Discovery of kilohertz QPOs in RXTE observations of SAX J1748.9-2021.
ATel #2426; D. Altamirano, A. Patruno, A. Watts , M. Armas Padilla, Y. Cavecchi, N. Degenaar, M. Kalamkar, R. Kaur, P. Soleri, Y. J. Yang, M. van der Klis, R. Wijnands (University of Amsterdam); P. Casella (Southampton), M. Linares (MIT) and N. Rea (IEEC-CSIC)
on 8 Feb 2010; 13:30 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Diego Altamirano (diego@science.uva.nl)
Subjects: X-ray, Binary, Globular Cluster, Neutron Star, Transient, Pulsar
We report on RXTE observations of the ongoing outburst of the
accreting millisecond X-ray pulsar SAX J1748.9-2021 (Altamirano et
al. 2008, 674, 45A, see ATEL #2360 and #2407).
Since the first detection of intermittent pulsations on January 27th,
2010, observations have been carried out on a daily basis. The source
remained between 120 and 160 mCrab (2-16 keV - see ATEL #
2407) until
February 3rd, when the intensity started to decrease. A preliminary
study of the energy spectra shows that since then, the source has
slowly been undergoing a soft-to-hard state transition. As expected
from this type of system, the state transition is being accompanied by
changes in the power spectra: on February 6th and 7th (at ~60 mCrab)
we detected for the first time in this source a single kilohertz
quasi-periodic oscillation peak (~760-790Hz, ~9% rms amplitude in the
2-60 keV range, >5 sigma single trial).
There is no evidence for intermittent pulsations near 442 Hz at
amplitudes similar to those in the first detection (ATEL #
2407)
For light curves of the current outburst in different energy bands,
please refer to the MAXI/GSC web-page:
http://maxi.riken.jp/top/index.php?cid=000000000001&disp_mode=source
More RXTE observations are planned.
We thank the RXTE team for the scheduling of our observations.
