Swift J0513.4-6547 = LXP 27.2 : a new Be/X-ray binary system in the Large Magellanic Cloud

Abstract

An exceptionally bright new X-ray source in the Large Magellanic Cloud was discovered by the Swift/BAT telescope on MJD 54923 (2 April 2009), and shown to have a pulse period of 27s using follow-up observations by RXTE/PCA. We report here on detailed timing observations taken over the following weeks using Fermi/GBM which reveal an excellent orbital solution and indicate that the source flux peaked at $\sim 10^{38}$ erg s${}^{-1}$. In addition, we report on follow-up optical observations (spectroscopic and photometric) which permit a classification of the mass donor star as B1Ve, and furthermore reveal a strong optical modulation at a period consistent with the binary period found from the Fermi/GBM data - 27.4 d. The dynamical mass estimate for the Be star is not in agreement with that expected for a B1V star - a mismatch similar to this has been previously reported for the few other Magellanic Cloud stars that also have dynamical mass estimates. In addition, the neutron star magnetic field determination from the X-ray data ($\sim 10^{13}$ G) adds further evidence to the possibility that many such stars in High Mass X-ray Binary systems may have magnetic fields greater than previously expected ($\sim 10^{12}$ G).

arXiv comment9 pages, 12 figures; accepted for publication in MNRAS

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• Multi-wavelength properties of IGR J05007-7047 (LXP 38.55) and identification as a Be X-ray binary pulsar in the LMC
• Interpreting the X-ray state transitions of Cygnus X-1
• Populations of highly variable X-ray sources in the XMM$-$Newton slew survey
• RXTE & Swift Observations of SWIFT J0513.4--6547
• Monitoring the X-ray Variability of Bright X-ray Sources in M33
• Monte-Carlo simulations on possible collimation effects of outflows to fan-beamed emission of ultraluminous accreting X-ray pulsars