Third RXTE Observation of RS Oph in Outburst: Beginning of the X-ray Decline
ATel #747; J. L. Sokoloski, G. J. M. Luna (SAO), K. Mukai (GSFC)
on 24 Feb 2006; 02:24 UT
Credential Certification: Jennifer L. Sokoloski (jsokolos@cfa.harvard.edu)
Subjects: X-ray, Binary, Cataclysmic Variable, Nova, Star, Transient, Variables
Referred to by ATel #: 754
We report on the third Rossi X-Ray Timing Explorer (RXTE) observation
of the symbiotic recurrent nova RS Oph in outburst. A preliminary
analysis of this 1.56 ks observation, performed on Feb 22.60 UT
(approximately 10 days after optical maximum), reveals that the source
is continuing to soften in the X-rays, and that it has started to
fade. We find a 2-10 keV flux of (7.10+/-0.05) e-10 erg/cm/cm/s and a
2-20 keV flux of (7.72+/-0.05) e-10 erg/cm/cm/s. These fluxes are
down by more than a factor of 2 compared to the previous RXTE
observation of RS Oph, performed 4 days earlier (see ATel #741).
Taking a distance of 1.6 kpc, the absorbed 2-20 keV luminosity is
(2.4+/-0.1) e35 erg/s. The hard X-ray spectrum can be roughly
characterized by thermal emission from a plasma with kT = 4 keV
(compared to a plasma temperature of near 10 keV approximately 3 days
after optical maximum and 5 to 6 keV approximately 6 days after
optical maximum). The Fe line complex near 6.6 keV has continued to
decrease in strength, with its equivalent width going from just over 1
keV in the first two RXTE observations to roughly 0.7 keV on Feb 22.
Although the RXTE data do not place strong constraints on the column
density, the spectrum is consistent with absorption solely from the
interstellar medium.
