Radio non-detection of XTEJ1856+053

ATel #7338; A. Rushton (Oxford, Southampton), C. Rumsey (Cambridge), S. Motta, G. Anderson, R. Fender (Oxford), A. Sanna (UNICA), D. Altamirano (Southampton), P. Jonker (SRON)
on 2 Apr 2015; 15:04 UT
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Credential Certification: Anthony Rushton (anthony.rushton@astro.ox.ac.uk)

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Following the announcement of a new X-ray outburst from the BHC XTE J1856+053 (Atel #7233, Atel #7278), we triggered the Arcminute Microkelvin Imager Large Array (AMI-LA) telescope in Cambridge, UK, as part of the 4 PI SKY project. We successfully observed six epochs on 2015 March 18, 19, 20, 24, 26 and 27, each for approximately four hours around transit, at a central frequency of 16.13 GHz and a bandwidth covering 4.5 GHz.

We detected no evidence of a radio counterpart within the Swift-XRT error circle and derive 5 sigma upper fluxes limits of ~1 mJy/bm for each epoch or Fr<1.6e+18 erg/cm2/s at a wavelength of 2 cm. These relatively poor limits are affected by an unidentified extended source with a integrated flux ~12mJy located 2 arcmins to the East of XTEJ1856+053, which we have attempted to extract by stacking images and subtracting the best model within the UV-plane.

Further Swift observations (2015/03/25) found an unabsorbed flux of ~ 5.1 e-10 erg/cm2/s in the 2-10 keV band. Assuming the empirical X-ray/radio correlation for X-ray binaries (e.g. Corbel et al. 2013, MRNAS, 428, 2500), the radio non-detection would limit the black hole to a distance of >20 kpc. This suggests the source may be on the radio-quiet branch (although we note the observations were not precisely simultaneous).

We thank the AMI staff for scheduling these observations and the ERC for funding 4 PI SKY.