Can the Central Compact Object in HESS J1731-347 Be Indeed the Lightest Neutron Star Observed?

The exceptionally low mass of 0.77-0.17+0.2M circle dot for the central compact object (CCO) XMMU J173203.3-344518 (XMMU J1732) in the supernova remnant (SNR) HESS J1731-347 challenges standard neutron star (NS) formation models. The nearby post-asymptotic giant branch star IRAS 17287-3443 (approximate to 0.6M circle dot), also within the SNR, enriches the scenario. To address this puzzle, we advance the possibility that the gravitational collapse of a rotating presupernova (SN) iron core (approximate to 1.2M circle dot) could result in a low-mass NS. We show that angular momentum conservation during the collapse of an iron core rotating at approximate to 45% of the Keplerian limit results in a mass loss of approximate to 0.3M circle dot, producing a stable newborn NS of approximate to 0.9M circle dot. Considering the possible spin-down, this indicates that the NS is now slowly rotating, thus fulfilling the observed mass-radius relation. Additionally, the NS's surface temperature (approximate to 2 x 106 K) aligns with canonical thermal evolution for its approximate to 4.5 kyr age. We propose the pre-SN star, likely an ultrastripped core of approximate to 4.2M circle dot, formed a tidally locked binary with IRAS 17287-3443, with a 1.43 day orbital period. The SN led to a approximate to 3M circle dot mass loss, imparting a kick velocity less than or similar to 670 km s-1, which disrupted the binary. This scenario explains the observed 0.3 pc offset between XMMU J1732 and IRAS 17287-3443 and supports the possibility of CCOs forming in binaries, with rotation playing a key role in core collapse, and the CCO XMMU J1732 being the lightest NS ever observed.