3,722 research outputs found
Distorted cyclotron line profile in Cep X-4 as observed by NuSTAR
We present spectral analysis of NuSTAR and Swift observations of Cep X-4
during its outburst in 2014. We observed the source once during the peak of the
outburst and once during the decay, finding good agreement in the spectral
shape between the observations. We describe the continuum using a powerlaw with
a Fermi-Dirac cutoff at high energies. Cep X-4 has a very strong cyclotron
resonant scattering feature (CRSF) around 30 keV. A simple absorption-like line
with a Gaussian optical depth or a pseudo-Lorentzian profile both fail to
describe the shape of the CRSF accurately, leaving significant deviations at
the red side of the line. We characterize this asymmetry with a second
absorption feature around 19 keV. The line energy of the CRSF, which is not
influenced by the addition of this feature, shows a small but significant
positive luminosity dependence. With luminosities between (1-6)e36 erg/s, Cep
X-4 is below the theoretical limit where such a correlation is expected. This
behavior is similar to Vela X-1 and we discuss parallels between the two
systems.Comment: 6 pages, 4 figure, accepted for publication in ApJ letter
Electrically-Responsive Reversible Polyketone/MWCNT Network through Diels-Alder Chemistry
This study examines the preparation of electrically conductive polymer networks based on furan-functionalised polyketone (PK-Fu) doped with multi-walled carbon nanotubes (MWCNTs) and reversibly crosslinked with bis-maleimide (B-Ma) via Diels-Alder (DA) cycloaddition. Notably, the incorporation of 5 wt.% of MWCNTs results in an increased modulus of the material, and makes it thermally and electrically conductive. Analysis by X-ray photoelectron spectroscopy indicates that MWCNTs, due to their diene/dienophile character, covalently interact with the matrix via DA reaction, leading to effective interfacial adhesion between the components. Raman spectroscopy points to a more effective graphitic ordering of MWCNTs after reaction with PK-Fu and B-Ma. After crosslinking the obtained composite via the DA reaction, the softening point (tan(delta) in dynamic mechanical analysis measurements) increases up to 155 degrees C, as compared to the value of 130 degrees C for the PK-Fu crosslinked with B-Ma and that of 140 degrees C for the PK-Fu/B-Ma/MWCNT nanocomposite before resistive heating (responsible for crosslinking). After grinding the composite, compression moulding (150 degrees C/40 bar) activates the retro-DA process that disrupts the network, allowing it to be reshaped as a thermoplastic. A subsequent process of annealing via resistive heating demonstrates the possibility of reconnecting the decoupled DA linkages, thus providing the PK networks with the same thermal, mechanical, and electrical properties as the crosslinked pristine systems
Current status of the CLIO project
CLIO (Cryogenic Laser Interferometer Observatory) is a Japanese gravitational
wave detector project. One of the main purposes of CLIO is to demonstrate
thermal-noise suppression by cooling mirrors for a future Japanese project,
LCGT (Large-scale Cryogenic Gravitational Telescope). The CLIO site is in
Kamioka mine, as is LCGT. The progress of CLIO between 2005 and 2007 (room- and
cryogenic-temperature experiments) is introduced in this article. In a
room-temperature experiment, we made efforts to improve the sensitivity. The
current best sensitivity at 300 K is about
around 400 Hz. Below 20 Hz, the strain (not displacement) sensitivity is
comparable to that of LIGO, although the baselines of CLIO are 40-times shorter
(CLIO: 100m, LIGO: 4km). This is because seismic noise is extremely small in
Kamioka mine. We operated the interferometer at room temperature for
gravitational wave observations. We obtained 86 hours of data. In the cryogenic
experiment, it was confirmed that the mirrors were sufficiently cooled (14 K).
However, we found that the radiation shield ducts transferred 300K radiation
into the cryostat more effectively than we had expected. We observed that noise
caused by pure aluminum wires to suspend a mirror was suppressed by cooling the
mirror.Comment: 8 pages, 9 figures. Amaldi7 proceedings, J. Phys.: Conf. Ser.
(accepted
Asymptotic Behavior of Ext functors for modules of finite complete intersection dimension
Let be a local ring, and let and be finitely generated
-modules such that has finite complete intersection dimension. In this
paper we define and study, under certain conditions, a pairing using the
modules \Ext_R^i(M,N) which generalizes Buchweitz's notion of the Herbrand
diference. We exploit this pairing to examine the number of consecutive
vanishing of \Ext_R^i(M,N) needed to ensure that \Ext_R^i(M,N)=0 for all
. Our results recover and improve on most of the known bounds in the
literature, especially when has dimension at most two
Reverberation Mapping of the Seyfert 1 Galaxy NGC 7469
A large reverberation mapping study of the Seyfert 1 galaxy NGC 7469 has
yielded emission-line lags for Hbeta 4861 and He II 4686 and a central black
hole mass measurement of about 10 million solar masses, consistent with
previous measurements. A very low level of variability during the monitoring
campaign precluded meeting our original goal of recovering velocity-delay maps
from the data, but with the new Hbeta measurement, NGC 7469 is no longer an
outlier in the relationship between the size of the Hbeta-emitting broad-line
region and the AGN luminosity. It was necessary to detrend the continuum and
Hbeta and He II 4686 line light curves and those from archival UV data for
different time-series analysis methods to yield consistent results.Comment: 9 Pages, 7 figures, 6 tables. Accepted for publication in The
Astrophysical Journa
Modeling the high-energy emission in GRB 110721A and implications on the early multiwavelength and polarimetric observations
GRB 110721A was detected by the Gamma-ray Burst Monitor and the Large Area
Telescope (LAT) onboard the Fermi satellite and the Gamma-ray Burst Polarimeter
onboard the IKAROS solar mission. Previous analysis done of this burst showed:
i) a linear polarization signal with position angle stable () and high degree of , ii) an extreme peak
energy of a record-breaking at 152 MeV, and iii) a subdominant prompt
thermal component observed right after the onset of this burst. In this paper,
the LAT data around the reported position of GRB 110721A are analysed with the
most recent software and then, the LAT light curve above 100 MeV was obtained.
The LAT light curve is modelled in terms of adiabatic early-afterglow external
shocks when the outflow propagates into a stellar wind. Additionally, we
discuss the possible origins and also study the implications of the
early-afterglow external shocks on the extreme peak energy observed at 152
MeV, the polarization observations and the subdominant prompt thermal
component.Comment: 9 pages and one figure. Accepted for publication in Ap
Millimeter multiplicity in DR21(OH): outflows, molecular cores and envelopes
We present sensitive high angular resolution ( 1) millimeter
continuum and line observations from the massive star forming region DR21(OH)
located in the Cygnus X molecular cloud. Within the well-known dusty MM1-2
molecular cores, we report the detection of a new cluster of about ten compact
continuum millimeter sources with masses between 5 and 24 M, and sizes
of a few thousands of astronomical units. These objects are likely to be large
dusty envelopes surrounding massive protostars, some of them most probably
driving several of the outflows that emanate from this region. Additionally, we
report the detection of strong millimeter emission of formaldehyde (HCO)
and methanol (CHOH) near 218 GHz as well as compact emission from the
typical outflow tracers carbon monoxide and silicon monoxide (CO and SiO)
toward this massive star-forming region. The HCO and CHOH emission is
luminous ( 10 L), well resolved, and found along the
collimated methanol maser outflow first identified at centimeter wavelengths
and in the sources SMA6 and SMA7. Our observations suggest that this maser
outflow might be energized by a millimeter source called SMA4 located in the
MM2 dusty core. The CO and SiO emission traces some other collimated outflows
that emanate from MM1-2 cores, and are not related with the low velocity maser
outflow.Comment: Accepted to Ap
Reverberation Mapping Results for Five Seyfert 1 Galaxies
We present the results from a detailed analysis of photometric and
spectrophotometric data on five Seyfert 1 galaxies observed as a part of a
recent reverberation mapping program. The data were collected at several
observatories over a 140-day span beginning in 2010 August and ending in 2011
January. We obtained high sampling-rate light curves for Mrk 335, Mrk 1501,
3C120, Mrk 6, and PG2130+099, from which we have measured the time lag between
variations in the 5100 Angstrom continuum and the H-beta broad emission line.
We then used these measurements to calculate the mass of the supermassive black
hole at the center of each of these galaxies. Our new measurements
substantially improve previous measurements of MBH and the size of the broad
line-emitting region for four sources and add a measurement for one new object.
Our new measurements are consistent with photoionization physics regulating the
location of the broad line region in active galactic nuclei.Comment: 45 pages, 5 figures. Accepted for publication in ApJ. For a brief
video explaining the key results of this paper, see
http://www.youtube.com/user/OSUAstronom
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