The Magnetar SGR 1935+2154’s Quiet Local Environment: Clues for Its Progenitor

Abstract Magnetars are highly magnetized neutron stars whose evolution and radiation are governed by the decay and/or reconfiguration of their magnetic fields. The origin of magnetars remains an open question, with proposed progenitor scenarios including core collapse (CC) of very massive stars (≥25 M ⊙ ) or not very massive stars (8 M ⊙ &lt; M * &lt; 25 M ⊙ ), mergers of stellar systems, and accretion-induced collapse of white dwarfs. Investigating the environments of magnetars can offer valuable clues to this issue. In this work, we study the local (radius of 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 87, ∼100 pc at 6.6 kpc) stellar environment of SGR 1935+2154, which is spatially associated with the supernova remnant (SNR) G57.2+0.8, based on astrometry from Gaia DR3 and multiband photometry from optical to infrared. We discover that the upper limit of the surface density of massive stars around SGR 1935+2154 is only a quarter of that of the solar neighborhood, where the star formation rate is modest in the Galaxy. This quiet environment implies that the magnetar was likely formed by the CC of either a not very massive star or a binary merger product rather than the CC of a very massive star. Although alternative channels cannot be excluded, their probabilities may be substantially lower. The studies of magnetars associated with SNRs consistently favor not very massive progenitors, implying that such progenitors may produce a considerable fraction of magnetars. We also backtrack the trajectories of SGR 1935+2154 and its surrounding stars to search for its potential massive companions, yet no such companions are found.