X-Ray Luminosity and Size Relationship of Supernova Remnants in the LMC

The Large Magellanic Cloud (LMC) has ∼60 confirmed supernova remnants (SNRs). Because of the known distance, 50 kpc, the SNRs' angular sizes can be converted to linear sizes, and their X-ray observations can be used to assess X-ray luminosities (L _X). We have critically examined the LMC SNRs' sizes reported in the literature to determine the most plausible sizes. These sizes and the L _X determined from XMM-Newton observations are used to investigate their relationship to explore the environmental and evolutionary effects on the X-ray properties of SNRs. Our research provides the following three results. (1) Small LMC SNRs, a few to 10 pc in size, are all Type Ia with L _X > 10³⁶ erg s^-1. The scarcity of small core-collapse (CC) SNRs is a result of CC SNe exploding in the low-density interiors of interstellar bubbles blown by their massive progenitors during their main-sequence phase. (2) Medium-sized (10-30 pc) CC SNRs show bifurcation in L _X, with the X-ray-bright SNRs either in an environment associated with molecular clouds or containing pulsars and pulsar-wind nebulae and the X-ray-faint SNRs being located in low-density interstellar environments. (3) Large (size > 30 pc) SNRs show a trend of L _X fading with size, although the scatter is large. The observed relationship between L _X and sizes can help constrain models of SNR evolution.