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Observations of the neutron star merger GW170817 , which is thought to have generated a black hole shortly afterward , have refined the TOV limit estimate to ~ .
 location: GW170817
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: GW170817 
Answer:
 location: GW170817