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Detection of the low-frequency QPOs in MAXI J1535-571

ATel #10734; I. A. Mereminskiy, S. A.Grebenev (Space Research Institute, Moscow)
on 11 Sep 2017; 17:48 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Sergei Grebenev (sergei@hea.iki.rssi.ru)

Subjects: X-ray, Black Hole

Referred to by ATel #: 10761, 10768, 10816

During current (on September 11, 2007) Swift-XRT observations of the new black hole transient MAXI J1535-571 (ATel #10699) we detected a strong peak of QPOs at 1.9 Hz. Last days the source demonstrated spectral softening (ATel #10729, #10731), indicating the beginning of a transition between the hard and soft states. The observations were performed in WT-mode, giving time resolution of 1.7 ms. The first and second harmonics of the QPOs were observed at 1.87 and 3.87 Hz (barycenter corrected), with the Lorentzian widths of 0.19 and 0.49 Hz.

Since the source is extremely bright (about 800 counts/s) we checked for possible pile-up effects by excluding 5 brightest rows of CCD and using only events with energies above 1 keV. This had a little effect on the detected features, therefore we concluded that the pile-up is not responsible for this QPOs and they are intrinsic features of the source.

The extracted power spectrum with the overplotted best-fit (powerlaw plus two Lorentzians) can be found here: https://drive.google.com/open?id=0B_vv997IdS4xamcza0tzMi1GSzA

MAXI J1535-571