TITLE:   GCN CIRCULAR
NUMBER:  22362
SUBJECT: GRB 180115A: SEDM Observations
DATE:    18/01/18 20:21:52 GMT
FROM:    Virginia Cunningham at U of MD  <vcunning@astro.umd.edu>

V. Cunningham, J. D. Neill, S. B. Cenko, and R. Walters report on
behalf of the SEDM team:

We obtained a spectrum of the optical afterglow of GRB181105A
(Cannizzo et al., GCN 22335; Cano et al., GCN 22345; de Ugarte
Postigo et al., GCN 22346; Marshall et al., GCN 22357) 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., 2017,
astro-ph/1710.02917).

Observations began at 4:30 UTC on January 15 (14 minutes after
the Swift BAT trigger) and covered the wavelength range from
3800-9200 A with an exposure time of 2700 s.  Continuum emission
is clearly seen at wavelengths redder than 4500 A and is well fit by
a relatively steep power-law spectrum with index alpha = 1.93
(f_nu ~ nu^-alpha).  No obvious emission or absorption features are
clearly detected in the spectrum; due to the low SNR at wavelengths
shorter than 4500 A we cannot confirm the detection of Ly-alpha at
z = 2.487 reported by de Ugarte Postigo et al. (GCN 22346).

[GCN OPS NOTE(07sep19): Per author's request, in the last paragraph
the "alpha = 1.93" was changed to "alpha = 0.93".]