We report the discovery of a very young high-mass X-ray binary ( HMXB ) system associated with the supernova remnant ( SNR ) MCSNR J0513-6724 in the Large Magellanic Cloud ( LMC ) , using XMM-Newton X-ray observations .
The HMXB is located at the geometrical centre of extended soft X-ray emission , which we confirm as an SNR .
The HMXB spectrum is consistent with an absorbed power law with spectral index \sim 1.6 and a luminosity of 7 \times 10 ^ { 33 } erg s ^ { -1 } ( 0.2–12 keV ) .
Tentative X-ray pulsations are observed with a periodicity of 4.4 s and the OGLE I-band light curve of the optical counterpart from more than 17.5 years reveals a period of 2.2324 \pm 0.0003 d , which we interpret as the orbital period of the binary system .
The X-ray spectrum of the SNR is consistent with non-equilibrium shock models as expected for young/less evolved SNRs .
From the derived ionisation time scale we estimate the age of the SNR to be < 6 kyr .
The association of the HMXB with the SNR makes it the youngest HMXB , in the earliest evolutionary stage known to date .
A HMXB as young as this can switch on as an accreting pulsar only when the spin period has reached a critical value .
Under this assumption , we obtain an upper limit to the magnetic field of < 5 \times 10 ^ { 11 } G. This implies several interesting possibilities including magnetic field burial , possibly by an episode of post-supernova hyper-critical accretion .
Since these fields are expected to diffuse out on a timescale of 10 ^ { 3 } -10 ^ { 4 } years , the discovery of a very young HMXB can provide us the unique opportunity to observe the evolution of the observable magnetic field for the first time in X-ray binaries .