e-VLBI detection of SN2007gr

ATel #1215; Z. Paragi (JIVE), C. Kouveliotou (NASA/MFSC), M. A. Garrett (Astron), E. Ramirez-Ruiz (Univ. Santa Cruz), H. J. van Langevelde (JIVE/Leiden), A. Szomoru (JIVE), M. Argo (JBO)
on 12 Sep 2007; 20:22 UT
Credential Certification: Zsolt Paragi (zparagi@jive.nl)

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We observed the Type Ibc SN2007gr on 6-7 September for 12 hours (21:00-09:00 UTC) at 4.97 GHz with the the European VLBI Network (EVN) using the e-VLBI technique. Participating telescopes were Darnhall, Jodrell Bank (MkII), Medicina, Onsala, Torun and Westerbork (phased array of 14 telescopes). The aggregate bitrate was 256 Mbps, except for Darnhall which contributed with an effective data rate of 128 Mbps due to analog bandwidth restrictions. There were 4*8 MHz subbands observed in both RCP and LCP polarizations. The target was phase-referenced to the nearby calibrator J0253+3835. The achieved rms noise level was 75 microJy/beam.

There is an unresolved source (beamsize 7 milliarcsecond) with a flux density of 422+-21 microJy (5.6 sigma) at coordinates RA 02 43 27.97151 DEC +37 20 44.6873 (J2000). This position is within 102 milliarcseconds of the reported optical counterpart of SN2007gr (CBET 1034), and is in agreement with the VLA position of RA=02 43 27.9725 Dec=+37 20 44.702 (Soderberg et al., in prep.). There are no other spurious sources exceeding the 5-sigma level within 1 arcsecond. We consider, therefore, our result as a VLBI detection of the supernova. Further observations are planned.

The VLBI position error is likely dominated by the position accuracy of the reference source J0253+3835 which is given as 0.55 mas in the VLBA Calibrator List. We used the Westerbork synthesis array data to calibrate the flux scale of our VLBI dataset. As a result, the VLBI flux scale is accurate to within 5%. Note that the VLBI amplitudes may be ~10% low due to coherence losses in phase-referencing.

e-VLBI is a technique where the signals from far away radio telescopes are directly streamed to the central data processor for real-time correlation, instead of recording. The data are immediately available to the astronomers for further processing.

e-VLBI developments in Europe are supported by the EC DG-INFSO funded Communication Network Developments project 'EXPReS', Contract No. 02662 The European VLBI Network is a joint facility of European, Chinese, South African and other radio astronomy institutes funded by their national research councils.