Discovery of a ~205 Hz X-ray pulsar in the globular cluster NGC 6440
ATel #2182; D. Altamirano (UvA), T. E. Strohmayer (NASA/GSFC), Craig O. Heinke(Univ. of Alberta), C. B. Markwardt (U. Maryland & NASA/GSFC), J. H. Swank (NASA/GSFC), D. Pereira (GSFC), E. Smith (GSFC), R. Wijnands, M. Linares, A. Patruno, P. Casella and M. van der Klis (UvA)
on 31 Aug 2009; 19:36 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Diego Altamirano (diego@science.uva.nl)
Subjects: X-ray, Request for Observations, Binary, Transient
Discovery of a 205 Hz X-ray pulsar in the globular cluster NGC 6440
The globular cluster NGC 6440 was observed by the PCA instrument
aboard RXTE on August 30, 2009 at 01:42 (UTC). The observation lasted
for approximately 3000 seconds and the source was detected with an
intensity of ~7 mCrab (2-10 keV).
Pulsations were detected at a barycentric frequency of 205.893 Hz,
with a pulsed amplitude of approximately 7%. The data suggest an
orbital period between 40 and 70 minutes, but more data is needed to
better constrain this, as well as, the other orbital parameters.
The ~205 Hz spin frequency is inconsistent with the ~442 Hz spin
frequency of the other accreting millisecond X-ray pulsar (AMXP) which
is in this globular cluster (SAX J1748.9-2021, Altamirano et
al. 2008). Although a new transient has recently been identified in
the globular cluster NGC 6440 (see Atels #2139, #2143 and #2180),
images with higher spatial resolution are necessary to identify this
source. In any case, it is interesting to note that NGC 6440 has two AMXPs,
while no AMXPs have been detected in any other globular cluster.
We request immediate observations of this new transient in all
wavelengths. Further RXTE, Swift and Gemini observations are planned.
