1,136 research outputs found
Multiwavelength analysis as a probe of accretion and radiative processes in LINERs
We study the multiwavelength properties of an optically selected sample of
Low Ionization Nuclear Emission-line Regions (LINERs), in an attempt to
determine the accretion mechanism powering their central engine. We show how
their X-ray spectral characteristics, and their spectral energy distribution
compare to luminous AGN, and briefly discuss their connection to their less
massive counter-parts galactic black-hole X-ray binaries.Comment: 2 Pages. Proceedings of IAUS 290 "Feeding Compact Objects: Accretion
on All Scales", C. M. Zhang, T. Belloni, M. Mendez & S. N. Zhang (eds.
XMM-Newton and Chandra observations of the candidate Fermi-LAT pulsar 4FGL J1015.5-6030
4FGL J1015.5-6030 is an unidentified Fermi-LAT source hosting a bright,
extended X-ray source whose X-ray spectrum is consistent with that of a young
pulsar, yet no pulsations have been found. Here we report on XMM-Newton timing
and Chandra imaging observations of the X-ray counterpart of 4FGL J1015.5-6030.
We find no significant periodicity from the source and place a 3
upper-limit on its pulsed fraction of 34. The Chandra observations resolve
the point source from the extended emission. We find that the point source's
spectrum is well fit by a blackbody model, with temperature
keV, plus a weak power-law component, which is consistent with a thermally
emitting neutron star with a magnetospheric component. The extended emission
spans angular scales of a few arcseconds up to about 30 from the point
source and its spectrum is well fit by a power-law model with a photon index
. The extended emission's spectrum and 0.5-10 keV
luminosity of 4 erg s (at a plausible distance of 2 kpc)
are consistent with that of a pulsar wind nebula. Based on a comparison to
other GeV and X-ray pulsars, we find that this putative pulsar is likely a
middle-aged (i.e., --1 Myr) radio-quiet pulsar with
erg s.Comment: Accepted for publication in Ap
The Sleeping Monster: NuSTAR observations of SGR 1806-20, 11 years after the Giant Flare
We report the analysis of 5 NuSTAR observations of SGR 1806-20 spread over a
year from April 2015 to April 2016, more than 11 years following its Giant
Flare (GF) of 2004. The source spin frequency during the NuSTAR observations
follows a linear trend with a frequency derivative
Hz s, implying a surface dipole
equatorial magnetic field G. Thus, SGR 1806-20 has
finally returned to its historical minimum torque level measured between 1993
and 1998. The source showed strong timing noise for at least 12 years starting
in 2000, with increasing one order of magnitude between 2005 and
2011, following its 2004 major bursting episode and GF. SGR 1806-20 has not
shown strong transient activity since 2009 and we do not find short bursts in
the NuSTAR data. The pulse profile is complex with a pulsed fraction of
with no indication of energy dependence. The NuSTAR spectra are well
fit with an absorbed blackbody, keV, plus a power-law,
. We find no evidence for variability among the 5
observations, indicating that SGR 1806-20 has reached a persistent and
potentially its quiescent X-ray flux level after its 2004 major bursting
episode. Extrapolating the NuSTAR model to lower energies, we find that the
0.5-10 keV flux decay follows an exponential form with a characteristic
timescale days. Interestingly, the NuSTAR flux in this energy
range is a factor of weaker than the long-term average measured between
1993 and 2003, a behavior also exhibited in SGR . We discuss our
findings in the context of the magnetar model.Comment: 10 pages, 5 figures, accepted for publication in Ap
NuSTAR Hard X-ray View of Low-luminosity Active Galactic Nuclei: High-energy Cutoff and Truncated Thin Disk
We report the analysis of simultaneous XMM-Newton+NuSTAR observations of two
low-luminosity Active Galactic Nuclei (LLAGN), NGC 3998 and NGC 4579. We do not
detect any significant variability in either source over the ~3 day length of
the NuSTAR observations. The broad-band 0.5-60 keV spectrum of NGC 3998 is best
fit with a cutoff power-law, while the one for NGC 4579 is best fit with a
combination of a hot thermal plasma model, a power-law, and a blend of
Gaussians to fit an Fe complex observed between 6 and 7 keV. Our main spectral
results are the following: (1) neither source shows any reflection hump with a
reflection fraction upper-limits and for NGC 3998
and NGC 4579, respectively; (2) the 6-7 keV line complex in NGC 4579 could
either be fit with a narrow Fe K line at 6.4 keV and a moderately broad Fe XXV
line, or 3 relatively narrow lines, which includes contribution from Fe XXVI;
(3) NGC 4579 flux is 60% brighter than previously detected with XMM-Newton,
accompanied by a hardening in the spectrum; (4) we measure a cutoff energy
keV in NGC 3998, which represents the lowest and
best constrained high-energy cutoff ever measured for an LLAGN; (5) NGC 3998
spectrum is consistent with a Comptonization model with either a sphere
() or slab () geometry, corresponding
to plasma temperatures between 20 and 150 keV. We discuss these results in the
context of hard X-ray emission from bright AGN, other LLAGN, and hot accretion
flow models.Comment: 14 pages, 11 figures, 4 tables, accepted for publication in Ap
Polarized Radiation Signals from Highly Magnetized Neutron Star Surfaces
The surfaces of neutron stars are likely sources of strongly polarized soft X
rays due to the presence of strong magnetic fields. Scattering transport in the
surface layers is critical to the determination of the emergent anisotropy of
light intensity, and is strongly influenced by the complicated interplay
between linear and circular polarization information. We have developed a
magnetic Thomson scattering simulation to model the outer layers of
fully-ionized atmospheres in such compact objects. Here we summarize emergent
intensities and polarizations from extended atmospheric simulations, spanning
considerable ranges of magnetic colatitudes. General relativistic propagation
of light from the surface to infinity is fully included. The net polarization
degrees are moderate and not very small when summing over a variety of field
directions. These results provide an important foundation for observations of
magnetars to be acquired by NASA's new IXPE X-ray polarimeter and future X-ray
polarimetry missions.Comment: 4 pages, 3 figures, accepted for publication in the proceedings of
the IAU Symposium 363, Neutron Star Astrophysics at the Crossroads: Magnetars
and the Multimessenger Revolution, eds. E. Troja & M. G. Barin
A study of serum levels of B cell-attracting chemokine-13 (CXCL 13) and rheumatologic manifestations of chronic hepatitis C virus infection in a cohort of Egyptian patients
AbstractMany rheumatologic manifestations have been associated with Hepatitis C virus (HCV) infection including; arthralgia, myalgia, fatigue, fibromyalgia, vasculitis, and sicca syndrome. The relationship between emergence and persistence of intrahepatic or circulating B cell clonotypes and HCV infection is still unknown. However accumulating evidences indicate that certain chemokines play a critical role in providing the appropriate environment for activation and expansion of naïve lymphocytes, one of these chemokines is B cell-attracting chemokine-13 (CXCL13).CXCL13 is a major regulator of B-cell trafficking. This study evaluates circulating levels of CXCL13 protein in chronically HCV-infected Egyptian patients compared with healthy controls and its association with articular synovial hypertrophy. Rheumatic manifestations were present in 85% of patients; included fatigue (20%), arthralgia (the commonest manifestation) (65%), fibromyalgia (22%), myalgia (37%), Rayunad’s phenomenon (10%), peripheral neuropathy and arthritis (2.5%), and tendenitis (7.5). Cryoglobulins recorded in this study were of type II & III mixed cryoglobulins (MC) positive in 25% all of which showed positive rheumatoid factor (RF). Significant low levels of C3 and C4 were reported in the patient group. CXCL13 serum levels were significantly high in the patient group especially in the MC positive group compared to controls. The highest levels of CXCL13 were significantly associated with rheumatologic manifestations with or without mixed cryoglobulinemia and significantly associated with articular synovial hypertrophy
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