721 research outputs found
Di-higgs enhancement by neutral scalar as probe of new colored sector
We study a class of models in which the Higgs pair production is enhanced at
hadron colliders by an extra neutral scalar. The scalar particle is produced by
the gluon fusion via a loop of new colored particles, and decays into di-Higgs
through its mixing with the Standard Model Higgs. Such a colored particle can
be the top/bottom partner, such as in the dilaton model, or a colored scalar
which can be triplet, sextet, octet, etc., called leptoquark, diquark, coloron,
etc., respectively. We examine the experimental constraints from the latest
Large Hadron Collider (LHC) data, and discuss the future prospects of the LHC
and the Future Circular Collider up to 100TeV. We also point out that the
2.4 excess in the final state reported by the
ATLAS experiment can be interpreted as the resonance of the neutral scalar at
300GeV.Comment: 27 pages, 10 figures (v1); references added, 28 pages (v2); minor
modifications, published version (v3
Discovery of X-Ray-Emitting O-Ne-Mg-Rich Ejecta in the Galactic Supernova Remnant Puppis A
We report on the discovery of X-ray--emitting O-Ne-Mg-rich ejecta in the
middle-aged Galactic O-rich supernova remnant Puppis A with Chandra and
XMM-Newton. We use line ratios to identify a low-ionization filament running
parallel to the northeastern edge of the remnant that requires supersolar
abundances, particularly for O, Ne, and Mg, which we interpret to be from
O-Ne-Mg-rich ejecta. Abundance ratios of Ne/O, Mg/O, and Fe/O are measured to
be ~2, ~2, and <0.3 times the solar values. Our spatially-resolved spectral
analysis from the northeastern rim to the western rim otherwise reveals
sub-solar abundances consistent with those in the interstellar medium. The
filament is coincident with several optically emitting O-rich knots with high
velocities. If these are physically related, the filament would be a peculiar
fragment of ejecta. On the other hand, the morphology of the filament suggests
that it may trace ejecta heated by a shock reflected strongly off the dense
ambient clouds near the northeastern rim.Comment: Published onlin
X-ray ejecta kinematics of the Galactic core-collapse supernova remnant G292.0+1.8
We report on the results from the analysis of our 114 ks Chandra HETGS
observation of the Galactic core-collapse supernova remnant G292.0+1.8. To
probe the 3D structure of the clumpy X-ray emitting ejecta material in this
remnant, we measured Doppler shifts in emission lines from metal-rich ejecta
knots projected at different radial distances from the expansion center. We
estimate radial velocities of ejecta knots in the range of -2300 <~ v_r <~ 1400
km s^-1. The distribution of ejecta knots in velocity vs. projected-radius
space suggests an expanding ejecta shell with a projected angular thickness of
~90" (corresponding to ~3 pc at d = 6 kpc). Based on this geometrical
distribution of the ejecta knots, we estimate the location of the reverse shock
approximately at the distance of ~4 pc from the center of the supernova
remnant, putting it in close proximity to the outer boundary of the radio
pulsar wind nebula. Based on our observed remnant dynamics and the standard
explosion energy of 10^51 erg, we estimate the total ejecta mass to be <~ 8
M_sun, and we propose an upper limit of <~ 35 M_sun on the progenitor's mass.Comment: 5 figures, accepted by Ap
An X-Ray Study of Supernova Remnant N49 and Soft Gamma-Ray Repeater 0526-66 in the Large Magellanic Cloud
We report on the results from our deep Chandra observation (120 ks) of the
supernova remnant (SNR) N49 and soft Gamma-ray repeater (SGR) 0526-66 in the
Large Magellanic Cloud. We firmly establish the detection of an ejecta "bullet"
beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is
distinguished from that of the main SNR shell, showing significantly enhanced
Si and S abundances. We also detect an ejecta feature in the eastern shell,
which shows metal overabundances similar to those of the bullet. If N49 was
produced by a core-collapse explosion of a massive star, the detected Si-rich
ejecta may represent explosive O-burning or incomplete Si-burning products from
deep interior of the supernova. On the other hand, the observed Si/S abundance
ratio in the ejecta may favor Type Ia origin for N49. We refine the Sedov age
of N49, tau_Sed ~ 4800 yr, with the explosion energy E_0 ~ 1.8 x 10^51 erg. Our
blackbody (BB) + power law (PL) model for the quiescent X-ray emission from SGR
0526-66 indicates that the PL photon index (Gamma ~ 2.5) is identical to that
of PSR 1E1048.1-5937, the well-known candidate transition object between
anomalous X-ray pulsars and SGRs. Alternatively, the two-component BB model
implies X-ray emission from a small (R ~ 1 km) hot spot(s) (kT ~ 1 keV) in
addition to emission from the neutron star's cooler surface (R ~ 10 km, kT ~
0.4 keV). There is a considerable discrepancy in the estimated column toward
0526-66 between BB+PL and BB+BB model fits. Discriminating these spectral
models would be crucial to test the long-debated physical association between
N49 and 0526-66.Comment: Accepted by ApJ, 27 pages in total (aastex preprint format) including
5 figures (4 in color) and 5 table
Chandra X-Ray Study of Galactic Supernova Remnant G299.2-2.9
We report on observations of the Galactic supernova remnant (SNR)
G299.22.9 with the {\it Chandra X-Ray Observatory}. The high resolution
images with {\it Chandra} resolve the X-ray-bright knots, shell, and diffuse
emission extending beyond the bright shell. Interior to the X-ray shell is
faint diffuse emission occupying the central regions of the SNR.
Spatially-resolved spectroscopy indicates a large foreground absorption
( 3.5 10 cm), which supports a
relatively distant location ( 5 kpc) for the SNR. The blast wave is
encountering a highly inhomogeneous ambient medium with the densities ranging
over more than an order of magnitude ( 0.1 4 cm).
Assuming the distance of 5 kpc, we derive a Sedov age of
4500 yr and an explosion energy of 1.6 10
ergs. The ambient density structure and the overall morphology suggest that
G299.22.9 may be a limb-brightened partial shell extending to 7 pc
radius surrounded by fainter emission extending beyond that to a radius of
9 pc. This suggests the SNR exploded in a region of space where there is
a density gradient whose direction lies roughly along the line of sight. The
faint central region shows strong line emission from heavy elements of Si and
Fe, which is caused by the presence of the overabundant stellar ejecta there.
We find no evidence for stellar ejecta enriched in light elements of O and Ne.
The observed abundance structure of the metal-rich ejecta supports a Type Ia
origin for G299.22.9.Comment: 16 pages (AASTex emulator style), 3 Tables, 10 Figures (including 1
color: Figure 1), Accepted by Ap
Chandra View of Pulsar Wind Nebula Tori
The results from a systematic study of eleven pulsar wind nebulae with a
torus structure observed with the Chandra X-ray observatory are presented. A
significant observational correlation is found between the radius of the tori,
r, and the spin-down luminosity of the pulsars, Edot. A logarithmic linear fit
between the two parameters yields log r = (0.57 +- 0.22) log Edot -22.3 +- 8.0
with a correlation coefficient of 0.82, where the units of r and Edot are pc
and ergs s^-1, respectively. The value obtained for the Edot dependency of r is
consistent with a square root law, which is theoretically expected. This is the
first observational evidence of this dependency, and provides a useful tool to
estimate the spin-down energies of pulsars without direct detections of
pulsation. Applications of this dependency to some other samples are also
shown.Comment: 8 pages, 2 figures, ApJ in pres
A Super-Solar Metallicity for the Progenitor of Kepler's Supernova
We have performed deep X-ray observations of the remnant of Kepler's
supernova (SN 1604) as a Key Project of the Suzaku Observatory. Our main goal
is to detect secondary Fe-peak elements in the SN ejecta to gain insights into
the Type Ia supernova explosion mechanism and the nature of the progenitor.
Here we report our initial results. We made a conclusive detection of X-ray
emission lines from highly ionized Mn, Cr, and Ni as well as Fe. The observed
Mn-to-Cr line flux ratio is ~0.60, ~30% larger than that measured in Tycho's
remnant. We estimate a Mn-to-Cr mass ratio of ~0.77, which is strongly
suggestive of a large neutron excess in the progenitor star before the onset of
the thermonuclear runaway. The observed Ni-to-Fe line flux ratio (~0.03)
corresponds to a mass ratio of ~0.06, which is generally consistent with the
products of explosive Si-burning regime in Type Ia explosion models, and rules
out contamination from the products of neutron-rich nuclear statistical
equilibrium in the shocked ejecta. Together with the previously suggested
luminous nature of the explosion, these mass ratios provide strong evidence for
a super-solar metallicity in the SN progenitor (~3 Z_sun). Kepler's supernova
was likely the thermonuclear explosion of a white dwarf formed in the recent
past that must have exploded through a relatively prompt channel.Comment: Total 12 pages including 2 tables and 2 color figures. Accepted by
ApJ
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