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

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We report the discovery of quasi-periodic oscillations (QPO) at ~11 mHz in two RXTE observations and one Chandra observation of the black hole candidate H1743-322.

• The QPO is observed only at the beginning of the 2010 and 2011 outbursts at similar hard colour and intensity, suggestive of an accretion state dependence for the QPO.
• Although its frequency appears to be correlated with X-ray intensity on timescales of a day, in successive outbursts eight months apart we measure a QPO frequency that differs by less than ~2.2 mHz while the intensity had changed significantly.
• We show that this ~11 mHz QPO is different from the so-called Type-C QPOs seen in black holes and that the mechanisms that produce the two flavours of variability are most probably independent.