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XMMU J054134.7-682550 is a 61 s X-ray Pulsar with Cyclotron Features

ATEL # 1176; C. B. Markwardt (CRESST/NASA/GSFC), J. H. Swank (NASA/GSFC), R. Corbet (CRESST/NASA/GSFC)
on 10 Aug 2007; 2:36 UT
Password Certification: Craig B. Markwardt (

Subjects: X-ray, Gamma Ray, Binaries, Neutron Stars, Pulsars, Transients

Based on the recent report of activity from XMMU J054134.7-682550 (ATEL #1169), RXTE observed the source on 09 Aug 2007 at 03:35 UTC for about 3500 seconds.

X-ray pulsations are clearly detected. The pulse period is 61.601 +/- 0.017 seconds, with a pulsed semi-amplitude of about 40%. There are no obvious signs of orbital Doppler modulation. Assuming this source is a Be star system having a giant, "Type II" outburst, the estimated orbital period is about 80 days -- within a factor of ~2 -- based on a fit to the P_{spin} vs. P_{orb} for other similar systems. Thus the lack of orbital modulation is not surprising.

For the mean PCA spectrum, the best-fitting model is a cut-off power law, with photon index 0.47 and an e-folding cut-off energy of 16 keV. Cyclotron features are apparent at ~10 and ~20 keV with absorption depths of about 10%. A weak iron line at 6.4 keV and equivalent width 100 eV is also apparent. For a distance of 52 kpc, the mean 2-40 keV luminosity is 2.0e38 erg/s. The fluxes in the 2-10, 10-20 and 20-40 keV bands were 1.75, 2.08 and 2.49, in units of 1e-10 erg/s/cm2.

These observations confirm the suggestion by Shtykovskiy and Gilfanov (2005, A&A, 431, 597) that this source is a likely High Mass X-ray Binary.

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R. E. Rutledge , Editor
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