Low/Hard State Spectra of GRO J1655-40 Observed with Suzaku

Abstract

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.

32 pages, 12 figures; accepted for publication in Publications of the Astronomical Society of Japan (PASJ)

References in corpus (8)

• In-Orbit Performance of the Hard X-ray Detector on board Suzaku
• The magnetic nature of disk accretion onto black holes
• Suzaku observations of the hard X-ray variability of MCG-6-30-15: the effects of strong gravity around a Kerr black hole
• Revealing the High Energy Emission from the Obscured Seyfert Galaxy MCG -5-23-16 with Suzaku
• XMM-Newton and INTEGRAL spectroscopy of the microquasar GRO J1655-40 during its 2005 outburst
• GRO J1655-40: Early Stages of the 2005 Outburst
• On the distance of GRO J1655-40
• The highly ionized disk wind of GRO J1655-40

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