31 research outputs found
X-ray follow-up observations of the two γ-ray pulsars PSR J1459–6053 and PSR J1614–2230
International audienceAims. We have observed two newly detected γ-ray pulsars, PSR J1459−6053 and PSR J1614−2230, in the X-ray domain withXMM-Newton to try to enlarge the sample of pulsars for which multi-wavelength data exist. We use these data with the aim of understandingthe pulsar emission mechanisms of these pulsars.Methods. We analysed the X-ray spectra to determine whether the emission emanates from the neutron star surface (thermal emission)or from the magnetosphere (non-thermal emission) and compared this to the region in the magnetosphere in which the γ-rayemission is generated. Furthermore, we compared the phase-folded X-ray lightcurves with those in the γ-ray and, where possible,radio domains, to elicit additional information on the emission sites.Results. J1459−6053 shows X-ray spectra that are best fitted with a power law model with a photon index Γ = 2.10+1.24−0.85. The γ-raydata suggest that either the slot gap or the outer gap model may be best to describe the emission from this pulsar. Analysis of theX-ray lightcurve folded on the γ-ray ephemeris shows modulation at the 3.7σ level in the 1.0−4.5 keV domain. Possible alignmentof the main γ-ray and X-ray peaks also supports the interpretation that the emission in the two energy domains emanates from similarregions. The millisecond pulsar J1614−2230 exhibits an X-ray spectrum with a substantial thermal component, where the best-fittingspectral model is either two blackbodies, with kT = 0.15+0.04−0.04 and 0.88+2.54−0.54 keV or a blackbody with similar temperature to the previouscooler component, kT = 0.13+0.04−0.02 keV and a power law component with a photon index Γ = 1.25+2.30−1.75. The cooler blackbodycomponent is likely to originate from the hot surface at the polar cap. Analysis of the X-ray lightcurve folded on the radio ephemerisshows modulation at the 4.0σ level in the 0.4−3.0 keV domain
Zika virus induces FOXG1 nuclear displacement and downregulation in human neural progenitors
Congenital alterations in the levels of the transcription factor Forkhead box g1 (FOXG1) coding gene trigger "FOXG1 syndrome," a spectrum that recapitulates birth defects found in the "congenital Zika syndrome," such as microcephaly and other neurodevelopmental conditions. Here, we report that Zika virus (ZIKV) infection alters FOXG1 nuclear localization and causes its downregulation, thus impairing expression of genes involved in cell replication and apoptosis in several cell models, including human neural progenitor cells. Growth factors, such as EGF and FGF2, and Thr271 residue located in FOXG1 AKT domain, take part in the nuclear displacement and apoptosis protection, respectively. Finally, by progressive deletion of FOXG1 sequence, we identify the C-terminus and the residues 428-481 as critical domains. Collectively, our data suggest a causal mechanism by which ZIKV affects FOXG1, its target genes, cell cycle progression, and survival of human neural progenitors, thus contributing to microcephaly
A New 626 s Periodic X-ray Source in the Direction of the Galactic Center
Here we report the detection of a 626 s periodic modulation from the X-ray
source 2XMM J174016.0-290337 located in the direction of the Galactic center.
We present temporal and spectral analyses of archival XMM-Newton data and
photometry of archived near-infrared data in order to investigate the nature of
this source. We find that the X-ray light curve shows a strong modulation at
626 +/- 2 s with a confidence level > 99.9% and a pulsed fraction of 54%.
Spectral fitting demonstrates that the spectrum is consistent with an absorbed
power law. No significant spectral variability was observed over the 626 s
period. We have investigated the possibility that the 626 s period is orbital
in nature (either that of an ultra-compact X-ray binary or an AM CVn) or
related to the spin of a compact object (either an accretion powered pulsar or
an intermediate polar). The X-ray properties of the source and the photometry
of the candidate near-infrared counterparts are consistent with an accreting
neutron star X-ray binary on the near-side of the Galactic bulge, where the 626
s period is most likely indicative of the pulsar spin period. However, we
cannot rule out an ultra-compact X-ray binary or an intermediate polar with the
data at hand. In the former case, if the 626 s modulation is the orbital period
of an X-ray binary, it would be the shortest period system known. In the latter
case, the modulation would be the spin period of a magnetic white dwarf.
However, we find no evidence for absorption dips over the 626 s period, a low
temperature black body spectral component, or Fe Kalpha emission lines. These
features are commonly observed in intermediate polars, making 2XMM
J174016.0-290337 a rather unusual member of this class if confirmed. We instead
suggest that 2XMM J174016.0-290337 could be a new addition to the emerging
class of symbiotic X-ray binaries.Comment: 11 pages, 10 figures, submitted to A&A on 18th January 2010, accepted
for publication 20th August 201
Pulsed Gamma Rays from the Original Millisecond and Black Widow Pulsars: a case for Caustic Radio Emission?
We report the detection of pulsed gamma-ray emission from the fast
millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20
(J1959+2048) using 18 months of survey data recorded by the \emph{Fermi} Large
Area Telescope (LAT) and timing solutions based on radio observations conducted
at the Westerbork and Nan\c{c}ay radio telescopes. In addition, we analyzed
archival \emph{RXTE} and \emph{XMM-Newton} X-ray data for the two MSPs,
confirming the X-ray emission properties of PSR B1937+21 and finding evidence
() for pulsed emission from PSR B1957+20 for the first time. In
both cases the gamma-ray emission profile is characterized by two peaks
separated by half a rotation and are in close alignment with components
observed in radio and X-rays. These two pulsars join PSRs J0034-0534 and
J2214+3000 to form an emerging class of gamma-ray MSPs with phase-aligned peaks
in different energy bands. The modeling of the radio and gamma-ray emission
profiles suggests co-located emission regions in the outer magnetosphere.Comment: Accepted for publication in the Astrophysical Journa
A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope
Globular clusters with their large populations of millisecond pulsars (MSPs)
are believed to be potential emitters of high-energy gamma-ray emission. Our
goal is to constrain the millisecond pulsar populations in globular clusters
from analysis of gamma-ray observations. We use 546 days of continuous
sky-survey observations obtained with the Large Area Telescope aboard the Fermi
Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular
clusters. Steady point-like high-energy gamma-ray emission has been
significantly detected towards 8 globular clusters. Five of them (47 Tucanae,
Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices and clear evidence for an exponential cut-off in the range
1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission
from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral
indices , however the presence of an exponential cut-off
can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC
6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral
properties. From the observed gamma-ray luminosities, we estimate the total
number of MSPs that is expected to be present in these globular clusters. We
show that our estimates of the MSP population correlate with the stellar
encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters,
commensurate with previous estimates. The observation of high-energy gamma-ray
emission from a globular cluster thus provides a reliable independent method to
assess their millisecond pulsar populations that can be used to make
constraints on the original neutron star X-ray binary population, essential for
understanding the importance of binary systems in slowing the inevitable core
collapse of globular clusters.Comment: Accepted for publication in A&A. Corresponding authors: J.
Kn\"odlseder, N. Webb, B. Pancraz
A New 626 s Periodic X-ray Source in the Direction of the Galactic Center
Here we report the detection of a 626 s periodic modulation from the X-ray source 2XMM J174016.0-290337 located in the direction of the Galactic center. We present temporal and spectral analyses of archival XMM-Newton data and photometry of archived near-infrared data in order to investigate the nature of this source. We find that the X-ray light curve shows a strong modulation at 626 +/- 2 s with a confidence level > 99.9% and a pulsed fraction of 54%. Spectral fitting demonstrates that the spectrum is consistent with an absorbed power law. No significant spectral variability was observed over the 626 s period. We have investigated the possibility that the 626 s period is orbital in nature (either that of an ultra-compact X-ray binary or an AM CVn) or related to the spin of a compact object (either an accretion powered pulsar or an intermediate polar). The X-ray properties of the source and the photometry of the candidate near-infrared counterparts are consistent with an accreting neutron star X-ray binary on the near-side of the Galactic bulge, where the 626 s period is most likely indicative of the pulsar spin period. However, we cannot rule out an ultra-compact X-ray binary or an intermediate polar with the data at hand. In the former case, if the 626 s modulation is the orbital period of an X-ray binary, it would be the shortest period system known. In the latter case, the modulation would be the spin period of a magnetic white dwarf. However, we find no evidence for absorption dips over the 626 s period, a low temperature black body spectral component, or Fe Kalpha emission lines. These features are commonly observed in intermediate polars, making 2XMM J174016.0-290337 a rather unusual member of this class if confirmed. We instead suggest that 2XMM J174016.0-290337 could be a new addition to the emerging class of symbiotic X-ray binaries