mh; Grove, Je; Guillemot, L; Guiriec, S; Hadasch, D; Hardino, Ak; Hays, E; Hughes, Re; Johannesson, G; Johnson, As; Johnson, Tj; Johnson, Wn; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knodlseder, J; Kuss, M; Lande, J; Latronico, L; Lemoine Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, Mn; Lubrano, P; Makeev, A; Marelli, M; Mazziotta, Mn; Mcenery, Je; Meurer, C; Michelson, Pf; Mitthumsiri, W; Mizuno, T; Moiseev, Aa; Monte, C; Monzani, Me; Morselli, A; Moskalenk, Iv; Murgia, S; Nolan, Pl; Norris, Jp; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, Jf; Ozaki, M; Paneque, D; Panetta, Jh; Parent, D; Pelassa, V; Pepe, M; Pesce Rollins, M; Piron, F; Porter, Ta; Raino, S; Rando, R; Rayi, Ps; Razzano, M; Reimer, A; Reimer, O; Reposeur, T; Rochester, Ls; Rodriguez, Ay; Romani, Rw; Roth, M; Ryde, F; Sadrozinski, Hfw; Sander, A; Parkinson, Pms; Scargle, Jd; Sgro, C; Siskind, Ej; Smith, Da; Smith, Pd; Spandre, G; Spinelli, P; Strickman, Ms; Suson, Dj; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, Jb; Thayer, Jg; Thompson, Dj; Tibaldo, L; Torres, Df; Tosti, G; Tramacere, A; Usher, Tl; Van Etten, A; Vasileiou, V; Venter, C; Vilchez, N; Vitale, V; Waite, Ap; Wang, P; Watters, K; Winer, Bl; Wood, Ks; Ylinen, T; Ziegler, M.. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - STAMPA. - 720:1(2010), pp. 272-283. [10.1088/0004-637X/720/1/272]
Fermi-LAT observations of the Geminga pulsar
FAVUZZI, Cecilia;GIGLIETTO, Nicola;
2010-01-01
Abstract
We report on the Fermi-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the gamma-ray sky and the first example of a radio-quiet gamma-ray pulsar. The observations cover one year, from the launch of the Fermi satellite through 2009 June 15. A data sample of over 60,000 photons enabled us to build a timing solution based solely on gamma-rays. Timing analysis shows two prominent peaks, separated by Delta phi = 0.497 +/- 0.004 in phase, which narrow with increasing energy. Pulsed gamma-rays are observed beyond 18 GeV, precluding emission below 2.7 stellar radii because of magnetic absorption. The phase-averaged spectrum was fitted with a power law with exponential cutoff of spectral index Gamma = (1.30 +/- 0.01 +/- 0.04), cutoff energy E(0) = (2.46 +/- 0.04 +/- 0.17) GeV, and an integral photon flux above 0.1 GeV of (4.14 +/- 0.02 +/- 0.32) x 10(-6) cm(-2) s(-1). The first uncertainties are statistical and the second ones are systematic. The phase-resolved spectroscopy shows a clear evolution of the spectral parameters, with the spectral index reaching a minimum value just before the leading peak and the cutoff energy having maxima around the peaks. The phase-resolved spectroscopy reveals that pulsar emission is present at all rotational phases. The spectral shape, broad pulse profile, and maximum photon energy favor the outer magnetospheric emission scenarios.| File | Dimensione | Formato | |
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