New Constraints on the Cooling of the Central Compact Object in Cas A

Abstract

To examine the previously claimed fast cooling of the Central Compact Object (CCO) in the Cas A supernova remnant (SNR), we analyzed two Chandra observations of this CCO, taken in a setup minimizing instrumental spectral distortions. We fit the two CCO X-ray spectra from 2006 and 2012 with hydrogen and carbon neutron star atmosphere models. The temperature and flux changes in the 5.5 years between the two epochs depend on the adopted constraints on the fitting parameters and the uncertainties of the effective area calibrations. If we allow a change of the equivalent emitting region size, R em , the effective temperature remains essentially the same. If R Em is held constant, the best-fit temperature change is negative, but its statistical significance ranges from 0.8σ to 2.5σ, depending on the model. If we assume that the optical depth of the ACIS filter contaminant in 2012 was ±10 % different from its default calibration value, the significance of the temperature drop becomes 0.8σ to 3.1σ, for the carbon atmospheres with constant R Em . Thus, we do not see a statistically significant temperature drop in our data, but the involved uncertainties are too large to firmly exclude the previously reported fast cooling. Our analysis indicate a decrease of 4%-6% (1.9-2.9σ significance) for the absorbed flux in the energy range 0.6 − 6 keV between 2006 and 2012, most prominent in the ≈ 1.4-1.8 keV energy range. It could be caused by unaccounted changes of the detector response or contributions from unresolved SNR material along the line of sight to the CCO.

Massive and massless modes of the triplet phase of neutron matter

“…10. We find that the modes corresponding to M (3,4) are degenerate. This is due to the remaining symmetry in the (x, y)-plane resulting from our choice for the ground state (Eq.…”

“…We find two solutions for the equation Π −1 (3,4) (iω (3,4) ) = 0. Numerical solutions for ω (3,4) are plotted in Fig. 1.…”

“…Since the early days of pulsar physics it was recognized that at densities equal to or higher than nuclear saturation densities, neutrons near the Fermi surface should form Cooper pairs in the 3 P 2 channel, and since then, model calculations have strengthened that belief [1][2][3][4]. An intuitive way to understand this is to observe that the neutronneutron phase shifts become repulsive at momenta comparable to the Fermi momentum in dense matter in all but the 3 P 2 channel.…”

Neutron Stars—Cooling and Transport

“…3.3), which helps to explain the variety of the observed surface temperatures of cooling neutron stars (Gusakov et al 2004;Page et al 2004). A spectacular example is the neutron star CXO J232327.9+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). This decline can be comfortably explained by the PBF emission (Page et al 2011;Shternin et al 2011; see also Ho et al 2015 for a recent analysis including modern observational data).…”

Neutron Star Cooling with Various Superfluid and Superconducting States

“…This scenario seemed to be fine until the recent observations of the central source of Cas A [1][2][3]. The surface temperature of Cas A is relatively high and it matches to the standard cooling curve, but the mass of Cas A has been found to be unexpectedly large.…”