Title: The infrared counterpart and proper motion of magnetar SGR0501+4516 Show Chinese title

Title: 脉冲星 SGR0501+4516 的红外对应体和自行

Abstract: Soft gamma repeaters (SGRs) are highly magnetised neutron stars (magnetars) notable for their gamma-ray and X-ray outbursts. In this paper, we use near-infrared (NIR) imaging of SGR 0501+4516 in the days, weeks, and years after its 2008 outburst to characterise the multi-wavelength emission, and to obtain a proper motion from our long temporal baseline observations. Unlike most magnetars, the source has only moderate foreground extinction with minimal crowding. Our observations began only 2 hours after the first activation of SGR 0501+4516 in August 2008, and continued for 4 years, including two epochs of Hubble Space Telescope (HST) imaging. The proper motion constraint is improved by a third HST epoch 10 years later. The near-infrared and X-rays faded slowly during the first week, thereafter following a steeper power-law decay. The behaviour is satisfactorily fit by a broken power-law. Three epochs of HST imaging with a 10-year baseline allow us to determine a quiescent level, and to measure a proper motion of 5.4+/-0.6 mas/yr. This corresponds to a low transverse peculiar velocity of 51+/-14 km/s (at 2 kpc). The magnitude and direction of the proper motion rules out supernova remnant HB9 as the birth-site. We can find no other supernova remnants or groups of massive stars within the region traversed by SGR 0501+4516 during its characteristic lifetime (20 kyr). Our observations of SGR 0501+4516 suggest that some magnetars may be either significantly older than expected, that their progenitors produce low supernova ejecta masses, or alternatively that they can be formed through accretion-induced collapse (AIC) or low-mass neutron star mergers. Although the progenitor of SGR 0501+4516 remains unclear, we propose that SGR 0501+4516 is the best Galactic candidate for a magnetar formed through a mechanism other than massive star core-collapse. Show Chinese abstract

Abstract: 软伽马射线重复暴（SGRs）是高度磁化的中子星（磁星），以其伽马射线和X射线爆发而著称。在本文中，我们使用2008年爆发后几天、几周和几年内对SGR 0501+4516的近红外（NIR）成像，以表征多波段辐射，并通过我们的长期时间基线观测获得自行。与大多数磁星不同，该源具有适度的前景消光和最小的拥挤。我们的观测始于2008年8月SGR 0501+4516首次激活后的2小时，并持续了4年，包括两次哈勃空间望远镜（HST）成像时刻。十年后第三次HST时刻提高了自行限制。在第一周内，近红外和X射线缓慢衰减，之后遵循更陡的幂律衰减。这种行为可以用分段幂律很好地拟合。三次具有10年基线的HST成像使我们能够确定平静水平，并测量出自行速度为5.4+/-0.6毫角秒/年。这对应于低横向特殊速度为51+/-14公里/秒（在2千秒差距处）。自行的速度大小和方向排除了超新星遗迹HB9作为诞生地。在SGR 0501+4516在其特征寿命（2万年）内经过的区域内，我们找不到其他超新星遗迹或大质量恒星群。我们对SGR 0501+4516的观测表明，一些磁星可能比预期要老得多，它们的前身产生的超新星抛射质量较低，或者它们可以通过吸积诱导塌缩（AIC）或低质量中子星合并形成。尽管SGR 0501+4516的前身仍然不清楚，但我们提出SGR 0501+4516是银河系中通过不同于大质量恒星核心塌缩机制形成的磁星的最佳候选者。