[vsnet-grb-info 16262] BAT trigger 633105 (GRB 150301C): NOT r-band upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17543
SUBJECT: BAT trigger 633105 (GRB 150301C): NOT r-band upper limit
DATE:    15/03/04 22:05:01 GMT
FROM:    Zach Cano at U of Iceland  <zewcano at gmail.com>

Z. Cano (Univ. Iceland), D. Malesani, J. P. U. Fynbo (DARK/NBI),
A. de Ugarte Postigo (IAA/CSIC and DARK/NBI), N. R. Tanvir (Univ.
Leicester),
P. Jakobsson (Univ. Iceland), M. Saajasto, T. Pursimo (NOT), report on
behalf of a larger collaboration:

We observed the field of BAT trigger 633105 (Lien et al., GCN Circ. 17512)
with the
2.5-m Nordic Optical Telescope (NOT) equipped with ALFOSC on 01-Mar-2015 and
03-Mar-2015, obtaining 6x300 s of SDSS r-band exposures in each epoch.  The
mid
exposure times of our observations correspond to +0.60 and +2.59 days from
the
initial trigger, respectively.

Consistent with the X-ray position of the known source [PFH2005] 622
(thought to
be associated with the gamma-ray transient; Evans et al., GCN Circ. 17536),
we
detect one object at coordinates:

RA = 00:45:14.80
Dec = +41:50:32.35

Its magnitude is R =  22.7 +- 0.1 (using a USNO-A2.0 star in the field for
calibration). Two more objects are also detected in close proximity of the
XMM
position (Pietsch et al. 2005, A&A, 434, 483), and potentially consistent
with
it, including the source seen by UVOT by Hagen & Lien (GCN 17541), which
appears
to be quite blue (it has R = 22.3 +- 0.1 in our image).

We carried out digital image subtraction between our two images, where we
subtracted the first epoch from the second by using an adaptation of the
ISIS
software. In our difference image we do not detect any residual flux at the
combined XRT and XMM location, down to an upper limit of R > 23.2.

All objects seen in the NOT image are also apparent in the deep, archival
data
from the PAndAS survey (McConnachie et al. 2009, Nature, 461, 66), which
also reveals
a few more, fainter objects in the close proximity of the XMM position. No
object seems
to have varied significantly.

A gif animation of the two epochs of NOT imaging, and the difference image,
can
be retrieved from:
http://www.astro.ku.dk/~malesani/GRB/150301C/subtraction.gif

A comparison image of the NOT image from 01-Mar-2015 and the PAndAS image
can be found at:
http://www.astro.ku.dk/~malesani/GRB/150301C/comparison_NOT_PAndAS.png