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We report the discovery of quasi-periodic oscillations (QPO) at ~11 mHz intwo RXTE observations and one Chandra observation of the black hole candidateH1743-322. The QPO is observed only at the beginning of the 2010 and 2011outbursts at similar hard colour and intensity, suggestive of an accretionstate dependence for the QPO. Although its frequency appears to be correlatedwith X-ray intensity on timescales of a day, in successive outbursts eightmonths apart we measure a QPO frequency that differs by less than ~2.2 mHzwhile the intensity had changed significantly. We show that this ~11 mHz QPO isdifferent from the so-called Type-C QPOs seen in black holes and that themechanisms that produce the two flavours of variability are most probablyindependent. After comparing this QPO with other variability phenomena seen inaccreting black holes and neutron stars, we conclude that it best resembles theso-called "1 Hz" QPOs seen in dipping neutron star systems, although having asignificantly lower (1-2 orders of magnitude) frequency. If confirmed,H1743-322 is the first black hole showing this type of variability. Given theunusual characteristics and the hard-state dependence of the ~11 mHz QPO, wealso speculate whether these oscillations could instead be related to the radiojets observed in H1743-322. A systematic search for this type of low-frequencyQPOs in similar systems is needed to test this speculation. In any case, itremains unexplained why these QPOs have only been seen in the last twooutbursts of H1743-322.

Low Frequency (11 mHz) Oscillations in H1743-322: A New Class of Black Hole QPOs?