[vsnet-grb-info 4820] GRB 070612A: NOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6555
SUBJECT: GRB 070612A: NOT observations
DATE:    07/06/18 21:24:53 GMT
FROM:    Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center  <malesani at astro.ku.dk>

D. Malesani, J. Hjorth, J.P.U. Fynbo (DARK), J. Sollerman (DARK &
Stockholm obs.), G. Olofsson (Stockholm Obs.), D. Paraficz (NOT & DARK),
M. Durant (IAC), report:

We observed the afterglow (Updike et al., GCN 6515; Cenko et al., GCN
6525) of GRB 070612A (Grupe et al., GCN 6509) with the NOT telescope at
several epochs. The afterglow is detected in all our images. The galaxy
seen in the SDSS images (first noted by Updike et al., GCN 6515) may be
resolved into two components, one roughly coincident with the afterglow,
and the other 1.8" South.

>From our measurements, the light curve has been slowly declining between
Jun 14.9 and Jun 17.9 UT. The data after 1 day (including the MDM points
by Mirabal et al., GCNs 6526, 6529) are consistent with a steep power-law
decay (alpha ~ 3) superimposed on a constant contribution. From our latest
image (Jun 17.90 UT) we measure R=21.45+-0.2 (against USNO-B1.0), where
the error is mostly due to calibration. This value includes some
contribution from the underlying host galaxy.

If the redshift of the GRB is z=0.096, our measurement implies that any
associated SN was fainter than SN1998bw by at least 1.5 mag (and likely
more, after considering the host contribution). Alternatively, an
unextinguished SN as bright as SN1998bw should be at redshift >0.2. We
note that the SDSS catalog provides two redshift determinations for this
object, the largest one being z=0.42+-0.14:

http://cas.sdss.org/astrodr5/en/tools/explore/obj.asp?id=587728931336684102

Our data are consistent with a SN akin to SN1998bw at z=0.4. In this case,
a rebrightening by ~0.5 mag is expected during the next week. Observations
will continue for as long as visibility contraints allow.