AIP astronomy picture of the month

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First supernova observed with an integral field spectrograph


A supernova (SN 2002er) in the galaxy UGC 10743 was discovered on Aug. 23 and reported in IAUC 7959. The host galaxy, which is probably of Type Sa, has a redshift of z=0.0086, which corresponds to a distance of approximately 40 Mpc. The SN was reported to be of the Type Ia and expected to be brightest 10 days after the discovery, i.e. Sep 3. (which is an unusually long time span before the peak).

SN 2002er

click here for a full-size image (0.9 MB)

SN 2002er observed with the PMAS acquisition and guiding camera

Observing with PMAS at the 3.5m at Calar Alto from Aug. 28 to Sep. 6, 2002 we had an excellent opportunity to study for the second time a SN with an integral field spectrograph. The first one was discovered by the OASIS instrument. The image above shows the target acquisition taken with the acquisition and guiding camera (AG camera). PMAS is a unique integral field instrument in the sense that is has two cameras. In addition to the imaging spectrograph itself, the AG camera provides a much wider field of view in broad-band filters. To obtain this true colour picture we observed the field with the R, V, and B filter, respectively. The field of view of this frame is 3.7'*3.7'. The blue/green circle in the center indicates the position of the integral field unit for spectroscopy.

SN spectra

We obtained spectra of the SN on several days during the run and have identified several absorption lines, which clearly confirm the supernova to be of Type Ia. The observations will allow tracing the change in velocity of the outflow. In addition to this we also obtained a spectrum of the bulge of the host galaxy. The reduced spectra of the SN were obtained with an interval of 48 hours. It is seen that the supernova is still getting brighter at the time of the last spectrum. The deep SiII absorption feature at 6150 Angstrom, which identifies the SN as a Type Ia event, is blueshifted from the rest frame of 6355 A. This corresponds to a blueshift of 12000 km/s, which is not unusual for a Type Ia SN.

An integral field spectrum of a SN is useful since it allows a very accurate estimate of the background flux and sky lines can be removed efficiently, so the physical conditions of the SN can be analysed. Specifically, the extinction by dust in the host galaxy can be measured.

For this reason, other groups have started to construct dedicated Integral Field Spectrographs just for the purpose to study supernovae, such as the SNIFS instrument. Utilising the standard candle nature of Type Ia SNe, the team behind the instrument will collect integral field spectroscopic data of nearby Type Ia SNe in order to calibrate the very distant SNe Type Ia. This will eventually lead to estimations of OmegaL and Omegam with an accuracy of 5% and 2%, respectively, with data from the future SNAP satellite.

(credits: L. Christensen, T. Becker, K. Jahnke, A. Kelz, M. Roth, S.F. Sanchez, L. Wisotzki, AIP)

last change 2002 October 16, R. Arlt