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ATEL # 999; J.H. Swank (NASA/GSFC), D. M. Smith (U.C. Santa Cruz), C. B. Markwardt (CRESST/U. Md./NASA/GSFC)
on 10 Feb 2007; 22:24 UT
Password Certification: Jean Swank (email@example.com)
Subjects: X-ray, Binaries, Pulsars, Transients
RXTE has performed pointed observations of IGR J11215-5952 on Feb 6, 7, 8, 9 and 10, 2007, at various times, for a total exposure of 23.3 ks.
During the observations of Feb 6-8, the source was mostly quiescent. However, in the observations on Feb 9, 01:20 - 03:20 UTC, the source exhibited strong pulsations. Using a Lomb-Scargle periodogram, the pulse period was found to be 186.78s, with an approximate error of 0.3 s. The source became faint again after 03:20 UTC. On Feb 10, at 02:32 UTC, it was also low, but active enough to detect the pulsations and at 04:26 UTC, the intensity rose to about half the intensity of the Feb 9 peak until the end of the observations at 06:07 UTC.
In observations Feb 6-8 the Swift XRT (Romano et al. ATel #994) found that the source was below the PCA's sensitivity limits. The PCA flux through early Feb 8 (06:43 UTC), 0.8 mCrab 2-10 keV, is probably from other sources of emission in the galactic ridge (l=291.8, b=1.53). Spectra were analyzed for the subsequent observations, starting Feb 8 21:43 UTC, in terms of the excess over this amount. A typical pulsar spectrum of a power law with a high energy cutoff was always acceptable. The column density was low enough that it could not be independently constrained and fixing it to the value measured by Mangano et al. (ATel #995) with the Swift XRT (1.02e22 cm^-2) always allowed an acceptable fit. Then the best value for the power law when the pulses were present was 1.07+-0.08, with a cutoff starting at 5.8 +-0.7 keV and an e-folding energy of 15 +-2 keV. There is a marginal indication of an iron line, but less than a 3 sigma upper limit of 220 eV equivalent width. The amount of line emission could also be diffuse.
The pulse-averaged fluxes in the 2-10 keV band were 0.18 mCrab at the end of Feb 8; 3.0 mCrab at maximum on Feb 9, falling to 0.13 mCrab; initially 0.13 mCrab on Feb. 10, rising to 1.7 mCrab. In the 10-30 keV band, the range was 0.06-5.1 mCrab. In the light curves shown at the link below, 3 mCrab corresponds to about 9 counts/s.
Brief RXTE observations will monitor the source for 3 more days.
RXTE PCA Light curves of IGR J11215-5952