XTE J1807-294: Modulation of the pulsed flux with a refined spin period and orbit parameters
ATel #148; M. G.F. Kirsch (ESA XMM-SOC), E. Kendziorra (IAATuebingen)
on 16 Apr 2003; 17:04 UT
Credential Certification: Marcus G. F. Kirsch (mkirsch@xmm.vilspa.esa.es)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The accreting millisecond pulsar XTE J1807-294, discovered
by RXTE on February 21 (Markwardt et al., IAUC 8080 ), was observed
by XMM-Newton March 22, 2003 under ObsId 01579601 in revolution
number 0601. The observation started on 2003-03-22T13:40:27Z.
The EPIC pn-CCD camera was operated in Timing mode with the thick
filter, while the two MOS cameras were in Small Window mode(MOS1)
and Full Frame mode(MOS2). For this analysis only data from the
9.293 ks long pn exposure were used.
The count rate in 9 CCD columns (~ 37 arcsec) centred on the source was
33 cts/s in the 0.5-10 keV band (~ 3.7 mCrab). This compares to a
background of 0.4 cts/s for a region of the same size.
Using the best fit orbital period of 40.0741 +/- 0.0005 minutes found
by Markwardt et al. (ATEL #127) we grouped the events into 20 phase
bins of the binary orbit. Chi-square maximum epoch folding on individual
phase bins revealed a clear modulation of the spin period. Assuming, in
first approximation, a circular orbit, we derived 4.8 +/-0.1 light-ms
for the projected orbital radius. The barycentric mean spin period of
the pulsar was found at 5.2459427 +/- 0.0000004 ms.
The modulation is seen over the entire energy band from 0.5 to 10 keV.
The pulse profile shows a single peak (~ 1.5 ms FWHM), its shape varies
only slightly with energy. The combined pulse profile in the 0.5-10 keV
band shows a modulation of 6.0 +/- 0.1 percent (90-percent confidence level).
We note that the results of our timing analysis of EPIC pn-CCD data are
different from those recently published by Campana et al. (IAUC 8113 ).
