Modeling SN 1996crs X-ray lines at high-resolution: Sleuthing the ejecta/CSM geometry

arXiv:1102.1442v1 [astro-ph.HE] 7 Feb 2011 Modeling SN 1996cr’s X-ray lines at high-resolution: Sleuthing the ejecta/CSM geometry Daniel Dewey∗, Franz E. Bauer† and Vikram V. Dwarkadas∗∗ ∗MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139, USA †Dept. de Astronomía y Astrofísica, Pontificia U. Católica de Chile, Casilla 306, Santiago 22, Chile ∗∗Dept. of Astronomy and Astrophysics, U. of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA Abstract. SN 1996cr, located in the Circinus Galaxy (3.7 Mpc, z ∼0.001) was non-detected in X-rays at ∼1000 days yet brightened to Lx ∼4 × 1039 erg/s (0.5-8 keV) after 10 years (Bauer et al. 2008). A 1-D hydrodynamic model of the ejecta- CSM interaction produces good agreement with the measured X-ray light curves and spectra at multiple epochs. We conclude that the progenitor of SN 1996cr could have been a massive star, M > 30 M⊙, which went from an RSG to a brief W-R phase before exploding within its r ∼0.04 pc wind-blown shell (Dwarkadas et al. 2010). Further analysis of the deep Chandra HETG observations allows line-shape fitting of a handful of bright Si and Fe lines in the spectrum. The line shapes are well fit by axisymmetric emission models with an axis orientation ∼55 degrees to our line-of-sight. In the deep 2009 epoch the higher ionization Fe XXVI emission is constrained to high lattitudes: the Occam-est way to get the Fe H-like emission coming from high latitude/polar regions is to have more CSM at/around the poles than at mid and lower lattitudes, along with a symmetric ejecta explosion/distribution. Similar CSM/ejecta characterization may be possible for other SNe and, with higher-throughput X-ray observations, for gamma-ray burst remnants as well. Keywords: methods: numerical, techniques: spectroscopic, circumstellar matter, super-novae: individual: SN 1996cr, stars: winds outflows, X-rays: individual: SN 1996cr. PACS: 95.75.Fg, 95.85.Nv, 97.60.Bw, 98.58.Mj, 98.58.Ay. INTRODUCTION TO SN 1996CR SN 1996cr, located comparatively nearby in the Circinus Galaxy (3.7 Mpc, z ∼0.001) was serendipitously detected as a ULX at an age of ∼5 years [1]. As detailed in Bauer et al. [2] : i) followup archival research and VLT observations (at age ∼10 years) allowed SN 1996cr to be classified as a Type IIn SNe, and ii) archival X-ray data showed that it was not detected at an age of ∼1000 days, yet brightened to Lx ∼4×1039 erg/s (0.5-8 keV) after 10 years. This X-ray behavior is shared only with SN 1987A, and is roughly shown in Figure 1 in the context of other X-ray-detected SNe and core-collapse (CC) SNRs. Because of this behavior, and given an indication of Doppler structure in 2004 Chandra HETG data, we proposed and obtained a deep, 485 ks HETG observation (PI Bauer) near the beginning of 2009. In large part because of the high quality of this recent data we were able to tune a 1-D hydrodynamic model to agree with the multi-epoch X-ray data (next section), and we are now investigating signatures of the ejecta/CSM geometry in the HETG line shapes (last section.) HYDRODYNAMIC MODEL AND X-RAY EMISSION A 1-D (spherical) hydrodynamic model of the ejecta-CSM interaction is developed in Dwarkadas et al. [4]; post- processing calculates the X-ray emission from the non-radiative shocks, showing good agreement with the measured X-ray light curve and spectra at multiple epochs. Given our inferred configuration, Figure 2, a realistic evolutionary scenario for SN 1996cr’s progenitor has it evolving from the RSG to the W-R stage, creating a wind-blown bubble with a dense shell at about 0.04 pc, and then exploding as a SN. Some conclusions from the modeling are that: • The 1-D model explains the majority of the observed X-ray continuum and lines, and their variation in time. • The velocities of plasma in the model agree with the scale of the line broadening seen in the HETG data. • The inner ejecta core is opaque to HETG X-rays as late as 2009 when it has a plateau density of 105 amu cm−3 and a radius of 0.065 pc, giving a column density along the diameter of 4.0 × 1022 amu cm−2 of high-Z material. FIGURE 1. The unique behavior of SN 1996cr and SN 1987A. Their X-ray light curves are overplotted on an LX vs Age plot from Immler & Kuntz [3]. Unlike other X-ray-bright SNe, these two show a dramatic (re-)brightening at ages of a few years to decades. As these and other SNe age we will begin to fill in the CC SNe-SNR gap seen between ages of 30 to 300 years. FIGURE 2. Initial density profile for the hydrodynamic model of SN 1996cr. Several months after the SN explosion the ejecta (near the origin at left) is seen making its way into the low density W-R wind cavity while the shell of swept-up RSG wind material doesn’t know what’s going to hit it. See Figure 3 of Dwarkadas et al. [4] for snapshots of the further evolution of the hydrodynamics beyond this initial configuration. • Initially the flux from the forward-shocked shell dominates. However, at ∼8 years the reverse-s

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