194 research outputs found
Characterizing a new class of variability in GRS 1915+105 with simultaneous INTEGRAL/RXTE observations
We report on the analysis of 100 ks INTEGRAL observations of the Galactic
microquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when the
source was found to exhibit a new type of variability as preliminarily reported
in Hannikainen et al. (2003). The variability pattern, which we name , is
characterized by a pulsing behaviour, consisting of a main pulse and a shorter,
softer, and smaller amplitude precursor pulse, on a timescale of 5 minutes in
the JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From a
study of the individual RXTE/PCA pulse profiles we find that the rising phase
is shorter and harder than the declining phase, which is opposite to what has
been observed in other otherwise similar variability classes in this source.
The position in the colour-colour diagram throughout the revolution corresponds
to State A (Belloni et al. 2000) but not to any previously known variability
class. We separated the INTEGRAL data into two subsets covering the maxima and
minima of the pulses and fitted the resulting two broadband spectra with a
hybrid thermal--non-thermal Comptonization model. The fits show the source to
be in a soft state characterized by a strong disc component below ~6 keV and
Comptonization by both thermal and non-thermal electrons at higher energies.Comment: Accepted for publication in A&A. 11 pages, 10 figures, 4 in colour.
Original figures can be found at
http://www.astro.helsinki.fi/~diana/grs1915_rev48. Author affiliations
correcte
A Systematic Study on Energy Dependence of Quasi-Periodic Oscillation Frequency in GRS 1915+105
Systematically studying all the RXTE/PCA observations for GRS 1915+105 before
November 2010, we have discovered three additional patterns in the relation
between Quasi-Periodic Oscillation (QPO) frequency and photon energy, extending
earlier outcomes reported by Qu et al. (2010). We have confirmed that as QPO
frequency increases, the relation evolves from the negative correlation to
positive one. The newly discovered patterns provide new constraints on the QPO
models
Diminished Expression of Corticotropin-Releasing Hormone Receptor 2 in Human Colon Cancer Promotes Tumor Growth and Epithelial-to-Mesenchymal Transition via Persistent Interleukin-6/Stat3 Signaling
Cellular mechanisms in basic and clinical gastroenterology and hepatolog
Study of the Largest Multiwavelength Campaign of the Microquasar GRS 1915+105
We present the results from a multiwavelength campaign of GRS 1915+105
performed from 2000 April 16 to 25. This is one of the largest coordinated set
of observations ever performed for this source, covering the wide energy band
in radio (13.3-0.3 cm), near-infrared (J-H-K), X-rays and Gamma-rays (from 1
keV to 10 MeV). During the campaign GRS 1915+105 was predominantly in the
"plateau" (or low/hard) state but sometimes showed soft X-ray oscillations:
before April 20.3, rapid, quasi-periodic (~= 45 min) flare-dip cycles were
observed. The radio flares observed on April 17 shows frequency- dependent peak
delay, consistent with an expansion of synchrotron-emitting region starting at
the transition from the hard-dip to the soft-flare states in X-rays. On the
other hand, infrared flares on April 20 appear to follow (or precede) the
beginning of X-ray oscillations with an inconstant time delay of ~= 5-30 min.
This implies that the infrared emitting region is located far from the black
hole by >~ 10E13 cm, while its size is <~ 10E12 cm constrained from the time
variability. We find a good correlation between the quasi-steady flux level in
the near-infrared band and in the X-ray band. From this we estimate that the
reprocessing of X-rays, probably occurring in the outer parts of the accretion
disk, accounts for about 20-30% of the observed K magnitude in the plateau
state. The OSSE spectrum in the 0.05-10 MeV band is represented by a single
power law with a photon index of 3.1 extending to ~1 MeV with no cutoff. The
power-law slope above ~30 keV is found to be very similar between different
states in spite of large flux variations in soft X-rays, implying that the
electron energy distribution is not affected by the change of the state in the
accretion disk.Comment: 31 pages, 11 figures. Accepted for publication in ApJ, vol. 571,
2002. Minor corrections. Figure 2 is revised (numbers on the top axis are
corrected). References are update
XTE J1739-302 as a Supergiant Fast X-ray Transient
XTE J1739-302 is a transient X-ray source with unusually short outbursts,
lasting on the order of hours. Here we give a summary of X-ray observations we
have made of this object in outburst with the Rossi X-ray Timing Explorer
(RXTE) and at a low level of activity with the Chandra X-ray Observatory, as
well as observations made by other groups. Visible and infrared spectroscopy of
the mass donor of XTE J1739-302 are presented in a companion paper. The X-ray
spectrum is hard both at low levels and in outburst, but somewhat variable, and
there is strong variability in the absorption column from one outburst to
another. Although no pulsation has been observed, the outburst data from
multiple observatories show a characteristic timescale for variability on the
order of 1500-2000 s. The Chandra localization (right ascension 17h 39m 11.58s,
declination -30o 20' 37.6'', J2000) shows that despite being located less than
2 degrees from the Galactic Center and highly absorbed, XTE J1739-302 is
actually a foreground object with a bright optical counterpart. The combination
of a very short outburst timescale and a supergiant companion is shared with
several other recently-discovered systems, forming a class we designate as
Supergiant Fast X-ray Transients (SFXTs). Three persistently bright X-ray
binaries with similar supergiant companions have also produced extremely short,
bright outbursts: Cyg X-1, Vela X-1, and 1E 1145.1-6141.Comment: 16 pages, 7 figures, 2 tables, in press in The Astrophysical Journal;
see also the companion paper by Negueruela et a
GRS 1915+105: The first three months with INTEGRAL
GRS 1915+105 is being observed as part of an Open Time monitoring program
with INTEGRAL. Three out of six observations from the monitoring program are
presented here, in addition to data obtained through an exchange with other
observers. We also present simultaneous RXTE observations of GRS 1915+105.
During INTEGRAL Revolution 48 (2003 March 6) the source was observed to be in a
highly variable state, characterized by 5-minute quasi-periodic oscillations.
During these oscillations, the rise is faster than the decline, and is harder.
This particular type of variability has never been observed before. During
subsequent INTEGRAL revolutions (2003 March-May), the source was in a steady or
''plateau'' state (also known as class according to Belloni et al.
2000). Here we discuss both the temporal and spectral characteristics of the
source during the first three months of observations. The source was clearly
detected with all three gamma-ray and X-ray instruments onboard INTEGRAL.Comment: 7 pages, 12 figures. Proceedings of the 5th INTEGRAL Workshop, Munich
16-20 February 2004. ESA SP-552. High resolution version of Fig. 6 can be
obtained from http://www.astro.helsinki.fi/~diana/Figure6.p
The 2005 outburst of the halo black hole X-ray transient XTE J1118+480
We present optical and infrared monitoring of the 2005 outburst of the halo black hole X-ray transient XTE J1118+480. We measured a total outburst amplitude of ~5.7 ± 0.1 mag in the R band and ~5 mag in the infrared J, H, and Ks bands. The hardness ratio HR2 (5-12 keV : 3-5 keV) from the RXTE ASM data is 1.53 ± 0.02 at the peak of the outburst, indicating a hard spectrum. Both the shape of the light curve and the ratio LX(1-10 keV)/Lopt resemble the minioutbursts observed in GRO J0422+32 and XTE J1859+226. During early decline, we find a 0.02 mag amplitude variation consistent with a superhump modulation, like the one observed during the 2000 outburst. Similarly, XTE J1118+480 displayed a double-humped ellipsoidal modulation distorted by a superhump wave when settled into a near-quiescence level, suggesting that the disk expanded to the 3 : 1 resonance radius after outburst, where it remained until early quiescence. The system reached quiescence at R = 19.02 ± 0.03, about 3 months after the onset of the outburst. The optical rise preceded the X-ray rise by at most 4 days. The spectral energy distributions (SEDs) at the different epochs during outburst are all quasi-power laws with FΜ Μα increasing toward the blue. At the peak of the outburst, we derived α = 0.49 ± 0.04 for the optical data alone and α = 0.1 ± 0.1 when fitting solely the infrared. This difference between the optical and the infrared SEDs suggests that the infrared is dominated by a different component (a jet?), whereas the optical is presumably showing the disk evolution
A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni
Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (>10 kiloÂâelectron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems.
This article has a correction. Please see: http://science.sciencemag.org/content/360/6386/eaat927
Furiously fast and red: sub-second optical flaring in V404 Cyg during the 2015 outburst peak
We present observations of rapid (sub-second) optical flux variability in V404 Cyg during its 2015 June outburst. Simultaneous three-band observations with the ULTRACAM fast imager on four nights show steep power spectra dominated by slow variations on âŒ100â1000 s time-scales. Near the peak of the outburst on June 26, a dramatic change occurs and additional, persistent sub-second optical flaring appears close in time to giant radio and X-ray flaring. The flares reach peak optical luminosities of ⌠few Ă 1036 erg sâ1. Some are unresolved down to a time resolution of 24 ms. Whereas the fast flares are stronger in the red, the slow variations are bluer when brighter. The redder slopes, emitted power and characteristic time-scales of the fast flares can be explained as optically thin synchrotron emission from a compact jet arising on size scales âŒ140â500 Gravitational radii (with a possible additional contribution by a thermal particle distribution). The origin of the slower variations is unclear. The optical continuum spectral slopes are strongly affected by dereddening uncertainties and contamination by strong Hα emission, but the variations of these slopes follow relatively stable loci as a function of flux. Cross-correlating the slow variations between the different bands shows asymmetries on all nights consistent with a small red skew (i.e. red lag). X-ray reprocessing and non-thermal emission could both contribute to these. These data reveal a complex mix of components over five decades in time-scale during the outburst
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