FERMI-LAT OBSERVATIONS OF THE GEMINGA PULSAR

Journal Article · Wed Sep 01 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/720/1/272· OSTI ID:21460140

Abdo, A A ^[1]; Ackermann, M; Ajello, M; Bechtol, K; Berenji, B; Blandford, R D; Bloom, E D; Borgland, A W ^[2]; Baldini, L; Bellazzini, R; Bregeon, J; Brez, A ^[3]; Ballet, J ^[4]; Barbiellini, G ^[5]; Bastieri, D ^[6]; Baughman, B M ^[7]; Bignami, G F ^[8]; Bonamente, E ^[9]; Brigida, M ^[10]; Bruel, P ^[11]

---

1. Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)
2. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
3. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
4. Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d'Astrophysique, CEA Saclay, 91191 Gif sur Yvette (France)
5. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
6. Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
7. Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210 (United States)
8. Istituto Universitario di Studi Superiori (IUSS), I-27100 Pavia (Italy)
9. Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy)
10. Dipartimento di Fisica 'M. Merlin' dell'Universita e del Politecnico di Bari, I-70126 Bari (Italy)
11. Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, Palaiseau (France)

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 {sub 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{sup -6} cm{sup -2} s{sup -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.

• OSTI ID: 21460140
• Journal Information: Astrophysical Journal, Vol. 720, Issue 1; Other Information: DOI: 10.1088/0004-637X/720/1/272; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION
EMISSION
GALACTIC EVOLUTION
GAMMA RADIATION
PHOTONS
PULSARS
PULSES
SATELLITES
SPECTROSCOPY
STARS
BOSONS
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
EVOLUTION
IONIZING RADIATIONS
MASSLESS PARTICLES
RADIATIONS
SORPTION