179 research outputs found
ESG Disclosure Scores and CEO Compensation
This paper examines the impact of environmental, social, governance (ESG) disclosure scores on chief executive officer (CEO) compensation. I analyze the S&P 500 from 2011 â 2021 utilizing the within estimation method for fixed effects regression models to find that a one point increase in a firmâs ESG disclosure score is associated with a 0.49% increase in CEO compensation, ceteris paribus. However, certain S&P 500 industries have an advantage in boosting their ESG disclosure score relative to other industries. After including interaction terms between industry and ESG disclosure score, I find that, for the median industry, a one point increase in a firmâs ESG disclosure score is associated with a 0.22% decrease in CEO compensation, ceteris paribus. When compared to alternative executive compensation packages (chief financial officer, chief operations officer, etc.), I find that a one point increase in a firmâs ESG disclosure score is associated with a 0.37% decrease in the average executive compensation for the median industry. Based on my findings, CEOs can gain a better overall understanding of how ESG disclosure effects CEO compensation within the S&P 500
Constraining the Geometry of the Neutron Star RX J1856.5-3754
RX J1856.5-3754 is one of the brightest, nearby isolated neutron stars, and
considerable observational resources have been devoted to its study. In
previous work, we found that our latest models of a magnetic, hydrogen
atmosphere matches well the entire spectrum, from X-rays to optical (with
best-fitting neutron star radius R=14 km, gravitational redshift z_g~0.2, and
magnetic field B~4x10^12 G). A remaining puzzle is the non-detection of
rotational modulation of the X-ray emission, despite extensive searches. The
situation changed recently with XMM-Newton observations that uncovered 7 s
pulsations at the 1% level. By comparing the predictions of our model (which
includes simple dipolar-like surface distributions of magnetic field and
temperature) with the observed brightness variations, we are able to constrain
the geometry of RX J1856.5-3754, with one angle < 6 deg and the other angle =
20-45 deg, though the solutions are not definitive given the observational and
model uncertainties. These angles indicate a close alignment between the
rotation and magnetic axes or between the rotation axis and the observer. We
discuss our results in the context of RX J1856.5-3754 being a normal radio
pulsar and a candidate for observation by future X-ray polarization missions
such as Constellation-X or XEUS.Comment: 7 pages, 6 figures; MNRAS, accepte
First IXPE Observations of the Accreting X-ray Pulsar Her X-1
Theoretical models for the X-ray emission of accretion-powered pulsars predict a high degree and a strong spin-phase dependence of the X-ray polarization. Using observations of the Imaging X-ray Polarimetry Explorer of the accreting pulsar Her X-1, we were able to test these predictions for the first time ever
Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826-238 in the High Soft State
The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in X-ray astronomy. We report here the results of the first IXPE observation of a weakly magnetized neutron star, GS 1826â238, performed on 2022 March 29-31 when the source was in a high soft state. An upper limit (99.73% confidence level) of 1.3% for the linear polarization degree is obtained over the IXPE 2-8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. The spectral parameters obtained from the fits to the broadband spectrum were used as inputs for Monte Carlo simulations considering different possible geometries of the X-ray emitting region. Comparing the IXPE upper limit with these simulations, we can put constraints on the geometry and inclination angle of GS 1826-238
The detection of polarized X-ray emission from the magnetar 1E 2259+586
We report on IXPE, NICER, and XMMâNewton observations of the magnetar 1E 2259+586. We find that the source is significantly polarized at about or above 20 per cent for all phases except for the secondary peak where it is more weakly polarized. The polarization degree is strongest during the primary minimum which is also the phase where an absorption feature has been identified previously. The polarization angle of the photons are consistent with a rotating vector model with a mode switch between the primary minimum and the rest of the rotation of the neutron star. We propose a scenario in which the emission at the source is weakly polarized (as in a condensed surface) and, as the radiation passes through a plasma arch, resonant cyclotron scattering off of protons produces the observed polarized radiation. This confirms the magnetar nature of the source with a surface field greater than about 1015 G
Discovery of strongly variable X-ray polarization in the neutron star low-mass X-ray binary transient XTE J1701-462
CONTEXT:
After about 16 years since its first outburst, the transient neutron star low-mass X-ray binary XTE J1701â462 turned on again in September 2022, allowing for the first study of its X-ray polarimetric characteristics by a dedicated observing program with the Imaging X-ray Polarimeter Explorer (IXPE).
AIMS:
Polarimetric studies of XTE J1701â462 have been expected to improve our understanding of accreting weakly magnetized neutron stars, in particular, the physics and the geometry of the hot inner regions close to the compact object.
METHOD:
The IXPE data of two triggered observations were analyzed using time-resolved spectroscopic and polarimetric techniques, following the source along its Z-track of the colorâcolor diagram.
RESULTS:
During the first pointing on 2022 September 29, an average 2â8 keV polarization degree of (4.6â
屉
0.4)% was measured, the highest value found up to now for this class of sources. Conversely, only a âŒ0.6% average degree was obtained during the second pointing ten days later.
CONCLUSIONS:
The polarimetric signal appears to be strictly related to the higher energy blackbody component associated with the boundary layer (BL) emission and its reflection from the inner accretion disk, and it is as strong as 6.1% and 1.2% (> 95% significant) above 3â4 keV for the two measurements, respectively. The variable polarimetric signal is apparently related to the spectral characteristics of XTE J1701â462, which is the strongest when the source was in the horizontal branch of its Z-track and the weakest in the normal branch. These IXPE results provide new important observational constraints on the physical models and geometry of the Z-sources. Here, we discuss the possible reasons for the presence of strong and variable polarization among these sources
Accretion geometry of the neutron star low mass X-ray binary Cyg X-2 from X-ray polarization measurements
We report spectro-polarimetric results of an observational campaign of the
bright neutron star low-mass X-ray binary Cyg X-2 simultaneously observed by
IXPE, NICER and INTEGRAL. Consistently with previous results, the broad-band
spectrum is characterized by a lower-energy component, attributed to the
accretion disc with 1 keV, plus unsaturated
Comptonization in thermal plasma with temperature keV and
optical depth , assuming a slab geometry. We measure the
polarization degree in the 2-8 keV band per cent and
polarization angle , consistent with the
previous X-ray polarimetric measurements by OSO-8 as well as with the direction
of the radio jet which was earlier observed from the source. While polarization
of the disc spectral component is poorly constrained with the IXPE data, the
Comptonized emission has a polarization degree per cent and a
polarization angle aligned with the radio jet. Our results strongly favour a
spreading layer at the neutron star surface as the main source of the
polarization signal. However, we cannot exclude a significant contribution from
reflection off the accretion disc, as indicated by the presence of the iron
fluorescence line.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16
We report on the first observation of a radio-quiet Active Galactic Nucleus
(AGN) using polarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source
was pointed with the Imaging X-ray Polarimetry Explorer (IXPE) starting on May
14, 2022 for a net observing time of 486 ks, simultaneously with XMM-Newton (58
ks) and NuSTAR (83 ks). A polarization degree smaller than (at the
99% c.l.) is derived in the 2-8 keV energy range, where emission is dominated
by the primary component ascribed to the hot corona. The broad-band spectrum,
inferred from a simultaneous fit to the IXPE, NuSTAR, and XMM-Newton data, is
well reproduced by a power law with photon index and a
high-energy cutoff keV. A comparison with Monte Carlo
simulations shows that a lamp-post and a conical geometry of the corona are
consistent with the observed upper limit, a slab geometry is allowed only if
the inclination angle of the system is less than 50.Comment: 7 pages, 3 figures, 1 table. Submitted to MNRAS Letter
X-ray polarimetry reveals the magnetic field topology on sub-parsec scales in Tycho's supernova remnant
Supernova remnants are commonly considered to produce most of the Galactic
cosmic rays via diffusive shock acceleration. However, many questions about the
physical conditions at shock fronts, such as the magnetic-field morphology
close to the particle acceleration sites, remain open. Here we report the
detection of a localized polarization signal from some synchrotron X-ray
emitting regions of Tycho's supernova remnant made by the Imaging X-ray
Polarimetry Explorer. The derived polarization degree of the X-ray synchrotron
emission is 9+/-2% averaged over the whole remnant, and 12+/-2% at the rim,
higher than the 7-8% polarization value observed in the radio band. In the west
region the polarization degree is 23+/-4%. The X-ray polarization degree in
Tycho is higher than for Cassiopeia A, suggesting a more ordered magnetic-field
or a larger maximum turbulence scale. The measured tangential polarization
direction corresponds to a radial magnetic field, and is consistent with that
observed in the radio band. These results are compatible with the expectation
of turbulence produced by an anisotropic cascade of a radial magnetic-field
near the shock, where we derive a magnetic-field amplification factor of
3.4+/-0.3. The fact that this value is significantly smaller than those
expected from acceleration models is indicative of highly anisotropic
magnetic-field turbulence, or that the emitting electrons either favor regions
of lower turbulence, or accumulate close to where the magnetic-field
orientation is preferentially radially oriented due to hydrodynamical
instabilities.Comment: 31 pages, 7 figures, 3 tables. Accepted for publication in ApJ.
Revised versio
Uncovering the geometry of the hot X-ray corona in the Seyfert galaxy NGC 4151 with IXPE
We present an X-ray spectropolarimetric analysis of the bright Seyfert galaxy NGC 4151. The source has been observed with the Imaging X-ray Polarimetry Explorer (IXPE) for 700 ks, complemented with simultaneous XMMâNewton (50 ks) and NuSTAR (100 ks) pointings. A polarization degree Î Â = 4.9 ± 1.1 per cent and angle Κ = 86° ± 7° east of north (68 perâcent confidence level) are measured in the 2â8 keV energy range. The spectropolarimetric analysis shows that the polarization could be entirely due to reflection. Given the low reflection flux in the IXPE band, this requires, however, a reflection with a very large (&gt;38 per cent) polarization degree. Assuming more reasonable values, a polarization degree of the hot corona ranging from âŒ4 to âŒ8 per cent is found. The observed polarization degree excludes a âsphericalâ lamppost geometry for the corona, suggesting instead a slab-like geometry, possibly a wedge, as determined via Monte Carlo simulations. This is further confirmed by the X-ray polarization angle, which coincides with the direction of the extended radio emission in this source, supposed to match the disc axis. NGC 4151 is the first active galactic nucleus with an X-ray polarization measure for the corona, illustrating the capabilities of X-ray polarimetry and IXPE in unveiling its geometry
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