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Astron. Astrophys. 350, 997-1006 (1999)

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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 [FORMULA] 3[FORMULA]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 [FORMULA] 1500 yrs and the distance to [FORMULA]1 kpc. The case of RX J0852.0-4622 being an SNR was clinched by the detection of [FORMULA]-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[FORMULA]10-5 M[FORMULA] age and distance are uniquely determined to [FORMULA]680 yrs and [FORMULA]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] Fig. 1. Grey scale image of RX J0852.0-4622 for E [FORMULA] 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.

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 [FORMULA]-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 [FORMULA]-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 [FORMULA]-ray data published published earlier by us (Aschenbach 1998, Iyudin et al. 1998). We discuss their approach and conclusions in the relevant section.

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© European Southern Observatory (ESO) 1999

Online publication: October 14, 1999