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The distribution of radioactive 44Ti in Cassiopeia A

Grefenstette, Brian W.; Fryer, Chris L.; Harrison, Fiona A.; Boggs, Steven E.; DeLaney, Tracey; Laming, J. Martin; Reynolds, Stephen P.; Alexander, David M.; Barret, Didier; Christensen, Finn E.; Craig, William W.; Forster, Karl; Giommi, Paolo; Hailey, Charles J.; Hornstrup, Alan; Kitaguchi, Takao; Koglin, J.E.; Lopez, Laura; Mao, Peter H.; Madsen, Kristin K.; Miyasaka, Hiromasa; Mori, Kaya; Perri, Matteo; Pivovaroff, Michael J.; Puccetti, Simonetta; Rana, Vikram; Stern, Daniel; Westergaard, Niels J.; Wik, Daniel R.; Zhang, William W.; Zoglauer, Andreas

The distribution of radioactive 44Ti in Cassiopeia A Thumbnail


Brian W. Grefenstette

Chris L. Fryer

Fiona A. Harrison

Steven E. Boggs

Tracey DeLaney

J. Martin Laming

Stephen P. Reynolds

Didier Barret

Finn E. Christensen

William W. Craig

Karl Forster

Paolo Giommi

Charles J. Hailey

Alan Hornstrup

Takao Kitaguchi

J.E. Koglin

Laura Lopez

Peter H. Mao

Kristin K. Madsen

Hiromasa Miyasaka

Kaya Mori

Matteo Perri

Michael J. Pivovaroff

Simonetta Puccetti

Vikram Rana

Daniel Stern

Niels J. Westergaard

Daniel R. Wik

William W. Zhang

Andreas Zoglauer


The distribution of elements produced in the innermost layers of a supernova explosion is a key diagnostic for studying the collapse of massive stars. Here we present the results of a 2.4 Ms NuSTAR observing campaign aimed at studying the supernova remnant Cassiopeia A (Cas A). We perform spatially resolved spectroscopic analyses of the 44Ti ejecta, which we use to determine the Doppler shift and thus the three-dimensional (3D) velocities of the 44Ti ejecta. We find an initial 44Ti mass of (1.54 ± 0.21) × 10−4 M⊙, which has a present-day average momentum direction of 340° ± 15° projected onto the plane of the sky (measured clockwise from celestial north) and is tilted by 58° ± 20° into the plane of the sky away from the observer, roughly opposite to the inferred direction of motion of the central compact object. We find some 44Ti ejecta that are clearly interior to the reverse shock and some that are clearly exterior to it. Where we observe 44Ti ejecta exterior to the reverse shock we also see shock-heated iron; however, there are regions where we see iron but do not observe 44Ti. This suggests that the local conditions of the supernova shock during explosive nucleosynthesis varied enough to suppress the production of 44Ti by at least a factor of two in some regions, even in regions that are assumed to be the result of processes like α-rich freezeout that should produce both iron and titanium.

Journal Article Type Article
Acceptance Date Oct 29, 2016
Online Publication Date Dec 27, 2016
Publication Date Jan 1, 2017
Deposit Date Jun 21, 2017
Publicly Available Date Jul 3, 2017
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 834
Issue 1
Article Number 19
Public URL


Published Journal Article (2.7 Mb)

Copyright Statement
© 2016. The American Astronomical Society. All rights reserved.

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