GCN Circular 21781

A.J. Levan (Warwick), E. Troja (UMD/GSFC), N.R. Tanvir (Leicester),
O. Fox (STScI), J. Hjorth (DARK, Copenhagen), S. B. Cenko (GSFC),
A. S. Fruchter (STScI), R. Ryan (STScI), Z. Cano (Granada), A. de
Ugarte Postigo (Granada), P. Evans (Leicester), J. Greiner (MPE
Garching), N. Kawai (Tokyo Tech), H. Khandrika (STScI), A. Lien
(UMBC/GSFC), J. Lyman (Warwick), I. Mandel (Birmingham), P. O'Brien
(Leicester), J. Osborne (Leicester), E. Palazzi (INAF-IASF Bologna),
D. Perley (LJMU), E. Pian (INAF-IASF Bologna), L. Piro (INAF/IAPS),
T. Sakamoto (AGU), S. Schulze (Weizmann Institute of Science),
S. Rosswog (Stockholm), D. Steeghs (Warwick), P. Sutton (Cardiff),
D. Watson (DARK, Copenhagen) report:

We obtained both multi-wavelength imaging and spectroscopy of
the proposed counterpart (LVC GCN 21529
Not found
 
 
) of LIGO/Virgo G298048 
(LVC GCN 21509
Not found
 
 
) with the Hubble Space Telescope at several epochs 
between 22 and 28 August (under programmes GO 14804 (Levan), 
GO 14850 (Troja) and GO 14771 (Tanvir)). The transient is well 
detected in both the nIR and optical imaging, but is fading rapidly at the 
end of the observations, with a factor two fading between Aug 26 
and Aug 28 in the F160W filter.

Spectroscopy at the first epoch covers the range 0.9-1.6 microns,
and the counterpart is well detected across this spectral range.
The spectrum is dominated by a range of broad features, most notably
a peak at ~1.1 microns, but additional features are observed between
1.2 and 1.6 microns.

An image of the field, as observed by HST is shown at

http://www.astro.warwick.ac.uk/people/levan/gw_hst001

NOTE: The page is password protected with password HsT_G298048, and
the image should not be shared.

We thank the staff of STScI, in particular Patrica Royle, Alison
Vick, Neill Reid and Lou Strolger for their rapid work in scheduling
these ToO observations.