Swift J1822.3-1606: pre-outburst ROSAT limits (plus erratum)
ATel #3495; P. Esposito (INAF-OACagliari), N. Rea (CSIC-IEEC, Barcelona), G. L. Israel (INAF-OARoma), A. Tiengo (IUSS-Pavia) report on behalf of a larger collaboration
on 17 Jul 2011; 22:35 UT
Credential Certification: Nanda Rea (rea@ieec.uab.es)
Subjects: X-ray, Transient
We report on a pre-outburst ROSAT PSPC observation of the new SGR discovered by Swift-BAT on 2011 July 14 (Cummings et al. Atel #3488). The PSPC observation was performed on 1993 September 12 for ~6.7ks.
We find a source at: RA (2000) = 18 22 18.1 and Dec (2000)= -16 04 26.4, with a 5sigma detection significance. The count-rate (corrected for the PSPC PSF, sampling dead time, and vignetting) is about 0.012 counts/s. This position is ~1.5" from the refined Swift XRT position of Swift J1822.3-1606 (Pagani et al. Atel #3493), and ~10" and 20" from two other ROSAT catalogued sources (2RXP J182217.9-160417 and 1WGA J1822.2-1604). Given the relatively large ROSAT positional uncertainty, we believe the latter two sources and our detected source being the same object, which we propose as the quiescent counterpart to SGR J1822-1606. Assuming that its quiescent emission is well modeled by an absorbed blackbody with NH = 3e21 cm^-2 and kT = 0.5 keV, we infer a flux of ~2x10^-13 ergs/cm2/s in 0.1-2.4 keV, in line with a typical transient magnetar (see Rea & Esposito 2011, ASSP 247, for a recent review).
We also note that in Atel #3490 we did an error when comparing the source position with the three archival Chandra observations of the field. The correct-refined position (Pagani et al. Atel #3493) does not fall inside the Chandra FoV of any of those observations. We apologize for any inconvenience this incorrect information might have caused.
