34 research outputs found
Radial Star Formation Histories in 32 Nearby Galaxies
The spatially resolved star formation histories are studied for 32 normal
star-forming galaxies drawn from the the Spitzer Extended Disk Galaxy
Exploration Science survey. At surface brightness sensitivities fainter than 28
mag arcsec, the new optical photometry is deep enough to complement
archival ultraviolet and infrared imaging and to explore the properties of the
emission well beyond the traditional optical extents of these nearby galaxies.
Fits to the spectral energy distributions using a delayed star formation
history model indicate a subtle but interesting average radial trend for the
spiral galaxies: the inner stellar systems decrease in age with increasing
radius, consistent with inside-out disk formation, but the trend reverses in
the outermost regions with the stellar age nearly as old as the innermost
stars. These results suggest an old stellar outer disk population formed
through radial migration and/or the cumulative history of minor mergers and
accretions of satellite dwarf galaxies. The subset of S0 galaxies studied here
show the opposite trend compared to what is inferred for spirals:
characteristic stellar ages that are increasingly older with radius for the
inner portions of the galaxies, and increasingly younger stellar ages for the
outer portions. This result suggests that either S0 galaxies are not well
modeled by a delayed- model, and/or that S0 galaxies have a more
complicated formation history than spiral galaxies.Comment: Accepted for publication in the Astronomical Journal. arXiv admin
note: text overlap with arXiv:1511.0328
X-ray polarimetry of the accreting pulsar GX 301-2
The phase- and energy-resolved polarization measurements of accreting X-ray
pulsars (XRPs) allow us to test different theoretical models of their emission,
as well as to provide an avenue to determine the emission region geometry. We
present the results of the observations of the XRP GX 301-2 performed with the
Imaging X-ray Polarimetry Explorer (IXPE). GX 301-2 is a persistent XRP with
one of the longest known spin periods of ~680 s. A massive hyper-giant
companion star Wray 977 supplies mass to the neutron star via powerful stellar
winds. We do not detect significant polarization in the phase-averaged data
using spectro-polarimetric analysis, with the upper limit on the polarization
degree (PD) of 2.3% (99% confidence level). Using the phase-resolved
spectro-polarimetric analysis we get a significant detection of polarization
(above 99% c.l.) in two out of nine phase bins and marginal detection in three
bins, with a PD ranging between ~3% and ~10%, and a polarization angle varying
in a very wide range from ~0 deg to ~160 deg. Using the rotating vector model
we obtain constraints on the pulsar geometry using both phase-binned and
unbinned analysis getting excellent agreement. Finally, we discuss possible
reasons for a low observed polarization in GX 301-2.Comment: 10 pages, 10 figures, submitted to A&
A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375
Accreting X-ray pulsars (XRPs) are presumably ideal targets for polarization
measurements, as their high magnetic field strength is expected to polarize the
emission up to a polarization degree of ~80%. However, such expectations are
being challenged by recent observations of XRPs with the Imaging X-ray
Polarimeter Explorer (IXPE). Here we report on the results of yet another XRP,
EXO 2030+375, observed with IXPE and contemporarily monitored with Insight-HXMT
and SRG/ART-XC. In line with recent results obtained with IXPE for similar
sources, analysis of the EXO 2030+375 data returns a low polarization degree of
0%-3% in the phase-averaged study and variation in the range 2%-7% in the
phase-resolved study. Using the rotating vector model we constrain the geometry
of the system and obtain a value for the magnetic obliquity of ~.
Considering also the estimated pulsar inclination of ~, this
indicates that the magnetic axis swings close to the observer line of sight.
Our joint polarimetric, spectral and timing analysis hint to a complex
accreting geometry where magnetic multipoles with asymmetric topology and
gravitational light bending significantly affect the observed source behavior.Comment: A&A accepted. Proofs versio
X-ray pulsar GRO J100857 as an orthogonal rotator
X-ray polarimetry is a unique way to probe geometrical configuration of
highly-magnetized accreting neutron stars (X-ray pulsars). GRO J100857 is
the first transient X-ray pulsar observed at two different flux levels by the
Imaging X-ray Polarimetry Explorer (IXPE) during its outburst in November 2022.
The polarization properties were found to be independent of the source
luminosity, with the polarization degree varying between non-detection to about
15% over the pulse phase. Fitting the phase-resolved spectro-polarimetric data
with the rotating vector model allowed us to estimate the pulsar inclination
(130 deg, which is in good agreement with the orbital inclination), the
position angle (75 deg) of the pulsar spin axis, and the magnetic obliquity (74
deg). This makes GRO J100857 the first confidently identified X-ray pulsar
as a nearly orthogonal rotator. The results are discussed in the context of the
neutron star atmosphere models and theories of pulsars' axis alignment.Comment: 11 pages, 7 figures, submitted to A&A. arXiv admin note: text overlap
with arXiv:2209.0244
IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1
The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer. Vela X-1 is considered to be the archetypal example of a wind-accreting, high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectropolarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3% ± 0.4% at the polarization angle (PA) of −47.°3 ± 5.°4. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6%–10% and a ∼90° difference in the PA compared to the data in the 2–3 keV range. The phase-resolved spectropolarimetric analysis finds a PD in the range 0%–9% with the PA varying between −80° and 40°
The first X-ray polarimetric observation of the black hole binary LMC X-1
We report on an X-ray polarimetric observation of the high-mass X-ray binary
LMC X-1 in the high/soft state, obtained by the Imaging X-ray Polarimetry
Explorer (IXPE) in October 2022. The measured polarization is below the minimum
detectable polarization of 1.1 per cent (at the 99 per cent confidence level).
Simultaneously, the source was observed with the NICER, NuSTAR and SRG/ART-XC
instruments, which enabled spectral decomposition into a dominant thermal
component and a Comptonized one. The low 2-8 keV polarization of the source did
not allow for strong constraints on the black-hole spin and inclination of the
accretion disc. However, if the orbital inclination of about 36 degrees is
assumed, then the upper limit is consistent with predictions for pure thermal
emission from geometrically thin and optically thick discs. Assuming the
polarization degree of the Comptonization component to be 0, 4, or 10 per cent,
and oriented perpendicular to the polarization of the disc emission (in turn
assumed to be perpendicular to the large scale ionization cone orientation
detected in the optical band), an upper limit to the polarization of the disc
emission of 1.0, 0.9 or 0.9 per cent, respectively, is found (at the 99 per
cent confidence level).Comment: 12 pages, 9 figures, 4 tables. Accepted for publication in MNRA
Tandem mass tag-based quantitative proteomic profiling identifies candidate serum biomarkers of drug-induced liver injury in humans
Diagnosis of drug-induced liver injury (DILI) and its distinction from other liver diseases are significant challenges in drug development and clinical practice. We used Tandem Mass Tag-labeled quantitative proteomics detecting 2323 proteins in a cohort comprising patients with DILI [at onset (DO) and follow-up (DF)], acute non-DILI [at onset (NDO) and follow-up (NDF)], and healthy volunteers (HV) to identify novel serum biomarkers. Thirteen candidates selected based on differential expression, liver-specific expression, and mechanistic relevance to liver pathology, were assessed in confirmatory and replication cohorts of HV (n=94), DO (n=123), DF (n=110), NDO (n=58) and NDF (n=37) using a targeted label-free SureQuant assay. Area under the receiver operating characteristic curve (AUC) ranging between 0.94 and 0.99 across cohorts for five of these biomarkers, reflected differentiation between DO and HV with high sensitivity and specificity. In addition, fructose-1,6-bisphosphatase 1 distinguished NDO from DO (AUC: 0.75 and 0.65) on its own or in combination with glutathione S-transferase A1 and leukocyte cell derived chemotaxin 2 (AUC: 0.78 and 0.68). These can potentially differentiate DILI and acute liver injury from non-drug etiologies
Tracking the X-ray Polarization of the Black Hole Transient Swift J1727.8-1613 during a State Transition
We report on a campaign on the bright black hole X-ray binary Swift
J1727.81613 centered around five observations by the Imaging X-ray
Polarimetry Explorer (IXPE). This is the first time it has been possible to
trace the evolution of the X-ray polarization of a black hole X-ray binary
across a hard to soft state transition. The 2--8 keV polarization degree slowly
decreased from 4\% to 3\% across the five observations, but
remained in the North-South direction throughout. Using the Australia Telescope
Compact Array (ATCA), we measure the intrinsic 7.25 GHz radio polarization to
align in the same direction. Assuming the radio polarization aligns with the
jet direction (which can be tested in the future with resolved jet images),
this implies that the X-ray corona is extended in the disk plane, rather than
along the jet axis, for the entire hard intermediate state. This in turn
implies that the long (10 ms) soft lags that we measure with the
Neutron star Interior Composition ExploreR (NICER) are dominated by processes
other than pure light-crossing delays. Moreover, we find that the evolution of
the soft lag amplitude with spectral state differs from the common trend seen
for other sources, implying that Swift J1727.81613 is a member of a hitherto
under-sampled sub-population.Comment: Submitted to ApJ. 20 pages, 8 figure
Magnetic Field Properties inside the Jet of Mrk 421: Multiwavelength Polarimetry Including the Imaging X-ray Polarimetry Explorer
We conducted a polarimetry campaign from radio to X-ray wavelengths of the
high-synchrotron-peak (HSP) blazar Mrk 421, including Imaging X-ray Polarimetry
Explorer (IXPE) measurements on 2022 December 6-8. We detected X-ray
polarization of Mrk 421 with a degree of =141 and an
electric-vector position angle =1073 in the 2-8
keV band. From the time variability analysis, we find a significant episodic
variation in . During 7 months from the first IXPE pointing of
Mrk 421 in 2022 May, varied across the range of 0 to
180, while maintained similar values within
10-15. Furthermore, a swing in in 2022 June was
accompanied by simultaneous spectral variations. The results of the
multiwavelength polarimetry show that the X-ray polarization degree was
generally 2-3 times greater than that at longer wavelengths, while the
polarization angle fluctuated. Additionally, based on radio, infrared, and
optical polarimetry, we find that rotation of occurred in the opposite
direction with respect to the rotation of over longer timescales
at similar epochs. The polarization behavior observed across multiple
wavelengths is consistent with previous IXPE findings for HSP blazars. This
result favors the energy-stratified shock model developed to explain variable
emission in relativistic jets. The accompanying spectral variation during the
rotation can be explained by a fluctuation in the physical
conditions, e.g., in the energy distribution of relativistic electrons. The
opposite rotation direction of between the X-ray and longer-wavelength
polarization accentuates the conclusion that the X-ray emitting region is
spatially separated from that at longer wavelengths.Comment: 17 pages, 13 figures, 4 tables; Accepted for publication in A&