📝 Original Info
- Title: Bursting SN 1996crs Bubble: Hydrodynamic and X-ray Modeling of its Circumstellar Medium
- ArXiv ID: 1005.1090
- Date: 2015-05-18
- Authors: Researchers from original ArXiv paper
📝 Abstract
SN1996cr is one of the five closest SNe to explode in the past 30 years. Due to its fortuitous location in the Circinus Galaxy at ~ 3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485 ks Chandra HETG spectrum. In order to interpret this data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at 4 epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium, the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium before interacting with a dense shell of material about 0.03pc away from the progenitor star. We speculate that the shell could be due to the interaction of a blue supergiant or Wolf-Rayet wind with a previously existing red supergiant (RSG) wind. The shock wave has now exited the shell and is expanding in the medium exterior to it, possibly the undisturbed continuation of the dense RSG wind. The narrow lines that earned SN 1996cr its IIn designation possibly arise from dense, shocked clumps in the CSM. Although the possibility for an LBV progenitor for this Type IIn SN cannot be completely excluded, it is inconsistent with much of the data. These calculations allow us to probe the stellar mass loss in the very last phases ($ < 10^4$ years) of a massive star's life ($> 10^6$ years), and provide another means to deducing the progenitor of the SN.
💡 Deep Analysis
Deep Dive into Bursting SN 1996crs Bubble: Hydrodynamic and X-ray Modeling of its Circumstellar Medium.
SN1996cr is one of the five closest SNe to explode in the past 30 years. Due to its fortuitous location in the Circinus Galaxy at ~ 3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485 ks Chandra HETG spectrum. In order to interpret this data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at 4 epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium, the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium
📄 Full Content
Core-collapse supernovae (SNe) arise from stars with zeroage main-sequence masses 8M⊙. However, decades of research has failed to determine a direct relationship between the various SNe types (as classified based on their optical spectra and light curves) and the progenitor stars that gave rise to the SNe. It is not clear how the type IIP, IIL, IIb, IIn, Ib and Ic types relate to the properties of their respective progenitor stars. The progenitors themselves, as it turns out, are not very well known, with the handful of identified ones appearing to be associated almost exclusively with Type IIP SNe (Smartt 2009). It had been surmised that the main progenitors of core-collapse SNe were red supergiants (RSGs) and Wolf-Rayet (W-R) stars (Falk & Arnett 1977;Podsiadlowski 1992). The explosion of SN 1987A revealed that blue supergiants (BSGs) could also be SN progenitors (Sonneborn et al. 1987), perhaps in a binary system (Morris & Podsiadlowski 2007;Podsiadlowski et al. 2007). In the last decade there has been discussion of LBV stars being the progenitors of Type IIn SNe (Chu et al. 1999;Salamanca 2000;Kotak & Vink 2006;Vink 2008;Smith 2008;Trundle et al. 2008Trundle et al. , 2009;;Gal-Yam & Leonard 2009), which is problematic because stellar theorists have mainly placed the LBV stage as an intermediate post-main sequence stage, not as a pre-explosion phase (Schaller et al. 1992;Langer 1993;Langer et al. 1994;Stothers & Chin 1996;Garcia-Segura et al. 1996;Maeder et al. 2005;Maeder & Meynet 2008).
The problem is clear -we rarely know the progenitor star that led to a SN explosion, because it has to be typed from pre-explosion images, leading to significant ambiguity and potential bias. The expansion of the SN shock wave and the resulting emission due to circumstellar interaction (Chevalier & Fransson 1994) opens up another window into the exploration of the pre-SN star. The thermal emission from this interaction, including the X-ray and optical emission, and to some extent the non-thermal radio emission (Chevalier 1982b), depends directly on the external density. Thus an accurate analysis and interpretation of this emission acts as a probe of the density profile. In the case of core-collapse SNe, which lose a significant amount of mass prior to collapse, the surrounding medium is formed by material from the pre-explosion star. Decoding the structure of this circumstellar medium therefore will allow us to probe the mass-loss parameters of the pre-SN star, which can then be linked to the stellar parameters. Thus this provides a way to explore the stellar parameters even after the star ceases to exist, and allows us to probe the pre-SN properties of classes of SN that have heretofore lacked progenitor counterparts.
In this paper we pursue this method for the unusual Type IIn SN 1996cr. This SN, which exploded around 1996 but was only discovered about 11 years later, is only the second SN after SN 1987A which shows increasing radio and X-ray emission over a sustained period of a few years (Bauer et al. 2008). Bauer et al. (2008) suggested that the increasing X-ray and radio emission may be associated with a dense shell of material which the expanding SN shock wave interacts with a couple of years after explosion. Herein we carry out hydrodynamical simulations to evaluate this hypothesis, and to decipher the detailed structure of the circumstellar medium into which the shock wave from SN 1996cr is expanding. We compute the X-ray lightcurves and X-ray spectra using non-equilibrium ionization conditions, which we compare with high-resolution Chandra observations. We achieve a detailed agreement which, given that we are using a single model across multiple epochs, affirms the validity of our hydrodynamical model, and allows us to constrain a range of abundances for both the material ejected in the explosion and the surrounding circumstellar medium.
The plan of this paper is as follows: In §2 we review the observational details of SN 1996cr, including our recent High Energy Transmission Grating (HETG) spectra which motivated this analysis. §3 describes the reasoning behind our model of the circumstellar medium (CSM), and the results of the hydrodynamical modelling of the SN ejecta interacting with the CSM. Our techniques for computation of the X-ray light curves and spectra from the hydrodynamical models, and the resultant X-ray emission, are outlined in §4.
§5 puts the narrow lines that earned SN 1996cr its Type IIn designation into the context of the overall model. In §6, the implications for the progenitor, and the abundance determinations, are discussed in depth. Finally, §7 summarizes our results and outlines future work in this area.
This luminous type IIn SN was only identified in the nearby Circinus Galaxy (3.7±0.3 Mpc; Koribalski et al. 2004) ∼11 years after it was believed to have exploded (Bauer 2007;Bauer et al. 2008), but its remarkable evolution was fortuitously captured in archival data from HST, Chand
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