The search have produced till now the detections of
4 SNe. Two objects, SN 1999gd and SN 2000db, where recovered by our data
but resulted already discovered by optical searches a few days before our
discovery image. The other two SNe, discovered by our images, are presented
et al., (2002)
. In particular, SN 2001db is the first SN discovered
in the NIR to be confirmed spectroscopically. It is one of the more extincted
event ever observed, with AV
in the range 4.6 - 6.7 mag. This
result highlights the power of infrared monitoring in detecting Obscured
SNe and indicates that optical surveys are probably missing a significant
fraction of SNe, especially in obscured systems such as starburst galaxies.
The infrared imaging observations were obtained with the SOFI near-IR
camera at the NTT ESO telescope in the Ks band. NGC3256 was observed for
the first time on January 9, 2001, and subsequently three more times: February
8, March 18, and April 1. The images obtained during the monitoring in 2001
were compared with an archival image obtained with SOFI on November 28,
In Fig. we show the archival SOFI image of NGC3256 (left) and the first
image obtained in 2001 (right) where SN2001db has been detected. The magnitude
of the SN at the discovery epoch was Ks=16.03. The SN is located at R.A.(J2000)
= 10h27m50s.4, Decl.(J2000) = -43 54' 21'', i.e. offset 5".7 to the West
and 5".7 to the South of the Ks nucleus of the galaxy. Photometric measurements
performed on ESO archival images (Feb 1993) and FORS images (Apr 2001,
May 2001) imply mV >22 for the SN.
The spectroscopic follow-up was performed both in the optical and
in the infrared.
The optical spectrum
was obtained with
FORS1 at the ESO VLT-UT1 on May 16, 2001 (i.e. when the SN was at least 4
months old) with a spectral resolution of 500. In the obtained optical spectrum
there are several narrow emission lines most of which are probably to ascribe
to HII regions and SNRs in the environment of the SN. The spectrum
clearly shows a broad component of H(alpha) (FWHM =5000 km/s) which is a
clear signature of the SN. The H(alpha) has a strongly asymmetric profile,
whose peak is blueshifted by about 2000 km/s with respect to the parent galaxy,
but it also has a prominent red tail, a profile similar to that observed in
type IIL and IIP SNe. No other SN signatures are found in the blue part of
the spectrum, which is indicative of a highly reddened object.
The infrared spectrum
was obtained in
the J band with ISAAC at the ESO VLT-UT1 on April 21, 2001. Observations
were performed with a spectral resolution of 500. Here we show the infrared
ISAAC spectrum extracted from an aperture of 1''. The broad component of
Pa(beta) is more prominent, relative to the narrow component, with respect
to H(alpha). The profile of the broad component of Pa(beta) is nearly identical
to that of H(alpha).
The extinction along the line of sight towards the SN can be evaluated
from the Pa(beta)/H(alfa) intensity ratio. We obtain an AV=5.6, with an
uncertainty of about 1 mag. This is one of the most extincted SN ever observed.
The presence of H in the spectrum shows that this SN is a type II, and the
light curve suggest that it was discovered less than three months after
SN 1999gw (Cresci et al. 2002) is the first object discovered by our
NIR observations. It was detected in an image taken on December 16, 1999
with ARNICA at TNG in the Ks filter. The new object was disentagled by the
bright nucleus of the galaxies using the image subtraction software ISIS
, using as reference an image obtained on August
2, 2001 with NICS at TNG.
The figure presents the image of the discovery and the result of the
subtraction, where the SN is evident in emission. We don't have a spectroscopic
observation of this object, but from the light curve we can classify the
SN as a type II or Ib/c.
SN 1999gd and SN 2000db