Evolution of Calvera and Descendants of Calvera-like Central Compact Objects

Abstract

Calvera (1RXS J141256.0+792204) is an isolated neutron star recently classified as a central compact object (CCO) after its association with the supernova remnant (SNR) candidate G118.4+37.0. In this work, we investigate the long-term evolution and descendants of Calvera and the CCOs with similar initial conditions in the fallback disc model. We show that the observed spin period, period derivative, and X-ray luminosity of Calvera can be reproduced simultaneously with a magnetic field strength of $\simeq 4 \times 10^{10}$ G at the pole of the neutron star at an age of $\sim 10^4$ yr which is consistent with the estimated SNR age of the source. In the model, the lack of ordinary radio pulsations is due to ongoing mass accretion on to the star. From our simulations, we estimate that the source will become an ordinary radio pulsar (RP) after the termination of the accretion. The source will spin down under the weak dipole torque alone as an RP for a very long time ($\gtrsim 10^8$ yr) after the inactivation of the disc. From our simulations, we find that most of the CCOs with initial conditions similar to those of Calvera also become RPs which remain above or close to the upper border of the pulsar death valley after the inactivation of their discs. In the period-period derivative diagram, there is indeed a cluster of RPs in the region where the descendants of Calvera-like CCOs are estimated to be located in our model.