GROND limits for NIR counterpart of Swift J2058.4+0516

ATel #3385; J. Greiner, F. Olivares E., P. Schady (all MPE Garching)
on 28 May 2011; 23:25 UT
Credential Certification: J. Greiner (jcg@mpe.mpg.de)

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We observed the new transient Swift J2058.4+0516 (Krimm et al. 2011, ATEL 3384) with GROND (Greiner et al. 2008, PASP 120, 405), the 7-channel imager mounted at the 2.2m MPI/ESO telescope at La Silla Observatory (Chile). In total, 72 10-sec images in JHK (the object is outside the g'r'i'z' field of views) were obtained, starting May 28, 2011 at 8:50 UT. Observations were hampered by thin cirrus, illuminated by the nearby Moon.
Within the 1.7 arcsec Swift/XRT error circle (Krimm et al. 2011, ATEL #3384) we detect no credible source, with 3-sigma upper limits (all in AB) of
J>19.8 mag
H>19.2 mag
K>17.2 mag
calibrated against 2MASS field stars. Using the UVOT b>21.6 mag limit, or alternatively the GROND limits with the assumption of no drastic variability during the 11 hrs between the Swift XRT and GROND observations, the flux ratio between X-rays and UV/NIR is >2500, surprisingly large.
We encourage deeper observations - La Silla is clouded out for tonight.