Swift J1822.3-1606: refined X-ray timing and spectral parameters
ATel #3501; N. Rea (CSIC-IEEC, Barcelona), P. Esposito (INAF-OACagliari), G. L. Israel (INAF-OARoma), A. Tiengo (IUSS, Pavia), S. Zane (MSSL-UCL) report on behalf of a larger collaboration
on 19 Jul 2011; 22:37 UT
Credential Certification: Nanda Rea (rea@ieec.uab.es)
Subjects: X-ray, Soft Gamma-ray Repeater
Between 2011 July 15-19 Swift-XRT continued its monitoring of the new SGR discovered by Swift-BAT, namely Swift J1822.3-1606 (Cummings et al. Atel #3488).
Using the first four available Swift-XRT observations we find a best period of 8.437716(5)s. No evidence for a period derivative has been observed in the first days of monitoring, yielding a Pdot limit of about a few 10^-10 s/s, still consistent with the SGR nature of this new transient.
Furthermore, we could now perform a more accurate spectral modeling which resulted in a higher NH than previously claimed (Esposito et al. Atel #3490). In particular the spectra of the four Swift-XRT observations are well modeled by an absorbed blackbody plus a power-law with NH=(1.56+/-0.07)x10^22 cm^-2 (1 sigma error) tight to be the same in all observations (chi^2 = 1.14 with 708 dof), and kT and Gamma varying between the four observations in the ranges: 0.75-0.95keV and 3.5-4.3, respectively. Note that the NH value is model dependent, and modeling the spectra with two blackbodies gives an NH=(0.9+/-0.1)x10^22 cm^-2, although with a slightly worse chi^2 value (1.25 with 708 dof). The source 1-10keV observed flux is now at ~1.7x10^-10 erg/cm^2/s .
We note that the spectral shape and parameters, the SGR-like bursts, and the timing characteristics (i.e. spin period and current Pdot limit) are typical of a transient magnetar rather than of a Be X-ray binary (see also Halpern GCN #12170).
