A Refined Orbital Solution and the Transient Pulsar in Terzan 5 is Not Eclipsing
ATel #2946; T. E. Strohmayer (NASA/GSFC), C. B. Markwardt (NASA/GSFC), D. Pereira (GSFC/Wyle IS), E. A. Smith (GSFC/Wyle IS)
on 15 Oct 2010; 21:34 UT
Credential Certification: Tod Strohmayer (email@example.com)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
We report results of recent RXTE observations of the new bursting and
pulsing transient in Terzan 5 (ATels #2919, #2920, #2922 ,#2924,
#2929, #2932, #2933, #2937, #2939, #2940). Barycentric pulse
frequency measurements from eight orbits of data spanning 00:13 on 2010-10-13
to 2010-10-15 at 10:53 UTC are consistent with a circular orbit with parameters;
Orbital Period = 21.252 +- 0.02 hrs; Pulsar frequency = 11.044893 +- 8.7 x 10-6 Hz;
vsini = 62.13 +- 0.46 km/sec; asini = 2503.12 +- 19 lt-ms; Epoch of T90 = 55482.8883 +- 0.0013 MJD (TDB)
The epoch of T90 based on this solution is approximately
47 minutes earlier than the mid-eclipse point (ATEL #2929),
which is inconsistent if the orbit is indeed circular (ATEL #2939).
Fits with an eccentric orbit do not improve the fit, suggesting the
orbit is circular to the accuracy of the present data. Moreover, an
eclipse ephemeris derived from the above solution suggests that
an eclipse should have been observed in the orbit beginning near
2010-10-14 18:30 UTC, but none was seen. These considerations
raised concerns about the interpretation of the eclipse event.
It subsequently came to our attention that the Moon was near
to the position of the transient during the epoch of the putative eclipse.
Closer study confirms that the event originally identified as an
eclipse intrinsic to the new transient is in fact a lunar
occultation of the source, and not an eclipse. RXTE continues to
observe this interesting source.