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Evidence for a Massive Neutron Star from a Radial-velocity Study of the Companion to the Black-widow Pulsar PSR B1957+20

van Kerkwijk, M. H. and Breton, R. P. and Kulkarni, S. R. (2011) Evidence for a Massive Neutron Star from a Radial-velocity Study of the Companion to the Black-widow Pulsar PSR B1957+20. Astrophysical Journal, 728 (2). Art. No. 95. ISSN 0004-637X.

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The most massive neutron stars constrain the behavior of ultra-dense matter, with larger masses possible only for increasingly stiff equations of state. Here, we present evidence that the black-widow pulsar, PSR B1957+20, has a high mass. We took spectra of its strongly irradiated companion and found an observed radial-velocity amplitude of K_(obs) = 324 ± 3 km s^(-1). Correcting this for the fact that, due to the irradiation, the center of light lies inward relative to the center of mass, we infer a true radial-velocity amplitude of K_2 = 353 ± 4 km s^(-1) and a mass ratio q = M_(PSR)/M_2 = 69.2 ± 0.8. Combined with the inclination i = 65° ± 2° inferred from models of the light curve, our best-fit pulsar mass is M_(PSR) = 2.40 ± 0.12 M_⊙. We discuss possible systematic uncertainties, in particular, in the light curve modeling. Taking an upper limit of i < 85° based on the absence of radio eclipses at high frequency, combined with a conservative lower limit to the motion of the center of mass, K_2 > 343 km s^(-1) (q > 67.3), we infer a lower limit to the pulsar mass of M_(PSR) > 1.66 M_⊙.

Item Type:Article
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Kulkarni, S. R.0000-0001-5390-8563
Additional Information:© American Astronomical Society 2011. Received 2010 September 27; accepted 2010 December 13; published 2011 January 25. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We also used data from the UVES Paranal Observatory Project UVESPOP (ESO DDT Program ID 266.D-5655). We made extensive use of SIMBAD and ADS. Facilities: Keck:I (LRIS)
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
UVES Paranal Observatory Project UVESPOP266.D-5655
Subject Keywords:pulsars: individual (PSR B1957+20) – stars: neutron
Issue or Number:2
Classification Code:PACS: 97.60.Jd, 95.30.Ky, 97.10.Ri, 97.60.Gb, 97.10.Wn
Record Number:CaltechAUTHORS:20110321-092425129
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Official Citation:M. H. van Kerkwijk et al. 2011 ApJ 728 95 doi: 10.1088/0004-637X/728/2/95
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23004
Deposited By: Benjamin Perez
Deposited On:21 Mar 2011 20:42
Last Modified:03 Oct 2019 02:42

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