Modeling the non-recycled Fermi Gamma-ray pulsar population

Journal Article · Wed Sep 25 00:00:00 EDT 2013 · The Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/776/1/61· OSTI ID:1356561

Perera, B. B. P. ^[1]; McLaughlin, M. A. ^[1]; Cordes, J. M. ^[2]; Kerr, M. ^[3]; Burnett, T. H. ^[4]; Harding, A. K. ^[5]

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1. West Virginia Univ., Morgantown, WV (United States)
2. Cornell Univ., Ithaca, NY (United States)
3. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.
4. Univ. of Washington, Seattle, WA (United States)
5. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)

Here, we use Fermi Gamma-ray Space Telescope detections and upper limits on non-recycled pulsars obtained from the Large Area Telescope (LAT) to constrain how the gamma-ray luminosity L γ depends on the period P and the period derivative $$\dot{P}$$. We use a Bayesian analysis to calculate a best-fit luminosity law, or dependence of L γ on P and $$\dot{P}$$, including different methods for modeling the beaming factor. An outer gap (OG) magnetosphere geometry provides the best-fit model, which is $$L_\gamma \propto P^{-a} \dot{P}^{b}$$ where a = 1.36 ± 0.03 and b = 0.44 ± 0.02, similar to but not identical to the commonly assumed $$L_\gamma \propto \sqrt{\dot{E}} \propto P^{-1.5} \dot{P}^{0.5}$$. Given upper limits on gamma-ray fluxes of currently known radio pulsars and using the OG model, we find that about 92% of the radio-detected pulsars have gamma-ray beams that intersect our line of sight. By modeling the misalignment of radio and gamma-ray beams of these pulsars, we find an average gamma-ray beaming solid angle of about 3.7π for the OG model, assuming a uniform beam. Using LAT-measured diffuse fluxes, we place a 2σ upper limit on the average braking index and a 2σ lower limit on the average surface magnetic field strength of the pulsar population of 3.8 and 3.2 × 1010 G, respectively. We then predict the number of non-recycled pulsars detectable by the LAT based on our population model. Using the 2 yr sensitivity, we find that the LAT is capable of detecting emission from about 380 non-recycled pulsars, including 150 currently identified radio pulsars. Using the expected 5 yr sensitivity, about 620 non-recycled pulsars are detectable, including about 220 currently identified radio pulsars. As a result, we note that these predictions significantly depend on our model assumptions.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1356561
• Journal Information: The Astrophysical Journal, Vol. 776, Issue 1; ISSN 0004-637X
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

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