TY  - JOUR
A1  - Hamaguchi, K.
A1  - Oskinova, Lida
A1  - Russell, C. M. P.
A1  - Petre, R.
A1  - Enoto, T.
A1  - Morihana, K.
A1  - Ishida, M.
T1  - DISCOVERY OF RAPIDLY MOVING PARTIAL X-RAY ABSORBERS WITHIN GAMMA CASSIOPEIAE
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - detected six rapid X-ray spectral hardening events called "softness dips" in a similar to 100 ks observation in 2011. All the softness dip events show symmetric softness-ratio variations, and some of them have flat bottoms apparently due to saturation. The softness dip spectra are best described by either similar to 40% or similar to 70% partial covering absorption to kT similar to 12 keV plasma emission by matter with a neutral hydrogen column density of similar to(2-8) x 10(21) cm(-2), while the spectrum outside these dips is almost free of absorption. This result suggests the presence of two distinct X-ray-emitting spots in the.. Cas system, perhaps on a white dwarf (WD) companion with dipole mass accretion. The partial covering absorbers may be blobs in the Be stellar wind, the Be disk, or rotating around the WD companion. Weak correlations of the softness ratios to the hard X-ray flux suggest the presence of stable plasmas at kT similar to 0.9 and 5 keV, which may originate from the Be or WD winds. The formation of a Be star and WD binary system requires mass transfer between two stars; gamma Cas may have experienced such activity in the past.
KW  - blue stragglers
KW  - stars: emission-line, Be
KW  - stars: individual (gamma Cassiopeiae)
KW  - stars: winds, outflows
KW  - white dwarfs
KW  - X-rays: stars
Y1  - 2016
U6  - https://doi.org/10.3847/0004-637X/832/2/140
SN  - 0004-637X
SN  - 1538-4357
VL  - 832
SP  - 33
EP  - 49
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Hamaguchi, K.
A1  - Corcoran, M. F.
T1  - Extremely Hard X-ray Emission from η Car Observed with XMM-Newton and NuSTAR around Periastron in 2014.6
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - The super massive binary system, η Car, experienced periastron passage in the summer of 2014. We observed the star twice around the maximum (forb =0.97, 2014 June 6) and just before the minimum (ϕorb =0.99, 2014 July 28) of its wind-wind colliding (WWC) X-ray emis-sion using the XMM-Newton and NuSTAR observatories, the latter of which is equipped with extremely hard X-ray (>10 keV) focusing mirrors. In both observations, NuSTAR detected the thermal X-ray tail up to 40-50 keV. The hard slope is consistent with an electron tem- perature of ∼6 keV, which is significantly higher than the ionization temperature (kT ∼4 keV) measured from the Fe K emission lines, assuming collisional equilibrium plasma. The spectrum did not show a hard power-law component above this energy range, unlike earlier detections with INTEGRAL and Suzaku. In the second NuSTAR observation, the X-ray flux above 5 keV declined gradually in ∼1 day. This result suggests that the WWC apex was gradually hidden behind the optically thick primary wind around conjunction.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87926
SP  - 159
EP  - 162
ER  - 
TY  - JOUR
A1  - Townsley, Leisa K.
A1  - Broos, Patrick S.
A1  - Corcoran, Michael F.
A1  - Feigelson, Eric D.
A1  - Gagne, Marc
A1  - Montmerle, Thierry
A1  - Oey, M. S.
A1  - Smith, Nathan
A1  - Garmire, Gordon P.
A1  - Getman, Konstantin V.
A1  - Povich, Matthew S.
A1  - Evans, Nancy Remage
A1  - Naze, Yael
A1  - Parkin, E. R.
A1  - Preibisch, Thomas
A1  - Wang, Junfeng
A1  - Wou, Scott J.
A1  - Chu, You-Hua
A1  - Cohen, David H.
A1  - Gruendl, Robert A.
A1  - Hamaguchi, Kenji
A1  - King, Robert R.
A1  - Mac Low, Mordecai-Mark
A1  - McCaughrean, Mark J.
A1  - Moffat, Anthony F. J.
A1  - Oskinova, Lida
A1  - Pittard, Julian M.
A1  - Stassun, Keivan G.
A1  - Ud-Doula, Asif
A1  - Walborn, Nolan R.
A1  - Waldron, Wayne L.
A1  - Churchwell, Ed
A1  - Nictiols, J. S.
A1  - Owocki, Stanley P.
A1  - Schulz, Norbert S.
T1  - An introduction to the chandra carina complex project
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series
N2  - The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of > 14,000 X-ray point sources;> 9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results.
KW  - H II regions
KW  - stars: massive
KW  - stars: pre-main sequence
KW  - X-rays: individual (Carina)
KW  - X-rays: ISM
KW  - X-rays: stars
Y1  - 2011
U6  - https://doi.org/10.1088/0067-0049/194/1/1
SN  - 0067-0049
VL  - 194
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Russell, C. M. P.
A1  - Corcoran, M. F.
A1  - Cuadra, J.
A1  - Owocki, S. P.
A1  - Wang, Q. D.
A1  - Hamaguchi, K.
A1  - Sugawara, Y.
A1  - Pollock, A. M. T.
A1  - Kallman, T. R.
T1  - Hydrodynamic and radiative transfer modeling of X-ray emission from colliding WR winds
BT  - WR 140 & the Galactic center
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Colliding Wolf-Rayet (WR) winds produce thermal X-ray emission widely observed by X-ray telescopes. In wide WR+O binaries, such as WR 140, the X-ray flux is tied to the orbital phase, and is a direct probe of the winds’ properties. In the Galactic center, ~30 WRs orbit the super massive black hole (SMBH) within ~10”, leading to a smorgasbord of wind-wind collisions. To model the X-ray emission of WR 140 and the Galactic center, we perform 3D hydrodynamic simulations to trace the complex gaseous flows, and then carry out 3D radiative transfer calculations to compute the variable X-ray spectra. The model WR 140 RXTE light curve matches the data well for all phases except the X-ray minimum associated with periastron, while the model spectra agree with the RXTE hardness ratio and the shape of the Suzaku observations throughout the orbit. The Galactic center model of the Chandra flux and spectral shape match well in the region r ≤ 3”, but the model flux falls off too rapidly beyond this radius.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88255
SP  - 309
EP  - 312
ER  - 
TY  - JOUR
A1  - Shrader, C. R.
A1  - Hamaguchi, K.
A1  - Sturner, Steven J.
A1  - Oskinova, Lida
A1  - Almeyda, T.
A1  - Petre, R.
T1  - Hifg-energy properties of the enigmatic be STAR gamma Cassiopeiae
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present the results of a broadband X-ray study of the enigmatic Be star Gamma Cassiopeiae (herein gamma Cas) based on observations made with both the Suzaku and INTEGRAL observatories.. Cas has long been recognized as the prototypical example of a small subclass of Be stars with moderately strong X-ray emission dominated by a hot thermal component in the 0.5-12 keV energy range (L-x approximate to 10(32)-10(33) erg s(-1)). This places them at the high end of the known luminosity distribution for stellar emission, but several orders of magnitude below typical accretion-powered Be X-ray binaries. The INTEGRAL observations spanned an eight-year baseline and represent the deepest measurement to date at energies above similar to 50 keV. We find that the INTEGRAL data are consistent within statistics to a constant intensity source above 20 keV, with emission extending up to similar to 100 keV, and that searches for all of the previously reported periodicities of the system at lower energies led to null results. We further find that our combined Suzaku and INTEGRAL spectrum, which we suggest is the most accurate broadband X-ray measurement of gamma Cas to date, is fitted extremely well with a thermal plasma emission model with a single absorption component. We found no compelling need for an additional non-thermal high-energy component. We discuss these results in the context of a currently favored models for gamma Cas and its analogs.
KW  - gamma rays: stars
KW  - stars: emission-line, Be
KW  - stars: individual (gamma Cassiopeiae)
KW  - white dwarfs
KW  - X-rays: binaries
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/799/1/84
SN  - 0004-637X
SN  - 1538-4357
VL  - 799
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -