Spin-down evolution and radio disappearance of the magnetar PSR J1622-4950

We report on 2.4 yr of radio timing measurements of the magnetar PSR J1622−4950 using the Parkes telescope, between 2011 November and 2014 March. During this period the torque on the neutron star (inferred from the rotational frequency derivative) varied greatly, though much less erratically than
in the 2 yr following its discovery in 2009. During the last year of our measurements the frequency derivative decreased in magnitude monotonically by 20%, to a value of −1.3 × 10⁻¹³ s⁻², a factor of 8 smaller than when discovered. The flux density continued to vary greatly during our monitoring
through 2014 March, reaching a relatively steady low level after late 2012. The pulse profile varied secularly on a similar timescale as the flux density and torque. A relatively rapid transition in all three properties is evident in early 2013. After PSR J1622−4950 was detected in all of our 87 observations up to 2014 March, we did not detect the magnetar in our resumed monitoring starting in 2015 January and have not detected it in any of the 30 observations done through 2016 September.