13,623 research outputs found
Exploring Accretion and Disk-Jet Connections in the LLAGN M81*
We report on a year-long effort to monitor the central supermassive black
hole in M81 in the X-ray and radio bands. Using Chandra and the VLA, we
obtained quasi-simultaneous observations of M81* on seven occasions during
2006. The X-ray and radio luminosity of M81* are not strongly correlated on the
approximately 20-day sampling timescale of our observations, which is
commensurate with viscous timescales in the inner flow and orbital timecales in
a radially-truncated disk. This suggests that short-term variations in black
hole activity may not be rigidly governed by the "fundamental plane", but
rather adhere to the plane in a time-averaged sense. Fits to the X-ray spectra
of M81* with bremsstrahlung models give temperatures that are inconsistent with
the outer regions of very simple advection-dominated inflows. However, our
results are consistent with the X-ray emission originating in a transition
region where a truncated disk and advective flow may overlap. We discuss our
results in the context of models for black holes accreting at small fractions
of their Eddington limit, and the fundamental plane of black hole accretion.Comment: Accepted for publication in Ap
The under-explored radio-loudness of quasars and the possibility of radio-source--environment interactions
I demonstrate that radio observations in the literature to date of
optically-selected quasars are largely inadequate to reveal the full extent of
their jet-activity. I discuss a recent example of an optically-powerful quasar,
which is radio-quiet according to all the standard classifications, which
Blundell & Rawlings discovered to have a >100 kpc jet, and show that other than
being the first FRI quasar to be identified, there is no reason to presume it
is exceptional. I also discuss a possible new probe of accounting for the
interactions of radio sources with their environments. This tool could help to
avoid over-estimating magnetic fields strengths within cluster gas. I briefly
describe recent analyses by Rudnick & Blundell which confront claims in the
literature of cluster gas B-fields > 10 micro-G.Comment: invited talk at "The Physics of Relativistic Jets in the CHANDRA and
XMM Era", proceedings edited by G. Brunetti, D.E. Harris, R.M. Sambruna, and
G. Setti, to be published in New Astronomy Review
The low-temperature energy calibration system for the CUORE bolometer array
The CUORE experiment will search for neutrinoless double beta decay (0nDBD)
of 130Te using an array of 988 TeO_2 bolometers operated at 10 mK in the
Laboratori Nazionali del Gran Sasso (Italy). The detector is housed in a large
cryogen-free cryostat cooled by pulse tubes and a high-power dilution
refrigerator. The TeO_2 bolometers measure the event energies, and a precise
and reliable energy calibration is critical for the successful identification
of candidate 0nDBD and background events. The detector calibration system under
development is based on the insertion of 12 gamma-sources that are able to move
under their own weight through a set of guide tubes that route them from
deployment boxes on the 300K flange down into position in the detector region
inside the cryostat. The CUORE experiment poses stringent requirements on the
maximum heat load on the cryostat, material radiopurity, contamination risk and
the ability to fully retract the sources during normal data taking. Together
with the integration into a unique cryostat, this requires careful design and
unconventional solutions. We present the design, challenges, and expected
performance of this low-temperature energy calibration system.Comment: To be published in the proceedings of the 13th International Workshop
on Low Temperature Detectors (LTD), Stanford, CA, July 20-24, 200
Warm Absorbers and Outflows in the Seyfert-1 Galaxy NGC 4051
We present both phenomenological and more physical photoionization models of
the Chandra HETG spectra of the Seyfert-1 AGN NGC 4051. We detect 40 absorption
and emission lines, encompassing highly ionized charge states from O, Ne, Mg,
Si, S and the Fe L-shell and K-shell. Two independent photoionization packages,
XSTAR and Cloudy, were both used to self-consistently model the continuum and
line spectra. These fits detected three absorbing regions in this system with
densities ranging from 10^{10} to 10^{11} cm^{-3}. In particular, our XSTAR
models require three components that have ionization parameters of log \xi =
4.5, 3.3, & 1.0, and are located within the BLR at 70, 300, and 13,000 R_g,
respectively, assuming a constant wind density. Larger radii are inferred for
density profiles which decline with radius. The Cloudy models give a similar
set of parameters with ionization parameters of log \xi = 5.0, 3.6, & 2.2
located at 40, 200, and 3,300 R_g. We demonstrate that these regions are
out-flowing from the system, and carry a small fraction of material out of the
system relative to the implied mass accretion rate. The data suggest that
magnetic fields may be an important driving mechanism.Comment: 21 pages, 11 Figures, Accepted to Ap
The Relativistic Fe Emission Line in XTE J1650-500 with BeppoSAX: Evidence for Black Hole Spin and Light Bending Effects?
We report spectral results from three BeppoSAX observations of the black hole
candidate XTE J1650-500 during its 2001/2002 outburst. We find strong evidence
for the presence of a broad and strongly relativistic Fe emission line. The
line profile indicates an accretion disc extending down to two gravitational
radii (or less) suggesting the presence of a rapidly rotating central Kerr
black hole. Thanks to the broadband spectral coverage of BeppoSAX, we could
analyze the 1.5-200 keV spectra of the three observations and report the
presence of a strong reflection component from the accretion disc, which is
totally consistent with the observed broad Fe emission line. The shape of the
reflection component appears to be affected by the same special and general
relativistic effects that produce the broad Fe line. We study the variation of
the different spectral components from the first to the third observation and
we find that they are well reproduced by a recently proposed light bending
model.Comment: Minor changes in text and in Figures/Tables. Section 3.1.2 added.
Accepted by MNRA
A systematic look at the Very High and Low/Hard state of GX 339-4: Constraining the black hole spin with a new reflection model
We present a systematic study of GX 339-4 in both its very high and low hard
states from simultaneous observations made with XMM-Newton and RXTE in 2002 and
2004. The X-ray spectra of both these extreme states exhibit strong reflection
signatures, with a broad, skewed Fe-Kalpha line clearly visible above the
continuum. Using a newly developed, self-consistent reflection model which
implicitly includes the blackbody radiation of the disc as well as the effect
of Comptonisation, blurred with a relativistic line function, we were able to
infer the spin parameter of GX 339-4 to be 0.935 +/- 0.01 (statistical) +/-
0.01 (systematic) at 90 per cent confidence. We find that both states are
consistent with an ionised thin accretion disc extending to the innermost
stable circular orbit around the rapidly spinning black hole.Comment: 10 pages, 10 figures, accepted for publication in MNRAS 17/04/0
Discussing Sudden Unexpected Death in Epilepsy (SUDEP) with Patients: Practices of Health-Care Providers
COMPTEL gamma-ray observations of the C4 solar flare on 20 January 2000
The âPre-SMMâ (Vestrand and Miller 1998) picture of gamma-ray line (GRL) flares was that they are relatively rare events. This picture was quickly put in question with the launch of the Solar Maximum Mission (SMM). Over 100 GRL flares were seen with sizes ranging from very large GOES class events (X12) down to moderately small events (M2). It was argued by some (Bai 1986) that this was still consistent with the idea that GRL events are rare. Others, however, argued the opposite (Vestrand 1988; Cliver, Crosby and Dennis 1994), stating that the lower end of this distribution was just a function of SMMâs sensitivity. They stated that the launch of the Compton Gamma-ray Observatory (CGRO) would in fact continue this distribution to show even smaller GRL flares. In response to a BACODINE cosmic gamma-ray burst alert, COMPtonTELescope on the CGRO recorded gamma rays above 1 MeV from the C4 flare at 0221 UT 20 January 2000. This event, though at the limits of COMPTELâs sensitivity, clearly shows a nuclear line excess above the continuum. Using new spectroscopy techniques we were able to resolve individual lines. This has allowed us to make a basic comparison of this event with the GRL flare distribution from SMM and also compare this flare with a well-observed large GRL flare seen by OSSE
Conserved Charges in the Principal Chiral Model on a Supergroup
The classical principal chiral model in 1+1 dimensions with target space a
compact Lie supergroup is investigated. It is shown how to construct a local
conserved charge given an invariant tensor of the Lie superalgebra. We
calculate the super-Poisson brackets of these currents and argue that they are
finitely generated. We show how to derive an infinite number of local charges
in involution. We demonstrate that these charges Poisson commute with the
non-local charges of the model
MeV measurements of Îł-ray bursts by CGRO-COMPTEL: Revised catalog
The imaging COMPTEL telescope has accumulated 0.1â30 MeV spectra, time-histories, and positions of more than forty Îł-ray bursts within its âŒ3 sr field of view in the eight years since its launch. CGRO-COMPTEL measures in both imaging âtelescopeâ and single detector âburst spectroscopyâ mode. In an ongoing collaboration with BACODINE/GCN, bursts are imaged automatically, with localizations relayed to a global network of multiwavelength observers in near real time (âŒ10 minutes). We have updated our burst search procedure in two ways: 1) using more sensitive search algorithms; and 2) using data from more detectors. The first are double change-point algorithms. With these we can find regions of significant excess flux with no assumptions on the wide range of burst time-scales (e.g., rise-times or decay-times) or intensities, and only one adjustable parameter (the time-averaged count-rate of the detectors). This makes it simpler to combine information on burst time-histories from the larger effective area (but cruder time bins) burst spectroscopy detectors, and hence better pinpoint the best times for imaging each burst. We report the eight bursts detected during 1998â1999
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