152 research outputs found
X-ray Reflection Spectroscopy of the Black Hole GX 339-4: Exploring the Hard State with Unprecedented Sensitivity
We analyze {\it simultaneously} six composite {\it RXTE} spectra of GX 339--4
in the hard state comprising 77 million counts collected over 196 ks. The
source spectra are ordered by luminosity and spanthe range 1.6\% to 17\% of the
Eddington luminosity. Crucially, using our new tool {\tt pcacorr}, we
re-calibrate the data to a precision of 0.1\%, an order of magnitude
improvement over all earlier work. Using our advanced reflection model {\tt
relxill}, we target the strong features in the component of emission reflected
from the disk, namely, the relativistically-broadened Fe K emission line, the
Fe K edge and the Compton hump. We report results for two joint fits to the six
spectra: For the first fit, we fix the spin parameter to its maximal value
() and allow the inner disk radius to vary. Results
include (i) precise measurements of , with evidence that the disk
becomes slightly truncated at a few percent of Eddington; and (ii) an
order-of-magnitude swing with luminosity in the high energy cutoff, which
reaches keV at our lowest luminosity. For the second fit, we make the
standard assumption in estimating spin that the inner edge of the accretion
disk is located at the innermost stable circular orbit () and find (90\% confidence,
statistical). For both fits, and at the same level of statistical confidence,
we estimate that the disk inclination is deg and that the Fe
abundance is super-solar, .Comment: Accepted for publication in ApJ, 20 pages, 13 figure
Simultaneous multiwavelength observations of V404 Cygni during its 2015 June outburst decay strengthen the case for an extremely energetic jet-base
We present results of multiband optical photometry of the black hole X-ray
binary system V404 Cygni obtained using Wheaton College Observatory's 0.3m
telescope, along with strictly simultaneous INTEGRAL and Swift observations
during 2015 June 25.15--26.33 UT, and 2015 June 27.10--27.34 UT. These
observations were made during the 2015 June outburst of the source when it was
going through an epoch of violent activity in all wavelengths ranging from
radio to -rays. The multiwavelength variability timescale favors a
compact emission region, most likely originating in a jet outflow, for both
observing epochs presented in this work. The simultaneous INTEGRAL/Imager on
Board the Integral Satellite (IBIS) 20--40 keV light curve obtained during the
June 27 observing run correlates very strongly with the optical light curve,
with no detectable delay between the optical bands as well as between the
optical and hard X-rays. The average slope of the dereddened spectral energy
distribution was roughly flat between the - and -bands during the June
27 run, even though the optical and X-ray flux varied by 25 during
the run, ruling out an irradiation origin for the optical and suggesting that
the optically thick to optically thin jet synchrotron break during the
observations was at a frequency larger than that of -band, which is quite
extreme for X-ray binaries. These observations suggest that the optical
emission originated very close to the base of the jet. A strong H
emission line, probably originating in a quasi-spherical nebula around the
source, also contributes significantly in the -band. Our data, in
conjunction with contemporaneous data at other wavelengths presented by other
groups, strongly suggest that the jet-base was extremely compact and energetic
during this phase of the outburst.Comment: 15 pages, 2 tables, 5 figures. Accepted for publication in Ap
Accretion Disc Evolution in GRO J1655-40 and LMC X-3 with Relativistic and Non-Relativistic Disc Models
Black hole X-ray binaries are ideal environments to study the accretion
phenomena in strong gravitational potentials. These systems undergo dramatic
accretion state transitions and analysis of the X-ray spectra is used to probe
the properties of the accretion disc and its evolution. In this work, we
present a systematic investigation of 1800 spectra obtained by RXTE PCA
observations of GRO J1655-40 and LMC X-3 to explore the nature of the accretion
disc via non-relativistic and relativistic disc models describing the thermal
emission in black-hole X-ray binaries. We demonstrate that the non-relativistic
modelling throughout an outburst with the phenomenological multi-colour disc
model DISKBB yields significantly lower and often unphysical inner disc radii
and correspondingly higher (50-60\%) disc temperatures compared to its
relativistic counterparts KYNBB and KERRBB. We obtained the dimensionless spin
parameters of and for GRO
J1655-40 with KERRBB and KYNBB, respectively. We report a spin value of
for LMC X-3 using the updated black hole mass of 6.98
. Both measurements are consistent with the previous studies.
Using our results, we highlight the importance of self-consistent modelling of
the thermal emission, especially when estimating the spin with the
continuum-fitting method which assumes the disc terminates at the innermost
stable circular orbit at all times.Comment: Accepted for publication in MNRAS, 23 pages 17 figure
Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system III. Dipping in the low/hard state
We present an analysis of three Chandra High Energy Transmission Gratings
observations of the black hole binary Cyg X-1/HDE 226868 at different orbital
phases. The stellar wind that is powering the accretion in this system is
characterized by temperature and density inhomogeneities including structures,
or "clumps", of colder, more dense material embedded in the photoionized gas.
As these clumps pass our line of sight, absorption dips appear in the light
curve. We characterize the properties of the clumps through spectral changes
during various dip stages. Comparing the silicon and sulfur absorption line
regions (1.6-2.7 keV 7.7-4.6 {\AA}) in four levels of varying column
depth reveals the presence of lower ionization stages, i.e., colder or denser
material, in the deeper dip phases. The Doppler velocities of the lines are
roughly consistent within each observation, varying with the respective orbital
phase. This is consistent with the picture of a structure that consists of
differently ionized material, in which shells of material facing the black hole
shield the inner and back shells from the ionizing radiation. The variation of
the Doppler velocities compared to a toy model of the stellar wind, however,
does not allow us to pin down an exact location of the clump region in the
system. This result, as well as the asymmetric shape of the observed lines,
point at a picture of a complex wind structure.Comment: 19 pages, 15 figures, accepted for publication in A&
Spectral and Timing Properties of IGR J17091-3624 in the Rising Hard State During its 2016 Outburst
We present a spectral and timing study of the NuSTAR and Swift observations
of the black hole candidate IGR J17091-3624 in the hard state during its
outburst in 2016. Disk reflection is detected in each of the NuSTAR spectra
taken in three epochs. Fitting with relativistic reflection models reveals that
the accretion disk is truncated during all epochs with , with the data favoring a low disk inclination of . The steepening of the continuum spectra between epochs
is accompanied by a decrease in the high energy cut-off: the electron
temperature drops from keV to keV, changing
systematically with the source flux. We detect type-C QPOs in the power spectra
with frequency varying between 0.131 Hz and 0.327 Hz. In addition, a secondary
peak is found in the power spectra centered at about 2.3 times the QPO
frequency during all three epochs. The nature of this secondary frequency is
uncertain, however a non-harmonic origin is favored. We investigate the
evolution of the timing and spectral properties during the rising phase of the
outburst and discuss their physical implications.Comment: 11 pages, 9 figures, accepted by Ap
The SMC SNR 1E0102.2-7219 as a Calibration Standard for X-ray Astronomy in the 0.3-2.5 keV Bandpass
The flight calibration of the spectral response of CCD instruments below 1.5
keV is difficult in general because of the lack of strong lines in the on-board
calibration sources typically available. We have been using 1E 0102.2-7219, the
brightest supernova remnant in the Small Magellanic Cloud, to evaluate the
response models of the ACIS CCDs on the Chandra X-ray Observatory (CXO), the
EPIC CCDs on the XMM-Newton Observatory, the XIS CCDs on the Suzaku
Observatory, and the XRT CCD on the Swift Observatory. E0102 has strong lines
of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate the
spectrum. The spectrum of E0102 has been well characterized using
high-resolution grating instruments, namely the XMM-Newton RGS and the CXO
HETG, through which a consistent spectral model has been developed that can
then be used to fit the lower-resolution CCD spectra. We have also used the
measured intensities of the lines to investigate the consistency of the
effective area models for the various instruments around the bright O (~570 eV
and 654 eV) and Ne (~910 eV and 1022 eV) lines. We find that the measured
fluxes of the O VII triplet, the O VIII Ly-alpha line, the Ne IX triplet, and
the Ne X Ly-alpha line generally agree to within +/-10 % for all instruments,
with 28 of our 32 fitted normalizations within +/-10% of the RGS-determined
value. The maximum discrepancies, computed as the percentage difference between
the lowest and highest normalization for any instrument pair, are 23% for the O
VII triplet, 24% for the O VIII Ly-alpha line, 13% for the Ne IX triplet, and
19% for the Ne X Ly-alpha line. If only the CXO and XMM are compared, the
maximum discrepancies are 22% for the O VII triplet, 16% for the O VIII
Ly-alpha line, 4% for the Ne IX triplet, and 12% for the Ne X Ly-alpha line.Comment: 16 pages, 11 figures, to be published in Proceedings of the SPIE
7011: Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray 200
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