Detection of the second period derivative in the timing evolution of SGR 1833-0832

ATel #2691; P. Esposito (INAF-O. A.Cagliari), G. L. Israel (INAF-O. A.Roma), R. Turolla (U. Padua), N. Rea (CSIC-ICE Barcelona), M. Burgay (INAF-O. A.Cagliari), A. Possenti (INAF-O. A.Cagliari), A. Tiengo (INAF-IASF Mi), S. Mereghetti (INAF-IASF Mi), D. Gotz (Irfu/SAp/CEA Saclay), L. Stella (INAF-0. A.Roma), S. Zane (MSSL/UCL) on behalf of a larger collaboration
on 22 Jun 2010; 18:14 UT
Credential Certification: Paolo Esposito (paoloesp@iasf-milano.inaf.it)

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SGR 1833-0832 was monitored with XMM-Newton, Swift, and RossiXTE since its discovery by Swift, thanks to the BAT detection of a short burst on 2010 March 19 (MJD 55274; GCN #10526).

After about 90 days since the BAT event, we detect an additional component with respect to the phase-coherent timing solutions previously reported, which included only the period and its first time derivative (ATel #2550, #2553; Gogus et al. 2010, astroph/1005.3029).

Based on our preliminary analysis the new timing solution is (1 sigma uncertainties; reference epoch 55274.0 MJD):

P = 7.5654091(6) s

P_dot = 2.8(5)E-12 s/s

P_dotdot = 8(3)E-19 s/s^2

or

ν = 0.13218056(1) Hz

ν_dot = -4.9(9)E-14 Hz/s

ν_dotdot = -1.5(6)E-20 Hz/s^2.

The second time derivative of the spin period (P_dotdot) is detected at a confidence level of 4.2 sigma (as evaluated by the Fisher test on the significance of the additional component). The positive sign of the period second derivative implies that the spin down rate of the source is increasing, similarly to the case of 1E 1547.0-5408 (Camilo et al. 2008, ApJ, 679, 681; Israel et al. 2010, astroph/1006.2950).

Under the standard assumption that the neutron star slows down because of magnetic braking, these P and P_dot values imply a dipole magnetic field of 1.5E+14 G (for a neutron star with radius of 10 km and mass of 1.4 solar masses).