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GCN Circular 28381

Subject
GRB 200906A: LBT near-infrared upper limit
Date
2020-09-07T18:02:35Z (4 years ago)
From
Andrea Rossi at INAF <andrea.rossi@inaf.it>
A. Rossi (INAF-OAS) reports on behalf of the CIBO collaboration:

We observed the location of the X-ray afterglow (Beardmore et al., GCN 
28373) of the Swift GRB 200906A (Page et al., GCN 28371) simultaneously 
in the H and Ks bands with the LUCI near-infrared imager and 
spectrograph mounted on the Large Binocular Telescope (LBT, Mt Graham, 
AZ, USA).
Observations started at 03:57 UT on 2020-09-07, and allowed us to obtain 
18 min of exposure in each band. Unfortunately, observations were 
performed under variable sky conditions with passing clouds.

Inspection of the combined H-band images (mid-time of 0.628 days after 
the GRB), does not reveal any source down to the limiting magnitude 
H<21.8 mag (AB system).

A preliminary comparison of the simultaneous Swift/XRT flux of 1.06e-07 
Jy at a mid-frequency 3.8E+17 Hz (1.6 keV), gives a X-ray to infrared 
slope-index b_OX<0.5, confirming the dark nature of this GRB. This XRT 
flux has been obtained modelling the XRT lightcurve after 200 seconds 
with a power-law with decay-index 0.60+-0.04.

We acknowledge the excellent support from the LBTO and LBT-INAF staff, 
particularly B. Rothberg, F. Cusano, S. Paiano and D. Paris, in 
obtaining these observations.
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