A comparative study of the infrared and X-ray fluxes and morphologies of supernova remnants (SNR) can yield valuable information on their evolution and on their interaction with the smbient interstellar medium (ISM)

Dwek, E.

Petre, R.

Szymkowiak, A.

English

NASA Technical Reports Server

N87-15104
INFRARED STUDIES OF SUPERNOVA _ANTS
WITH THE IRAS
E. Dsek, R. Petre, and A. Szymkoxiak
NASA/Goddard Space Flight Center
Abstract: A comparative study of the infrared and X-ray fluxes and morphologies
of supernova remnants (SNR) can yield valuable information on their evolution
and on their interaction with the ambient interstellar medium (ISM).
Infrared observations of SNR: The infrared observations used in this study were
obtained with the Infrared Astronomical Satellite (IRAS) which performed an all-
sky survey at 12, 25, 60, and I00 microns. Galactic remnants detected in the
IRAS survey include the historical remnants: Cas A, Tycho, Kepler; and the
adiabatic remnants: IC 443, Puppis A, RCW 86, and the 6h/gnus Loop. Among those
not detected are SN 1006 and RCH 103.
Infrared emission mechanisms: Mechanisms operating within a SNR that can
contribute to the observed infrared (IR) emission are: synchrotron emission from
accelerated electrons; infrared line and free-free emission from shocked optical
nebulosities; and thermal emission from dust. Thermal dust emission can arise
either from interstellar or circumstellar dust swept up by the expanding
supernova (SN) shock, or from circumstellar or supernova dust that is swept up
by the reverse shock that propagates through the ejecta.
Comparison of IR to X-ray cooling of SNR: Thermal dust emission is the dominant
source of IR radiation in all the detected remnants listed above. A comparison
of the IR and X-ray morphologies of the extended remnants shows that they are
spatially well correlated, suggesting that the IR emission arises from
collisionally heated dust that resides in the X-ray emitting plasma. For a
given dust-to-gas mass ratio and dust model the ratio of infrared to X-ray
cooling of a remnant (hereafter the IRX ratio) is then only a function of gas
temperature. He calculated this ratio for all remnants listed above, and
compared it with the theoretically predicted value (Figure i). He found that:
i) the observed IRX ratio follows the general theoretical trend of decreasing
IRX ratio with increasing remnant age; and 2) the IRX ratio is significantly
larger than unity for all remnants, suggesting that gas-grain collisions are the
dominant cooling mechanism of the shocked gas. The enhanced cooling resulting
from gas-grain collisions will, however, have a negligible effect on the
dynamical evolution of the remnants considered here.
Interaction with the ISM: Some remnants have IRX ratios that deviate
significantly from the theoretical value. These deviations can be shown to
result from varying conditions in the ambient ISM.
Nature of the emitting dust: A detailed analysis of the spectrum of Cas A
(Dwek, Dinerstein, Gillett, Hauser, and Rice; submitted to Ap. J.; see Figure
2), and a preliminary study of that of Tycho and Kepler indicate that the IR
spectrum from these remnants arises from an interstellar mixture of silicate and
graphite dust. The excess 12 microns emission, over that expected from a
standard MRN grain size distribution, suggests the presence of very small dust
particles in the ISM which are stochastically heated by the shocked gas.
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https://ntrs.nasa.gov/search.jsp?R=19870005671 2020-03-20T12:28:11+00:00Z
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100
10
1
106
Figure i: The IRX ratio of selected SNR
I i i If'IllI i.....I
I
eRCW 86
Cas A
IC443
• Tycho
I I Ii'I=P
nus Loop
• Kepler
Puppls A
,,,.,,,,I, ,,,,J,,l.
10 7 i0 a
I
theoret leal
curve
I .i i I Ill
10
Gas Temperature
v
X
c_
100
10
Figure 2: The infrared spectrum of Cas A
' ' ' 'I ' ' ' ' ' ' ' 'I
- • IRAS
observations /_
-- /_ the stochastlc heat_ing _._
,/,, ,I _ j , , , ,, ,I I
10 100
Wavelength(/zm)
124


Infrared studies of supernova remnants with the IRAS

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