Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 680, Issue 2, Pages L125-L128Publisher
UNIV CHICAGO PRESS
DOI: 10.1086/589996
Keywords
gamma rays : theory; globular clusters : individual (47 Tucanae); pulsars : general; radiation mechanisms : nonthermal
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Although only 22 millisecond pulsars (MSPs) are currently known to exist in the globular cluster (GC) 47 Tucanae, this cluster may harbor 30-60 MSPs, or even up to similar to 200. In this Letter, we model the pulsed curvature radiation (CR) gamma- ray flux expected from a population of MSPs in 47 Tucanae. These MSPs produce gamma rays in their magnetospheres via accelerated electron primaries which are moving along curved magnetic field lines. A GC such as 47 Tucanae containing a large number of MSPs provides the opportunity to study a randomized set of pulsar geometries. Geometry-averaged spectra make the testing of the underlying pulsar model more reliable, since in this case the relative flux uncertainty is reduced by 1 order of magnitude relative to the variation expected for individual pulsars ( if the number of visible pulsars). Our predicted spectra violate the N = 100 EGRET upper limit at 1 GeV, constraining the product of the number of visible pulsars N and the average integral flux above 1 GeV per pulsar. GLAST LAT should place even more stringent constraints on this product, and may also limit the maximum average accelerating potential by probing the CR spectral tail. For N = 22-200, a GLAST LAT nondetection will lead to the constraints that the average integral flux per pulsar should be lower by factors of 0.03 - 0.003 than current model predictions.
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