We describe the ``Monitor e Imageador de Raios-X'' (MIRAX), an X-ray
astronomy satellite mission proposed by the high energy astrophysics group at
the National Institute for Space Research (INPE) in ...Brazil to the Brazilian
Space Agency. MIRAX is an international collaboration that includes, besides
INPE, the University of California San Diego, the University of Tuebingen in
Germany, the Massachusetts Institute of Technology and the Space Research
Organization Netherlands. The payload of MIRAX will consist in two identical
hard X-ray cameras (10 -200 keV) and one soft X-ray camera (2-28 keV), both
with angular resolution of ~ 5-6 arcmin. The basic objective of MIRAX is to
carry out continuous broadband imaging spectroscopy observations of a large
source sample (~ 9 months/yr) in the central Galactic plane region. This will
allow the detection, localization, possible identification, and
spectral/temporal study of the entire history of transient phenomena to be
carried out in one single mission. MIRAX will have sensitivities of ~ 5
mCrab/day in the 2-10 keV band (~2 times better than the All Sky Monitor on
Rossi X-ray Timing Explorer) and 2.6 mCrab/day in the 10-100 keV band (~40
times better than the Earth Occultation technique of the Burst and Transient
Source Experiment on the Compton Gamma-Ray Observatory). The MIRAX spacecraft
will weigh about 200 kg and is expected to be launched in a low-altitude (~ 600
km) circular equatorial orbit around 2007/2008.
Astrophys.J.567:1102,2002 The Chandra AO1 HETGS observation of the micro-quasar GRS 1915+105 in the low
hard state reveals (1) neutral K absorption edges from Fe, Si, Mg, and S in
cold gas, and (2) ...highly ionized (Fe XXV and Fe XXVI) absorption attributed to
a hot disk, disk wind, or corona. The neutral edges reveal anomalous Si and Fe
abundances which we attribute to surrounding cold material in/near the
environment of GRS 1915+105. We also point out the exciting possibility for the
first astrophysical detection of XAFS attributed to material in interstellar
grains. We place constraints on the ionization parameter, temperature, and
hydrogen equivalent number density of the absorber near the accretion disk
based on the detection of the H- and He-like Fe absorption. Observed spectral
changes in the ionized lines which track the light curve point to changes in
both the ionizing flux and density of the absorber, supporting the presence of
a flow. Details can be found in Lee et al., 2002, ApJ., 567, 1102
RXTE observations of GRB afterglows Marshall, Francis E.; Swank, Jean; Valinia, Azita ...
Nuclear physics. Section B, Proceedings supplement,
1999, 1999-1-00, Volume:
69, Issue:
1
Journal Article
Variable X-ray sources that appear to be the afterglows of the strong gamma-ray bursts GRB 970616 and GRB 970828 have been discovered with the RXTE PCA. First seen less than 4 hours after the burst, ...the flux from the sources decreased with time. Although near the sensitivity limit of the PCA, the sources are the brightest afterglows yet seen in X-rays. Similar observations of two other bursts did not detect any afterglows. These results are part of a continuing collaboration between RXTE, BATSE, and IPN scientists to rapidly detect X-ray afterglows of bright gamma-ray bursts.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We present simultaneous infrared and X-ray observations of the Galactic
microquasar GRS 1915+105 using the Palomar 5-m telescope and Rossi X-ray Timing
Explorer on July 10, 1998 UT. Over the course ...of 5 hours, we observed 6 faint
infrared (IR) flares with peak amplitudes of $\sim 0.3-0.6 $ mJy and durations
of $\sim 500-600 $ seconds. These flares are associated with X-ray
soft-dip/soft-flare cycles, as opposed to the brighter IR flares associated
with X-ray hard-dip/soft-flare cycles seen in August 1997 by Eikenberry et al.
(1998). Interestingly, the IR flares begin {\it before} the X-ray oscillations,
implying an ``outside-in'' origin of the IR/X-ray cycle. We also show that the
quasi-steady IR excess in August 1997 is due to the pile-up of similar faint
flares. We discuss the implications of this flaring behavior for understanding
jet formation in microquasars.
The time-averaged 30 ks Chandra HETGS observation of the micro-quasar GRS
1915+105 in the low hard state reveals for the first time in this source
neutral K absorption edges from Fe, Si, Mg, & S. ...Ionized resonance absorption
from H-, and He-like Fe (XXV, XXVI), Ca XX and possibly emission from neutral
Fe Kalpha and ionized Fe XXV (forbidden, or the resonance emission component of
a P-Cygni profile) are also seen. We report the tentative detection of the
first astrophysical signature of XAFS in the photoelectric edge of Si (and
possibly Fe and Mg), attributed to material in grains. The large column
densities measured from the neutral edges reveal anomalous Si and Fe
abundances. Scenarios for which the anomalous abundances can be attributed to
surrounding cold material associated with GRS 1915+105 and/or that the
enrichment may signify either a highly unusual supernova/hypernova, or external
supernova activity local to the binary are discussed. We attribute the ionized
features to a hot disk, disk-wind, or corona environment. These features allow
for constraints on the ionization parameter (log xi > 4.15), temperature (T >
2.4 x 10^6 K), and hydrogen equivalent number density (n > 10^{12} cm^{-3}) for
this region. Variability studies with simultaneous RXTE data show that the
light curve count rate tracks changes in the disk blackbody and the power-law
flux. Spectral changes in the Chandra data also track the behavior of the light
curve, and may point to changes in both the ionizing flux and density of the
absorber. A 3.69 Hz QPO and weak first harmonic is seen in the RXTE data.
A&A 407, 1039-1058 (2003) We present the long term evolution of the timing properties of the black hole
candidate Cygnus X-1 in the 0.002-128 Hz frequency range as monitored from 1998
to 2001 with ...the RXTE. The hard state power spectral density (PSD) is well
modeled as the sum of four Lorentzians, which describe distinct broad noise
components. Before 1998 July, Cyg X-1 was in a "quiet" hard state characterized
primarily by the first three of these broad Lorentzians. Around 1998 May, this
behavior changed: the total fractional rms amplitude decreased, the peak
frequencies of the Lorentzians increased, the average time lag slightly
increased, and the X-ray spectrum softened. The change in the timing parameters
is mainly due to a strong decrease in the amplitude of the third Lorentzian.
Since then, an unusually large number of X-ray flares have been observed.
During these "failed state transitions", the X-ray power spectrum changes to
that of the intermediate state. Modeling this PSD with the four Lorentzians, we
find that the first Lorentzian component is suppressed relative to the second
and third Lorentzian. Also the frequency-dependent time lags increase
significantly. We confirm the interpretation as failed state transitions with
observations from the 2001 Jan. and 2001 Oct. soft states. Such behavior
suggests that some or all of the Lorentzian components are associated with the
accretion disk corona. We discuss the physical interpretation of our results.
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