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Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system1, 2, but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models1, 3: double-degenerate (involving two white dwarfs in a close binary system2, 4) and single-degenerate models5, 6. In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy7. Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10–100 times fainter than previous limits on other type Ia supernova progenitor systems8, 9, 10, allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf.

arXiv:1510.05750v2.-- et al., Supernova "Refsdal", multiply imaged by cluster MACS1149.5+2223, represents a rare opportunity to make a true blind test of model predictions in extragalactic astronomy, on a timescale that is short compared to a human lifetime. In order to take advantage of this event, we produced seven gravitational lens models with five independent methods, based on Hubble Space Telescope (HST) Hubble Frontier Field images, along with extensive spectroscopic follow-up observations by HST, the Very Large and the Keck Telescopes. We compare the model predictions and show that they agree reasonably well with the measured time delays and magnification ratios between the known images, even though these quantities were not used as input. This agreement is encouraging, considering that the models only provide statistical uncertainties, and do not include additional sources of uncertainties such as structure along the line of sight, cosmology, and the mass sheet degeneracy. We then present the model predictions for the other appearances of supernova >Refsdal.> A future image will reach its peak in the first half of 2016, while another image appeared between 1994 and 2004. The past image would have been too faint to be detected in existing archival images. The future image should be approximately one-third as bright as the brightest known image (i.e., mag at peak and mag six months before peak), and thus detectable in single-orbit HST images. We will find out soon whether our predictions are correct., This work is supported by NASA through grants HST-GO-13459 and HST-GO-14041 from the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. T.T. is supported by the Packard Foundation in the form of a Packard Research Fellowship. J.M.D. is grateful for support from the consolider project CSD2010-00064 and AYA2012-39475-C02-01 funded by the Ministerio de Economia y Competitividad. A.V.F.'s research is supported by the Christopher R. Redlich Fund, the TABASGO Foundation, and NSF grant AST-1211916. C.G. acknowledges support by the VILLUM FONDEN Young Investigator Programme through grant no. 10123. Support for A.Z. was provided by NASA through Hubble Fellowship grant #HST-HF2-51334.001-A awarded by STScI. The work of M.O. was supported in part by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan, and Grant-in-Aid for Scientific Research from the JSPS (26800093). Financial support for this work was provided to S.A.R. by NASA through grants HST-HF-51312 and HST-GO-13386 from STScI. A.H. is supported by NASA Head-quarters under the NASA Earth and Space Science Fellowship Program, grant ASTRO14F-0007. R.J.F. gratefully acknowledges support from NSF grant AST-1518052, NASA grants HST-GO-14041 and HST-GO-13386, and the Alfred P. Sloan Foundation. This work was supported in part by a NASA Keck PI Data Award (PID 47/2014B N125D, PI Jha).

Facility: HST (WFC3).-- Rodney, Steven A. et al., SN HFF14Tom is a Type Ia SN discovered at Z = 1.3457 ± 0.0001 behind the galaxy cluster Abell 2744 (Z = 0.308). In a cosmology-independent analysis, we find that HFF14Tom is 0.77 ± 0.15 mag brighter than unlensed Type Ia SNe at similar redshift, implying a lensing magnification of μ = 2.03 ± 0.29. This observed magnification provides a rare opportunity for a direct empirical test of galaxy cluster lens models. Here we test 17 lens models, 13 of which were generated before the SN magnification was known, qualifying as pure >blind tests. > The models are collectively fairly accurate: 8 of the models deliver median magnifications that are consistent with the measured μ to within 1λ. However, there is a subtle systematic bias: the significant disagreements all involve models overpredicting the magnification. We evaluate possible causes for this mild bias, and find no single physical or methodological explanation to account for it. We do find that model accuracy can be improved to some extent with stringent quality cuts on multiply imaged systems, such as requiring that a large fraction have spectroscopic redshifts. In addition to testing model accuracies as we have done here, Type Ia SN magnifications could also be used as inputs for future lens models of Abell 2744 and other clusters, providing valuable constraints in regions where traditional strong- and weak-lensing information is unavailable., Financial support for this work was provided to S.A.R. by NASA through grants HST-HF-51312 and HST-GO-13386 from STScI, which is operated by Associated Universities for Research in Astronomy, Inc. (AURA), under NASA contract NAS 5-26555. A.M. acknowledge the financial support of the Brazilian funding agency FAPESP (Post-doc fellowship—process number 2014/11806-9). Support for this research at Rutgers University was provided in part by NSF CAREER award AST-0847157 to SWJ. The Dark Cosmology Centre is supported by the Danish National Research Foundation. J.M.D. acknowledges support of the consolider project CSD2010-00064 and AYA2012–39475-C02-01 funded by the Ministerio de Economia y Competitividad. J.M. contributed to this research from the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA and acknowledges support from NASA Grants HST-GO-13343.05-A and HST-GO-13386.13-A. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/20072013) under REA grant agreement number 627288. A.Z. acknowledges financial support from NASA through grant HST-HF-51334.01-A awarded by STScI and operated by AURA. T.T. acknowledges support by the Packard Foundation in the form of Packard Research Fellowship. GLASS is funded by NASA through HST grant GO-13459. L.L.R.W. acknowledges the support of the Minnesota Supercomputing Institute.

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z=0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z=1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses., Published in the 6 March 2015 issue of Science; 17 pages, 7 figures, and 3 tables including Supplementary Materials

In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses.