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In core-collapse supernovae, titanium-44 (44Ti) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32–kilo–electron volt emission lines from decay of 44Ti produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ∼700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.

The observation of non-uniformly distributed titanium emission in the interior of Cassiopeia A, a core-collapse supernova, is an indicator of asymmetries in the stellar explosion and provides strong evidence for the development of low-mode convective instabilities in such supernovae. Cassiopeia A — remnant of an asymmetric explosion Most simulations of stellar core collapse events indicate that the explosions are asymmetric, but the resulting shapes differ in the various models. Brian Grefenstette et al . analysed the distribution of radioactive titanium-44 in Cassiopeia A, a young core-collapse remnant, as a proxy for explosion asymmetry. They report a degree of non-uniform distribution in the unshocked interior of Cas A greater than that expected from a spherical explosion, yet not as pronounced as would follow a highly bipolar explosion. On the basis of these findings, the authors conclude that the type of explosion for the Cas A core-collapse explosion was part-way between the two extremes of asymmetry. 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 1 , directly probes the explosion asymmetries. Cassiopeia A is a young 2 , nearby 3 , core-collapse 4 remnant from which 44 Ti emission has previously been detected 5 , 6 , 7 , 8 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 9 , from optical light echoes 10 , and from jet-like features seen in the X-ray 11 and optical 12 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.

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 [sup.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 (1), directly probes the explosion asymmetries. Cassiopeia A is a young (2), nearby (3), core-collapse (4) remnant from which [sup.44]Ti emission has previously been detected (5-8) but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed [sup.44]Ti emission to estimated [sup.56]Ni emission (9), from optical light echoes (10), and from jet-like features seen in the X-ray (11) and optical (12) ejecta. Here we report spatial maps and spectral properties of the [sup.44]Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the [sup.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.

A laser interferometer typically combines a number of beams that travel different optical paths to determine factors such as lengths, surface irregularities or the index of refraction of materials. Heterodyne detection is a well-established method for sensing tiny optical pathlength displacements through measurements of the phase shift between interfering signals. The ability of measuring displacements with high dynamic range and accuracy at the picometer-level has made this technique a crucial resource in many high-precision metrology applications, particularly for gravitational physics experiments in space, where one of the interfering beams is sensed at ultra-low light power. This article provides an overview of the design, construction and test facilities for an optical phase readout instrument able to extract picometer-stable displacement and nanometer-stable tilt measurements over thousands of seconds from a laser link operating at MHz heterodyne frequencies. The optical pathlength sensitivity of the instrument has been measured down to 1 pmWHz for frequencies above 3 mHz. The pitch and yaw pointing sensitivity is required below 5 nrad/^Hz and performed by applying the differential wavefront sensing technique. The instrument sensitivity seems to be limited above 3 mHz by ADC clock timing jitter and below 1 mHz by phase distortion caused by temperature fluctuations in the front-end electronics circuitry. Noise budgets and coupling mechanisms for both longitudinal and angular displacements are still under investigation with the design goal of an enhanced instrument performance with reasonable margins over the stringent sensitivity requirements.

Taking a different look at a familiar star may still yield surprises. Boggs et al. trained the x-ray vision of the NuSTAR observatory on the well-studied supernova 1987A. Core-collapse explosions such as SN 1987A produce a titanium isotope, 44 Ti, whose radioactive decay yields hard x-ray emission lines. All the emission associated with 44Ti appears to be from material moving toward us, with none moving away. This implies that the explosion was not symmetric. These findings help to explain the mechanics of SN 1987A and of core-collapse supernovae in general. Science , this issue p. 670 Asymmetric signatures of radioactive decay are seen from a metal deep within a supernova. In core-collapse supernovae, titanium-44 ( 44 Ti) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32–kilo–electron volt emission lines from decay of 44 Ti produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.

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 ^sup 44^Ti, synthesized in an exploding star near the boundary between material falling back on to 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 ^sup 44^Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed ^sup 44^Ti emission to estimated ^sup 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 ^sup 44^Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the ^sup 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 in stabilities in core-collapse supernovae. [PUBLICATION ABSTRACT]

In core-collapse supernovae, titanium-44 (Ti-44) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32-kilo-electron volt emission lines from decay of Ti-44 produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.

In core-collapse supernovae, titanium-44 ((44)Ti) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32-kilo-electron volt emission lines from decay of (44)Ti produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.