25 research outputs found
The Physics of Disk Winds, Jets,and X-ray Variability in GRS 1915+105
We present new insights about accretion and ejection physics based on joint
RXTE/Chandra HETGS studies of rapid X-ray variability in GRS 1915+105. For the
first time, with fast phase-resolved spectroscopy of the rho state, we are able
to show that changes in the broadband X-ray spectrum (RXTE) on timescales of
seconds are associated with measurable changes in absorption lines (Chandra
HETGS) from the accretion disk wind. Additionally, we make a direct detection
of material evaporating from the radiation-pressure-dominated inner disk. Our
X-ray data thus reveal the black hole as it ejects a portion of the inner
accretion flow and then drives a wind from the outer disk, all in a bizarre
cycle that lasts fewer than 60 seconds but can repeat for weeks. We find that
the accretion disk wind may be sufficiently massive to play an active role in
GRS 1915+105, not only in quenching the jet on long timescales, but also in
possibly producing or facilitating transitions between classes of X-ray
variability.Comment: 3 pages, 1 Figure. Proceedings of IAU Symposium 275 (Jets at all
Scales), Buenos Aires, 13-17.09.2010; eds. G. Romero, R. Sunyaev, T. Bellon
\u3cem\u3eXMM-Newton\u3c/em\u3e discovery of the X-ray transient XMMU J181227.8-181234 in the Galactic plane
We report the discovery of an X-ray transient, observed in outburst with XMM-Newton on 2003 March 20, and with position (J2000, approximate positional error 2arcsec). No known source is present at this position and the source was not detected during published ROSAT or ASCA observations of that region. However, the source may be associated with 1H1812-182 detected by HEAO 1, although the error bars on the HEAO 1 position are very large and the two sources could also be unrelated. Therefore, we name the source XMMU J181227.8-181234. Initially, the source was not detected using the All-Sky Monitor (ASM) on-board the Rossi X-ray Timing Explorer, however, reprocessing of the ASM data shows that the source was in fact detected and it was active for about 50d. The X-ray spectrum of this transient is fitted equally well by an absorbed power law (with a spectral index of 2.5) or multicolour disc blackbody model (with kT ~ 2keV), where we find that the source is highly absorbed. We detect an unabsorbed 0.5-10keV flux in the range (2-5) × 10-9ergcm-2s-1, which at a distance of 8kpc corresponds to a 0.5-10keV luminosity of (1-4) × 1037ergs-1. No pulsations were detected by timing analysis. A colour-colour diagram from ASM data of different accreting objects suggests that the transient is a high-mass X-ray binary, as is also suggested by the high absorption compared to the average interstellar value in the direction of the source. However, the power-law spectral index is far more typical of a low-mass X-ray binary. Thus, we are unable to conclusively identify the nature of the transient. We also report on three sources first detected by the ASCA Galactic Plane Survey that are close to this transient
Thirteen new BL Lacertae objects discovered by an efficient x ray/radio/optical technique
The discovery of 13 serendipitous BL Lac objects in the Einstein IPC Slew Survey by means of x ray/radio vs. x ray/optical color-color diagrams and confirmation by optical spectroscopy are reported. These 13 BL Lacs were discovered using a technique which exploits the characteristic broad band spectra of BL Lacs. New VLA detections provide accurate fluxes (f(6 cm) is approximately 0.5 mJy) and 2 in. positions, facilitating the determination of an optical counterpart. All 13 new BL Lacs show essentially featureless optical spectra. Nine of these lie within the range of colors of known x ray selected BL Lacs. Of the remaining four, one is apparently x ray louder (by a factor of 1.5) or optically quieter (by 0.8 mags); and three are optically louder (by 1-1.3 mags) than x ray selected BL Lacs. Approximately 50 new BL Lacs in total are expected from VLA work and upcoming Australia Telescope observations, yielding a complete Slew Survey sample of approximately 90 BL Lacs
Decade time-scale modulation of low mass X-ray binaries
Regular observations by the All Sky Monitor aboard the Rossi X-ray Timing
Explorer satellite have yielded well-sampled light-curves with a time baseline
of over ten years. We find that up to eight of the sixteen brightest persistent
low mass X-ray binaries show significant, possible sinusoidal, variations with
periods of order ten years. We speculate on its possible origin and prevalence
in the population of low mass X-ray binaries and we find the presence of a
third object in the system, or long-period variability intrinsic to the donor
star, as being attractive origins for the X-ray flux modulation we detect. For
some of the objects in which we do not detect a signal, there is substantial
short-term variation which may hide modest modulation on long time-scales.
Decade time-scale modulations may thus be even more common.Comment: 8 pages, 4 figures, 2 tables. Accepted by MNRA
STROBE-X: X-Ray Timing and Spectroscopy on Dynamical Timescales from Microseconds to Years
The Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays
(STROBE-X) probes strong gravity for stellar mass to supermassive black holes
and ultradense matter with unprecedented effective area, high time-resolution,
and good spectral resolution, while providing a powerful time-domain X-ray
observatory.Comment: Accepted for Publication in Results in Physic
XMM-Newton Discovery of the X-ray Transient XMMU J181227.8-181234 in the Galactic Plane
We report the discovery of an X-ray transient, observed in outburst with
XMM-Newton on March 20, 2003, and with position 18h12m27.8s, -18 12 34 (J2000,
approximate positional error 2"). No known source is present at this position
and the source was not detected during published ROSAT or ASCA observations of
that region. However, the source may be associated with 1H1812-182 detected by
HEAO 1, although the error bars on the HEAO 1 position are very large and the
two sources could also be unrelated. Therefore, we name the source XMMU
J181227.8-181234. Initially, the source was not detected using the All-Sky
Monitor (ASM) on-board the Rossi X-ray Timing Explorer, however, reprocessing
of the ASM data shows that the source was in fact detected and it was active
for about 50 days. The X-ray spectrum of this transient is fitted equally well
by an absorbed power-law (with a spectral index of 2.5) or multi-colour disk
blackbody model (with kT ~ 2 keV), where we find that the source is highly
absorbed. We detect an unabsorbed 0.5-10 keV flux in the range (2-5)E-9 ergs
cm^{-2} s^{-1}, which at a distance of 8 kpc corresponds to a 0.5-10 keV
luminosity of (1-4)E37 ergs s^{-1}. No pulsations were detected by timing
analysis. A colour-colour diagram from ASM data of different accreting objects
suggests that the transient is a high-mass X-ray binary, as is also suggested
by the high absorption compared to the average interstellar value in the
direction of the source. However, the power-law spectral index is far more
typical of a low-mass X-ray binary. Thus, we are unable to conclusively
identify the nature of the transient. We also report on three sources first
detected by the ASCA Galactic Plane Survey that are close to this transient.Comment: 7 pages, 6 figures, 1 table, accepted for publication in MNRA
Disk, Corona, Jet Connection in the Intermediate State of MAXI J1820+070 Revealed by NICER Spectral-timing Analysis
We analyze five epochs of Neutron star Interior Composition Explorer (NICER) data of the black hole X-ray binary MAXI J1820+070 during the bright hard-to-soft state transition in its 2018 outburst with both reflection spectroscopy and Fourier-resolved timing analysis. We confirm the previous discovery of reverberation lags in the hard state, and find that the frequency range where the (soft) reverberation lag dominates decreases with the reverberation lag amplitude increasing during the transition, suggesting an increasing X-ray emitting region, possibly due to an expanding corona. By jointly fitting the lag-energy spectra in a number of broad frequency ranges with the reverberation model reltrans, we find the increase in reverberation lag is best described by an increase in the X-ray coronal height. This result, along with the finding that the corona contracts in the hard state, suggests a close relationship between spatial extent of the X-ray corona and the radio jet. We find the corona expansion (as probed by reverberation) precedes a radio flare by ~5 days, which may suggest that the hard-to-soft transition is marked by the corona expanding vertically and launching a jet knot that propagates along the jet stream at relativistic velocities
Conclusion
Par la mise en oeuvre et la confrontation de deux méthodes complémentaires : l'enquête historique dans la documentation scriptuaire et la fouille archéologique, tant par l'analyse des structures et des stratigraphies que par l'étude de l'ensemble du matériel recueilli, les recherches effectuées sur le château du Vuache attirent l'attention sur la complexité d'un édifice castrai et permettent l'évocation de l'histoire d'un des cadres essentiels de la vie rurale sous l'Ancien Régime, les seigne..
The RS Oph outburst of 2021 monitored in X-rays with NICER
The 2021 outburst of the symbiotic recurrent nova RS Oph was monitored with
the Neutron Star Interior Composition Explorer Mission (NICER) in the 0.2-12
keV range from day one after the optical maximum, until day 88, producing an
unprecedented, detailed view of the outburst development. The X-ray flux
preceding the supersoft X-ray phase peaked almost 5 days after optical maximum
and originated only in shocked ejecta for 21 to 25 days. The emission was
thermal; in the first 5 days only a non-collisional-ionization equilibrium
model fits the spectrum, and a transition to equilibrium occurred between days
6 and 12. The ratio of peak X-rays flux measured in the NICER range to that
measured with Fermi in the 60 MeV-500 GeV range was about 0.1, and the ratio to
the peak flux measured with H.E.S.S. in the 250 GeV-2.5 TeV range was about
100. The central supersoft X-ray source (SSS), namely the shell hydrogen
burning white dwarf (WD), became visible in the fourth week, initially with
short flares. A huge increase in flux occurred on day 41, but the SSS flux
remained variable. A quasi-periodic oscillation every ~35 s was always observed
during the SSS phase, with variations in amplitude and a period drift that
appeared to decrease in the end. The SSS has characteristics of a WD of mass >1
M(solar). Thermonuclear burning switched off shortly after day 75, earlier than
in 2006 outburst. We discuss implications for the nova physics.Comment: Accepted for publication in the Astrophysical Journa
STROBE-X: X-Ray Timing and Spectroscopy on Dynamical Timescales from Microseconds to Years
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