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Record 15 of 947
Gamma-ray burst constraints on the galactic frequency of extrasolar Oort Clouds
External Online Source: doi:10.1086/117311
Author and Affiliation:
Shull, J. Michael(Univ. of Colorado, Boulder, CO, United States)
Stern, S. Alan(Southwest Research Inst., Boulder, CO, United States)
Abstract: With the strong Compton Gamma-Ray Observatory/Burst and Transient Source Experiment (CGRO/BATSE) evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approx. equals 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NSs penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequence stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on time scales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating, events. Comparing these estimates to the 3-4 soft gamma-ray repeater sources detected by BATSE, one is forced to conclude that (1) comet impacts on NSs are inefficient at producing gamma rays; or (2) the gamma rays from such events are highly beamed; or (3) the fraction of stars in the galaxy with Oort Clouds like our own is not higher than a few percent.
Publication Date: Feb 01, 1995
Document ID:
19950060546
(Acquired Dec 28, 1995)
Accession Number: 95A92145
Subject Category: ASTROPHYSICS
Document Type: Journal Article
Publication Information: Astronomical Journal (ISSN 0004-6256); 109; 2; p. 690-697
Publisher Information: United States
Contract/Grant/Task Num: NAGW-3023; NAGW-766
Financial Sponsor: NASA; United States
Organization Source: NASA; Washington, DC, United States
Description: 8p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: COMETS; CONSTRAINTS; GAMMA RAY BURSTS; MAIN SEQUENCE STARS; MILKY WAY GALAXY; NEUTRON STARS; OORT CLOUD; GAMMA RAY OBSERVATORY; PLANETARY EVOLUTION; STELLAR LUMINOSITY
Imprint And Other Notes: Astronomical Journal vol. 109, no. 2 p. 690-697 February 1995
Availability Source: Other Sources
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