Soft gamma repeaters (SGRs) are highly magnetised neutron stars (magnetars)notable for their gamma-ray and X-ray outbursts. In this paper, we usenear-infrared (NIR) imaging of SGR 0501+4516 in the days, weeks, and yearsafter its 2008 outburst to characterise the multi-wavelength emission, and toobtain a proper motion from our long temporal baseline observations. Unlikemost magnetars, the source has only moderate foreground extinction with minimalcrowding. Our observations began only 2 hours after the first activation of SGR0501+4516 in August 2008, and continued for 4 years, including two epochs ofHubble Space Telescope (HST) imaging. The proper motion constraint is improvedby a third HST epoch 10 years later. The near-infrared and X-rays faded slowlyduring the first week, thereafter following a steeper power-law decay. Thebehaviour is satisfactorily fit by a broken power-law. Three epochs of HSTimaging with a 10-year baseline allow us to determine a quiescent level, and tomeasure a proper motion of 5.4+/-0.6 mas/yr. This corresponds to a lowtransverse peculiar velocity of 51+/-14 km/s (at 2 kpc). The magnitude anddirection of the proper motion rules out supernova remnant HB9 as thebirth-site. We can find no other supernova remnants or groups of massive starswithin the region traversed by SGR 0501+4516 during its characteristic lifetime(20 kyr). Our observations of SGR 0501+4516 suggest that some magnetars may beeither significantly older than expected, that their progenitors produce lowsupernova ejecta masses, or alternatively that they can be formed throughaccretion-induced collapse (AIC) or low-mass neutron star mergers. Although theprogenitor of SGR 0501+4516 remains unclear, we propose that SGR 0501+4516 isthe best Galactic candidate for a magnetar formed through a mechanism otherthan massive star core-collapse.
The infrared counterpart and proper motion of magnetar SGR0501+4516
P. Esposito;
2025-01-01
Abstract
Soft gamma repeaters (SGRs) are highly magnetised neutron stars (magnetars)notable for their gamma-ray and X-ray outbursts. In this paper, we usenear-infrared (NIR) imaging of SGR 0501+4516 in the days, weeks, and yearsafter its 2008 outburst to characterise the multi-wavelength emission, and toobtain a proper motion from our long temporal baseline observations. Unlikemost magnetars, the source has only moderate foreground extinction with minimalcrowding. Our observations began only 2 hours after the first activation of SGR0501+4516 in August 2008, and continued for 4 years, including two epochs ofHubble Space Telescope (HST) imaging. The proper motion constraint is improvedby a third HST epoch 10 years later. The near-infrared and X-rays faded slowlyduring the first week, thereafter following a steeper power-law decay. Thebehaviour is satisfactorily fit by a broken power-law. Three epochs of HSTimaging with a 10-year baseline allow us to determine a quiescent level, and tomeasure a proper motion of 5.4+/-0.6 mas/yr. This corresponds to a lowtransverse peculiar velocity of 51+/-14 km/s (at 2 kpc). The magnitude anddirection of the proper motion rules out supernova remnant HB9 as thebirth-site. We can find no other supernova remnants or groups of massive starswithin the region traversed by SGR 0501+4516 during its characteristic lifetime(20 kyr). Our observations of SGR 0501+4516 suggest that some magnetars may beeither significantly older than expected, that their progenitors produce lowsupernova ejecta masses, or alternatively that they can be formed throughaccretion-induced collapse (AIC) or low-mass neutron star mergers. Although theprogenitor of SGR 0501+4516 remains unclear, we propose that SGR 0501+4516 isthe best Galactic candidate for a magnetar formed through a mechanism otherthan massive star core-collapse.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
