TY - JOUR
T1 - Spectral evolution of a New X-Ray transient MAXIJ0556-332 observed by MAXI, swift, and RXTE
AU - Sugizaki, Mutsumi
AU - Yamaoka, Kazutaka
AU - Matsuoka, Masaru
AU - Kennea, Jamie A.
AU - Mihara, Tatehiro
AU - Hiroi, Kazuo
AU - Ishikawa, Masaki
AU - Isobe, Naoki
AU - Kawai, Nobuyuki
AU - Kimura, Masashi
AU - Kitayama, Hiroki
AU - Kohama, Mitsuhiro
AU - Matsumura, Takanori
AU - Morii, Mikio
AU - Nakagawa, Yujin E.
AU - Nakahira, Satoshi
AU - Nakajima, Motoki
AU - Negoro, Hitoshi
AU - Serino, Motoko
AU - Shidatsu, Megumi
AU - Sootome, Tetsuya
AU - Sugimori, Kousuke
AU - Suwa, Fumitoshi
AU - Toizumi, Takahiro
AU - Tomida, Hiroshi
AU - Tsuboi, Yoko
AU - Tsunemi, Hiroshi
AU - Ueda, Yoshihiro
AU - Ueno, Shiro
AU - Usui, Ryuichi
AU - Yamamoto, Takayuki
AU - Yamauchi, Makoto
AU - Yamazaki, Kyohei
AU - Yoshida, Atsumasa
PY - 2013/6/25
Y1 - 2013/6/25
N2 - We report on the spectral evolution of a new X-ray transient, MAXIJ0556-332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD = 55572) by the MAXI Gas Slit Camera allsky survey at (l , b) = (238.i9, -25.i2), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source, which led to optical identification. For more than one year since its appearance, MAXIJ0556-332 has been X-ray active, with a 2-10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following ×70 days, the 0.5-30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4-1 and a high-energy exponential cutoff at 1.5-5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus Comptonized emission from a boundary layer around a neutron star. This supports the source identification as being a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8 × 1037 erg s-1. This suggests a source distance of >17 kpc.
AB - We report on the spectral evolution of a new X-ray transient, MAXIJ0556-332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD = 55572) by the MAXI Gas Slit Camera allsky survey at (l , b) = (238.i9, -25.i2), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source, which led to optical identification. For more than one year since its appearance, MAXIJ0556-332 has been X-ray active, with a 2-10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following ×70 days, the 0.5-30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4-1 and a high-energy exponential cutoff at 1.5-5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus Comptonized emission from a boundary layer around a neutron star. This supports the source identification as being a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8 × 1037 erg s-1. This suggests a source distance of >17 kpc.
UR - https://www.scopus.com/pages/publications/84880973080
UR - https://www.scopus.com/pages/publications/84880973080#tab=citedBy
U2 - 10.1093/pasj/65.3.58
DO - 10.1093/pasj/65.3.58
M3 - Article
AN - SCOPUS:84880973080
SN - 0004-6264
VL - 65
JO - Publications of the Astronomical Society of Japan
JF - Publications of the Astronomical Society of Japan
IS - 3
M1 - 58
ER -