GRB 970228. In order to determine the optical and IR magnitudes of
the OT of this GRB
we subtracted from the available measurements the following host galaxy
magnitudes: (extrapolated), V=25.75, R=25.3, I=24.45
(Fruchter et al. 1998),
J=24.0 (interpolated), H=23.2 and K=22.8
(Fruchter et al. 1998);
next, we dereddened the data using AV=0.75
(Fruchter et al. 1998).
Three SEDs were constructed. The first contains the X-ray data by
Frontera et al. (1998a),
the optical data by
van Paradijs et al. (1997)
and
Guarnieri et al. (1997)
- the latter ones were corrected for the
contribution of the nearby K star - and the radio upper limits by
Frail et al. (1998).
Note that the optical points by
Guarnieri et al. (1997)
were collected about 4 hours earlier than those
of
van Paradijs et al. (1997),
that is when, according to those authors, the
OT luminosity was still rising. This could explain the difference in the flux level
between the two data sets.
The second SED shows the ASCA
(Yoshida et al. 1997)
and ROSAT
(Frontera et al. 1998b)
X-ray data, the optical points and upper limits
by
van Paradijs et al. (1997),
and the radio upper limits by
Frail et al. (1998a).
The last SED includes V, I (interpolated between the HST V and I
data sets by
Fruchter et al. 1998)
and R
(Metzger et al. 1997)
optical points, J and K
(Soifer et al. 1997)
IR data, and radio upper
limits by
Frail et al. (1998a).
GRB 970508. Among GRB afterglows, this is the best monitored at all
wavelengths, therefore five SEDs could be constructed.
The first four SEDs were obtained with the data by
Piro et al. (1998;
X-rays),
Galama et al. (1998a;
U),
Sokolov et al. (1998;
BVRI),
Castro-Tirado et al. (1998;
R),
Pedersen et al. (1998;
R),
Morris et al. (1997;
K),
Bremer et al. (1998;
mm) and
Frail et al. (1997;
radio). The fifth SED
contains the data gathered by
Galama et al. (1998b)
and the 12-m ISO measurement
by
Hanlon et al. (1998).
The host galaxy contribution was not removed since
it was negligible at the considered epochs due to its faintness
(Zharikov et al. 1998).
Optical and IR data were dereddened with AV=0.08
(Galama et al. 1998a).
GRB 980329. To obtain the first SED for this GRB afterglow we used
the data by
in't Zand et al. (1998; X-rays),
Palazzi et al. (1998;
V, R) and
Rhoads et al. (1998a;
I).
The second SED was constructed with observations by
Djorgovski et al. (1998;
R),
Metzger (1998;
K),
Smith et al. (1998;
mm) and
Taylor et al. (1998,
radio), made about 8 days after the burst.
No host galaxy contribution has been subtracted, since its brightness is
uncertain. Correction for foreground Galactic absorption AV=0.4
(Palazzi et al. 1998)
was applied to the optical and IR data.
We note that the revision of the I band photometric measurement on
March 29.9
(Rhoads et al. 1998a)
suggests a very sharp and narrow local
spectral peak. If true, this would be inconsistent with a single
optical-to-X-ray emission component. The change of the continuum spectral
slope occurring in the optical has been tentatively explained as
Lyman- absorption up to
(Fruchter 1999).
GRB 980703. Two SEDs for this GRB afterglow were constructed using the X-ray data by Vreeswijk et al. (1999), the optical data by Bloom et al. (1998), Vreeswijk et al. (1999) and Rhoads et al. (1998b) and, for the first epoch, the radio data by Frail et al. (1998b). Host galaxy magnitudes V=23.04, R=22.58, I=21.95, J=20.87, H=20.27 and K=19.62 (Vreeswijk et al. 1999) were subtracted from the measurements. A foreground absorption AV=0.019 (Vreeswijk et al. 1999) was taken into account. The optical/IR bump could be accounted for by intrinsic extinction in the OT environment at the source redshift (z = 0.966; Djorgovski et al. 1998b).
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