The distribution of neutron star masses

Abstract

From the beginning of current century to the present, the sample of observed neutron star (NS) with measured masses grew owing to the great effort in the observational field, and the so-called "canonical" unique value formerly attributed to NS at birth was put into question. Different groups pointed out the existence of different channels for a NS formation, possibly leading to a multimodal distribution. We employ in the present work tools from frequentist and Bayesian analysis to test some inferences about the mass distribution of neutron stars, in order to clarify if the observed objects belong to the same populations or show differences at the birth/evolutionary history.

Nuclear Pairing Gaps and Neutron Star Cooling

“…In the absence of this possibility we dedicate this work to another consistency check, namely the theoretical derivation of the NS mass distribution of the currently available data points from their position among the theoretical cooling curves for different masses. This mass distribution can then be compared to mass distributions of NSs obtained in different, independent theoretical ways [80][81][82][83][84][85].…”

“…(a) there is no bias on the masses (and thus luminosities) in the current data set of isolated NSs, that is, bright and dim objects are supposed to be present with equal probability, thus the detection of these sources is independent of their brightness; (b) the mass distribution of isolated NSs in the cooling diagram is not different from the mass distributions of NSs in binary systems [82][83][84][85][86] or all NSs in the Universe, which were addressed in the other theoretical studies.…”

“…The different results in Figure 5 can now be compared with other theoretical studies of the NS mass distribution. There is a long-lasting discussion whether this distribution is unimodal or bimodal due to different classes of NS evolution histories [80][81][82][83][84][85], and in Figure 6 we show a compilation of some recent theoretical studies for the NS mass distribution. We provide a binning consistent with Figure 5 in order to compare directly with our results.…”

“…Table 2. Root-mean-square variances between deduced NS mass distributions with different p1S0 gap scale factors s x , s y for Fe or light-elements atmospheres, shown in Figure 5, and different theoretical models [82][83][84][85], shown in Figure 6. Preferred values are indicated in boldface.…”

“…Figure 6. Theoretical NS mass distributions by several authors [82][83][84][85] (red curves) binned and normalized in the same way as Figure 5 (black histograms).…”