GCN Circular 28319

B. Rothberg (LBTO/George Mason University), O. Kuhn (LBTO), C. Veillet
(LBTO), S. Allanson (LBTO).

We observed the optical afterglow of GRB 200826A  (Gupta et al. GCN Circ.
28288
Not found
 
 
, Hurley et al., GCN Circ. 28291
Not found
 
 
) using the Large Binocular Telescope
Observatory equipped with the Multi-Object Double Spectrographs (MODS).
Our spectra cover the wavelength range 0.38-1.0 microns. The observations
consist of 4 exposures of 900 seconds each in three of the four available
channels (MODS-1 Red, MODS-2 Blue, and MODS-2 Red).  The observation mid
time was 09:39 UT 28 Aug 2020.

In two 60 second acquisition images taken simultaneously wiith the g-sloan
and r-sloan filters we measure a magnitude of g=22.96 +/- 0.07 and r=22.15
+/- 0.07 (both ABmags). The photometry was calibrated against the DR12
catalog magnitudes of nearby stars (Alam et al. 2015, ApJS 219,12A). The
acquisition images were taken at 08:52:34 and 08:54:35 UT 28 Aug 2020.

The spectroscopic observations were taken at a Position Angle = 17 degrees
in order to cover both GRB 200826A and a possible nearby galaxy 15" NE. The
observations used a 1" wide slit and the spectra were extracted for both
sources using a 1" wide aperture. We clearly detect a continuum from
0.38-0.9 microns. From the detection of multiple emission features, which
we interpret as [OII], [NeIII], H-gamma, H-beta, [OIII]/4959, [OIII]/5007,
we calculate a redshift of 0.7481 +/-0.0003.

The nearby galaxy, 15" NE, is determined to be unrelated to GRB 200826A.
From the detection of multiple emission features which we interpret as
[OII]/5007, [NII]/6548, H-alpha, [NII]/6583, [SII]/6716, and [SII]/6730, we
infer a redshift of 0.1730 +/- 0.0003.

Additional spectroscopic observations are planned.

We acknowledge and heartily thank the rest of the LBTO staff for excellent
support in readying the telescope for nighttime on-sky activities during
these chaotic times.
B. Rothberg also acknowledges the assistance of R.T. Gatto.