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Astron. Astrophys. 350, 997-1006 (1999)
1. Introduction
Recently, we have published our discoveries of a previously unknown
galactic supernova remnant (SNR) (Aschenbach 1998, Iyudin et al.
1998). The X-ray image obtained in the ROSAT all-sky survey shows a
disk-like, partially limb brightened emission region of 2o
in diameter, which is the typical appearance of a shell-like SNR (cf.
Fig. 1). The PSPC X-ray spectra reveal rather high temperatures of
3 107 K, which indicate that
RX J0852.0-4622 is a young object. Combining the low age and the
2o angular extent it is concluded that RX J0852.0-4622 is
relatively close-by. Comparison with historical SNRs limits the age to
about 1500 yrs and the distance to
1 kpc. The case of RX J0852.0-4622
being an SNR was clinched by the detection of
-ray line emission from
44Ti, which is a titanium isotope exclusively produced in
supernovae. The centre of the 44Ti source, called GRO
J0852-4642, is off-set from the center of RX J0852.0-4622 by
0.4o, but this is significantly less than the angular
resolution of the COMPTEL instrument, so that RX J0852.0-4622 and GRO
J0852-4642 are considered to be the same object. Using a weighted mean
lifetime of 44Ti of 90.4 yrs, the angular diameter and
adopting a mean expansion velocity of 5000 km s-1 as well
as a 44Ti yield of
5 10-5
M age and distance are uniquely
determined to 680 yrs and
200 pc, respectively. Therefore, RX
J0852.0-4622/GRO J0852-4642 could be the nearest supernova to Earth to
have occured during recent human history.
![[FIGURE]](img10.gif) |
Fig. 1. Grey scale image of RX J0852.0-4622 for E 1.3 keV. Coordinates are right ascension, declination of epoch 2000.0. Contour levels are (in black) 1.5, 2.3, (in white) 3.5, 5.2, 8.2, 9.2 in units of 10-4 PSPC counts s-1 arcmin-2.
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The discovery of RX J0852.0-4622 and the interpretation as an SNR
was made by one of us (BA) in early 1996. During the time which
followed it was attempted to associate some fraction of the
26Al -ray line emission
from the Vela SNR region measured by COMPTEL (Oberlack et al. 1994,
Diehl et al. 1995) with RX J0852.0-4622. The results have not been
conclusive basically because of the unknown distance of RX
J0852.0-4622 (Oberlack 1997). The discovery of 44Ti
-ray line emission, however, made it
clear that RX J0852.0-4622 is indeed a nearby object, so that we could
take up again the discussion of the association of 26Al
emission with RX J0852.0-4622. For example the combination of just the
26Al and 44Ti data allow to derive a distance
independent estimate of the age of GRO J0852-4642. Furthermore, if a
major fraction of the Vela 26Al mass would be associated
with the SNR, a type Ia supernova is excluded within the framework of
current explosion models. Under the assumption of adiabatic expansion
(Sedov-like) of the SNR we give an estimate of the supernova explosion
energy E0 related to the progenitor star and the ambient
matter density n0. The uncertainties in the determination
of age and distance by exploiting the X-ray spectra are discussed to
come up with a time span in which to search for the historical
supernova event.
In a recent paper Chen & Gehrels (1999) conclude that RX
J0852.0-4622 was created by a core-collapse supernova of a massive
star. Their analysis is based on the X-ray data and
-ray data published published earlier
by us (Aschenbach 1998, Iyudin et al. 1998). We discuss their approach
and conclusions in the relevant section.
© European Southern Observatory (ESO) 1999
Online publication: October 14, 1999
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