Swift J1745.1-2624 is still active in radio
ATel #4760; M. Coriat (Univ. Cape Town), Phil Edwards (ATNF), R. Fender (Univ. Southampton), S. Corbel (Univ. Paris Diderot & CEA Saclay), Tasso Tzioumis (ATNF), James Miller-Jones (Curtin), Peter Curran (Curtin), Richard Armstrong (Univ. Cape Town)
on 24 Jan 2013; 18:17 UT
Credential Certification: Mickael Coriat (mickael@coriat.eu)
Subjects: Radio, Binary, Black Hole, Transient
After a period of Sun constraints, the monitoring of the black hole candidate Swift J1745.1-2624 (e.g. Atel #4380 #4381 #4393 #4394 #4450) by Swift/BAT started again on 2013 January 2. The BAT lightcurve indicates the source is still in outburst (http://heasarc.gsfc.nasa.gov/docs/swift/results/transients/weak/SwiftJ1745.1-2624/).
We conducted a radio observation on 2013 January 11 (00:06-03:31 UT; MJD 56303.08) with the Australia Telescope Compact Array in the EW352 configuration (maximum baseline 4.4 km). We detect a faint radio source at a location consistent with the coordinates of Swift J1745 (Atel #4394). The source is unresolved to the beamsize of 9.9 x 3.4 arcseconds (at 9 GHz), oriented 1.7 degrees E of N. The preliminary flux densities are 0.68 +/- 0.07 mJy at 5.5 GHz and 0.70 +/- 0.05 mJy at 9 GHz, which implies a spectral index alpha = 0.06 +/- 0.25 (S = k nu^+alpha). Uncertainties are given at a 1 sigma level and are statistical only. The derived spectral index suggests optically thick synchrotron emission from a compact jet. The source might therefore be in a hard X-ray state. Spectroscopic/timing X-ray observations would be necessary to confirm the state, however, narrow field of view instruments will still be Sun-constrained toward Swift J1745-26 until at least Feb 2nd. Follow-up observations at other wavelengths are therefore encouraged.
