GCN Circular 17358
Subject
GRB 150120A: Gemini-N imaging and host redshift
Date
2015-01-28T22:40:07Z (9 years ago)
From
Ryan Chornock at Ohio U <chornock@ohio.edu>
R. Chornock (Ohio University) and W. Fong (University of Arizona) report:
We re-imaged the field of the possibly-short GRB 150120A (D'Elia et al.,
GCN 17310) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the
Gemini-North 8-m telescope starting on 2015 Jan 22.284 UT (2.16 days
post-burst and 49.8 hr after our first Gemini observations; Fong et al.,
GCN 17313). We obtained a total of 2160s of observations in r-band in
1.0" seeing at an airmass of 1.6. Image subtraction using the ISIS package
reveals no residuals in or around the enhanced XRT position (Evans et al.,
GCN 17317). Based on the 3-sigma limit of the second epoch, which is not
deep as our first epoch due to poorer conditions, we place a limit of r(AB)>25.0
mag on the optical afterglow of GRB 150120A at 2.0 hr
post-burst.
We note that the enhanced XRT position (Evans et al., GCN 17317) shifted
relative to the prompt enhanced XRT position (Evans, GCN 17311) and now
encompasses Source A of Perley & Cenko (GCN 17312), while Source B is now
just outside the XRT error circle. We placed a spectroscopic slit across
both Sources A and B and obtained a pair of 900s GMOS spectra on 2014 Jan.
27 with the R400 grating (range 4900-9200 Angs). Both galaxies exhibit
nebular emission lines (H-beta, [O III]) at the same common redshift of
z=0.460.
We thank the staff at Gemini for their assistance scheduling and
performing these observations.