X-ray bounds on cooling, composition, and magnetic field of the Cassiopeia A neutron star and young central compact objects

Abstract

We present analysis of multiple Chandra and XMM-Newton spectra, separated by 9–19 years, of four of the youngest central compact objects (CCOs) with ages <2500yr: CXOU J232327.9+584842 (Cassiopeia A), CXOU J160103.1−513353 (G330.2+1.0), 1WGA J1713.4−3949 (G347.3−0.5), and XMMU J172054.5−372652 (G350.1−0.3). By fitting these spectra with thermal models, we attempt to constrain each CCO’s long-term cooling rate, composition, and magnetic field. For the CCO in Cassiopeia A, 14 measurements over 19 years indicate a decreasing temperature at a ten-year rate of 2.2 ± 0.2 or 2.8 ± 0.3 percent (1σ error) for a constant or changing X-ray absorption, respectively. We obtain cooling rate upper limits of 17 percent for CXOU J160103.1−513353 and 6 percent for XMMU J172054.5−372652. For the oldest CCO, 1WGA J1713.4−3949, its temperature seems to have increased by 4 ± 2 percent over a ten year period. Assuming each CCO’s preferred distance and an emission area that is a large fraction of the total stellar surface, a non-magnetic carbon atmosphere spectrum is a good fit to spectra of all four CCOs. If distances are larger and emission areas are somewhat smaller, then equally good spectral fits are obtained using a hydrogen atmosphere with B ≤ 7 × 1010G or B ≥ 1012G for CXOU J160103.1−513353 and B ≤ 1010G or B ≥ 1012G for XMMU J172054.5−372652 and non-magnetic hydrogen atmosphere for 1WGA J1713.4−3949. In a unified picture of CCO evolution, our results suggest most CCOs, and hence a sizable fraction of young neutron stars, have a surface magnetic field that is low early in their life but builds up over several thousand years.

Cold Quark–Gluon Plasma EOS Applied to a Magnetically Deformed Quark Star with an Anomalous Magnetic Moment

“…An interesting extension of this work would be to explicitly examine the effects of quark flavor chemical potentials that are expected to further soften the EOS, resulting in a larger equatorial radius for fixed mass and deformation. We are also exploring the impact of the effective massive gluon term on the cooling rate of the quark core, which can be compared to data from objects such as 3C 58 [100] and Cassiopeia A [101].…”

Hybrid cooling of the Cassiopeia A neutron star

“…(1.6 ÷ 1.65) M , depending on the accepted equation of state (EOS) (Heinke & Ho 2010;Ho et al 2015Ho et al , 2021Shternin et al 2021). The Cas A NS model, considered below, uses the most modern EOSs based on the Brussels-Skyrme nucleon interaction functional, BSk24, BSk25 (Pearson et al 2018), which have been precisely fitted to almost all available data on atomic mass and constrained to fit, up to the densities prevailing in neutronstar cores.…”

“…This is clearly seen in the lower panel, where these cooling trajectories are plotted on a large scale. The asterisks with error bars are the surface temperature of a neutron star in a supernova remnant Cassiopeia A, measured from the Chandra ACIS-S Graded spectra over the past 18 years, as reported in (Ho et al 2021). (The surface temperature data were recalculated in accordance with the mass M = 1.62M and radius R = 12.36 km of the simulated NS, assuming that T 2 e R = const at a fixed distance to the NS.)…”

“…The spot indicates the current location of Casa NS. Lower panel: a comparison of simulated results for M/M = 1.6, 1.62 with the data points ofHo et al (2021). Gray area shows the 99% confidence interval for the Cas A NS surface temperature.…”

“…Figure6. The best fit cooling trajectories for NS with a mass M = 1.60M and a radius R = 12.55 km, with iron and carbon envelopes in comparison with data points fromHo et al (2021) …”