RXTE and Swift observations of XTE J1751-305 Show a Return to Quiescence
ATel #1051; C. B. Markwardt (CRESST/U. Maryland/NASA/GSFC), D. Pereira (RSIS), J. H. Swank (NASA/GSFC)
on 6 Apr 2007; 16:49 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The X-ray millisecond pulsar XTE J1751-305 was reported active on 04
April 2007 by RXTE (Markwardt & Swank, ATEL #1045) and INTEGRAL
(Falanga et al., ATEL #1046).
Follow-up observations were obtained by RXTE and Swift, which show the
source is already returning to quiescence.
The Swift observation began on 05 April 2007 16:25 UT and had a
duration of about 2000 sec. The Swift XRT observation confirms the
presence of XTE J1751-305, and no other bright source in the field of
view. The 2-10 keV flux is comparable to 1 mCrab.
The RXTE observations occurred on April 5.16, 5.66 and 5.79. The 2-10
keV X-ray fluxes were 5 mCrab, 2 mCrab, and 2 mCrab respectively, with
uncertainties of about 2 mCrab. The primary uncertainty is due to the
contributions of diffuse galactic emission and nearby point sources.
Given the flux of 10 mCrab on April 4.72 (ATEL #1045), the pulsar
emission is already fading into quiescence.
No obvious pulsations were present in RXTE PCA observations. Based on
the pointed observation on April 5.16, we can only set a pulsation
upper limit of about 35% (fractional r.m.s.; 2 sigma confidence).
Since the pulsation r.m.s. amplitude was typically 5% for this source,
it is quite likely the pulsations were too faint to be detected.
Thus, the entire outburst appears to have lasted less than a 2-3 days.
This behavior is similar to that reported in March 2005, when the
source faded to non-detectability over the course of a few days
(Grebenev et al. ATEL #446; Swank, Markwardt & Smith, ATEL #449).
