204 research outputs found
Spectral Variability and iron line emission in the ASCA Observations of the Seyfert 1 Galaxy NGC4051
We present the results of an extensive analysis of the ``ASCA'' AO2
observation of the Seyfert 1 galaxy NGC4051. The target exhibits broadband
[0.5--10 keV] variability by a factor on time scales ,
with a typical doubling time . The spectrum is characterized by a
strong emission excess over the extrapolated power law at energies . Absorption edges due to ionized oxygen species OVII and OVIII are
detected together with an emission-like feature at . The OVII
edge undergoes significant variability on a timescale as low as ,
whilst no contemporary variability of the OVIII feature is detected. Typical
variability time scales place constraints on the location and the density of
the absorbing matter. In the self-consistent hypothesis of a high energy () power law reflected by an infinite plane-parallel cold slab, a
photon index change () has also been observed; a natural
explanation can be found in the framework of non-thermal Comptonization models.
The iron line is redshifted (centroid energy ) and broad
(); multicomponent structure is suggestive of emission from a
relativistic accretion disk; however if the disk is not ionized a contribution
by a molecular torus or an iron overabundance by a factor are
required.Comment: 17 pages, latex, 12 figures. To be published in Publication of
Astronomical Society of Japa
Decades' long-term variations in NS-LMXBs observed with MAXI/GSC, RXTE/ASM and Ginga/ASM
We investigated the decades' long-term X-ray variations in bright low-mass
X-ray binaries containing a neutron star (NS-LMXB). The light curves of
MAXI/GSC and RXTE/ASM covers 26 yr, and high-quality X-ray light curves
are obtained from 33 NS-LMXBs. Among them, together with Ginga/ASM, two sources
(GX 31 and GX 91) showed an apparent sinusoidal variation with the period
of yr and yr in the 34 yr light curve. Their X-ray
luminosities were erg s in the middle of the
luminosity distribution of the NS-LMXB. Other seven sources (Ser X-1, 4U
1735--444, GX 99, 4U 174637, 4U 170840, 4U 1822000, and 1A
1246588) have also similar sinusoidal variation, although the profiles
(amplitude, period, and phase) are variable. Compering the 21 sources with
known orbital periods, a possible cause of the long-term sinusoidal variation
might be the mass transfer cycles induced by the irradiation to the donor star.Comment: 18 pages, accepted to PAS
- …