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SWIFT observation of the SMC Be/X-ray pulsar SXP46.6 in outburst

ATEL # 2876; R. Sturm, W. Pietsch, F. Haberl (Max-Planck-Institut fuer extraterrestrische Physik), S. Immler (NASA/CRESST/GSFC)
on 27 Sep 2010; 19:33 UT
Password Certification: Frank Haberl (fwh@mpe.mpg.de)

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

A 2.9 ks observation with SWIFT from 2010 Sep. 26, 15:55 to 19:01 UT revealed a strong X-ray source in the Small Magellanic Cloud at R.A. = 00:53:54.5, Dec. = -72:26:44 (J2000, uncertainty 3.7 arcseconds) with a count rate of 0.14 cts/s. Compared to a previous 2.66 ks SWIFT observation from 2005 Nov. 09, 17:34 to Nov. 10, 00:00 UT with a count rate of 0.023 cts/s this is a factor of six higher in brightness. The position is consistent with the Chandra position of the Be/X-ray binary pulsar SXP46.6 (McGowan et al. 2008, MNRAS 384, 821). A comparison with the outburst ephemeris derived by Galache et al. (2008, ApJS 177, 189) using RXTE yields phases of ~0.1 for both observations. The X-ray spectrum obtained by the Swift XRT of this source, can be modelled by an absorbed power law with the Galactic absorption column density fixed to 6x1020 cm-2 and an absorption column density of the SMC with metal abundances of 0.2 solar of 2.1x1021 cm-2 and a photon index of 1.0. The observed 0.2-10.0 keV flux was 1.53x10-11 erg cm-2 s-1 with a corresponding intrinsic source luminosity of 7.0x1036 ergs s-1 (assuming a distance of 60 kpc). The search for pulsations around 46.6 s revealed a period of 46.37 s, confirming the identification with SXP46.6. The pulsed fraction is 40%. This is the first observation of SXP46.6 with an imaging X-ray instrument where the pulsations could be detected, unambiguously confirming its optical counterpart proposed by Buckley et al. (2001, MNRAS 320, 281, their star B). We thank the SWIFT team for accepting and scheduling the observations.


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