The radio expansion and brightening of the very young supernova remnant G1.9+0.3

Recent radio observations of the small Galactic supernova remnant G1.9+0.3 made at 4.86 GHz with the Very Large Array are presented, and compared with earlier observations at 1.49 GHz which have a comparable resolution (10 × 4 arcsec2). These show that the radio emission from this remnant has expanded significantly, by about 15 per cent over 23 yr, with a current outer diameter of ≈92 arcsec. This expansion confirms that G1.9+0.3 is the youngest Galactic remnant yet identified, only about 150 yr old at most. Recent, lower resolution, 1.43-GHz observations are also discussed, and the integrated flux densities from these and the 4.86-GHz observations are compared with earlier results. This shows that the integrated flux density of G1.9+0.3 has been increasing recently.