3D SIMULATIONS OF TYPE IA SUPERNOVAE
A. Hirschmann, J. Isern, E. Bravo
Institut d´Estudis Espacials de Catalunya, (IEEC/CSIC/UPC), Barcelona, Spain
A 3D Monte Carlo code has been built to simulate the gamma-ray emission during Type Ia supernova explosions in order to properly take into account departures from symmetry (Isern
et al,1999; Isern et al, 2003)
A 3D Delayed Detonation (DDT) model has been used as input for the simulation results presented further ahead. Two calculations of gamma-ray emission were carried out: one taking
into account the whole structure of the DDT model, and the second carving out a conical hole from the sphere, where its density is almost negligible. The hole is representing the location
of a secondary star.
It is natural to wonder if this kind of situation will produce an observable feature in the γ-ray signature of the explosion. In the
simple degenerate scenario, the debris of the explosion will collide with the secondary star and, consequently, a hole of some
form will appear (Marietta et al., 2001) Figure 1
WHY A CONICAL HOLE ?
SEC
STAR
WD
We have computed
the γ-ray emission
assuming a conical
hole in the debris.
Figure 2
CONICAL
HOLE
∆θ
∆θ
In order to compare
results, we have also
computed the γ-ray
by
the
entire
expanding
ejecta.
Figure 3
∆θ
EJECTED
MATERI AL
FROM
EXPLOSION
∆θ
∆θ
∆θ
Figure 2
Figure 1
Figure 3
RESULTS FROM SIMULATIONS
HOLE NOT INCLUDED
GAMMA RAY SPECTRA
SYMMETRY CONSIDERATIONS
The spectra shown at day 20
as well as day 70 after the
explosion emphasizes the
almost perfect symmetry of
the system. From any
direction, there is no major
variation of the flux as a
function of the angle. In both
cases, the red line represents
the average radiation over
the whole sphere. The small
scale structure of the green
line, noticeable more on day
70 than day 20, is mainly due
to numerical noise. At day
20, two lines are seen:
812keV belonging to 56Ni
and 847keV to 56Co. At day
70, the 812keV line is no
longer seen since the lifetime
of this radioactive element is
of the order of eight days.
For the DDT model, the intensity of the lines 56Ni 158kev and 56Co 847keV remains constant
as a function of the viewing angle. Several days are plotted to show that the intensity flattens
out with time. The 56Ni 158 keV is only present during the first days after the explosion
(τ1/2~8.8days). This radioactive element decays into 56Co, which has a much longer lifetime
(τ1/2~111days) and peaks approximately between 70-100 days after the explosion. The left
figure displays the decrease of intensity of 158keV line vs θ with time, going from maximum at
day 20 to minimum at day 300. In the right figure, the intensity of line 847 kev vs. θ increases
with time till it reaches maximum at day 90 and then decreases until day 300. The intensity for
both figures remains almost constant for any inclination.
HOLE location: θi=154º θs=180º ϕi=0º ϕs=360º
HOLE INCLUDED
SYMMETRY CONSIDERATIONS
GAMMA RAY SPECTRA
As in the non-hole case, both 56Ni 158keV and 56Co 847keV line intensities are plotted as a
function of the viewing angle. Contrary to the previous case, the intensities do show a
dependence on the angle. The dotted line marks the beginning of the conical hole, at θ~ 154º.
The intensity remains constant outside the hole (except for the day 20) but increases as the
viewing angle approaches the cone. This phenomenon is seen for early days in line 158 keV
and mid epochs for 847 keV. The lines eventually become constant, with time, both outside
as inside the hole, since the medium becomes transparent, and thus, the system resembles
non-hole model conditions..
Spectra of day 20 and day
70 for line 847keV 56Co
are displayed in the figures
below. The line 812keV
56Ni is prominent at early
stages and stronger than
the 56Co 847 keV, but for
later days the lower energy
line disappears, as seen in
day 70. Evidently, there is
a flux dependence with the
viewing angle. The flux
increases when observing
the system right above the
conical hole (green line).
Since the density is much
lower inside than outside
the hole, the medium is
less dense and hence, more
photons will be able to
escape. Notice also that the
green
line
profile
resembles a gaussian much
more than the other lines.
●
●
CONCLUSIONS
●
In the case of having only one observation, it will be impossible to distinguish
if the observation was from inside or outside the hole, since we do not have
the possibility of viewing the system from different directions.
A numerous database of SN Ia explosions with high resolution spectra is
needed to be able to achieve such thorough analysis.
However, if the observation was to measure the line profile, this could help
to detect the presence of the hole.
GAMMA RAY LIGHTCURVE
The quasi symmetry of the system again is present
in the lightcurve of the 56Co 847 keV line; the flux
does not depend on the viewing angle. The lines are
zoomed in at maximum to show that there is a
slight variation, however small enough to be
considered negligible. (∆E=0.84-0.88 MeV)
GAMMA RAY LIGHTCURVE
The asymmetry of the system becomes relevant when
calculating the lightcurves. The intensity obtained when
looking down the hole (green line) is considerably higher
than the intensity obtained when looking from a line of
sight outside the cone. The peak shown at day 20
represents the contribution of the 56Ni 812 keV line. This
line disappears rather early in the explosion since 56Ni
has a lifetime of ~8 days. For later times, the material
becomes transparent enough both inside and outside the
hole such that the line intensities converge for all viewing
angles. (∆E=0.83-0.88 MeV)
References:
Gomez-Gomar, J., Isern, J., Jean, P., 1998, MNRAS, 295, 1
Isern, J, Bravo, E., Gomez-Gomar, J., & Garcia-Senz, D. 1999, Astro Lett & Comm., 38, 411
Isern,J., Bravo,E., Hirschmann, A.,Garcia-Senz, D., 2003, Seeon Proceedings
Kasen D.,Nugent P., Thomas R.C.,Wang L., 2003, asto-ph/0311009
Marietta, E., Burrows, A., & Fryxell, B. 2000 ApJS, 128, 615