ATCA monitoring of MAXI J1421-613: detection of fading compact jet emission

ATel #5802; M. Coriat (Univ. Cape Town), Tasso Tzioumis (ATNF), S. Corbel (Univ. Paris Diderot & CEA Saclay), R. Fender (Univ. Oxford)
on 24 Jan 2014; 09:22 UT
Credential Certification: Mickael Coriat (mickael@coriat.eu)

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Following our initial detection of a candidate radio counterpart of the newly discovered neutron star X-ray binary MAXI J1421-613 (ATel #5750, #5751, #5759, #5780), we observed the source again on 2014 January 17 (23:15-01:00 UT) with the Australia Telescope Compact Array. The source was detected with the following flux densities:

5.5 GHz: 79 +/- 9 uJy
9 GHz: 95 +/- 9 uJy

and coordinates:

RA(J2000): 14:21:37.2
Dec(J2000): -61:36:25.4

with uncertainties of 0.3 arcsec in both RA and Dec when taking into account the positional uncertainty of the phase calibrator. The source is located 0.2 arcsec away from the center of the revised Swift/XRT position (Kennea et al. Atel #5780). Together with the statistically significant decrease of ~ 50 uJy in both frequency bands, this definitely associates the ATCA source with MAXI J1421-613. The spectral index alpha = 0.4 +/- 0.3 (S = k nu^+alpha) is similar to our first observation and suggests synchrotron emission from self-absorbed compact jets.

Using the Swift/XRT count rate and spectral parameters given in Kennea et al. (Atel #5780) and a distance < 25 kpc, the source lies on the neutron star track of the radio/X-ray correlation (see e.g. Migliari & Fender 2006) consistent with the recent detection of Type I bursts (Bozzo et al. Atel #5765).

We thank Phil Edwards for the scheduling of these observations