An X-Ray Study of Supernova Remnant N49 and Soft Gamma-Ray Repeater 0526-66 in the Large Magellanic Cloud

TL;DR

This study uses deep Chandra X-ray observations to analyze supernova remnant N49 and SGR 0526-66, revealing ejecta features, estimating age and explosion energy, and exploring the nature of the SGR's X-ray emission.

Contribution

It provides new insights into the ejecta composition, age, and explosion energy of N49, and compares spectral models for SGR 0526-66 to understand its emission mechanisms and relation to N49.

Findings

Detection of ejecta 'bullet' with enhanced Si and S abundances.

Estimated Sedov age of N49 is approximately 4800 years.

Spectral analysis of SGR 0526-66 suggests possible hot spot emission or neutron star surface emission.

Abstract

We report on the results from our deep Chandra observation (120 ks) of the supernova remnant (SNR) N49 and soft Gamma-ray repeater (SGR) 0526-66 in the Large Magellanic Cloud. We firmly establish the detection of an ejecta "bullet" beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is distinguished from that of the main SNR shell, showing significantly enhanced Si and S abundances. We also detect an ejecta feature in the eastern shell, which shows metal overabundances similar to those of the bullet. If N49 was produced by a core-collapse explosion of a massive star, the detected Si-rich ejecta may represent explosive O-burning or incomplete Si-burning products from deep interior of the supernova. On the other hand, the observed Si/S abundance ratio in the ejecta may favor Type Ia origin for N49. We refine the Sedov age of N49, tau_Sed ~ 4800 yr, with the explosion energy E_0 ~ 1.8 x 10^51 erg. Our blackbody (BB) + power law (PL) model for the quiescent X-ray emission from SGR 0526-66 indicates that the PL photon index (Gamma ~ 2.5) is identical to that of PSR 1E1048.1-5937, the well-known candidate transition object between anomalous X-ray pulsars and SGRs. Alternatively, the two-component BB model implies X-ray emission from a small (R ~ 1 km) hot spot(s) (kT ~ 1 keV) in addition to emission from the neutron star's cooler surface (R ~ 10 km, kT ~ 0.4 keV). There is a considerable discrepancy in the estimated column toward 0526-66 between BB+PL and BB+BB model fits. Discriminating these spectral models would be crucial to test the long-debated physical association between N49 and 0526-66.