Radio Disappearance of the Magnetar Xte J1810–197 and Continued X-Ray Timing

Abstract

We report on timing, flux density, and polarimetric observations of the transient magnetar and 5.54 s radio pulsar XTEJ1810−197 using the Green Bank, Nançay, and Parkes radio telescopes beginning in early 2006, until its sudden disappearance as a radio source in late 2008. Repeated observations through 2016 have not detected radio pulsations again. The torque on the neutron star, as inferred from its rotation frequency derivativeṅ, decreased in an unsteady manner by a factor of three in the first year of radio monitoring, until approximately mid-2007. By contrast, during its final year as a detectable radio source, the torque decreased steadily by only 9%. The periodaveraged flux density, after decreasing by a factor of 20 during the first 10 months of radio monitoring, remained relatively steady in the next 22 months, at an average of 0.7±0.3 mJy at 1.4 GHz, while still showing day-to-day fluctuations by factors of a few. There is evidence that during this last phase of radio activity the magnetar had a steep radio spectrum, in contrast to earlier flat-spectrum behavior. No secular decrease presaged its radio demise. During this time, the pulse profile continued to display large variations; polarimetry, including of a new profile component, indicates that the magnetic geometry remained consistent with that of earlier times. We supplement these results with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the first 4 years, XTEJ1810 −197 experienced non-monotonic excursions in frequency derivative by at least a factor of eight. But since 2007, itsṅ has remained relatively stable near its minimum observed value. The only apparent event in the X-ray record that is possibly contemporaneous with the radio shutdown is a decrease of ≈20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However, the permanence of the high-amplitude, thermal X-ray pulse, even after the (unexplained) radio demise, implies continuing magnetar activity.

Understanding Recent Magnetar Observations from the Magnetospheric Point of View

“…[17] obtained a similar conclusion using a different model for magnetars). The final radio disappearance of these two radio-loud magnetars [9,15] are consistent with the general expectations in the wind braking model.…”

“…The radio luminosity finally disappears [15]. The spin-down torque of XTE J1810−197 decreased by a factor of three during the process.…”

Spin-down Evolution and Radio Disappearance of the Magnetar PSR J1622–4950

“…Camilo et al (2016) found that for XTEJ1810−197 the profiles varied greatly right up to the disappearance of radio emission in late 2008 with no obvious secular evolution. Following its 2013 outburst, the magnetar SGRJ1745−2900 showed a widening of its profile that stabilized after ∼100 days (Lynch et al 2015).…”

“…Very unusual compared to standard radio pulsars, their radio spectra are generally flat (e.g., Camilo et al 2007c). Both are transient radio sources: radio emission from XTEJ1810−197 turned off in 2008 (Camilo et al 2016) and 1E1547.0−5408 was detected intermittently following its 2009 outburst (Burgay et al 2009;Camilo et al 2009). The third radio magnetar, PSRJ1622−4950, is the subject of this work.…”

The Sleeping Monster: NuSTAR Observations of SGR 1806–20, 11 Years After the Giant Flare

“…A few months after the onset of its 2003 outburst, ν reached a factor of 8 larger than its minimum observed value (Halpern & Gotthelf 2005;Bernardini et al 2009). Interestingly, the source frequency derivative returned back to its pre-outburst minimum around 2007, four years after the outburst, and remained there until mid 2014 (Pintore et al 2016;Camilo et al 2016). 1E 1048.1−5937 also shows variation inν following its quasi-periodic outbursts, sometime as large as a factor of 10.…”