Constraints on thermal X-ray radiation from SAX J1808.4-3658 and implications for neutron star neutrino emission

C. O. Heinke*, P. G. Jonker, R. Wijnands, R. E. Taam

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

86 Scopus citations


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 Jl808.4-3658 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 68-13+15% 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 LNS < 1.1 × 1031 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 Urea processes involving nucleons and/or hyperons, in the cores of massive neutron stars.

Original languageEnglish (US)
Pages (from-to)1424-1427
Number of pages4
JournalAstrophysical Journal
Issue number2 I
StatePublished - May 10 2007


  • Dense matter
  • Neutrinos
  • Stars: neutron
  • X-rays: binaries

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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