Arcetri logo K-band Arcetri Obscured Supernova Search

Detected Supernovae

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 in Maiolino 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.

SN 2001db

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, 1999.
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 the maximum.SN1999gw

SN 1999gw

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

SN2000bg SN1999gd

SN 1999gd was discovered by Li (1999) with the KAIT telescope in NGC2623, on November 24, 1999, resulting a type Ia SN. This is our NIR image obtained with ARNICA at TNG.

SN2000bg was detected at the KAIT telescope on April 1, 2000 (Sato & Li 2000) and was classified as a type IIn SN. Here is our K band image obtained at the Kuiper telescope.

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