21 February 2006
IAU Circular No.8674
GRB 060218 = SUPERNOVA 2006aj
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A. Soderberg, California Institute of Technology; E. Berger,
Observatories of the Carnegie Institution of Washington; and B.
Schmidt, Australian National University, report that a spectrogram
(range 320-1000 nm) of GRB 060218 (cf. Cusumano et al., GCN
Observation Report Circ. 4775; R.A. = 3h21m37s, Decl. = +16o51'58",
equinox 2000.0), obtained with Gemini-South telescope (+ GMOS) on
Feb. 21.024 UT, shows that underlying a power-law continuum are
features consistent with a broad-lined type-Ib/c supernova
(designated 2006aj) near maximum light, confirming the findings of
Masetti et al. (GCN 4803). The Gemini-South spectrum also confirms,
from several narrow emission lines, the redshift of z = 0.033
(Mirabal, who reported r = 17.6 on Feb. 19.1438 via GCN 4784, and
who notes a pre-outburst extended object at the GRB location via
GCN 4783). Marshall et al. provide a precise position of the
optical counterpart of GRB 060218 from images obtained with the
Swift UltraViolet and Optical Telescope: R.A. = 3h21m39s.71, Decl.
= +16o52'02".6 (estimated 1-sigma error about 1".0; cf. GCN 4779).
Zheng et al. report (on GCN 4802) the following R magnitudes for
the optical counterpart of GRB 060218: Feb. 18.4522, 17.8; 20.4471,
18.2.
21 February 2006
IAU Electronic Telegram No.409
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SUPERNOVA 2006aj = GRB 060218
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N. Mirabal, University of Michigan; and J. P. Halpern, Columbia
University, report that the optical-afterglow candidate of GRB 060218
(cf. Cusumano et al., GCN 4775; IAUC 8674) was imaged at the MDM 2.4-m
telescope (with RETROCAM) on Feb. 19.134 UT, yielding r' = 17.55 in
comparison with SDSS photometry (Cool et al., GCN 4777). SN 2006aj
is centered, to less than 0".2 in each coordinate, on a compact galaxy
that has r = 19.93 in the SDSS pre-burst image, at R.A. = 3h21m39s.7,
+16o52'02" (equinox 2000.0). A 0.8-nm-resolution spectrum obtained
with the Boller & Chivens spectrograph on the same telescope on Feb.
20.097 reveals high-excitation starburst emission lines at z = 0.0331,
as well as a blue continuum with a broad dip around 600 nm, similar
to the type-Ic-supernova spectrum of SN 1998bw = GRB 980425. (See
also Masetti et al., GCN 4803; Soderberg et al., GCN 4804).
22 February 2006
IAU Electronic Telegram No.410
SUPERNOVA 2006aj = GRB 060218
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D. Fugazza and P. D'Avanzo, Istituto Nazionale di Astrofisica
(INAF) and Osservatorio Astronomico di Brera (OAB); D. Malesani,
International School for Advanced Studies; M. Della Valle, INAF and
Osservatorio Astrofisico di Arcetri; E. Pian, INAF and Osservatorio
Astrononomico di Trieste; G. Chincarini; Universita degli Studi di
Milano-Bicocca; L. Stella, INAF and Osservatorio Astronomico di Roma;
G. Tagliaferri, INAF and OAB; J. Deng, Chinese Academy of Sciences;
and K. Maeda and K. Nomoto, University of Tokyo, report that they
acquired a spectrogram (resolution 1.0 nm) with the 3.6-m Telescopio
Nazionale Galileo on Feb. 20.93 UT of the optical counterpart of GRB
060218 (cf. Cusumano et al., GCN 4775; IAUC 8674). Inspection of the
spectrum reveals a smooth continuum below several nebular emission
lines. Moreover, broad deviations from the power-law shape are
clearly visible, suggestive of bumps similar to those of broad-lined
type-Ib/c supernovae. In particular, a bump at about 500 nm is
consistent with the feature defined by the absorption troughs due to
Fe II and Si II, as observed in SN 1998bw (Patat et al. 2001, Ap.J.
555, 900). The spectrum is well matched by the superposition of a
power law plus the spectrum of SN 1998bw obtained at about one week
before maximum. The strength of the features implies that the
supernova was contributing about half of the received light, the
remaining part being due to a power-law continuum.
