ALBERT

Description: The Galactic Centre hosts a puzzling stellar population in its inner few parsecs, with a high abundance of surprisingly young, relatively massive stars bound within the deep potential well of the central supermassive black hole, Sagittarius A* (ref. 1). Previous studies suggest that the population of objects emitting soft X-rays (less than 10 kiloelectronvolts) within the surrounding hundreds of parsecs, as well as the population responsible for unresolved X-ray emission extending along the Galactic plane, is dominated by accreting white dwarf systems. Observations of diffuse hard-X-ray (more than 10 kiloelectronvolts) emission in the inner 10 parsecs, however, have been hampered by the limited spatial resolution of previous instruments. Here we report the presence of a distinct hard-X-ray component within the central 4 x 8 parsecs, as revealed by subarcminute-resolution images in the 20-40 kiloelectronvolt range. This emission is more sharply peaked towards the Galactic Centre than is the surface brightness of the soft-X-ray population. This could indicate a significantly more massive population of accreting white dwarfs, large populations of low-mass X-ray binaries or millisecond pulsars, or particle outflows interacting with the surrounding radiation field, dense molecular material or magnetic fields. However, all these interpretations pose significant challenges to our understanding of stellar evolution, binary formation, and cosmic-ray production in the Galactic Centre.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Perez, Kerstin -- Hailey, Charles J -- Bauer, Franz E -- Krivonos, Roman A -- Mori, Kaya -- Baganoff, Frederick K -- Barriere, Nicolas M -- Boggs, Steven E -- Christensen, Finn E -- Craig, William W -- Grefenstette, Brian W -- Grindlay, Jonathan E -- Harrison, Fiona A -- Hong, Jaesub -- Madsen, Kristin K -- Nynka, Melania -- Stern, Daniel -- Tomsick, John A -- Wik, Daniel R -- Zhang, Shuo -- Zhang, William W -- Zoglauer, Andreas -- England -- Nature. 2015 Apr 30;520(7549):646-9. doi: 10.1038/nature14353.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, Room 1027, New York, New York 10027, USA [2] Haverford College, 370 Lancaster Avenue, KINSC L109, Haverford, Pennsylvania 19041, USA. ; Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, Room 1027, New York, New York 10027, USA. ; 1] Instituto de Astrofisica, Facultad de Fisica, Pontificia Universidad Catolica de Chile, 306, Santiago 22, Chile [2] Millennium Institute of Astrophysics, Vicuna Mackenna 4860, 7820436 Macul, Santiago, Chile [3] Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, Colorado 80301, USA. ; Space Science Laboratory, UC Berkeley, 7 Gauss Way, Berkeley, California 94720, USA. ; Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 37-555, Cambridge, Massachusetts 02139, USA. ; DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark. ; 1] Space Science Laboratory, UC Berkeley, 7 Gauss Way, Berkeley, California 94720, USA [2] Lawrence Livermore National Laboratory, PO Box 808, Livermore, California 94551-0808, USA. ; Cahill Center for Astronomy and Astrophysics, 1200 East California Boulevard, MC 290-17, California Institute of Technology, Pasadena, California 91125, USA. ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-83, Cambridge, Massachusetts 02138, USA. ; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, 4800 Oak Grove Drive, MS 169-221, California 91109, USA. ; NASA Goddard Space Flight Center, 8800 Greenbelt Road, Code 662, Greenbelt, Maryland 20771, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25925477" target="_blank"〉PubMed〈/a〉

Description: Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive (44)Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. Cassiopeia A is a young, nearby, core-collapse remnant from which (44)Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed (44)Ti emission to estimated (56)Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the (44)Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the (44)Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Grefenstette, B W -- Harrison, F A -- Boggs, S E -- Reynolds, S P -- Fryer, C L -- Madsen, K K -- Wik, D R -- Zoglauer, A -- Ellinger, C I -- Alexander, D M -- An, H -- Barret, D -- Christensen, F E -- Craig, W W -- Forster, K -- Giommi, P -- Hailey, C J -- Hornstrup, A -- Kaspi, V M -- Kitaguchi, T -- Koglin, J E -- Mao, P H -- Miyasaka, H -- Mori, K -- Perri, M -- Pivovaroff, M J -- Puccetti, S -- Rana, V -- Stern, D -- Westergaard, N J -- Zhang, W W -- England -- Nature. 2014 Feb 20;506(7488):339-42. doi: 10.1038/nature12997.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA. ; Space Sciences Laboratory, University of California, Berkeley, California 94720, USA. ; Physics Department, North Carolina State University, Raleigh, North Carolina 27695, USA. ; CCS-2, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. ; NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA. ; Department of Physics, University of Texas at Arlington, Arlington, Texas 76019, USA. ; Department of Physics, Durham University, Durham DH1 3LE, UK. ; Department of Physics, McGill University, Rutherford Physics Building, Montreal, Quebec H3A 2T8, Canada. ; 1] Universite de Toulouse, UPS-OMP, IRAP, 9 Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France [2] CNRS, Institut de Recherche en Astrophysique et Planetologie, 9 Avenue colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France. ; DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark. ; 1] Space Sciences Laboratory, University of California, Berkeley, California 94720, USA [2] Lawrence Livermore National Laboratory, Livermore, California 94550, USA. ; Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc, I-00133 Roma, Italy. ; Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA. ; RIKEN, Nishina Center, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan. ; Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA. ; 1] Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc, I-00133 Roma, Italy [2] INAF - Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio, Italy. ; Lawrence Livermore National Laboratory, Livermore, California 94550, USA. ; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24553239" target="_blank"〉PubMed〈/a〉