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Title: SN 2009bb: a Peculiar Broad-Lined Type Ic Supernova
Authors: Giuliano Pignata, Maximilian Stritzinger, Alicia Soderberg, Paolo Mazzali, M. M. Phillips, Nidia Morrell, J. P. Anderson, Luis Boldt, Abdo Campillay, Carlos Contreras, Gastón Folatelli, Francisco Förster, Sergio González, Mario Hamuy, Wojtek Krzeminski, José Maza, Miguel Roth, Francisco Salgado Emily M. Levesque, Armin Rest, J. Adam Crain, Andrew C. Foster, Joshua B. Haislip, Kevin M. Ivarsen, Aaron P. LaCluyze, Melissa C. Nysewander, Daniel E. Reichart

Ultraviolet, optical, and near-infrared photometry and optical spectroscopy of the broad-lined Type Ic supernova (SN) 2009bb are presented, following the flux evolution from -10 to +285 days past B-band maximum. Thanks to the very early discovery, it is possible to place tight constraints on the SN explosion epoch. The expansion velocities measured from near maximum spectra are found to be only slightly smaller than those measured from spectra of the prototype broad-lined SN 1998bw associated with GRB 980425. Fitting an analytical model to the pseudo-bolometric light curve of SN 2009bb suggests that 4.1±1.9 solar masses of material was ejected with 0.22 ±0.06 solar masses of it being 56Ni. The resulting kinetic energy is 1.8±0.7x10^52 erg. This, together with an absolute peak magnitude of MB=-18.36±0.44, places SN 2009bb on the energetic and luminous end of the broad-lined Type Ic (SN Ic) sequence. Detection of helium in the early time optical spectra accompanied with strong radio emission, and high metallicity of its environment makes SN 2009bb a peculiar object. Similar to the case for GRBs, we find that the bulk explosion parameters of SN 2009bb cannot account for the copious energy coupled to relativistic ejecta, and conclude that another energy reservoir (a central engine) is required to power the radio emission. Nevertheless, the analysis of the SN 2009bb nebular spectrum suggests that the failed GRB detection is not imputable to a large angle between the line-of-sight and the GRB beamed radiation. Therefore, if a GRB was produced during the SN 2009bb explosion, it was below the threshold of the current generation of gamma-ray instruments.

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Title: VLBI Observations of SN 2009bb
Authors: M. F. Bietenholz, A. M. Soderberg, N. Bartel, S. P. Ellingsen, S. Horiuchi, C. J. Phillips, A. K. Tzioumis, M. H. Wieringa, N. N. Chugai

We report VLBI, as well as VLA radio observations of the Type Ibc supernova 2009bb. The high radio luminosity of this supernova seems to require relativistic outflow, implying that the early radio emission was "engine driven" even though no gamma-ray emission was seen. The radio light curve shows a general decline, with a "bump" near t = 52 d, seen most prominently at 5 GHz. The lightcurve bump could be either engine-driven, or it might represent the turn-on of the normal radio emission from a supernova, driven by interaction with the CSM rather than by the engine. We undertook VLBI observations to resolve SN 2009bb's relativistic outflow. Our observations constrain the angular outer radius at an age of 85 d to be <0.64 mas, corresponding to a size of <4 x 10^17 cm, and an average expansion speed of <1.74c. This result is consistent with the moderately relativistic ejecta speeds implied by the radio luminosity and spectrum.

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U.Va. astronomer part of team that discovered rare supernova explosion

For the first time, astronomers have found a supernova explosion with properties similar to a gamma-ray burst, but without detecting any gamma rays from it. The scientists say the discovery, using the National Science Foundation's Very Large Array radio telescope, located near Socorro, N.M., promises to point the way toward locating many more examples of these mysterious explosions.
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For the first time, astronomers have found a supernova explosion with properties similar to a gamma-ray burst, but without seeing any gamma rays from it. The discovery, using the National Science Foundation's Very Large Array (VLA) radio telescope, promises, the scientists say, to point the way toward locating many more examples of these mysterious explosions.

"We think that radio observations will soon be a more powerful tool for finding this kind of supernova in the nearby Universe than gamma-ray satellites" - Alicia Soderberg, of the Harvard-Smithsonian Centre for Astrophysics.

The telltale clue came when the radio observations showed material expelled from the supernova explosion, dubbed SN2009bb, at speeds approaching that of light. This characterized the supernova, first seen last March, as the type thought to produce one kind of gamma-ray burst.

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Title: The High-Metallicity Explosion Environment of the Relativistic Supernova 2009bb
Authors: E. M. Levesque, A. M. Soderberg, R. J. Foley, E. Berger, L. J. Kewley, S. Chakraborti, A. Ray, M. A. P. Torres, P. Challis, R. P. Kirshner, S. D. Barthelmy, M. F. Bietenholz, P. Chandra, V. Chaplin, R. A. Chevalier, N. Chugai, V. Connaughton, A. Copete, O. Fox, C. Fransson, J. E. Grindlay, M. A. Hamuy, P. A. Milne, G. Pignata, M. D. Stritzinger, M. H. Wieringa

We investigate the environment of the nearby (d ~ 40Mpc) broad-lined Type Ic supernova SN 2009bb. This event was observed to produce a relativistic outflow likely powered by a central accreting compact object. While such a phenomenon was previously observed only in long-duration gamma-ray bursts (LGRBs), no LGRB was detected in association with SN 2009bb. Using an optical spectrum of the SN 2009bb explosion site, we determine a variety of ISM properties for the host environment, including metallicity, young stellar population age, and star formation rate. We compare the SN explosion site properties to observations of LGRB and broad-lined SN Ic host environments on optical emission line ratio diagnostic diagrams. Based on these analyses, we find that the SN 2009bb explosion site has a very high metallicity of ~2x solar, in agreement with other broad-lined SN Ic host environments and at odds with the low-redshift LGRB host environments and recently proposed maximum metallicity limits for relativistic explosions. We consider the implications of these findings and the impact that SN 2009bb's unusual explosive properties and environment have on our understanding of the key physical ingredient that enables some SNe to produce a relativistic outflow.

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