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EVN e-VLBI detections of MAXI J1659-152

ATel #2906; Z. Paragi (JIVE), A. J. van der Horst (NASA/MSFC/ORAU),J. Granot (Univ. Hertfordshire),G. B. Taylor (Univ. New Mexico), C. Kouveliotou (NASA/MFSC),M. A. Garrett (Astron), R. A.M. J Wijers (Univ. Amsterdam),E. Ramirez-Ruiz (Univ. Santa Cruz),E. Kuulkers (ESA/ESAC), N. Gehrels (NASA/GSFC),P. M. Woods (Corvid)
on 5 Oct 2010; 17:31 UT
Credential Certification: Zsolt Paragi (zparagi@jive.nl)

Subjects: Radio, Black Hole, Neutron Star, Transient

Referred to by ATel #: 2918, 3358

We observed MAXI J1659-152 (Negoro et al. 2010, ATel #2873; Mangano et al. 2010, GCN #11296) following its sub-millimeter and centimeter radio detections (de Ugarte Postigo et al. 2010, GCN #11304; van der Horst et al. 2010, ATel #2874) with the European VLBI Network (EVN) in real-time e-VLBI mode on 30 September 2010, from 13:30 to 18:30 UT at 4.9 GHz. The participating telescopes were Cambridge, Effelsberg, Jodrell Bank (MkII), Hartebeesthoek, Medicina, Onsala, Torun and Westerbork sending data at a rate of ~1024 Mbps to the EVN Data Processor at JIVE. The target was phase-referenced to the nearby source J1707-1415 (2.2 degrees away) which is apparently in outburst and serves as a very good compact calibrator. MAXI J1659-152 was detected at RA(J2000) 16 59 01.67709, DEC(J2000) -15 15 28.7324 (uncertainty about 1 mas), in agreement with the optical position reported by Marshall (2010, GCN #11298), with a peak brightness of 6.1 mJy/beam, and a total flux density of about 10 mJy.

The source was observed again at the same frequency with the EVN on 4 October from 13:30 to 18:00 UT, now including the Yebes telescope in the array as well. Very preliminary data analysis shows that MAXI J1659-152 is fainter in this second run but clearly detected. Its peak emission coincides with the first epoch VLBI position within 1 milliarcsecond, which indicates no or very small proper motion. This corresponds to an upper limit of 1% of the speed of light for an assumed distance of 7 kiloparsec. Further analysis is required to reveal the detailed radio structure at these two epochs.

Although the source is suggested to be a black hole candidate (Kalamkar et al. 2010, ATel #2881), our initial analysis shows no evidence for collimated ejecta travelling at (mildly-)relativistic speeds, as in the case of, e.g., XTE J1752-223 (Yang et al. 2010, arXiv1009.1367). However, we note that relativistic ejecta are not always observed in black hole binary systems during X-ray state changes, see the recent observations of Cyg X-1 (Rushton et al. 2010, ATel #2734). It is also possible that the jet components are formed only at later stages of the X-ray spectral state change in black hole transients. Further observations are planned.

We thank the EVN PC Chair, Tiziana Venturi for supporting our ToO observations, and to the EVN stations who made this possible. e-VLBI developments in Europe are supported by NEXPReS, an Integrated Infrastructure Initiative (I3), funded under the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement RI-261525. The European VLBI Network (http://www.evlbi.org/) is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils.