1,105 research outputs found
Detection of a light echo from SN1998bu
About 500d after explosion the light curve of the Type Ia SN1998bu suddenly
flattened and at the same time the spectrum changed from the typical nebular
emission to a blue continuum with broad absorption and emission features
reminiscent of the SN spectrum at early phases. We show that in analogy to
SN1991Tbu (Schmidt et al. 1994), this can be explained by the emergence of a
light echo from a foreground dust cloud. Based on a simple model we argue that
the amount of dust required can consistently explain the extinction which has
been estimated by completely independent methods. Because of the similar echo
luminosity but much higher optical depth of the dust in SN1998bu compared with
SN1991T, we expect that the echo ring size of SN1998bu grows faster than in
SN1991T. HST observations have indeed confirmed this prediction.Comment: 5 pages (including 3 figures) - Accepted for pubblication in ApJ
Letter
Deep Chandra and multicolor HST observations of the jets of 3C 371 and PKS 2201+044
This paper presents multiwavelength imaging and broad-band spectroscopy of
the relativistic jets in the two nearby radio galaxies 3C 371 and PKS 2201+044,
acquired with Chandra, HST, VLA, and Merlin. Radio polarization images are also
available. The two sources stand out as "intermediate'' between FRIs and FRIIs;
their cores are classified as BL Lacs, although broad and narrow optical
emission lines were detected at times. The multiwavelength images show jet
morphologies with the X-ray emission peaking closer to the nucleus than the
longer wavelengths. The jets are resolved at all wavelengths in a direction
perpendicular to the jet axis. The jets SEDs are consistent with a single
spectral component from radio to X-rays, interpreted as synchrotron emission.
The SEDs show a progressive softening from the inner to the outer regions of
the jet, indicating that the electron break energy moves to lower energies with
distance from the core. Overall, the X-ray and multiwavelength properties of
the jets of 3C 371 and PKS 2201+044 appear intermediate between those of FRIs
and FRIIs.Comment: Accepted for publication in ApJ; 28 pages (emulateapj5), 17 figure
The Pediatric Sepsis Biomarker Risk Model (PERSEVERE) Biomarkers Predict Clinical Deterioration and Mortality in Immunocompromised Children Evaluated for Infection
Pediatric sepsis and bacterial infection cause significant morbidity and mortality worldwide, with immunocompromised patients being at particularly high risk of rapid deterioration and death. This study evaluated if PERSEVERE, PERSEVERE-II, or the PERSEVERE biomarkers, can reliably estimate the risk of clinical deterioration and 28-day mortality among immunocompromised pediatric patients. This is a single-center prospective cohort study conducted from July 2016 through September 2017 incorporating 400 episodes of suspected bacterial infection from the inpatient units at Cincinnati Children's Hospital Medical Center, a large, tertiary care children's hospital. The primary analysis assessed clinical deterioration within 72 hours of evaluation for infection. Secondarily, we assessed 28-day mortality. Clinical deterioration was seen in 15% of subjects. Twenty-eight day mortality was 5%, but significantly higher among critically ill patients. Neither PERSEVERE nor PERSEVERE-II performed well to predict clinical deterioration or 28-day mortality, thus we derived new stratification models using the PERSEVERE biomarkers with both high sensitivity and negative predictive value. In conclusion, we evaluated previously validated biomarker risk models in a novel population of largely non-critically ill immunocompromised pediatric patients, and attempted to stratify patients based on a new outcome metric, clinical deterioration. The new highly predictive models indicate common physiologic pathways to clinical deterioration or death from bacterial infection
The Local Group Census: planetary nebulae in Sextans B
Five planetary nebulae (PNe) have been discovered in the nearby dwarf
irregular galaxy. Emission line images were obtained using the Wide Field
Camera of the 2.5m Isaac Newton Telescope (INT) at La Palma (Spain). The
candidate PNe were identified by their point-like appearance and relatively
strong [OIII] emission-line fluxes. They are located within a galactocentric
distance of 2.8 arcmin, corresponding to 1.1 kpc at the distance of Sextans B.
Luminosities are in the range 1800--5600Lsolar. Sextans B is one of the
smallest dwarf irregular galaxies with a PN population. The number of PNe
detected suggest an enhanced star formation rate between 1 and 5 Gyr ago.Comment: 7 pages, 2 figure
Radio-Luminous Southern Seyfert Galaxies. I. Radio Images and Selected Optical/Near-Infrared Spectroscopy
This is the first of two papers in which a study is made of a sample of 12
southern radio-luminous Seyfert galaxies. Our aim is to investigate possible
correlations between radio morphology and nuclear/circumnuclear emission-line
properties. In this paper we present radio images at 13, 6, and 3 cm taken with
the Australia Telescope Compact Array (ATCA), global far-infrared (FIR)
properties for the whole sample, and optical and near-infrared (NIR)
spectroscopy of an interesting subset. We find a mixture of radio morphologies,
including linear, diffuse and compact sources. When the FIR colors of the
galaxies are considered there is an indication that the compact radio sources
have warmer FIR colors than the diffuse sources, whereas the linear sources
span a wide range of FIR colors. There is a wide variation in radio
spectral-indices, suggesting that free-free absorption is significant in some
systems, particularly IRAS 11249-2859, NGC 4507, and NGC 7213. Detailed
emission-line studies are presented of 4 galaxies IC 3639, NGC 5135, NGC 3393 &
IRAS 11249-2859. In IC 3639 we present evidence of vigorous, compact star
formation enclosed by very extended [OI]6300 emission, suggestive of the
boundary between a diffuse outflow and the surrounding ISM. In another galaxy,
IC 5063, we see evidence for the possible interaction of a highly collimated
outflow and the surrounding rotating inner disk. Of the 5 galaxies which show
compact radio emission, 4 have radio/FIR flux ratios consistent with an
energetically dominant AGN, whereas IC 4995 exhibits evidence for a very
compact starburst.Comment: 42 pages, including 7 tables, latex, 19 jpeg figures, Accepted to
ApJ. Replacement updates coordintes of galaxies in Table
BeppoSAX Detection and Follow-up of GRB980425
We present BeppoSAX GRBM and WFC light curves of GRB980425 and NFI follow-up
data taken in 1998 April, May, and November. The first NFI observation has
detected within the 8' radius error box of the GRB an X-ray source positionally
consistent with the supernova SN 1998bw, exploded within a day of GRB980425,
and a fainter X-ray source, not consistent with the position of the supernova.
The former source is detected in the following NFI pointings and exhibits a
decline of a factor of two in six months. If it is associated with SN 1998bw,
this is the first detection of hard X-ray emission from a Type I supernova. The
latter source exhibits only marginally significant variability. Based on these
data, it is not possible to select either source as a firm candidate for the
GRB counterpart.Comment: 2 pages, 1 PostScript figure, submitted to A&AS, Proc. of the
Conference "Gamma-Ray Bursts in the Afterglow Era", held in Rome, 1998
November 3-6. Results concerning 'Source 2' have been update
A Case for Renewed Activity in the Giant Radio Galaxy J0116-473
We present ATCA radio observations of the giant radio galaxy J0116-473 at 12
and 22 cm wavelengths in total intensity and polarization. The images clearly
reveal a bright inner-double structure within more extended edge-brightened
lobe emission. The lack of hotspots at the ends of the outer lobes, the strong
core and the inner-double structure with its edge-brightened morphology lead us
to suggest that this giant radio galaxy is undergoing a renewed nuclear
activity: J0116-473 appears to be a striking example of a radio galaxy where a
young double source is evolving within older lobe material. We also report the
detection of a Mpc-long linear feature which is oriented perpendicular to the
radio axis and has a high fractional polarization.Comment: 25 pages, 10 figures, appeared in 2002 ApJ, 565, 25
Extended Emission Line Gas in Radio Galaxies - PKS0349-27
PKS0349-27 is a classical FRII radio galaxy with an AGN host which has a
spectacular, spiral-like structure in its extended emission line gas (EELG). We
have measured the velocity field in this gas and find that it splits into 2
cloud groups separated by radial velocities which at some points approach 400
km/s Measurements of the diagnostic emission line ratios [OIII]5007/H-beta,
[SII]6716+6731/H-alpha, and [NII]6583/H-alpha in these clouds show no evidence
for the type of HII region emission associated with starburst activity in
either velocity system. The measured emission line ratios are similar to those
found in the nuclei of narrow-line radio galaxies, but the extended
ionization/excitation cannot be produced by continuum emission from the active
nucleus alone. We present arguments which suggest that the velocity
disturbances seen in the EELG are most likely the result of a galaxy-galaxy
collision or merger but cannot completely rule out the possibility that the gas
has been disrupted by the passage of a radio jet.Comment: 12 pages, 3 fig pages, to appear in the Astrophys.
The Local Group Census: planetary nebulae in IC 10, Leo A and Sextans A
In the framework of our narrow-band survey of the Local Group galaxies, we
present the results of the search for planetary nebulae (PNe) in the dwarf
irregular galaxies IC10, LeoA and SextansA. Using the standard on-band/off-band
technique, sixteen new candidate PNe have been discovered in the closest
starburst galaxy, IC10. The optical size of this galaxy is estimated to be much
larger than previously thought, considering the location of the new PNe in an
area of 3.6 kpc X 2.7 kpc. We also confirm the results of previous studies for
the other two dwarf irregular galaxies, with the detection of one candidate PN
in LeoA and another one in SextansA. We review the number of planetary nebulae
discovered in the Local Group to date and their behaviour with metallicity. We
suggest a possible fall in the observed number of PNe when [Fe/H]-1.0,
which might indicate that below this point the formation rate of PNe is much
lower than for stellar populations of near Solar abundances. We also find
non-negligible metallicity effects on the [OIII] luminosity of the brightest PN
of a galaxy.Comment: 10 pages, 4 figures, A&A accepte
BeppoSAX Observations of GRB980425: Detection of the Prompt Event and Monitoring of the Error Box
We present BeppoSAX follow-up observations of GRB980425 obtained with the
Narrow Field Instruments (NFI) in April, May, and November 1998. The first NFI
observation has detected within the 8' radius error box of the GRB an X-ray
source positionally consistent with the supernova 1998bw, which exploded within
a day of GRB980425, and a fainter X-ray source, not consistent with the
position of the supernova. The former source is detected in the following NFI
pointings and exhibits a decline of a factor of two in six months. If it is
associated with SN 1998bw, this is the first detection of X-ray emission from a
Type I supernova above 2 keV. The latter source exhibits only marginally
significant variability. The X-ray spectra and variability of the supernova are
compared with thermal and non-thermal models of supernova high energy emission.
Based on the BeppoSAX data, it is not possible to firmly establish which of the
two detected sources is the GRB X-ray counterpart, although probability
considerations favor the supernova.Comment: 16 pages, Latex, 6 PostScript figures and 1 GIF figure, 2 tables,
submitted to The Astrophysical Journa
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