Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Phase Lags of QPOs in Microquasar GRS 1915+105   I report the discovery of hard X-ray phase lags associated with the famous 67
Hz quasi-periodic oscillation (QPO) in microquasar GRS 1915+105. The QPO is
seen on multiple occasions. For this investigation, I have chosen one
particular observation when the oscillation is the strongest. The measured hard
lags show strong energy dependence. With respect to the 2-2.5 keV band, the
phase lag increases from insignificant detection at 5.2-7.0 keV to as much as
2.3 radians (which corresponds a time lag of $\sim$5.6 ms) above $\sim$13 keV.
Also detected in the same observation are one narrowly peaked, strong QPO at 67
mHz, along with its first three harmonics, one weak QPO at $\sim$400 mHz and
one broad QPO at $\sim$840 mHz. Similar cross spectral analyses have been
performed on these QPOs (and the harmonics), in order to measure any phase lags
associated with the features. Phase lags are detected in all, with similar
energy dependence. For the 67 mHz QPO, the results are quite intriguing: only
the first and third harmonic components show hard lags, while the fundamental
and the second harmonic components actually display smaller {\it soft} lags.
Coupled with the energy dependence of the QPO amplitude, the results seem to
indicate a complicated change in the signal profile with photon energy. I will
discuss the implication of the phase lags on possible origins of the QPOs.

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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
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The categories of this paper are: physics
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph