Swift/XRT early time observations of SGR 1935+2154
ATel #7138; P. D'Avanzo, S. Campana, F. Coti Zelati (INAF-OAB), D. M. Palmer (LANL)
on 25 Feb 2015; 11:39 UT
Credential Certification: Paolo D'Avanzo (paolo.davanzo@brera.inaf.it)
Subjects: X-ray, Gamma Ray, Soft Gamma-ray Repeater
We report on Swift/XRT observations of the 2015 Feb 22 outburst of SGR 1935+2154 (D'Avanzo et al., ATel #7123). We have analysed 15.3 ks of XRT data in Photon Counting (PC) mode from 93 s to 100.0 ks after the first BAT trigger reported in D'Avanzo et al. (ATel #7123). The XRT light curve is constant around 0.04 cts/s.
During the Swift/XRT observations four short (<32 ms) bursts occurred at times (UT):
2015-02-22 12:31:11.4
2015-02-22 14:23:47.9
2015-02-22 20:47:02.2
2015-02-23 12:27:52.6
The Swift/XRT detected these bursts during a single frame with a peak rate of 8 cts/s (not corrected for pile-up).
We fitted the spectrum with an absorbed power-law model (using C-statistics) and obtained a column density NH=(3.7+/-0.9)x10^22 cm^-2 (using TBABS) and a photon index Gamma=2.6+/-0.4. The 1-10 keV unabsorbed flux is F=(6+/-1)x10^-12 erg s^-1 cm^-2.
A fit with an absorbed blackbody model provides NH=(1.3+/-0.5)x10^22 cm^-2 (using TBABS) and a temperature of kT=0.9+/-0.1 keV. The 1-10 keV unabsorbed flux is F=(2.8+/-0.3)x10^-12 erg s^-1 cm^-2.
