Glitches from the AXP 1RXS J170849-400910

We carried out a long-term timing analysis of the Anomalous X-ray Pulsar 1RXS J170849-400910 based on archival observations made with the Rossi X-ray Timing Explorer between January 1998 and May 2002. We detected a new, large glitch from this source which occurred ~ 1.5 yr after a previous such event, already reported in the literature. The second glitch was much larger than the previous one and comparable to the largest glitches observed in radio pulsars (Δv/v ~ 4 × 10^-6). Its recovery was best-fit by an exponential with a timescale ~ 50 d, plus an apparently unrecovered 1% increase in the spin-down rate of the source. This last result needs confirmation, as a recovery timescale longer than 1 yr cannot be ruled out as yet. Timing residuals after subtraction of the two glitches show a high stability of the spin-down of 1RXS J170849-400910 during the ~ 5 yrs of monitoring, with an r.m.s. ~= 130 ms ~= 1.1 % of the rotation period. The glitch properties of this source reveal remarkable peculiarities compared to those of radio pulsars. An analysis of the glitches of 1RXS J170849-400910 in the light of glitch models seems to hint to the presence of peculiar sources of stress within AXPs, as expected in the magnetar model.