36 research outputs found
Integral and Rxte/Asm Observations on Igr J17098-3628
To probe further the possible nature of the unidentified source IGR
J17098-3628, we have carried out a detailed analysis of its long-term time
variability as monitored by RXTE/ASM, and of its hard X-ray properties as
observed by INTEGRAL. INTEGRAL has monitored this sky region over years and
significantly detected IGR J17098-3628 only when the source was in this dubbed
active state. In particular, at 20 keV, IBIS/ISGRI caught an outburst in
March 2005, lasting for 5 days with detection significance of 73
(20-40 keV) and with the emission at 200 keV. The ASM observations reveal
that the soft X-ray lightcurve shows a similar outburst to that detected by
INTEGRAL, however the peak of the soft X-ray lightcurve either lags, or is
preceded by, the hard X-ray (20 keV) outburst by 2 days. This
resembles the behavior of X-ray novae like XN 1124-683, hence it further
suggests a LMXB nature for IGR J17098-3628. While the quality of the ASM data
prevents us from drawing any definite conclusions, these discoveries are
important clues that, coupled with future observations, will help to resolve
the as yet unknown nature of IGR J17098-3628.Comment: 15 pages, 7 figure, accepted in PAS
High energy properties of PKS 1830-211
We report on an analysis of X- and -ray observations of PKS 1830-211,
based on the long-term campaigns carried out by \emph{INTEGRAL} and COMPTEL.
The \emph{INTEGRAL} data currently available present a significance
detection in the 20-100 keV band, while the COMPTEL 6-years data provide a
significance detection in the 1-3 MeV energy band. At hard X-rays,
\emph{INTEGRAL} and supplementary \emph{SWIFT} observations show flux
variability on timescales of months. At -rays, the source shows
persistent emission over years. The hard X-ray spectrum is well represented by
a power-law model, with in the 20-250 keV band. This photon
index is well consistent with the previous report of obtained
at keV from the best fit of \emph{XMM-Newton} data with a broken
power law model. The joint \emph{XMM-Newton}/\emph{INTEGRAL} spectrum presented
here is then fit with a broken power-law model and the parameters are refined
compared to the previous. The results show the photon index changes from to at a break energy keV. At MeV energies, the
spectrum softens to . These results, together with the EGRET
measurement at MeV, constitute a broad-band spectrum containing the
peak of the power output at MeV energies, similar to most high-luminosity
-ray blazars. The measured spectral characterstics are then discussed
in the framework of the gravitational lens effects.Comment: accepted for Ap
INTEGRAL/XMM views on the MeV source GRO J1411-64
The COMPTEL unidentified source GRO J 1411-64 was observed by INTEGRAL and
XMM-Newton in 2005. The Circinus Galaxy is the only source detected within the
4 location error of GRO J1411-64, but in here excluded as the possible
counterpart. At soft X-rays, 22 reliable and statistically significant sources
(likelihood ) were extracted and analyzed from XMM-Newton data. Only one
of these sources, XMMU J141255.6 -635932, is spectrally compatible with GRO
J1411-64 although the fact the soft X-ray observations do not cover the full
extent of the COMPTEL source position uncertainty make an association hard to
quantify and thus risky. At the best location of the source, detections at hard
X-rays show only upper limits, which, together with MeV results obtained by
COMPTEL suggest the existence of a peak in power output located somewhere
between 300-700 keV for the so-called low state. Such a spectrum resembles
those in blazars or microquasars, and might suggest at work by a similar
scenario.
However, an analysis using a microquasar model consisting on a magnetized
conical jet filled with relativistic electrons, shows that it is hard to comply
with all observational constrains. This fact and the non-detection at hard
X-rays introduce an a-posteriori question mark upon the physical reality of
this source, what is discussed here.Comment: Accepted for publication in Astrophysics and Space Science, as
proceedings of "The Multi-Messenger Approach to High-Energy Gamma-Ray
Sources", Barcelona, July 4-7, 2006, J. M. Paredes, O. Reimer, and D. F.
Torres, editor
INTEGRAL and XMM-Newton observations towards the unidentified MeV source GRO J1411-64.
The COMPTEL unidentified source GRO J1411-64 was observed by INTEGRAL, and its central part, also by XMM-Newton. The data analysis shows no hint for new detections at hard X-rays. The upper limits in flux herein presented constrain the energy spectrum of whatever was producing GRO J1411-64, imposing, in the framework of earlier COMPTEL observations, the existence of a peak in power output located somewhere between 300-700 keV for the so-called low state. The Circinus Galaxy is the only source detected within the 4 location error of GRO J1411-64, but can be safely excluded as the possible counterpart: the extrapolation of the energy spectrum is well below the one for GRO J1411-64 at MeV energies. 22 significant sources (likelihood ) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932, is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the COMPTEL source position uncertainty make an association hard to quantify and thus risky. The unique peak of the power output at high energies (hard X-rays and gamma-rays) resembles that found in the SED seen in blazars or microquasars. However, an analysis using a microquasar model consisting on a magnetized conical jet filled with relativistic electrons which radiate through synchrotron and inverse Compton scattering with star, disk, corona and synchrotron photons shows that it is hard to comply with all observational constrains. This and the non-detection at hard X-rays introduce an a-posteriori question mark upon the physical reality of this source, which is discussed in some detail
A combined model for the X-ray to gamma-ray emission of Cyg X-1
We use recent data obtained by three (OSSE, BATSE, and COMPTEL) of four
instruments on board the Compton Gamma Ray Observatory, to construct a model of
Cyg X-1 which describes its emission in a broad energy range from soft X-rays
to MeV gamma-rays self-consistently. The gamma-ray emission is interpreted to
be the result of Comptonization, bremsstrahlung, and positron annihilation in a
hot optically thin and spatially extended region surrounding the whole
accretion disk. For the X-ray emission a standard corona-disk model is applied.
We show that the Cyg X-1 spectrum accumulated by the CGRO instruments during a
~4 year time period between 1991 and 1995, as well as the HEAO-3 gamma1 and
gamma2 spectra can be well represented by our model. The derived parameters
match the observational results obtained from X-ray measurements.Comment: 11 pages including 6 ps-figures and 2 tables, latex2e, uses
emulateapj.sty (ver. of 18 Sep 96, enclosed), epsfig.sty, times.sty. To
appear in July 20, 1998 issue of ApJ (v.502
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INTEGRAL and RXTE Observations of Centaurus A
INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Centaurus A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the X-ray/low energy gamma ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. Cen A was detected by both sets of instruments from 3-240 keV. When combined with earlier archival RXTE results, we find the power law continuum flux and the line-of-sight column depth varied independently by 60% between 2000 January and 2003 March. Including the three archival RXTE observations, the iron line flux was essentially unchanging, and from this we conclude that the iron line emitting material is distant from the site of the continuum emission, and that the origin of the iron line flux is still an open question. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a variability in the column depth between 1.0 x 10{sup 23} cm{sup -2} and 1.5 x 10{sup 23} cm{sup -2} separated by approximately 20 years, and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause. The INTEGRAL OSA 4.2 calibration of JEM-X, ISGRI, and SPI yields power law indices consistent with the RXTE PCA and HEXTE values, but the indices derived from ISGRI alone are about 0.2 greater. Significant systematics are the limiting factor for INTEGRAL spectral parameter determination