250 research outputs found
Variable Ly alpha sheds light on the environment surrounding GRB 090426
Long duration gamma-ray bursts are commonly associated with the deaths of
massive stars. Spectroscopic studies using the afterglow as a light source
provide a unique opportunity to unveil the medium surrounding it, probing the
densest region of their galaxies. This material is usually in a low ionisation
state and at large distances from the burst site, hence representing the normal
interstellar medium in the galaxy. Here we present the case of GRB 090426 at
z=2.609, whose optical spectrum indicates an almost fully ionised medium
together with a low column density of neutral hydrogen. For the first time, we
also observe variations in the Ly alpha absorption line. Photoionisation
modeling shows that we are probing material from the vicinity of the burst (~80
pc). The host galaxy is a complex of two luminous interacting galaxies, which
might suggest that this burst could have occurred in an isolated star-forming
region outside its host galaxy created in the interaction of the two galaxies.Comment: 11 pages, 9 figures, submitted to MNRA
Functional ScaffoldâFree Bone Equivalents Induce Osteogenic and Angiogenic Processes in a Human In Vitro Fracture Hematoma Model
After trauma, the formed fracture hematoma within the fracture gap contains all the important components (immune/stem cells, mediators) to initiate bone regeneration immediately. Thus, it is of great importance but also the most susceptible to negative influences. To study the interaction between bone and immune cells within the fracture gap, up-to-date in vitro systems should be capable of recapitulating cellular and humoral interactions and the physicochemical microenvironment (eg, hypoxia). Here, we first developed and characterized scaffold-free bone-like constructs (SFBCs), which were produced from bone marrow-derived mesenchymal stromal cells (MSCs) using a macroscale mesenchymal condensation approach. SFBCs revealed permeating mineralization characterized by increased bone volume (mu CT, histology) and expression of osteogenic markers (RUNX2, SPP1, RANKL). Fracture hematoma (FH) models, consisting of human peripheral blood (immune cells) mixed with MSCs, were co-cultivated with SFBCs under hypoxic conditions. As a result, FH models revealed an increased expression of osteogenic (RUNX2, SPP1), angiogenic (MMP2, VEGF), HIF-related (LDHA, PGK1), and inflammatory (IL6, IL8) markers after 12 and 48 hours co-cultivation. Osteogenic and angiogenic gene expression of the FH indicate the osteoinductive potential and, thus, the biological functionality of the SFBCs. IL-6, IL-8, GM-CSF, and MIP-1 beta were detectable within the supernatant after 24 and 48 hours of co-cultivation. To confirm the responsiveness of our model to modifying substances (eg, therapeutics), we used deferoxamine (DFO), which is well known to induce a cellular hypoxic adaptation response. Indeed, DFO particularly increased hypoxia-adaptive, osteogenic, and angiogenic processes within the FH models but had little effect on the SFBCs, indicating different response dynamics within the co-cultivation system. Therefore, based on our data, we have successfully modeled processes within the initial fracture healing phase in vitro and concluded that the cross-talk between bone and immune cells in the initial fracture healing phase is of particular importance for preclinical studies. (c) 2021 American Society for Bone and Mineral Research (ASBMR)
Neuropsychiatric phenotype of post COVID-19 syndrome in non-hospitalized patients
The post COVID-19 syndrome (PCS) is an emerging phenomenon worldwide with enormous socioeconomic impact. While many patients describe neuropsychiatric deficits, the symptoms are yet to be assessed and defined systematically. In this prospective cohort study, we report on the results of a neuropsychiatric consultation implemented in May 2021. A cohort of 105 consecutive patients with merely mild acute course of disease was identified by its high symptom load 6 months post infection using a standardized neurocognitive and psychiatric-psychosomatic assessment. In this cohort, we found a strong correlation between higher scores in questionnaires for fatigue (MFI-20), somatization (PHQ15) and depression (PHQ9) and worse functional outcome as measured by the post COVID functional scale (PCFS). In contrast, neurocognitive scales correlated with age, but not with PCFS. Standard laboratory and cardiopulmonary biomarkers did not differ between the group of patients with predominant neuropsychiatric symptoms and a control group of neuropsychiatrically unaffected PCS patients. Our study delineates a phenotype of PCS dominated by symptoms of fatigue, somatisation and depression. The strong association of psychiatric and psychosomatic symptoms with the PCFS warrants a systematic evaluation of psychosocial side effects of the pandemic itself and psychiatric comorbidities on the long-term outcome of patients with SARS-CoV-2 infection
The Wolf-Rayet features and mass-metallicity relation of long-duration gamma-ray burst host galaxies
Aims. We have gathered optical spectra of 8 long-duration GRB host galaxies
selected from the archival data of VLT/FORS2. We investigated whether or not
Wolf-Rayet (WR) stars can be detected in these GRB host galaxies. We also tried
to estimate the physical properties of GRB host galaxies, such as metallicity.
Methods. We identified the WR features in these spectra by fitting the WR
bumps and WR emission lines in blue and red bumps. We also identified the
subtypes of the WR stars, and estimated the numbers of stars in each subtype,
then calculated the WR/O star ratios. The (O/H) abundances of GRB hosts were
estimated from both the electron temperature (Te) and the metallicity-sensitive
strong-line ratio (R23), for which we have broken the R23 degeneracy. We
compared the environments of long-duration GRB host galaxies with those of
other galaxies in terms of their luminosity (stellar mass)-metallicity
relations (LZ, MZ).
Results. We detected the presence of WR stars in 5 GRB host galaxies having
spectra with relatively high signal-to-noise ratios (S/N). In the comparison of
LZ, MZ relations, it shows that GRB hosts have lower metallicities than other
samples with comparable luminosity and stellar mass. The presence of WR stars
and the observed high WR/O star ratio, together with low metallicity, support
the core-collapsar model and implie the first stage of star formation in the
hosted regions of GRBs.Comment: 12 pages, 4 figures, A&A 514, A24 (2010
The mysterious optical afterglow spectrum of GRB140506A at z=0.889
Context. Gamma-ray burst (GRBs) afterglows probe sightlines to star-forming
regions in distant star-forming galaxies. Here we present a study of the
peculiar afterglow spectrum of the z = 0.889 Swift GRB 140506A. Aims. Our aim
is to understand the origin of the very unusual properties of the absorption
along the line-of-sight. Methods. We analyse spectroscopic observations
obtained with the X-shooter spectrograph mounted on the ESO/VLT at two epochs
8.8 h and 33 h after the burst as well as imaging from the GROND instrument. We
also present imaging and spectroscopy of the host galaxy obtained with the
Magellan telescope. Results. The underlying afterglow appears to be a typical
afterglow of a long-duration GRB. However, the material along the line-of-
sight has imprinted very unusual features on the spectrum. Firstly, there is a
very broad and strong flux drop below 8000 AA (4000 AA in the rest frame),
which seems to be variable between the two spectroscopic epochs. We can
reproduce the flux-drops both as a giant 2175 AA extinction bump and as an
effect of multiple scattering on dust grains in a dense environment. Secondly,
we detect absorption lines from excited H i and He i. We also detect molecular
absorption from CH+ . Conclusions. We interpret the unusual properties of these
spectra as reflecting the presence of three distinct regions along the
line-of-sight: the excited He i absorption originates from an H ii-region,
whereas the Balmer absorption must originate from an associated
photodissociation region. The strong metal line and molecular absorption and
the dust extinction must originate from a third, cooler region along the
line-of-sight. The presence of (at least) three separate regions is reflected
in the fact that the different absorption components have different velocities
relative to the systemic redshift of the host galaxy.Comment: 8 pages, 4 figures. Accepted for publications in A&
The shallow-decay phase in both optical and x-ray afterglows of Swift GRB 090529A: Energy injection into a wind-type medium?
The energy injection model is usually proposed to interpret the shallow-decay
phase in Swift GRB X-ray afterglows. However, very few GRBs have simultaneous
signatures of energy injection in their optical and X-ray afterglows. Here, we
report optical observations of GRB 090529A from 2000 sec to sec
after the burst, in which an achromatic decay is seen at both wavelengths. The
optical light curve shows a decay from 0.37 to 0.99 with a break at
sec. In the same time interval, the decay indices of the X-ray light curve
changed from 0.04 to 1.2. Comparing these values with the closure relations,
the segment after 3 sec is consistent with the prediction of the
forward shock in an ISM medium without any energy injection. The shallow-decay
phase between 2000 to 3 sec could be due to the external shock in
a wind-type-like medium with an energy injection under the condition of . However, the constraint of the spectral region is not well
consistent with the multi-band observations. For this shallow-decay phase,
other models are also possible, such as energy injection with evolving
microphysical parameters, or a jet viewed off-axis,etc.Comment: 19pages,2gigures, accepted by MNRA
Identifying the Location in the Host Galaxy of the Short GRB 111117A with the Chandra Sub-arcsecond Position
We present our successful Chandra program designed to identify, with
sub-arcsecond accuracy, the X-ray afterglow of the short GRB 111117A, which was
discovered by Swift and Fermi. Thanks to our rapid target of opportunity
request, Chandra clearly detected the X-ray afterglow, though no optical
afterglow was found in deep optical observations. The host galaxy was clearly
detected in the optical and near-infrared band, with the best photometric
redshift of z=1.31_{-0.23}^{+0.46} (90% confidence), making it one of the
highest known short GRB redshifts. Furthermore, we see an offset of 1.0 +- 0.2
arcseconds, which corresponds to 8.4 +- 1.7 kpc, between the host and the
afterglow position. We discuss the importance of using Chandra for obtaining
sub-arcsecond X-ray localizations of short GRB afterglows to study GRB
environments.Comment: 17 pages, 11 figures, accepted for publication in Ap
- âŠ