Deep radio observations of the rich globular clusters Terzan 5 and Liller 1 |
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| Authors: | A S Fruchter W M Goss |
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| Institution: | (1) Space Telescope Science Institute, 3700 San Martin Drive, 21210 Baltimore, MD;(2) NRAO, P.O. Box 0, 87801 Socorro, NM |
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| Abstract: | We have obtained deep 6, 20 and 90 cm observation of two of the richest globular clusters in the galaxy, Terzan 5 and Liller
1. In addition to the well known eclipsing pulsar, PSR1744-24A, our 20 cm image of Terzan 5 displays numerous point sources
within 30″, or 4 core radii of the cluster center. The density of these objects rises rapidly toward the core, where an elongated
region of emission is found. This feature may be due to the presence of a higher density of point sources than can be resolved
by the 1″ resolution of our data. Observations at 6 and 90 cm show that the brightest individual sources, as well as the extended
emission, possess the steep spectra expected of pulsars. Furthermore, we find that the strength of the sources in the 20 cm
image agrees well with the standard pulsar luminosity function. The total luminosity and number of objects observed in Terzan
5 suggest that this cluster may contain 100 pulsars — probably more than any other Galactic cluster. Although we do not resolve
individual sources in Liller 1, comparison of our images with other observations suggests that we are again observing the
sum of emission from a number of objects. The 90 cm flux densities of Terzan 5 and Liller 1 are 35 and 9 mJy, respectively,
implying that a number of bright pulsars in these clusters have been hidden from pulsed searches, perhaps by a combination
of dispersion smearing, scattering and doppler broadening. |
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