Benjamin Alan Weaver

Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope.

Revision 2.6, 2006/06/01 00:20:07 Nearby Supernova Factory Observations of SN 2005gj: Another Type Ia Supernova in a Massive Circumstellar Envelope. The Nearby Supernova Factory G. Aldering, P. Antilogus, S. Bailey, 1 C. Baltay, 8 A. Bauer, 8 N. Blanc, 2 S. Bongard, 1,5 Y. Copin, 2 E. Gangler, 2 S. Gilles, 3 R. Kessler, 7 D. Kocevski, 1,6 B. C. Lee, 1 S. Loken, 1 P. Nugent, 1 R. Pain, 3 E. P´ contal, 4 R. Pereira, 3 S. Perlmutter, 1,6 D. Rabinowitz, 8 e G. Rigaudier, R. Scalzo, G. Smadja, 2 R. C. Thomas, 1 L. Wang, 1 B. A. Weaver 1,5 ABSTRACT We report the independent discovery and follow-up observations of supernova 2005gj by the Nearby Supernova Factory. This is the second confirmed case of a “hybrid” Type Ia/IIn supernova, which like the prototype SN 2002ic, we inter- pret as the explosion of a white dwarf interacting with a circumstellar medium. Our early-phase photometry of SN 2005gj shows that the strength of the inter- action between the supernova ejecta and circumstellar material is much stronger than for SN 2002ic. Our first spectrum shows a hot continuum with broad and narrow Hα emission. Later spectra, spanning over 4 months from outburst, show clear Type Ia features combined with broad and narrow Hγ, Hβ, Hα and He I λλ5876,7065 in emission. At higher resolution, P Cygni profiles are appar- ent. Surprisingly, we also observe an inverted P Cygni profile for [O III ] λ5007. Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720 Institut de Physique Nucl´ aire de Lyon, UMR5822, CNRS-IN2P3; Universit´ Claude Bernard Lyon 1, e e F-69622 Villeurbanne France Laboratoire de Physique Nucl´ aire et des Hautes Energies IN2P3 - CNRS - Universit´ s Paris VI et Paris e e VII, 4 place Jussieu Tour 33 - Rez de chauss´ e 75252 Paris Cedex 05 e Centre de Recherche Astronomique de Lyon, 9, av. Charles Andr´ , 69561 Saint Genis Laval Cedex e University of California, Space Sciences Laboratory, Berkeley, CA 94720-7450 Department of Physics, University of California, Berkeley, CA 94720 Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, IL 60637 Department of Physics, Yale University, New Haven, CT 06250-8121

Evidence against stellar chromospheric origin of Galactic cosmic rays

Interstellar space is filled with a gas of relativistic ions and electrons — the Galactic cosmic rays. These energetic particles tie interstellar gas to ambient magnetic fields by ionizing the component molecules and atoms, and so play a role in stabilizing molecular clouds against collapse and regulating the collapse of protostellar clouds. The observed energy spectrum of cosmic rays up to [gsims]1015 eV is consistent with their acceleration by supernova shock waves, but the original source of cosmic-ray nuclei remains unclear. There has been a widely held belief that the source consists of a solar-like ionized medium, probably the chromospheres of late-type Sun-like stars. This model predicts an overabundance of easily ionized elements. Here we show that lead, which is easily ionized, is underabundant in the Galactic cosmic rays in contradiction with this model. Rather, our measurements are consistent with two other possible models: one in which the nuclei originate in interstellar gas, and in entire grains accelerated to about one per cent of the speed of light by supernova shock waves,; and another in which the cosmic rays contain an admixture of an exotic, freshly synthesized component, probably originating in neutrino-driven winds from newly born neutron stars.

How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging

We present the results of applying new object classificationtechniques to difference images in the context of the Nearby SupernovaFactory supernova search. Most current supernova searches subtractreference images from new images, identify objects in these differenceimages, and apply simple threshold cuts on parameters such as statisticalsignificance, shape, and motionto reject objects such as cosmic rays,asteroids, and subtraction artifacts. Although most static objectssubtract cleanly, even a very low false positive detection rate can leadto hundreds of non-supernova candidates which must be vetted by humaninspection before triggering additional followup. In comparison to simplethreshold cuts, more sophisticated methods such as Boosted DecisionTrees, Random Forests, and Support Vector Machines provide dramaticallybetter object discrimination. At the Nearby Supernova Factory, we reducedthe number of non-supernova candidates by a factor of 10 while increasingour supernova identification efficiency. Methods such as these will becrucial for maintaining a reasonable false positive rate in the automatedtransient alert pipelines of upcoming projects such as PanSTARRS andLSST.

Nearby supernova factory observations of SN 2006D : On sporadic carbon signatures in early type Ia supernova spectra

We present four spectra of the Type Ia supernova SN Ia 2006Dextending from -7 to +13 days with respect to B-band maximum. The spectrainclude the strongest signature of unburned material at photosphericvelocities observed in a SN Ia to date. The earliest spectrum exhibits CII absorption features below 14,000 km/s, including a distinctive C IIlambda 6580 absorption feature. The carbon signatures dissipate as the SNapproaches peak brightness. In addition to discussing implications ofphotospheric-velocity carbon for white dwarf explosion models, we outlinesome factors that may influence the frequency of its detection before andaround peak brightness. Two effects are explored in this regard,including depopulation of the C II optical levels by non-LTE effects, andline-of-sight effects resulting from a clumpy distribution of unburnedmaterial with low volume-filling factor.

Energy loss of relativistic heavy ions in matter

Abstract We have investigated the theory of energy loss of charged particles in matter due to ionization of the medium, integrating the work of other authors over several decades. We describe the most important corrections to standard energy-loss formulae. We compare our calculations to an improved measurement of the range of 1 A GeV U ions and to other codes and tabulations. We show that calculations based on the theory of ionization energy loss are at least as accurate as tabulations extrapolated from empirical data for the stopping of uranium ions in matter. We have made available the computer code resulting from our investigations.

Performance of the Ultraheavy Collector of the Trek experiment

Abstract We report on the performance of the trek ultraheavy cosmic ray collector, an array of track-etch detectors which was deployed on the Russian space station Mir . Trek is the first space-based cosmic ray experiment to exploit the unique properties of the track-recording glass BP-1. We describe the systematic analysis of the Trek experiment, with emphasis on the calibration and verification of the Trek detectors, the automated scanning system used to locate and measure cosmic ray tracks, and the sources of dispersion in the measurement of cosmic ray charge. We find that the resolution for measurement of charge of ultraheavy galactic cosmic rays in Mir orbit will be 0.39–0.45 e in the absence of strong thermal variations or episodes of significantly elevated temperature. We also will discuss the extremely heavy cosmic ray composition observer (ECCO), a planned second generation BP-1 experiment, which would measure the age of galactic cosmic ray nuclei using the actinides as radioactive clocks.

Nonobservation of {sup 12}C cluster decay of {sup 114}Ba

By means of the on-line mass separator at Gesellschaft f{umlt u}r Schwerionenforschung, Darmstadt, we produced {sup 114}Ba through the {sup 51}Ni({sup 58}Ni,2n) reaction, separated it as a {sup 114}Ba{sup 19}F{sup +} beam, and implanted it into a stopper foil positioned in the center of an array of track detectors, which were used to search for {sup 12}C radioactivity of {sup 114}Ba. A total number of (5.4{plus_minus}1.7){times}10{sup 4} {sup 114}Ba atoms were implanted. No {sup 12}C event was found after a total exposure time of 116 h, corresponding to a {sup 58}Ni beam dose of 1.3{times}10{sup 17}. The resulting upper limit of 3.4{times}10{sup {minus}5} (84{percent} C.L.) for the branching ratio for {sup 12}C decay of {sup 114}Ba is considerably lower than the limits obtained in previous experiments, which represents an inconsistency at levels of more than 90{percent}. A semiempirical estimate of 19.3 MeV for the upper limit of the Q value for {sup 12}C decay of {sup 114}Ba is derived. {copyright} {ital 1997} {ital The American Physical Society}

Extended Analysis of the Trek Ultraheavy Collector

We have made a measurement of the elemental abundance of cosmic rays with atomic number 72 < Z < 83. We made this measurement as part of the Extended Analysis of the Trek Detector (hereafter Extended-Trek). The Trek detector consisted of 150 stacks, each of 16 sheets, of BP-1 glass exposed on the Russian space station Mir. In the original analysis of Trek, 245 cosmic-ray events were analyzed. The cosmic-ray elemental abundance pattern observed by Trek was strongly inconsistent with a popular model of the Galactic cosmic-ray source. For Extended-Trek, we reanalyzed 146 events in the ~100 stacks that were calibrated with relativistic gold ions at two zenith angles. These correspond to a collecting area of approximately 0.7 m2. The Extended-Trek analysis improved the resolution of cosmic-ray charge to 0.34e over 0.39e-0.45e in the original Trek analysis and confirmed the cosmic-ray abundance pattern observed by Trek.

Th/U/Pu/Cm dating of galactic cosmic rays with the extremely heavy cosmic ray composition observer

The principal goal of ECCO, the Extremely-heavy Cosmic-ray Composition Observer, is the measurement of the age of heavy galactic cosmic-ray nuclei using the extremely rare actinides (Th, U, Pu, Cm) as clocks. ECCO is one of two cosmic-ray instruments comprising the Heavy Nuclei Explorer (HNX), which was recently selected as one of several missions for Phase A study under NASAs Small class Explorer (SMEX) program. ECCO is based on the flight heritage of Trek, an array of barium-phosphate glass tracketch detectors deployed on the Russian space station Mir from 1991–1995. Using Trek, we measured the abundances of elements with Z > 70 in the galactic cosmic rays (GCRs). Trek consisted of a 1 m2 array of stacks of individually polished thin BP-1 glass detectors. ECCO will be a much larger instrument, but will achieve both excellent resolution and low cost through use of a novel detector configuration. Here we report the results of recent accelerator tests of the ECCO detectors that verify detector performance. We also show the expected charge and energy resolution of ECCO as a function of energy.

Commutivity of track formation and surface preparation in BP-1 track-etch detectors

Abstract Using the Trek detector, an array of barium phosphate glass track-etch detectors deployed on the Russian space station Mir from 1991 to 1995, we have measured the abundances of elements with Z >70 in the galactic cosmic-rays (GCRs). Trek consisted of stacks of individually polished thin BP-1 glass detectors. The next generation BP-1 cosmic-ray detector, the Extremely heavy Cosmic-ray Composition Observer (ECCO), will be capable of measuring the age of GCR nuclei using the extremely rare actinides (Th, U, Pu, Cm) as clocks. ECCO will be a very large instrument (23–30 m 2 in area, depending on spacecraft), but will achieve both excellent resolution and low cost through use of a novel detector configuration. An essential feature of the new configuration is that detector surfaces are ground and polished after exposure on orbit. Naively, one might expect post-flight surface preparation to have a deleterious effect on detector signal. Here we show that, in BP-1 detectors, post-exposure surface preparation has no measurable effect on either the amplitude or the dispersion of the detector signal – in other words, latent nuclear track formation and detector surface preparation commute . This property of BP-1 enables ECCO to be effectively pointable, and also dramatically reduces the costs of pre-flight detector construction and post-flight detector processing.