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Swift observations of the Be/X-ray transient A1118-616

ATEL # 1889; A.K.H. Kong (NTHU, Taiwan)
on 4 Jan 2009; 16:44 UT
Password Certification: Albert Kong (

Subjects: X-ray, Binaries, Pulsars, Transients

We analyzed Swift XRT observations of the Be/X-ray transient 1A 1118-616 recently detected with Swift BAT (GCN#8777) on 2009 Jan 4. From a 105-sec photon-counting mode image, we obtained a refined X-ray position of the source. The source is the only bright X-ray object in the field and is located at R.A.=11h20m57.8s, Decl.=-61:54:57.9 (J2000) with an estimated uncertainty of 3.9 arcsec (90% confidence radius). We used 577-sec timing mode data for spectral fit. The energy spectrum of the source can be best fitted (reduced chi2 = 1.1 for 175 dof) with an absorbed blackbody model with N_H=(1.0+/-0.17)E22 cm^-2 and a blackbody temperature of 1.79+/-0.09 keV (90% confidence). A power-law fit with a best fitted photon index of 1.11+/-0.14 cannot provide an acceptable fit (reduced chi2 = 1.39 for 175 dof). There is an indication of soft excess and we fitted the spectrum with a two-blackbody model. The best fitted N_H is (1.4+/-0.3)E22 cm^-2 and the two blackbody temperatures are 0.13+/-0.04 keV and 1.68+/-0.10 keV. The additional soft component is significant at >99% via a F-test. The absorbed 0.5-10 keV flux is 7.2E-10 erg/cm^2/s. Assuming a distance of 4 kpc (Coe & Payne 1985), this corresponds to 1.4E36 erg/s.

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