Modeling SNR1987A with iHydra, I

17-Mar-2005-dd

Introduction

SNR 1987A: On Feb 23 1987 light and neutrinos from a star that had exploded in the LMC some 160,000 years earlier reached earth. SN 1987A, a "core collapse" supernova was born. In the years since the explosion a blast wave and the SN debris have expanded into the region around the SN. Most conspicuous is a thin dense ring of material which glows from an ionizing flash at the time of the SN. More recently, ~2002, the blast wave started to arrive at the inner protrusions of the ring causing bright optical "spots" or "beads" to appear:

. . .
Optical image from Hubble (left) and simple X-ray emission model (right.)
As the elliptical nature of the image suggests, we are viewing the system at a ~45 degree angle to the ring plane. The North part of the ring is closest to us.

Less conspicuous in the optical image is the existence of a thick torus of intermediate density material starting about half way between the SN and the dense ring. In ~1990-1991 the blast wave encountered this material, slowed to ~5,000 km/s and caused X-ray and radio emission. In the present day the blast wave has reached the dense inner ring driving shocks into it in the velocity range ~300 km/s depending on the local ring density.

The goal here is to produce a simple 3D model of the X-ray emission made up of high temperature emission from the shocked region of the thick torus and lower temperature emission from the shocked dense inner ring. Because of its high spectral resolution the HETG can tell the difference between these two velocity components as broad and narrow components in the spectrum.

See also Part 2, March 2006.

Software

Prototype code written in IDL was used, see the main routine:

The definition of the model geometrical/plasma components, the spectra assigned to some components, and the observations to be generated from the model are specified in the three files: The software makes use of "v3d" routines and other IDL code in the HAK distribution. (At MIT, in /nfs/cxc/a1/src/hak/hak_1.8/hak_code currently.)

Renderings of the System Geometry

These two images show the system geometry from a "front" view (left, perpendicular to the ring plane) and a "side" view. The main components are the SN center (the dot), the expanding SN debris (fuzzy sphere in the side view), and the thick torus ("Mmmm, donut...") and the dense inner ring:

A more 3D-ish rendering and a cross-section are shown in these views:

View similar to the above left one but made using volview:

The actual X-ray emitting regions are the shocked portions of the big tous and the inner ring and these are shown here rendered similarly to the full geometry above:

View similar to the above left one but made using volview:

Finally, these two X-ray emitting components are projected to the sky plane (45 degrees off the ring axis) and weighted by their X-ray flux to generate an approximation to the expected intensity distribution of the system seen in X-rays (by a telescope of high spatial resolution):

Quantitative Output Prouducts

The images above are useful to confirm/explore the model geometry. The same data structures that were used to create these images were then used to:

Examples of these are given below.

The volume and mass of the various components are given: 

 SNenv:  Volume[10^57 cm^3], Mass[SM]  =    0.000756185     0.610678
 SNdot:  Volume[10^57 cm^3], Mass[SM]  =    1.97917e-07      0.00000
 Ring:  Volume[10^57 cm^3], Mass[SM]  =    5.42859e-05     0.130914
 H_II:  Volume[10^57 cm^3], Mass[SM]  =     0.00134018     0.113160
 Fast:  Volume[10^57 cm^3], Mass[SM]  =    0.000353763     0.106122
 Slow:  Volume[10^57 cm^3], Mass[SM]  =    9.95241e-06    0.0362458
Note that the last two components are the X-ray emitting ones and their masses, 0.106 and 0.036 solar masses, are based on the source distance, emitting volume, electron and ion densities, and emission properties of the plasma they model.

The electron density is calculated through out the whole region and plotted here i) for all locations as a 1D array over the whole cube, and ii) just along the Y-axis, that is along the central vertical line in the crosssection plots. Note the low density of the shocked torus region, ~ 250 /cm^3, and the higher density of the shocked inner ring region, ~ 2000/cm^3.

Simulated Photons and Events

Simulated events and observations are specified in an observation table:

inst	params	expos	roll	date	product	gotdata	calcmod	method
------  ----    -----   -----   -----   ------  -----   -----   ------
Apert	1000	5.e3	0	2000.0	Photons	0	1	n/a
ACIS	S3	5.e4	0.0	2004.0	1D_pha	1	1	simple
HETG	zo	1.e5	12.0	2000.5	2D_img	1	0	simple
HETG	MEGm1	5.e5 	0.0	2006.5	2D_grat	0	1	simple
XMM	RGSm1	1.e5	0.0	2001.3	1D_grat	0	0	simple
AstroE2	XRS	1.e5	0.0	2005.9	1D_pha	0	1	simple
The ones with calcmod = 1 have been produced here and are shown below.

A file of emitted photons for an Aperture of 1000 cm^2 is created for use as a ray-trace input and is given here:

A simulation of the event image and pha spectrum from the Chandra ACIS S3 detector and the AstroE2 XRS detector are shown in these plots:




Simulated HETG MEG m=-1 images/spectra are given below for three cases:

Nominal model parameters:

Model with velocities of components set to zero:

The "slow" (narrow) ring component 3 times brighter: