Fermi -Lat Observations Of The Geminga Pulsar

Abdo, A. A.

doi:10.1088/0004-637X/720/1/272

Fermi -Lat Observations Of The Geminga Pulsar

Journal Article · Mon Aug 09 00:00:00 EDT 2010 · The Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/720/1/272· OSTI ID:1357531

Abdo, A. A. ^[1]

Naval Research Lab. (NRL), Washington, DC (United States); et al.

We report on the Fermi-LAT observations of the Geminga pulsar, the second brightest non-variable GeV source in the γ-ray sky and the first example of a radio-quiet γ-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 γ-rays. Timing analysis shows two prominent peaks, separated by Δphgr = 0.497 ± 0.004 in phase, which narrow with increasing energy. Pulsed γ-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 Γ = (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) × 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.

View Accepted Manuscript (DOE)

Research Organization:: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: AC02-76SF00515

OSTI ID:: 1357531

Alternate ID(s):: OSTI ID: 21460140

Journal Information:: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 1 Vol. 720; ISSN 0004-637X

Publisher:: Institute of Physics (IOP)Copyright Statement

Country of Publication:: United States

Language:: English

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