GCN Circular 1611

Isabel Salamanca(1), Evert Rol(1), Ralph Wijers (1), Sara Ellison(2),
Lex Kaper(1), and Nial Tanvir (3) (1) University of Amsterdam (2)
Universidad Catolica de Chile (3) University of Hertfordshire, report:

We obtained a spectrum with the double arm spectrograph ISIS at the
4.2-m WHT telescope at La Palma (Spain) on October 4. A partial
calibration of the blue arm spectrum (2 Angstrom spectral resolution)
reveals the presence of four absorption components at detected in CIV
at redshifts 2.295, 2.298, 2.320, and 2.327, i.e. spanning a total
velocity range of approximately 3000 km/s.  The latter three
components are also clearly detected in SiIV, with a marginal
detection of SiIV at z=2.295.  The lines around 4000-4050 Angstrom can
be then identified as Ly-alpha (for which we also detect the emission
component reported earlier); there is a close match for the components
at z=2.320 and 2.327, whilst the two lowest redshift Lya components
are blended.

The interpretation of this 4-component absorption system could be of
absorption local to the burst source, or of cosmological components.

If all arise local to the burst, we must be viewing through ejecta in
a supernova-like explosion. After a day, supernova ejecta are so
opaque that we cannot see through them, and so we must be viewing the
results of an explosion that occurred weeks or more before the burst,
as in the supranova model. The narrowness of the components then must
mean that the ejecta have already cooled and partly condensed into
filaments. It is a challenge to have this happen within weeks, and
given the small filling factor inherent to filamentation, to have our
line of sight intersect four filaments.

If cosmological, we see our line of sight pass through 4 mass
concentrations of a magnitude well in excess of lyman limit systems in
quasar absorption line terms. These would all be local to the host
galaxy in cosmological terms, but with velocity separations large for
even a present-day massive cluster. Given that only 10-20% of quasars
at redshift 1 - 2 have even one such system, one concludes nonetheless
that seeing four systems implies a physical relation between them.
Thus we would be seeing a very large cosmic structure at z=2.3 with an
extent of 3000 km/s in velocity space. This is very difficult to get
in any cosmology, and would push cosmological models to very low
values of Omega_matter.

Further high-resolution spectroscopy is required to resolve the
velocity structure, and to determine the abundances and thermodynamic
state of these absorption systems, in order that we may understand the
nature of this remarkable system. In local models, one might find
variability in the Lyman-alpha emission.  Since the source is now
fading past R=21, these observations are most urgent.

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