Magnetars are regarded as the most magnetized neutron stars in the Universe .
Aiming to unveil what kinds of stars and supernovae can create magnetars , we have performed a state-of-the-art spatially resolved spectroscopic X-ray study of the supernova remnants ( SNRs ) Kes 73 , RCW 103 , and N49 , which host magnetars 1E 1841 - 045 , 1E 161348 - 5055 , and SGR 0526 - 66 , respectively .
The three SNRs are O- and Ne-enhanced and are evolving in the interstellar medium with densities of > 1 – 2 ~ { } { cm } ^ { -3 } .
The metal composition and dense environment indicate that the progenitor stars are not very massive .
The progenitor masses of the three magnetars are constrained to be < 20 ~ { } M _ { \odot } ( 11– 15 ~ { } M _ { \odot } for Kes 73 , \lesssim 13 ~ { } M _ { \odot } for RCW 103 , and \sim 13 – 17 ~ { } M _ { \odot } for N49 ) .
Our study suggests that magnetars are not necessarily made from very massive stars , but originate from stars that span a large mass range .
The explosion energies of the three SNRs range from 10 ^ { 50 } ~ { } { erg } to \sim 2 \times 10 ^ { 51 } ~ { } { erg } , further refuting that the SNRs are energized by rapidly rotating ( millisecond ) pulsars .
We report that RCW 103 is produced by a weak supernova explosion with significant fallback , as such an explosion explains the low explosion energy ( \sim 10 ^ { 50 } ~ { } { erg } ) , small observed metal masses ( M _ { O } \sim 4 \times 10 ^ { -2 } ~ { } M _ { \odot } and M _ { Ne } \sim 6 \times 10 ^ { -3 } ~ { } M _ { \odot } ) , and sub-solar abundances of heavier elements such as Si and S. Our study supports the fossil field origin as an important channel to produce magnetars , given the normal mass range ( M _ { ZAMS } < 20 ~ { } M _ { \odot } ) of the progenitor stars , the low-to-normal explosion energy of the SNRs , and the fact that the fraction of SNRs hosting magnetars is consistent with the magnetic OB stars with high fields .