Radio and optical research was carried out in order to show that the supernova remnant RCW86 is a remnant of the earliest supernova event ever recorded in history (185 AD). The results are as follows: (1) an iron-line emission was found at 6.7 keV; (2) the temperature measured from HEAO-1 was approximately 6 keV; and (3) the equivalent width was consistent within the uncertainties with a cosmic iron abundance. These results support the identification of the supernova remnant RCW86 (it's X-ray source) with the historic supernova event

Winkler, P. F.

English

NASA Technical Reports Server

X-RAY IRON-LINE EMISSION FROM THE SN 185 REMNANT 
P. I?. Winkler 
Middlebury College 
Most of the results that we have been hearing about today are 
very recent ones. The story of the object which I would like to talk 
about begins quite a long time ago. The earliest supernova event which 
was recorded historically occurred in the year 185 AD; the chief point 
of the work which we carried out is to t r y  to show that the supernova 
remnant RCW86 is  in fact the remnant of this historical event. 
This remnant has the galactic designation G315.4-2-3; the non- 
thermal radio source is known as MSH 14-63, and the optical filaments 
are designated RCW86. It is thought to be at a distance of about 2 .5  
kiloparsecs , determined by Westerlund ( 1969) who established its asso- 
ciation with a group of OB stars at about that distance. Westerlund 
went on to suggest that the supernova was probably a type I1 event 
because of the association with early-type stars ,  which are generally % 
believed to give rise to type I1 supernovae. 
The association of this remnant with the supernova of 185 AD has 
long been suggested. Clark and Stephenson (1977) reviewed the evi- 
dence for this association, which I would characterize as good, but not 
certain. RCW 86 is the best candidate among four known supernova 
remnants in the vacinity of the historically recorded event. 
The radio and optical appearances of this object are shown in 
Figure 1. The optical picture is  from a broad-band red plate taken by 
Robert Kirshner and myself at the CTIO 4-m telescope. Superimposed 
on it are 5 GE!z radio contours as measured by Caswell, Clark and 
Crawford (1975).  The size of the radio shell i s  about 40 arc min which 
corresponds to a diameter of about 28 par sec at a distance of 2.5 kilo- 
parsec. The optical nebulosity consists primarily of two groups of 
filaments, one at the north and another near the southwestern edge of 
the radio shell. 
The situation in X-rays is that there is an X-ray source coincident 
with the supernova remnant RCW86 which was first discovered by 
Naranan, et a1 (1977) from the NRL experiment on the Apollo-Soyuz. 
It is very bright at about 1 keV. This was independently observed by 
the MIT OSO-7 experiment above 2 keV where it has a flux of about 
7 Uhuru counts (Winkler 1978). This source has been tentatively iden- 
tified with the supernova remnant, but its location near the galactic 
plane makes an identification based on positional coincidence alone less 
than positive. 
https://ntrs.nasa.gov/search.jsp?R=19800006731 2020-03-21T19:31:02+00:00Z
The results I am reporting today make the identification much more 
definite. These are based on data from a 3-hour pointed observation of 
RCW86 with HEAO-1, carried out in March 1978. Data from the Medium- 
Energy Detectors of the A-2 experiment are shown in Figure 2. These 
are raw pulse-height data which have been untouched except for back- 
ground subtraction. Attempts to fit the data points with a spectrum 
consisting only of a thermal continuum fail; but if we allow the computer 
to add a single line to the thermal spectrum, a successful fit is obtained. 
The statistical significance of the line is 2 100. Furthermore, the line 
energy, left as an adjustable parameter in the fit, i s  fixed by the 
computer at 6.7 keV. This corresponds to K-line emission from highly 
ionized states of iron similar to lines which have been observed in other 
supernova remnants such as Cas A and Tycho. The thermal spectrum 
of lines plus continuum indicate that we are definitely observing hot 
plasma in this source and reinforces the identification of the X-ray 
source with the supernova remnant. 
In Figure 3, we have the same spectrum which has now been . 
unfolded through the response of the detector to give us an incident 
spectrum. One sees the iron line standing up very dramatically. The 
best-fit temperature here is 5.9 keV. If we assume that the hot plasma 
has been heated by a shock wave, then the shock velocity must be very 
high, about 2000 km s-1. This indicates that the supernova remnant 
must be young, because i f  we run the picture backwards (just extrapolate 
backwards to when the supernova must have gone off) then the explosion 
occurred about 2000 years ago. We feel that this establishes the identi- 
fication with the 185 AD event beyond all reasonable doubt. 
Also shown in Figure 3 is the low-energy flux as determined by 
the NRL group. The remnant is very bright at about 1 keV and falls 
sharply at higher energies. I t ' i s  impossible to f i t  all these data with a 
thermal model at a single temperature, which suggests that plasma 
components at more than one temperature are present in this remnant. 
The spectral parameters are summarized in Table 1. 
The equivalent width in the iron line (a measure of the line 
strength relative to the continuum) is about 780 eV. This can be com- 
pared with what would be expected f~om a hot plasma with cosmic abund- 
ances. I have indicated the predicted equivalent width based on two 
models for a plasma at the measured temperature. The different between 
the two predictions lies primarily in different choices for the iron 
abundance. 
The iron line we observe falls within the range predicted by the 
models. This indicates that the iron abundance, assuming thermal 
equilibrium, is consistent with the cosmic abundance of iron. 
We may interpret the X-ray emission above 2 keV within the con- 
text of the canonical blast-wave model, with a shock wave expanding 
outward, heating swept-up interstellar material, and producing X-rays. 
We obtain the results which are shown in Table 2 for the age, the 
density of the interstellar medium, and the energy required for the 
supernova explosion. Since the distance is somewhat uncertain, I have 
indicated how these parameters scale with distance. In the right hand 
column I have scaled these so that the explosion occurs in the year 
185 AD. The results are similar to what is observed for other super- 
nova remnants, except that the blast energy is somewhat higher than 
for most of the other cases in which it has been determined. 
In summary, we first find that iron-line emission at 6.7 keV 
definitely stems from this source, which confirms that the X-ray source 
is indeed associated with the remnant. Second, the temperature 
measured from HEAO-1 is about 6 keV, (for the hard X-ray component 
at any rate) which requires a shock velocity of at least 2000 km s-1. 
This indicates that the remnant must be a young one and leads to our 
conclusion that the identification with the 185 AD event is correct. And 
third, the equivalent width which we observe is consistent within the 
uncertainties with a cosmic iron abundance. 
I would like to thank everyone involved in the HEAO project for 
the opportunity to participate as a guest investigator. In particular, 
I would like to thank Steve Pravdo, Rich Mushoteky, Elihu Boldt and : 
the other members of the X-ray astronomy group at Goddard Space 
Flight Center with whom I collaborated on this work. 
REFERENCES 
Bahcall, J .  N .  and Sarazin, C .  L .  : 1978, Ap. J . ,  219, 781. 
Caswell, J .  L . ,  Clark, D .  H . ,  an'd Crawford, D.  F.: 1975, Australian 
J .  Phys. Suppl. No. 37, 39. 
Clark, D. H.  and Stephenson, F. R .  : 1977, The Historical Supernovae, 
Oxford, Pergamon Press. 
Naranan, S. ,  Shalman, S . ,  Yentis, D., Fritz, G . ,  and Friedman, H . :  
1977, Ap. J. (Letters), 213, L53. 
Raymond, J .  C .  and Smith, B.  W . :  1977, A p .  J. Suppl., 35, 419. 
Westerlund, B. E . :  1969, A. J . ,  74, 879. 
Winkler, P. F.: 1978, Ap. J . ,  221 ,  220. 
Figure 1. Radio contour map of MSH 14-63 - RCW 86 
(from Caswell, Clark and Crawford 1975) 
superimposed on a broad-band red 4-m plate. 
E n e r g y  ( k e V  ) 
Figure 2. Raw pulse-height spectrum of RCW86 from HEAO A-2 
Medium Energy Detectors. Solid line indicates 
best fit to the data. 
Energy ( keV)  
I L  
-I 
10 
- 0 
> 
Q) 
Y 
- I Y) 16*_ 
CU 
I E 
0 
6 
'5 
c 
a. 
1 6 ~  
1 6 ~  
Figure 3 .  Deconvolved incident spectrum of RCW 86. Apollo-Soyuz 
data are from Naranan et al. (1977) ; HEAO-1 is this work. 
Note strong line at 6.7 keV. 
I I i l l ,  
- 
I I 1 I ' ' I  
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
-4-4 R C W 8 6  = SN185 - 
- 
- 
-4- -$- Apollo - Soyuz 
- 
-4- + H E A O - I  
1 - - 
- 
- 
i t  4 - - - +- - 
- 
- 
- 
- 
+ 
+ 
+ - 
++ 
- 
- 
- 
- ++ - - 
- 
+I+ - 
- ++ - 
- ++ 
+4 - 
- + + ++ - + 
++ + 
++ - 
- 
- 
t - 
- t - 
- 
++I t 
- 
- 
- 
- 
- + +t - 
- t - 
- t -  - 
- 
- 
- 
1 1  I l l 1  
- 
I I 1 I 1  1 1 1 1  
- 
0.5 I 2 5 10 20 
TABLE 1. 6315.4-2.3 HEAO-1 (A-2) SPECTRUM 
Cont inuum : The rma l ,  k T  = 5.9 k e V  
-2  -1 F l u x  (2-10 keV)  = 1.1 x 10-lo  ergs c m  s 
Addi t ional  Low-T Component (Apollo-Soyuz) 
Line : <E> = 6.75 keV  
F l u x  = 6.7 x 10'~ p h o t o n s  cm - 2s- 1 
EW = 0.78 keV 
P r e d i c t e d  EW (Cosmic Abundances )  : 
Raymond a n d  Smith (1977) : 1 .41  k e V  
Bahcal l  and Sa raz in  : 0.74 keV  
TABLE 2. G315.4-2.3 BLAST-WAVE MODEL 
Genera l  
(d ,  E d l 2 . 5  k p c )  Age-Scaled 
A g e  (Sedov )  2900 d, 1793 years 
Luminosi ty  (2-10 keV)  34 2 9.2 x 10  d,  3 4 -1 3.6 x : 1 0  ergs s 
D e n s i t y  -112 0.11 d, 0.14 
Blas t  E n e r g y  51  512 2.5 x 10  d* 5 1 0 .8  x 10  ergs 
Swept-Up Mass 5.2 34 d *  10 M 
0 


X-ray iron-line emission from the SN 185 remnant

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server