TITLE:   GCN CIRCULAR
NUMBER:  30290
SUBJECT: GRB 210619B: SEDM Optical Observations
DATE:    21/06/21 13:23:39 GMT
FROM:    Virginia Cunningham at U of MD  <vcunning@umd.edu>

V. Cunningham (U of Maryland), J. D. Neill (Caltech), S. B. Cenko
(NASA GSFC), and R. Walters (Caltech) report on behalf of the SEDM
team:

We observed the optical counterpart to GRB 210619B (D'Avanzo et al.,
GCN 30261) with the Spectral Energy Distribution Machine (SEDM) on
the 60 inch telescope at Palomar Observatory. The SEDM is a low
resolution (R ~ 100) integral field unit spectrometer with a multi-band
(ugri) rainbow camera imager (see Blagorodnova et al. 2018, PASP,
130, 035003, and Rigault et al. 2019, A&A, 627, A115). The SEDM
began observing the optical counterpart at 06:37:52 UTC (6.5 hours
after the burst trigger time). We performed a 2880 s exposure over the
wavelength range 3800-9200 A.

The continuum emission is well-fit by a power law spectrum with index
alpha = 2.8 (f_nu ~ nu^-alpha). The noise level of the spectrum,
especially at wavelengths bluer than 5000 A, make it difficult to confirm
the redshift reported by OSIRIS/GTC (GCN 30272).

[GCN OPS NOTE(22jun21):  Per author's request, the error in the sentence:
"The SEDM began observing the optical counterpart at 00:01:33 UTC
(1.5 hours after the burst trigger time)" and should be replaced with:
"The SEDM began observing the optical counterpart at 06:37:52 UTC
(6.5 hours after the burst trigger time)".]