RXTE PCA Pointed Observations of IGR J11215-5952
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
Credential Certification: Jean Swank (swank@milkyway.gsfc.nasa.gov)
Subjects: X-ray, Binary, Transient, Pulsar
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
