44Ti ejecta in young supernova remnants

Christoph Weinberger,Roland Diehl,Jochen Greiner,Thomas Siegert,Moritz M M Pleintinger

doi:10.1051/0004-6361/202037536

Abstract

Context. Tracing unstable isotopes produced in supernova nucleosynthesis provides a direct diagnostic of supernova explosion physics. Theoretical models predict an extensive variety of scenarios, which can be constrained through observations of the abundant isotopes 56Ni and 44Ti. Direct evidence of the latter was previously found only in two core-collapse supernova events, and appears to be absent in thermonuclear supernovae. Aims. We aim to to constrain the supernova progenitor types of Cassiopeia A, SN 1987A, Vela Jr., G1.9+0.3, SN1572, and SN1604 through their 44Ti ejecta masses and explosion kinematics. Methods. We analyzed INTEGRAL/SPI observations of the candidate sources utilizing an empirically motivated high-precision background model. We analyzed the three dominant spectroscopically resolved de-excitation lines at 68, 78, and 1157 keV emitted in the decay chain of 44Ti→44Sc→44Ca. The fluxes allow the determination of the production yields of 44Ti. Remnant kinematics were obtained from the Doppler characteristics of the lines. Results. We find a significant signal for Cassiopeia A in all three lines with a combined significance of 5.4σ. The fluxes are (3.3 ± 0.9) × 10−5 ph cm−2 s−1, and (4.2 ± 1.0) × 10−5 ph cm−2 s−1 for the 44Ti and 44Sc decay, respectively. This corresponds to a mass of (2.4 ± 0.7) × 10−4 M⊙ and (3.1 ± 0.8) × 10−4 M⊙, respectively. We obtain higher fluxes for 44Ti with our analysis of Cassiopeia A than were obtained in previous analyses. We discuss potential differences. We interpret the line width from Doppler broadening as expansion velocity of (6400 ± 1900) km s−1. We do not find any significant signal for any other candidate sources. Conclusions. We obtain a high 44Ti ejecta mass for Cassiopeia A that is in disagreement with ejecta yields from symmetric 2D models. Upper limits for the other core-collapse supernovae are in agreement with model predictions and previous studies. The upper limits we find for the three thermonuclear supernovae (G1.9+0.3, SN1572 and SN1604) consistently exclude the double detonation and pure helium deflagration models as progenitors.

Highlights

Supernova explosions play a crucial role in the chemical and kinematic evolution of the Universe
For modeling core-collapse supernova explosions, reviving the stalled shock and triggering an explosion presents a major challenge (Janka 2012; Burrows et al 2018), as it has long been understood that the prompt explosion mechanism following core bounce cannot explode the star
For six analyzed supernova remnants, we find significant detection only for Cassiopeia A, with an integrated flux of (4.2 ± 1.0) × 10−5 ph cm−2 s−1 corresponding to an 44Ti ejecta mass of (2.6 ± 0.6) × 10−4 M

Summary

Introduction

Supernova explosions play a crucial role in the chemical and kinematic evolution of the Universe. Self-consistent detailed models for the explosion mechanism and the ensuing kinematics of the ejected material are still lacking. For modeling core-collapse supernova explosions, reviving the stalled shock and triggering an explosion presents a major challenge (Janka 2012; Burrows et al 2018), as it has long been understood that the prompt explosion mechanism following core bounce cannot explode the star. SPI instrumental background mainly originates from the bombardment of the satellite by cosmic ray particles. The gray spectrum shows the average background count rate. Visible are the strong background lines between 50 and 68 keV and around 92 keV. Our background modeling approach efficiently suppresses contribution from strong lines. The gray line shows the average count rate for the background. Influence from strong background lines is suppressed by our modeling approach. Dead time corrected exposure at the positions is 9 Ms

Objectives

Findings

Discussion

Conclusion