2006/12/31 by C. O. Heinke, P. G. Jonker, R. Wijnands +1
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Black-body radiation #Galaxy #Luminosity #Neutrino #Neutron star #Nuclear physics #Photon #Physics #Pulsar #Pulsars and Gravitational Waves Research #Radiation #astro-ph
paper · pdf · doi:10.1086/513140
published as Astrophys.J.660:1424-1427,2007 · 5 pages, 2 figures; slight revisions, accepted by ApJ
arxiv created 2007/01/24 · openalex publication_date 2007/05/04 · arxiv updated 2011/02/11 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/05
Thermal X-ray radiation from neutron star soft X-ray transients in quiescence provides the strongest constraints on the cooling rates of neutron stars and thus on the interior composition and properties of matter in the cores of neutron stars. We analyze new (2006) and archival (2001) XMM-Newton observations of the accreting millisecond pulsar SAX J1808.4-3658 in quiescence, which provide the most stringent constraints to date. The X-ray spectrum of SAX J1808.4-3658 in the 2006 observation is consistent with a power law of photon index 1.83 ± 0.17, without requiring the presence of a blackbody-like component from a neutron star atmosphere. Our 2006 observation shows a slightly lower 0.5-10 keV X-ray luminosity, at a level of 68 % of that inferred from the 2001 observation. Simultaneous fitting of all available XMM-Newton data allows a constraint on the quiescent neutron star (0.01-10 keV) luminosity of L NS < 1.1 × 10 31 ergs s -1 . This limit excludes some current models of neutrino emission mediated by pion condensates and provides further evidence of additional cooling processes, such as neutrino emission via direct Urca processes involving nucleons and/or hyperons, in the cores of massive neutron stars.