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ATEL # 1439; C. J. Stockdale ( Marquette University and University of Oklahoma), K. W. Weiler (Naval Research Laboratory), S. Immler (Goddard Space Flight Center), S. D. Van Dyk (Spitzer Science Center, California Institute of Technology), N. Panagia (Space Telescope Science Institute and Observatory of Catania), J.M. Marcaide (University of Valencia), D. Pooley (University of Wisconsin at Madison), and R. A. Sramek (National Radio Astronomy Observatory)
on 22 Mar 2008; 0:49 UT
Distributed as an Instant Email Notice (Supernova)
Password Certification: Kurt W. Weiler (Kurt.Weiler@nrl.navy.mil)
Subjects: Radio, Nova, Supernova
Continuing radio monitoring of supernova 2008ax (CBET 1280) with the Very Large Array telescope (CBET 1299) show that the radio emission has clearly peaked at 22.5 GHz, 8.46 GHz, and 4.86 GHz and is declining rapidly. The most recent measurements from 21.06 March 2008 indicate a flux density of 2.63 +/- 0.21 mJy at 8.46 GHz and 3.45 +/- 0.24 mJy at 4.86 GHz. Very preliminary fitting of the data shows that the supernova is somewhat underluminous in the radio with a peak 6 cm radio spectral luminosity of ~4 x 10^26 erg/s/Hz, but not exceptionally so. Type Ic SN 1990B, Type II SN 1980K, Type II SN 1981K, and other radio supernovae (RSNe) had similar peak 6 cm spectral luminosities. However, the low intrinsic luminosity and the relatively flat spectral index of SN 2008ax (alpha ~ -0.8) are more typical of a Type II supernova than a normal Type Ib/c. Some GRB related Type Ib/c supernovae, such as SN 1998bw, have comparably flat radio spectra but are much more luminous. Such “intermediate type” radio behavior is perhaps consistent with the changing classification from the optical spectrum (e.g. for SN 2008ax: similar to SN 1987a, CBET 1285; Type IIb, CBET 1289; Type Ib, CBET 1305, CBET 1309) and is also another example of the increasingly common change of the optical spectral classification of supernovae as they age. The data, as well as a VERY PRELIMINARY fit are available on http://rsd-www.nrl.navy.mil/7213/weiler/sne-home.html Radio observations are continuing. We particularly want to thank the dynamic scheduling group at the NRAO-VLA for their outstanding help in obtaining these rapid Target of Opportunity observations.