1,408 research outputs found
Spectral Analysis of GRBs Measured by RHESSI
The Ge spectrometer of the RHESSI satellite is sensitive to Gamma Ray Bursts
(GRBs) from about 40 keV up to 17 MeV, thus ideally complementing the Swift/BAT
instrument whose sensitivity decreases above 150 keV. We present preliminary
results of spectral fits of RHESSI GRB data. After describing our method, the
RHESSI results are discussed and compared with Swift and Konus.Comment: 4 pages, 4 figures, conference proceedings, 'Swift and GRBs:
Unveiling the Relativistic Universe', San Servolo, Venice, 5-9 June 2006, to
appear in Il Nouvo Ciment
A Note on Frame Dragging
The measurement of spin effects in general relativity has recently taken
centre stage with the successfully launched Gravity Probe B experiment coming
toward an end, coupled with recently reported measurements using laser ranging.
Many accounts of these experiments have been in terms of frame-dragging. We
point out that this terminology has given rise to much confusion and that a
better description is in terms of spin-orbit and spin-spin effects. In
particular, we point out that the de Sitter precession (which has been mesured
to a high accuracy) is also a frame-dragging effect and provides an accurate
benchmark measurement of spin-orbit effects which GPB needs to emulate
Dark matter line emission constraints from NuSTAR observations of the Bullet Cluster
Line emission from dark matter is well motivated for some candidates e.g.
sterile neutrinos. We present the first search for dark matter line emission in
the 3-80keV range in a pointed observation of the Bullet Cluster with NuSTAR.
We do not detect any significant line emission and instead we derive upper
limits (95% CL) on the flux, and interpret these constraints in the context of
sterile neutrinos and more generic dark matter candidates. NuSTAR does not have
the sensitivity to constrain the recently claimed line detection at 3.5keV, but
improves on the constraints for energies of 10-25keV.Comment: 7 pages, 5 figures, submitted to Ap
A Soft X-Ray Spectral Episode for the Clocked Burster, GS 1826-24 as Measured by Swift and NuSTAR
We report on NuSTAR and Swift observations of a soft state of the neutron
star low-mass X-ray binary GS 1826-24, commonly known as the "clocked" burster.
The transition to the soft state was recorded in 2014 June through an increase
of the 2-20 keV source intensity measured by MAXI, simultaneous with a decrease
of the 15-50 keV intensity measured by Swift/BAT. The episode lasted
approximately two months, after which the source returned to its usual hard
state. We analyze the broad-band spectrum measured by Swift/XRT and NuSTAR, and
estimate the accretion rate during the soft episode to be about 13% of
Eddington, within the range of previous observations. However, the best fit
spectral model, adopting the double Comptonization used previously, exhibits
significantly softer components. We detect seven type-I X-ray bursts, all
significantly weaker (and with shorter rise and decay times) than observed
previously. The burst profiles and recurrence times vary significantly, ruling
out the regular bursts that are typical for this source. One burst exhibited
photospheric radius expansion, and we estimate the source distance at about
(5.7 / xi_b^1/2) kpc, where xi_b parameterizes the possible anisotropy of the
burst emission. Interpreting the soft state as a transition from an optically
thin inner flow to an optically thick flow passing through a boundary layer, as
is commonly observed in similar systems, is contradicted by the lower optical
depth measured for the double Comptonization model we find for this soft state.
The effect of a change in disk geometry on the burst behavior remains unclear.Comment: 40 pages (single-column, doubled spaced format), 9 figures, 3 tables;
submitted to Ap
Wind-tunnel study of Four Allen Center, Houston
May 1982.For Century Development Corporation.CER81-82JAP-JEC-BB-DWB66.Includes bibliographical references (pages 36-37).CSU Projects 2-27840 and 2-27940
New Constraints on the Black Hole Low/Hard State Inner Accretion Flow with NuSTAR
We report on an observation of the Galactic black hole candidate GRS 1739-278
during its 2014 outburst, obtained with NuSTAR. The source was captured at the
peak of a rising "low/hard" state, at a flux of ~0.3 Crab. A broad, skewed iron
line and disk reflection spectrum are revealed. Fits to the sensitive NuSTAR
spectra with a number of relativistically blurred disk reflection models yield
strong geometrical constraints on the disk and hard X-ray "corona". Two models
that explicitly assume a "lamppost" corona find its base to have a vertical
height above the black hole of h = 5 (+7, -2) GM/c^2 and h = 18 +/-4 GM/c^2
(90% confidence errors); models that do not assume a "lamppost" return
emissivity profiles that are broadly consistent with coronae of this size.
Given that X-ray microlensing studies of quasars and reverberation lags in
Seyferts find similarly compact coronae, observations may now signal that
compact coronae are fundamental across the black hole mass scale. All of the
models fit to GRS 1739-278 find that the accretion disk extends very close to
the black hole - the least stringent constraint is r = 5 (+3,-4) GM/c^2. Only
two of the models deliver meaningful spin constraints, but a = 0.8 +/-0.2 is
consistent with all of the fits. Overall, the data provide especially
compelling evidence of an association between compact hard X-ray coronae and
the base of relativistic radio jets in black holes.Comment: Accepted for publication in ApJ Letter
NuSTAR Observations of the Black Hole GS 1354-645: Evidence of Rapid Black Hole Spin
We present the results of a NuSTAR study of the dynamically confirmed
stellar-mass black hole GS 1354-645. The source was observed during its 2015
"hard" state outburst; we concentrate on spectra from two relatively bright
phases. In the higher-flux observation, the broadband NuSTAR spectra reveal a
clear, strong disk reflection spectrum, blurred by a degree that requires a
black hole spin of a = cJ/GM^2 > 0.98 (1 sigma statistical limits only). The
fits also require a high inclination: theta = 75(2) degrees. Strong "dips" are
sometimes observed in the X-ray light curves of sources viewed at such an
angle; these are absent, perhaps indicating that dips correspond to flared disk
structures that only manifest at higher accretion rates. In the lower-flux
observation, there is evidence of radial truncation of the thin accretion disk.
We discuss these results in the context of spin in stellar-mass black holes,
and inner accretion flow geometries at moderate accretion rates.Comment: Accepted for publication in ApJ Letter
South Dakota Retained Ownership Demonstration
Three hundred forty-five steer calves representing 53 cow-calf producers were consigned to a custom feedlot in late October. Cattle were fed in one of two pens. One pen of calves received a moderate roughage growing diet for 39 days and then were switched to a high energy finishing diet (ACC). The other pen of calves received a moderate roughage growing diet for 109 days and then were switched to a high energy finishing diet (TWO). The ACC calves weighed 574 lb initially, gained 2.94 Ib per head daily and were slaughtered at 1147 Ib after an average of 196 days on feed. Average cost of gain and profitability were 38.75 per head, respectively. The TWO calves weighed 504 Ib initially, gained 2.77 Ib per head daily and were slaughtered at 1096 Ib after an average of 214 days on feed. Average cost of gain and profitability were 16.69 per head, respectively. Cattle slaughtered later in the spring were less profitable than cattle slaughtered earlier in the spring due to a weaker cattle market and wider choice-select price spread. Across either feeding program, average profits for cattle slaughtered after 170, 192, 199, 200 and 242 days on feed were 64.42, 27.39 and -$16.78 per head, respectively
NuSTAR Reveals the Comptonizing Corona of the Broad-Line Radio Galaxy 3C 382
Broad-line radio galaxies (BLRGs) are active galactic nuclei that produce
powerful, large-scale radio jets, but appear as Seyfert 1 galaxies in their
optical spectra. In the X-ray band, BLRGs also appear like Seyfert galaxies,
but with flatter spectra and weaker reflection features. One explanation for
these properties is that the X-ray continuum is diluted by emission from the
jet. Here, we present two NuSTAR observations of the BLRG 3C 382 that show
clear evidence that the continuum of this source is dominated by thermal
Comptonization, as in Seyfert 1 galaxies. The two observations were separated
by over a year and found 3C 382 in different states separated by a factor of
1.7 in flux. The lower flux spectrum has a photon-index of
, while the photon-index of the higher flux
spectrum is . Thermal and anisotropic
Comptonization models provide an excellent fit to both spectra and show that
the coronal plasma cooled from keV in the low flux data to
keV in the high flux observation. This cooling behavior is
typical of Comptonizing corona in Seyfert galaxies and is distinct from the
variations observed in jet-dominated sources. In the high flux observation,
simultaneous Swift data are leveraged to obtain a broadband spectral energy
distribution and indicates that the corona intercepts % of the optical
and ultraviolet emitting accretion disk. 3C 382 exhibits very weak reflection
features, with no detectable relativistic Fe K line, that may be best
explained by an outflowing corona combined with an ionized inner accretion
disk.Comment: 8 pages, 8 figures, accepted by Ap
IC 751: a new changing-look AGN discovered by NuSTAR
We present the results of five NuSTAR observations of the type 2 active
galactic nucleus (AGN) in IC 751, three of which were performed simultaneously
with XMM-Newton or Swift/XRT. We find that the nuclear X-ray source underwent a
clear transition from a Compton-thick () to a Compton-thin () state on timescales of months, which makes
IC 751 the first changing-look AGN discovered by NuSTAR. Changes of the
line-of-sight column density at a level are also found on a
time-scale of hours ().
From the lack of spectral variability on timescales of ks we infer
that the varying absorber is located beyond the emission-weighted average
radius of the broad-line region, and could therefore be related either to the
external part of the broad-line region or a clumpy molecular torus. By adopting
a physical torus X-ray spectral model, we are able to disentangle the column
density of the non-varying absorber () from that of the varying clouds
[], and to constrain that of
the material responsible for the reprocessed X-ray radiation (). We find evidence of significant intrinsic X-ray
variability, with the flux varying by a factor of five on timescales of a few
months in the 2-10 and 10-50 keV band.Comment: Accepted for publication in ApJ, 11 pages, 6 figure
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