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The distribution of radioactive 44Ti in Cassiopeia A.

Grefenstette, Brian W. and Fryer, Chris L. and Harrison, Fiona A. and Boggs, Steven E. and DeLaney, Tracey and Laming, J. Martin and Reynolds, Stephen P. and Alexander, David M. and Barret, Didier and Christensen, Finn E. and Craig, William W. and Forster, Karl and Giommi, Paolo and Hailey, Charles J. and Hornstrup, Alan and Kitaguchi, Takao and Koglin, J. E. and Lopez, Laura and Mao, Peter H. and Madsen, Kristin K. and Miyasaka, Hiromasa and Mori, Kaya and Perri, Matteo and Pivovaroff, Michael J. and Puccetti, Simonetta and Rana, Vikram and Stern, Daniel and Westergaard, Niels J. and Wik, Daniel R. and Zhang, William W. and Zoglauer, Andreas (2017) 'The distribution of radioactive 44Ti in Cassiopeia A.', Astrophysical journal., 834 (1). p. 19.


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.

Item Type:Article
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Publisher statement:© 2016. The American Astronomical Society. All rights reserved.
Date accepted:29 October 2016
Date deposited:03 July 2017
Date of first online publication:27 December 2016
Date first made open access:03 July 2017

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