DIRECT OBSERVATION OF THE COOLING OF THE CASSIOPEIA A NEUTRON STAR
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The cooling rate of young neutron stars (NSs) gives direct insight into their internal makeup. Although the temperatures of several young NSs have been measured, until now a young NS has never been observed to decrease in temperature over time. We fit nine years of archival Chandra ACIS spectra of the likely NS in the ∼330 yr old Cassiopeia A supernova remnant with our non-magnetic carbon atmosphere model. Our fits show a relative decline in the surface temperature by 4% (5.4σ, from (2.12 ± 0.01) × 106 K in 2000 to (2.04 ± 0.01) × 106 K in 2009) and the observed flux by 21%. Using a simple model for NS cooling, we show that this temperature decline could indicate that the NS became isothermal sometime between 1965 and 1980, and constrains some combinations of neutrino emission mechanisms and envelope compositions. However, the NS is likely to have become isothermal soon after formation, in which case the temperature history suggests episodes of additional heating or more rapid cooling. Observations over the next few years will allow us to test possible explanations for the temperature evolution.
Subfields: Astronomy and Astrophysics, Instrumentation
View Paper: https://www.semanticscholar.org/paper/2e7708ac1269b01898c05c7c44434e6bbb95123f
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Citations in the corpus
- Cooling neutron star in the Cassiopeia A supernova remnant: evidence for superfluidity in the core (2010, methodology): “We fitted these spectra simultaneously, forcing the NS mass and radius, along with the distance andNH, to be the same as in the best fit of Heinke & Ho (2010) and Yakovlev et al. (2011), and finding the 1σ errors on the surface temperature at each epoch.”
- Cool WISPs for stellar cooling excesses (2015, background): “Finally, x-ray observations of the surface temperature of a neutron star in Cassiopeia A [16, 46, 47] showed a cooling rate considerably faster than expected.”
- Neutron Stars—Cooling and Transport (2015, background): “9+584842 in the Cassiopeia A supernova remnant, dubbed Cas A NS, which shows an unexpectedly appreciable temperature decline during several years (Heinke and Ho 2010; Elshamouty et al. 2013) (but see Posselt et al. 2013 for tentative alternative interpretations of the observations).”
- CONSTRAINING THE SYMMETRY PARAMETERS OF THE NUCLEAR INTERACTION (2012, background): “…determines the thermal relaxation time of the crust, which is important in the cooling of young neutron stars (Yakovlev & Pethick 2004), such as the recently detected rapid cooling of Cassiopeia A (Heinke & Ho 2010; Page et al. 2011) and in the cooling of soft X-ray transients (Page & Reddy 2012).”