SN 1998bw , especially after the discovery of GRB 030329/SN 2003dh , seems to be the equivalent of the Rosetta stone for the SN/GRB connection .
In this paper I review optical and near IR observations that have been carried out for this uncanny object , which has probably confirmed suspicions and ideas originally formulated in the early seventies of last century .

Thus , the observation of gamma-ray line emission from a young supernova seems very promising in the near future .
The observation , or even a null observation at a low threshold , will give significance in the fields of nuclear astrophysics and supernova theory .
The scientific importance of a positive measurement would be analogous with and comparable to the importance of successful detection of neutrinos from the Sun . 
Clayton , Colgate & Fishman ( ) .

This story probably begins in 1969 , with what I like to call a prophecy , and it is right with it that I wish to start this review on the optical and near-IR observations of SN 1998bw This talk was given in Valencia on April 25 , 2003 .
For some cabalistic reason , this coincided exactly with the fifth anniversary of GRB 980425/SN1998bw . .

As J. Sollerman said in one of his papers on this striking object , SN 1998bw was born famous .
And it was doomed to become even more famous as time went by , so famous that it was sometimes named the supernova of the century .
And this is indeed interesting , since it was born in the same century of SN 1987A , one of the most studied and referenced objects in the sky .

Just from the optical and near-IR observations point of view , this is witnessed by the large number of papers which have been published in the first four years .
Starting with the Nature papers by Galama et al . ( ) and Iwamoto et al . ( ) , a number of authors have presented the results of their observational campaigns : McKenzie & Schaefer ( ) , Galama et al . ( ) , Stathakis et al . ( ) , Fynbo et al . ( ) , Sollerman et al . ( ) , Patat et al . ( ) and Sollerman et al . ( ) .

The reader is referred to these papers for a detailed account on the observations , while here I will try to give only a general view of the SN 1998bw phenomenon .

SN 1998bw was discovered by Galama et al . ( ) in the BeppoSAX Wide Field Camera error box of GRB 980425 ( Soffita et al . ( ) , Pian et al . ( ) ) close to a spiral arm of the barred galaxy ESO 184–G82 ( see Fig . ) , by comparing two frames taken at the ESO New Technology Telescope on Apr 28.4 and May 1.3 UT .
Spectroscopic and photometric observations , both in the optical and in the near IR , started at ESO–La Silla immediately after the discovery , and showed that this object was profoundly different from all then known SNe ( Lidman et al . ( ) ) .

0.1 Contour plot of ESO-184-G82 .
The original image stack was obtained at VLT+FORS1 at about 900 days after the explosion .
Spatial scale was computed for a distance of 40 Mpc .
The SN position is marked . Figure 0.1 Contour plot of ESO-184-G82 .
The original image stack was obtained at VLT+FORS1 at about 900 days after the explosion .
Spatial scale was computed for a distance of 40 Mpc .
The SN position is marked . Its peculiar spectroscopic appearance , its unusually high radio luminosity at early phases ( Kulkarni et al . ( ) ) , its optical luminosity ( M _ { V } \sim - 19.2 + 5 log h _ { 65 } ) and , in particular , the probable association with GRB 980425 through positional and temporal coincidence ( Galama et al . ( ) , Pian et al . ( ) ) placed SN 1998bw at the center of discussion concerning the nature of Gamma Ray Bursts .
The object was tentatively classified as a peculiar Ic ( Patat & Piemonte ( ) , Filippenko ( ) ) , I would say by definition more than anything else , due to the complete absence of H lines , the weakness of the Si II 6355 Å line and no clear He I detection in the optical spectra ( see Fig . ) .
Main spectral features were identified as O I , Ca II , Si II and Fe II ( Iwamoto et al . ( ) ) .
The estimated expansion velocities were exceptionally high ( \sim 30,000 km s ^ { -1 } ) and this caused a severe line blending .
The evolution during the first months was unusually slow compared to known Ic , with the nebular spectra still retaining many of the features present during the photospheric phase ( Stathakis et al . ( ) , Patat et al . ( ) ) .

0.2 Spectrum of SN 1998bw taken at ESO-La Silla on May 5 , 1998 . Figure 0.2 Spectrum of SN 1998bw taken at ESO-La Silla on May 5 , 1998 . The late onset of the fully nebular phase has been interpreted as an indication for a large ejected mass ( Stathakis et al . ( ) ) as it was predicted by the early light curve models .
During the intermediate phase , the emission lines were definitely broader than in known Type Ib/c SNe and the simultaneous presence of iron–peak and \alpha -elements indicated unusual relative abundances or physical conditions in the SN ejecta ( Patat et al . ( ) ) .
The late spectroscopy presented by Sollerman et al . ( ) showed that the tentative morphological classification of SN 1998bw as a Type Ic event was indeed appropriate .
The main features have been identified as [ O I ] , Ca II , Mg I and Na I D , the latter possibly contaminated by He I 5876 Å .

As far as the Gamma-ray burst is concerned , GRB 980425 was pretty weak , since the implied energy for a 40 Mpc distance was 8.1 \pm 1.0 \times 10 ^ { 47 } erg ( Pian et al . ( ) ) , which is definitely smaller than the usual 10 ^ { 53 } erg value typical for the so-called cosmological GRBs .
This has led the community to believe that GRB 980425 is a member of an unusual class of GRBs/SNe ( see for example Fynbo et al . ( ) ) .

The galaxy which hosted GRB 980425/SN 1998bw , ESO 184–G82 , is an SBc galaxy with a recession velocity v _ { r } =2532 km s ^ { -1 } ( Patat et al . ( ) ) .
Its luminosity is L \sim 0.5 - 1.2 L _ { LMC } , it is currently undergoing strong star formation , it shows a bar and rather clear indications of morphological disturbances ( Fynbo et al . ( ) ) .
This is clearly visible in the late VLT images , which show a possibly double nucleus , isophotal twisting and asymmetry ( see Fig . ) .
All this suggests that the observed star formation is related to galaxy interaction/merging .

The HST images have shown that SN 1998bw exploded in a star-forming region ( Fynbo et al . ( ) ) , containing several bright and young stars within a projected distance of 100 pc .
This is consistent with the progenitor of SN 1998bw being a young and massive star

Due to its relatively high apparent brightness , Kay et al . ( ) 
and Patat et al . ( ) have attempted to perform some polarimetric measurements at different epochs .
After correcting for the interstellar polarization in the direction of the host galaxy , the estimated optical linear polarization was 0.6 % ( day - 7 ) , 0.4 % ( day +10 ) and 0.5 % ( day +42 ) .
The fluctuations in these values seem to suggest that the observed polarization is intrinsic to the SN , although a dusty medium in the parent galaxy can not be ruled out .

0.3 Comparison between SN 1998bw and other SNe at maximum light . Figure 0.3 Comparison between SN 1998bw and other SNe at maximum light . The small degree of polarization at optical wavelengths can be explained in terms of a moderate departure from sphericity ( axial ratio less than 2:1 ; Höflich et al . ( ) ) , either in the photosphere or in the outer scattering envelope when the line of sight is not coincident with an axis of symmetry .

Interestingly , no polarization , either circular or linear , was detected in the radio , and this has been interpreted as the signature of a spherically symmetric blast wave ( Kulkarni et al . ( ) ) .
This apparent discrepancy might suggest that the radio and the optical radiation were generated in regions of different geometry .