Central Compact Objects in Kes 79 and RCW 103 as ‘Hidden’ Magnetars with Crustal Activity

Abstract

We propose that observations of 'hidden' magnetars in central compact objects can be used to probe crustal activity of neutron stars with large internal magnetic fields. Estimates based on calculations by Perna & Pons, Pons & Rea and Kaminker et al. suggest that central compact objects, which are proposed to be 'hidden' magnetars, must demonstrate flux variations on the time scale of months-years. However, the most prominent candidate for the 'hidden' magnetars -CXO J1852.6+0040 in Kes 79 -shows constant (within error bars) flux. This can be interpreted by lower variable crustal activity than in typical magnetars. Alternatively, CXO J1852.6+0040 can be in a high state of variable activity during the whole period of observations. Then we consider the source 1E161348−5055 in RCW103 as another candidate. Employing a simple 2D-modelling we argue that properties of the source can be explained by the crustal activity of the magnetar type. Thus, this object may be supplemented for the three known candidates for the 'hidden' magnetars among central compact objects discussed in literature.

Neutron stars with variable internal heaters

“…In this case the heater should produce a very large amount of energy (H 0 /H c 10 3 ) at a low pre-burst amplitude H c . In particular, we confirm the possibility of a strong peak of the surface luminosity L ∞ max /L ∞ c ∼ 10 2 with a relaxation tail lasting 10 yr [26] in accordance with the observations of long outbursts of the central compact X-ray source 1E 161348-5055 in the supernova remnant RCW 103 [27,28].…”

Long X-ray flares from the central source in RCW 103

“…Over the years, the behavior of 1E 1613 has set it apart from any other compact object source (De Luca 2008, 2017: the source displays a strong variability on scales of months or years (a large outburst with an increase in luminosity from ∼3 × 10 33 to over 3 × 10 35 erg s −1 occurred in 1999), and features a modulation in flux with a period of 6.67 h, together with dramatic changes in the pulse profile (which are correlated with the flux level). Considering also the young age of 1E 1613 and the lack of an optical or IR counterpart, De Luca et al (2006) discussed two main possibilities: 1E 1613 could be either a very young lowmass X-ray binary (LMXB, the first observed inside an SNR, see also Bhadkamkar & Ghosh 2009), or an isolated magnetar that slowly revolves at an abnormal period of 6.67 h, possibly due to a propeller interaction with a fallback disk (see also Li 2007;Popov et al 2015). Even more exotic pictures have been proposed, such as an LMXB with a supermagnetic NS locked in synchronous rotation with the orbit (Pizzolato et al 2008), or an evolved Thorne-Żytkow object (Liu et al 2015).…”

Evolution of Neutron Star Magnetic Fields

“…Later on, it was found that the source is not only strongly variable on a timescale of years, but also has a very long-6.7 h-period [129], which is now assumed to be the spin period of the NS, the longest known so far for an isolated compact object. It was proposed that the NS is a hidden magnetar, and long-term flux variations are due to energy release in its crust [130]. However, later it was discovered that this source demonstrates magnetar-type bursts (see [131] and references therein for earlier observations of X-ray flares).…”