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A radio counterpart to the X-ray transient MAXI J1828-249 detected with the ATCA

ATel #5911; Stéphane Corbel (University Paris Diderot & CEA Saclay), John A. Tomsick (SSL/UCB), Tasso Tzioumis (ATNF)
on 21 Feb 2014; 07:33 UT
Credential Certification: S. CORBEL (stephane.corbel@cea.fr)

Subjects: Radio, Infra-Red, Optical, X-ray, Request for Observations, Binary, Black Hole, Transient

Following the recent detection of MAXI J1828-249 in the hard state by Swift/XRT (ATel #5886), we report on radio observations conducted on 2014 February 16 with the ATCA and the CABB backend.

A radio source is detected at the location of MAXI J1828-249 (ATel #5479) with preliminary flux densities of 1.38 +/- 0.05 mJy at 5.5 GHz and 1.28 +/- 0.06 mJy at 9 GHz. The radio spectrum is consistent with being flat and supports an origin from self-absorbed synchrotron emission from the compact jets that are usually observed during the hard state of black hole binaries in outburst. No radio emission was reported during the soft state (ATel #5484).

In addition to the Feb. 14 observation (ATel #5886), Swift observations occurred on Feb. 16, 18, and 20. The 0.5-10 keV XRT count rates for the four observations have been 0.76 +/- 0.02, 1.27 +/- 0.03, 1.47 +/- 0.03, and 1.21 +/- 0.03 c/s, respectively. This may indicate that a small reflare occurred, peaking on Feb. 18, but observations are continuing.

On Feb. 16, by fitting with an absorbed power-law model, we measure an unabsorbed 3-9 keV flux of (4.2+/-0.3)e-11 erg/cm2/s. The radio measurements imply a location in the radio/X-ray diagram consistent with the standard correlation (e.g. the one defined by GX 339-4, see Corbel et al. 2013, MNRAS, 428, 2500), assuming a distance near ~8 kpc. This further favors a black hole candidate identification for MAXI J1828-249.

With the recent increase in X-ray, further observations are strongly encouraged, especially in radio and optical/near-infrared.