MITSuME observation of V404 Cygni in the 2015 outburst: Two optical variable components with different variability

Abstract

The black hole binary V404 Cygni (= GS 2023+338) had an outburst on June 15, 2015 after 26 years of quiescence. We report the multi-color optical observation (g', Rc, and Ic) of this object at the beginning of its outburst performed by the MITSuME 50cm telescope in Akeno, Yamanashi, and the MURIKABUSHI 105 cm Telescope at Ishigakijima Astronomical Observatory. With time domain analysis of the multi-color light curves, we successfully decomposed optical variations into two components: a highly-variable, and a little-variable component. The loci of the little-variable component in the color-color diagram are consistent with that of the multi-temperature blackbody radiation, while those of the highly-variable component trace out a power-law spectrum with a spectral index α~0.6-1.0. For the little-variable component, we argue that an irradiated disk with the innermost temperature higher than ~2.0$\times 10^4$ K and the outermost temperature lower than ~6.5$\times 10^3$ K is the most plausible source. The gradual rise trend of the light curve during our observation is probably due to the growing of the little-variable component. The observed spectral energy distribution (SED) from the optical to ultraviolet can be expressed by a model consisting of a power-law component and an irradiated disk component.

11 pages, 7 figures, 3 tables

References in corpus (7)

• XMM-Newton study of the complex and variable spectrum of NGC 4051
• Repetitive Patterns in Rapid Optical Variations in the Nearby Black-hole Binary V404 Cygni
• The formation of the black hole in the X-ray binary system V404 Cyg
• Time-resolved optical/near-IR polarimetry of V404 Cyg during its 2015 outburst
• Suzaku Studies of the Central Engine in the Typical Type I Seyfert NGC 3227: Detection of Multiple Primary X-ray Continua with Distinct Properties
• MASTER optical polarization variability detection in the Microquasar V404 Cyg/GS2023+33
• The nova-like nebular optical spectrum of V404 Cygni at the beginning of the 2015 outburst decay

Cited by in corpus (3)

• Accretion and Outflow in V404 Cyg
• Optical and X-ray Correlations During the 2015 Outburst of the Black Hole V404 Cyg
• Discovery of the new X-ray transient MAXI J1807+132: a Candidate of a Neutron Star Low-mass X-ray binary