7–12 Jul 2024
Aurum, the ‘Gabriele d’Annunzio’ University and ICRANet
Europe/Rome timezone

The lightest neutron star formed from a binary system

12 Jul 2024, 17:45
15m
M6 (Palazzo Micara of the ‘Gabriele d’Annunzio’ University)

M6

Palazzo Micara of the ‘Gabriele d’Annunzio’ University

Viale Pindaro, 42, Pescara
Talk in a parallel session Galactic and extragalactic magnetars: recent observations and theoretical progress Galactic and extragalactic magnetars: recent observations and theoretical progress

Speaker

Shurui Zhang (ICRANet-UNIFE & USTC)

Description

The exceptionally low mass 0.770.17+0.2M inferred of the central compact object (CCO) XMMU J173203.3--344518 within the SNR HESS J1731--347, of age 4.5 kyr, challenges the standard core-collapse scenario of NS formation. The observed (likely post-AGB) star of 0.6M, at 0.3 pc from XMMU J1732, also within the SNR, enriches the scenario. To address this puzzle, we advance the possibility that the gravitational collapse of a rotating iron core of an evolved star can produce a light NS. We estimate the structure of the rotating pre-SN iron core of 1.2M and examine its gravitational collapse. We show that the angular momentum conservation during the collapse of an iron core rotating at 45% of the Keplerian limit leads to an 0.9M stable newborn NS. Assuming magnetic dipole radiation for a 1011 G field, the CCO must rotate relatively slowly with the upper limit of its rotation frequency being 530 Hz. Thus, the CCO mass and radius measurement probes the non-rotating NS mass-radius relation in the low-mass region. We show that a canonical NS thermal evolution agrees with the XMMU J1732 observed surface temperature of 2×106 K, assuming 4.5 kyr as its age. We propose the pre-SN evolved star, likely an ultra-stripped core of 4.2M, formed a tidally locked binary of 1.43 days orbital period with the post-AGB star. The SN produces a mass loss of 3M, imparting a kick velocity <670 km s1, disrupting the binary. This scenario agrees with the observed projected offset of 0.3 pc between XMMU J1732 and IRAS 17287--3443. Therefore, our findings support the possibility of CCOs originating in binaries, the relevant role of rotation in core-collapse events, and the CCO XMMU J1732 being the lightest NS ever observed.

Primary authors

Shurui Zhang (ICRANet-UNIFE & USTC) Jorge Armando Rueda Hernandez (ICRANet) Prof. Rodrigo Negreiros (Catholic Institute of Technology)

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