Swift J0513.4-6547 in outburst
ATel #6483; R. Sturm, S. Carpano, F. Haberl, P. Maggi, G. Vasilopoulos (MPE, Germany)
on 18 Sep 2014; 15:42 UT
Credential Certification: Richard Sturm (rsturm@mpe.mpg.de)
Subjects: X-ray, Binary, Neutron Star
We report an outburst of Swift J0513.4-6547, a 27.28 s pulsar Be/X-ray binary in the Large Magellanic Cloud,
which was discovered by Krimm et al. (2009, ATel #2011) and has an orbital period of 27 d (ATel #5511).
Recently, it was detected again in an XMM-Newton slew on 2014-08-25, named XMMSL1 J051328.1-654723, with a count rate of 1.13 cts s-1 in 7.2 s exposure.
In a follow-up observation with the XRT on board the Swift satellite (ObsId: 00031393004) starting at 2014-09-16 20:53 (UT),
the source is still seen with 105±10 net counts in 941 s exposure
at R.A.=05:13:27.80 and Dec.=-65:47:17.5 (J2000, uncertainty: 4.2"),
which is at an angular separation of 3.1" to the proposed optical counterpart 2MASS J05132826-6547187.
Fitting an absorbed power-law model in the 0.3-10.0 keV band,
we measure a photon index of Γ=0.92±0.43,
an absorbing column density of NH=1.1 (0-3.0)×1021cm-2,
a detected flux of 1.3±0.4 × 10-11erg cm-2 s-1,
and an unabsorbed luminosity of 4.1 (3.2-5.3) × 1036erg s-1 for a distance of 50 kpc.
For this spectrum, the XMM-Newton slew detection would translate into a flux of 0.7 × 10-11erg cm-2 s-1
indicating an ongoing brightening of the source.
However, both recent X-ray detections are close to the time of expected optical outbursts and therefore might be explained by two individual type-I outbursts.
By using a Bayesian periodic signal detection method around the known pulse period,
we find the most likely current pulse period to be 27.441±0.011 s,
but other beat frequencies are present due to a gap in the observation.
All uncertainties are given for a 90% confidence level.
We thank the Swift team for accepting and scheduling the target of opportunity observation.
