[vsnet-grb-info 14564] GRB 140219A: iPTF optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15878
SUBJECT: GRB 140219A: iPTF optical observations
DATE:    14/02/23 02:36:37 GMT
FROM:    Leo Singer at CIT/PTF  <lsinger at caltech.edu>

L. P. Singer (Caltech), M. M. Kasliwal (Carnegie Observatories/Princeton),
and S. B. Cenko (NASA/GSFC) report on behalf of the intermediate Palomar
Transient Factory (iPTF) collaboration:

We have searched for optical counterparts of GRB 140219A using the Palomar
48-inch Oschin telescope (P48). We observed 9 fields covering an area of
67.8 deg2 intersecting the Fermi GBM 1-sigma contour (Fermi trigger
414531995, Zhang et al., GCN 15866) and a preliminary MESSENGER-Suzaku IPN
annulus (K. Hurley, personal communication) that was available when the
GBM localization was first observable from Palomar. We observed all 9
fields for several epochs, with the first epoch extending from 7.0 to 8.1
hours after the burst. Sifting through candidate variable sources using
image subtraction and standard iPTF vetting procedures, we found no
compelling optical afterglow candidates to an average limiting magnitude
of r=21.1 mag.

About 80% of the published IPN error box (Hurley et al., GCN 15864) was
contained in these 9 fields, with most of the remaining 20% falling on a
disabled CCD on the P48. To fill the gap in the IPN error box, we observed
two additional fields starting 33.7 hours after the burst. The deepest
epoch of observations of these two fields had a limiting magnitude of
r=20.7 mag. Since we lacked reference images for these two offset fields,
we performed a catalog comparison search, examining any source that was
detected in our two deepest epochs but was not coincident with a stellar
object in SDSS. Of 342 sources meeting this criterion, all were known
galaxies and none were compelling optical afterglow candidates.

XRT source 1
(http://www.swift.ac.uk/xrt_products/TILED_GRB00024/index_1.php, Mangano
et al., GCN 15872) is contained in our nine early fields, and we associate
a coincident optical detection with the star SDSS J102559.46+073114.1.

XRT source 2
(http://www.swift.ac.uk/xrt_products/TILED_GRB00024/index_2.php, Mangano
et al., GCN 15872) is contained in our two late fields, and we detect no
coincident optical source to a limiting magnitude of r=20.5 mag at 35.7
hours after the burst.

XRT source 4
(http://www.swift.ac.uk/xrt_products/TILED_GRB00024/index_4.php) is
contained in our nine early fields, and we find no coincident optical
source to a limiting magnitude of r=20.2 mag at 8.1 hours after the burst.

XRT source 5
(http://www.swift.ac.uk/xrt_products/TILED_GRB00024/index_5.php, Mangano
et al., GCN 15875), the most plausible afterglow candidate due to its
observed fading, is also contained in our two late fields. We detect two
optical sources within the XRT error circle: the star SDSS
J102406.41+062937.6, and the galaxy SDSS J102406.58+062945.7. These were
also the sources detected by Pozanenko et al. (GCN 15876). For the star,
we report r=20.0+/-0.1, which is about 0.5 mag brighter than the value
given by SDSS DR10. We find no additional sources inside the XRT error
circle to a limiting magnitude of r=21.0.

The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi414531995.pdf
shows the footprints of the nine early P48 fields in relation to the Fermi
GBM 1-, 2-, and 3-sigma statistical+systematic contours (black) and the
IPN INTEGRAL-MESSENGER and WAM-HEND annuli (blue). The INTEGRAL-MESSENGER
annulus is comparable to the initial MESSENGER-Suzaku localization on
which we based these observations.

The diagram
http://www.its.caltech.edu/~lsinger/iptf/Fermi414531995_inset_1.pdf shows
the early P48 fields in relation to a six-sided IPN polygon and the XRT
candidates.

The diagram
http://www.its.caltech.edu/~lsinger/iptf/Fermi414531995_inset_2.pdf shows
the late P48 fields.