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X-ray Pulsations from AXP 1E 1547-5407 Detected with RXTE

ATEL # 1769; R. Dib, V. M. Kaspi (McGill U.), F. P. Gavriil (NASA/GSFC), P. M. Woods
on 8 Oct 2008; 5:51 UT
Password Certification: Rim Dib (rim@physics.mcgill.ca)

Subjects: X-ray, Pulsars
Referred to by ATEL #: 1770

We observed AXP 1E 1547-5407 which is currently in outburst (see ATELs #1756, #1761, #1763) with RXTE on October 4 (4 ks), and 6 (1.4 ks, 1.6 ks). The 2-20 keV pulse profile of these observations (October 04 UT 21:51:04, October 06 UT 01:46:04, and October 06 UT 23:31:04) shows a single broad pulse that is qualitatively similar to that reported in Halpern et al. (2008, ApJ, 676, 1178), though there is a possible hint of additional peaks. The 2-20 keV RMS pulsed fluxes in these three observations are 0.56 +/- 0.06 counts/s/PCU (with 2 operational PCUs), 0.55 +/- 0.10 counts/s/PCU (with 4 PCUs), and 0.44 +/- 0.09 counts/s/PCU (with 2 PCUs). Assuming the spectral parameters reported by Gelfand & Gaensler (2007, ApJ, 664, 1111; these parameters have likely changed in outburst; see Halpern et al. 2008), the unabsorbed pulsed flux in the 0.5-10 keV band is ~9x10^{-10} erg/s/cm2, a factor of >30 larger than reported by GG07 and at least twice the largest reported thus far (Halpern et al. 2008). Using phase-coherent timing performed on these three observations, we find a pulse period of 2.0713474(7) s. This confirms the period reported in ATEL #1763. This implies frequency derivative, measured since June 2007 (see Camilo et al. 2008, ApJ, 679, 681) of ~-8.6x10^{-12} s^-2, larger than has been seen thus far. Our preliminary burst searching reveals at least 4 bursts, and possibly as many as 14 bursts, during the 4 ks observation, and at least 4 additional bursts in the first observation on October 06. A more detailed study of these data is underway, and additional RXTE Target-of-Opportunity observations are scheduled.


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