NGC 3690 has been very active recently. Please see 1992bu and 1999D which have also occured, within the same decade, in this galaxy.
There is a great deal of discussion on the exact location of SN1998T. Make sure that you check the references images AND IAUC 6859
SN 1998T is now "officially" the SN that changed galaxies. Fortunatly it did this in name only. See IAUC 6859 for the final resolution of this argument.
According to http://www.cv.nrao.edu/~jhibbard/a299/a299.html and http://www.ifa.hawaii.edu/postdocs/vacca/images/arp299buv.html it follows that Arp 299 (aka Mrk 171) is made up of IC 694 (UGC 646471) on the east and NGC 3690 (H-247-1) (UGC 646472) on the west. Other names for IC 694 include MCG 10-17-002, and VV118c. Another good image of Apr 299 can be found at http://hplyot.obspm.fr/~lai/a299.html (reference Taichi Kato)
However, according to Dr. Corwin, on his IC catalog bugs web pages has notes on the original documentation reguarding IC 694 (You will need to do a search for IC 694 on this page, it's long). IC 694 is the quite faint galaxy about 1'.1 northwest of the double galaxy NGC 3690. The supernova appears in the northeast component of NGC 3690 this galaxy _is_not_ IC 694! Dr. Corwin did this research as part of the NGC/IC project (reference Brian Skiff)
Yamaoka Hitoshi reports the following:
The host galaxy of SN 1998T is the eastern part of Arp 299, and is shown as a fainter glow leftside of the brightest knot. SN 1998T is a fainter object than the host galaxy; it is located to the south of the brightest part of the eastern galaxy.
Some reports shows that this SN is very much brighter than other reports. Please check whether you are actually observing the SN.
In the Ayabe Astronomical Observatory image (confirmed by Dr. Filippenko)
The comment is partly written in Japanese, the top of the image is the title "Supernova 1998T" and the bottom left shows "Ayabe Astronomical Observatory (PAO)", then the bottom right is "By 95-cm refl. at PAO, chilled CCD with R-filter, 1998 Mar. 18.5 UT, 3 images of 3-minutes exposure are composed".
Other images of 1998T