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ATEL # 2881; M. Kalamkar (Amsterdam), Y. Yang (Amsterdam), D. Altamirano (Amsterdam), P. Casella (Southampton), M. Linares (MIT), A. Patruno (Amsterdam), M. Armas-Padilla (Amsterdam), Y. Cavecchi (Amsterdam), N. Degenaar (Amsterdam), D. Russell (Amsterdam), R. Kaur (Amsterdam), M. van der Klis (Amsterdam), A. Watts (Amsterdam), R. Wijnands (Amsterdam), N. Rea (CSIC-IEEC)
on 28 Sep 2010; 17:38 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Diego Altamirano (firstname.lastname@example.org)
Subjects: X-ray, Binaries, Black Holes, Transients
Referred to by ATEL #: 2884, 2887, 2888, 2890, 2906, 2912, 2918, 2951, 2976, 2999
We report on a pointed RXTE/PCA observation of the transient source MAXI J1659-152 (Atel #2873,#2874,#2875,#2877,#2880 GCN #11296,#11299, #11307 - initially referred to as GRB 100925A). The observation started on 28th September 2010 at 00:51:10 UT, for a total integration time of ~ 16 ks. We find strong variability in the X-ray light curve (average of ~520 cnts/sec/PCU in the 2-60 keV range). The fractional rms amplitude in the 0.01-100 Hz frequency range is 23.7(6)%.We find a strong QPO with a centroid frequency of 1.646(3) Hz (12.6(1)% fractional rms), as well as its second harmonic (peak frequency = 3.34(2) Hz, fractional rms = 5.4(3)%). The characteristics of the power spectrum suggest that it is a type-C QPO, strongly indicating that MAXI J1659-152 is a stellar-mass black-hole transient. By analogy with many other BH candidates (Belloni et. al. 2010,The Jet Paradigm, Lecture Notes in Physics, Volume 794), we infer that the source might have started its transition from the hard state to the soft state, currently being in its hard-intermediate state. An increase in QPO frequency and a decrease in overall amplitude is expected in the next few days, leading to a spectral transition into the soft-intermediate state and eventually to the soft state. We would like to thank the RXTE Team for promptly scheduling the observations.