Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low/Hard State Spectra of GRO J1655-40 Observed with Suzaku   The Galactic black-hole binary GRO J1655$-$40 was observed with Suzaku on
2005 September 22--23, for a net exposure of 35 ks with the X-ray Imaging
Spectrometer (XIS) and 20 ks with the Hard X-ray Detector (HXD). The source was
detected over a broad and continuous energy range of 0.7--300 keV, with an
intensity of $\sim$50 mCrab at 20 keV. At a distance of 3.2 kpc, the 0.7--300
keV luminosity is $ \sim 5.1 \times 10^{36}$ erg s$^{-1}$ ($\sim 0.7$ % of the
Eddington luminosity for a 6 $M_{\odot}$ black hole). The source was in a
typical low/hard state, exhibiting a power-law shaped continuum with a photon
index of $\sim 1.6$. During the observation, the source intensity gradually
decreased by 25% at energies above $\sim 3$ keV, and by 35% below 2 keV. This,
together with the soft X-ray spectra taken with the XIS, suggests the presence
of an independent soft component that can be represented by emission from a
cool ($\sim 0.2$ keV) disk. The hard X-ray spectra obtained with the HXD reveal
a high-energy spectral cutoff, with an e-folding energy of $\sim 200$ keV.
Since the spectral photon index above 10 keV is harder by $\sim 0.4$ than that
observed in the softer energy band, and the e-folding energy is higher than
those of typical reflection humps, the entire 0.7--300 keV spectrum cannot be
reproduced by a single thermal Comptonization model, even considering
reflection effects. Instead, the spectrum (except the soft excess) can be
successfully explained by invoking two thermal-Comptonization components with
different $y$-parameters. In contrast to the high/soft state spectra of this
object in which narrow iron absorption lines are detected with equivalent
widths of 60--100 eV, the present XIS spectra bear no such features beyond an
upper-limit equivalent width of 25 eV.

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The categories of this paper are: hep-th