Skip to main content
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 19600

GRB 160625B: VLT/X-shooter redshift
2016-06-27T09:50:38Z (8 years ago)
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <>
D. Xu (NAOC/CAS), D. Malesani (DARK/NBI), J. P. U. Fynbo (DARK/NBI), N. 
R. Tanvir (Univ. Leicester), A. J. Levan (Univ. Warwick), D. A. Perley 
(DARK/NBI), report on behalf of a larger collaboration:

We observed the optical afterglow of the Fermi GRB 160625B (Dirirsa et 
al., GCN 19580; Burns, GCN 19581; Troja et al., GCN 19588) with the ESO 
VLT UT2 (Kueyen) equipped with the X-shooter spectrograph. Observations 
started on 2016 June 27.19 UT (1.25 days after the Fermi trigger) and 
consisted of 4 spectra by 600 s each, covering the wavelength range 
3500-20000 AA.

The afterglow is well detected in the acquisition image with R ~ 19.1 +- 
0.3, where the large error is due to scatter in the USNO magnitudes used 
as reference, and the r versus R filter transformation.

The continuum trace is well detected in our exposures, down to ~3100 AA. 
The lack of any drop sets an upper limit to the redshift z < 1.55. A 
number of superimposed absorption features are visible; among others, we 
detect Mg I, Mg II, Fe II, C IV, Si IV, O I, Si II, Zn II, Al II, and Al 
III, all at a common redshift z = 1.406, which we conclude to be the 
redshift of GRB 160625B. We also detect an intervening Mg II absorption 
system at z = 1.319.

At z = 1.406, the fluence in the 10-1000 keV Fermi band (Burns, GCN 
19587) corresponds to an isotropic-equivalent energy of ~2.5*10^54 erg.

We acknowledge excellent support from the ESO observing staff in 
Paranal, in particular Juan Carlos Munoz, Elizabeth (Liz) Bartlett, 
Dimitri Gadotti and Francisco Caceres.
Looking for U.S. government information and services? Visit