Central Bureau for Astronomical Telegrams
IAUC 6895: GRB 980425
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Circular No. 6895
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GRB 980425
T. J. Galama and P. M. Vreeswijk, University of Amsterdam; E.
Pian and F. Frontera, CNR, Bologna; and V. Doublier and J.-F.
Gonzalez, European Southern Observatory (ESO), report: "Comparison
of ESO New Technology Telescope images obtained on Apr. 28.4 and
May 1.3 UT shows that a point source in the BeppoSAX WFC error box
of GRB 980425 (IAUC 6884) not visible in the Digitized Sky Survey
brightened by 0.7 mag from R = 15.7 to 15.0 (+/- 0.1). The object
is located at R.A. = 19h35m03s.31, Decl. = -52o50'44".8 (equinox
2000.0), offset from the nucleus of the face-on spiral galaxy (ESO
184-G82). Its position does not coincide with either of the two
x-ray sources in the error box of GRB 980425 (Pian et al. 1998, GCN
61), and it is therefore not clear whether the source is related to
GRB 980425, or whether it is, e.g., a supernova. A finding chart
for it can be found at http://www.astro.uva.nl/titus/grb980425.html."
C. Lidman, V. Doublier, J.-F. Gonzalez, T. Augusteijn, O. R.
Hainaut, H. Boehnhardt, F. Patat, and B. Leibundgut, ESO, write:
"We have observed the supernova candidate discovered by Galama et
al. (see above). The object is located in a spiral arm of the
barred spiral galaxy ESO 184-G82, the redshift of which was
measured at 2528 km/s (heliocentric) from a spectrum obtained with
the 3.6-m NTT (+ EMMI). The object displays a steep magnitude
increase, as indicated by the following photometry (+/- 0.05 mag)
with the NTT (Danish 1.54-m telescope on May 3): Apr. 28.4 UT, R =
15.77; May 1.3, R = 14.83; 3.30-3.38, V = 14.81, R = 14.35, I =
14.40; 4.4, V = 14.23, R = 14.28, I = 14.27; 6.4, V = 14.00, R =
14.04, I = 14.30. With the ESO/MPI 2.2-m telescope (+ IRAC2) on
May 6.4, we obtained the following preliminary photometry J = 11.5,
H = 11.6; K = 11.9. A finding chart and secondary photometric
standards are available at http://sc6.sc.eso.org/~ohainaut/SN.
Spectra were obtained on May 1.4 (NTT), 3.4 (1.5-m Danish telescope
+ DFOSC), 4.4 (ESO 3.6-m telescope + EFOSC2), and 6.4 (NTT). Apart
from H-alpha (probably from the galaxy), the mostly featureless
spectra display some broad lines in the range 350-500 nm, then a
steep decrease over 500-700 nm, and a plateau from 700 to 1000 nm,
with very broad bumps at 620 and 800 nm (spectra of the region
350-900 nm are displayed at the same URL). The relative intensity
of the different regions of the spectrum is changing from day to
day. The absence of H lines suggests that the object is not a
type-II supernova; the lack of Si at 615 nm indicates that it is
not a regular type-Ia supernova. The nature of this puzzling
object still evades identification, as does its relation to GRB
980425 or to the galaxy. The ESO team continues monitoring."
(C) Copyright 1998 CBAT
1998 May 7 (6895) Daniel W. E. Green
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