X-ray evidence for spectroscopic diversity of type Ia supernovae:

XMM observation of the elemental abundance pattern in M 87

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
² Service d'Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France

Corresponding author: A. Finoguenov, alexis@xray.mpe.mpg.de

Received: 4 July 2001
Accepted: 15 October 2001

Abstract

We present the results of a detailed element abundance study of hot gas in M 87, observed by XMM-Newton. We choose two radial bins, and ( for EMOS; hereafter the central and the outer zones), where the temperature is almost constant, to carry out the detailed abundance measurements of O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni using EPIC-PN (EPN) and -MOS (EMOS) data. First, we find that the element abundance pattern in the central compared to the outer zone in M 87 is characterized by SN Ia enrichment of a high (roughly solar) ratio of Si-group elements (Si, S, Ar, Ca) to Fe, implying that Si burning in SN Ia is highly incomplete. In nucleosynthesis modeling this is associated with either a lower density of the deflagration-detonation transition and/or lower C/O and/or lower central ignition density and observationally detected as optically subluminous SNe Ia in early-type galaxies. Second, we find that SN Ia enrichment has a systematically lower ratio of the Si-group elements to Fe by 0.2 dex in the outer zone associated with the ICM of the Virgo cluster. We find that such a ratio and even lower values by another 0.1 dex are a characteristic of the ICM in many clusters using observed Si:S:Fe ratios as found with ASCA. Third, the Ni/Fe ratio in the central zone of M 87 is solar (meteoritic), while values around 3 times solar are reported for other clusters. In modeling of SN Ia, this implies a reduced influence of fast deflagration SN Ia models in the chemical enrichment of M 87's ISM. Thus, to describe the SN Ia metal enrichment in clusters, both deflagration as well as delayed detonation scenarios are required, supporting a similar conclusion, derived from optical studies on SNe Ia. We discuss implications of our results for observations of SN Ia and also suggest a link between the element abundances observed in the M 87 X-ray halo with the observed characteristics of M 87 globular clusters.