Indication of a fast ejecta fragment in the atomic cloud interacting with the southwestern limb of SN 1006

¹ Dipartimento di Fisica e Chimica E. Segrè, Università degli Studi di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
² INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
e-mail: roberta.giuffrida@inaf.it
³ Université de Paris, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
⁴ Sorbonne Université, Observatoire de Paris, PSL Research University, LERMA, CNRS UMR 8112, 75005 Paris, France
⁵ Institute for Theoretical Particle Physics and Cosmology (TTK), RWTH Aachen University, 52056 Aachen, Germany

Received: 12 October 2023
Accepted: 9 January 2024

Abstract

Context. Supernova remnants interacting with molecular and atomic clouds are interesting X-ray sources for studies of broadband nonthermal emission. X-ray line emission in these systems can be produced by different processes, such as low-energy cosmic rays (LECRs) interacting with the cloud and fast ejecta fragments moving in the cloud.

Aims. This paper is aimed at studying the origin of the non-thermal X-ray emission of the southwestern limb of SN 1006 beyond the main shock to determine whether the emission is due to LECRs diffusing in the cloud or to ejecta knots moving into the cloud.

Methods. We analyzed the X-ray emission of the southwestern limb of SN 1006, where the remnant interacts with an atomic cloud, using three different X-ray telescopes: NuSTAR, Chandra, and XMM-Newton. We also performed a combined spectro-imaging analysis of this region.

Results. Our analysis of the nonthermal X-ray emission of the southwestern limb of SN 1006 interacting with an atomic cloud has led to the detection of an extended X-ray source in the atomic cloud, approximately 2 pc upstream of the shock front. The source is characterized by a hard continuum (described by a power law with photon index Γ ∼ 1.4) and by Ne, Si, and Fe emission lines. The observed flux suggests that the origin of the X-ray emission is not associated with LECRs interacting with the cloud. On the other hand, the spectral properties of the source, together with the detection of an IR counterpart visible with Spitzer-MIPS at 24 μm, are in good agreement with the general expectations for a fast ejecta fragment moving within the atomic cloud.

Conclusions. We detected X-ray and IR emission from a possible ejecta fragment, with an approximate radius of 1 × 10¹⁷ cm and approximate mass of 10⁻³ M_⊙ at about 2 pc out of the shell of SN 1006, in the interaction region between the southwestern limb of the remnant and the atomic cloud.