3,280 research outputs found
The Swift X-Ray Telescope: Status and Performance
We present science highlights and performance from the Swift X-ray Telescope
(XRT), which was launched on November 20, 2004. The XRT covers the 0.2-10 keV
band, and spends most of its time observing gamma-ray burst (GRB)afterglows,
though it has also performed observations of many other objects. By mid-August
2007, the XRT had observed over 220 GRB afterglows, detecting about 96% of
them. The XRT positions enable followup ground-based optical observations, with
roughly 60% of the afterglows detected at optical or near IR wavelengths.
Redshifts are measured for 33% of X-ray afterglows. Science highlights include
the discovery of flaring behavior at quite late times, with implications for
GRB central engines; localization of short GRBs, leading to observational
support for compact merger progenitors for this class of bursts; a mysterious
plateau phase to GRB afterglows; as well as many other interesting observations
such as X-ray emission from comets, novae, galactic transients, and other
objects.Comment: 9 pages, 14 figure
HI study of the environment around ESO 243-49, the host galaxy of an intermediate mass black hole
The lenticular galaxy ESO 243-49 hosts the ultraluminous X-ray source HLX-1,
the best candidate intermediate mass black hole (IMBH) currently known. The
environments of IMBHs remain unknown, however the proposed candidates include
the nuclei of dwarf galaxies or globular clusters. Evidence at optical
wavelengths points at HLX-1 being the remnant of an accreted dwarf galaxy. Here
we report the Australia Telescope Compact Array radio observations of HI
emission in and around ESO 243-49 searching for signatures of a recent merger
event. No HI line emission is detected in ESO 243-49 with a 5 upper
limit on the HI gas mass of a few . A likely reason for this
non-detection is the cluster environment depleting ESO 243-49's HI gas
reservoir. The upper limit is consistent with an interpretation of HLX-1 as a
dwarf satellite of ESO 243-49, however more sensitive observations are required
for a detection. We detect ~ of HI gas in the peculiar
spiral galaxy AM 0108-462, located at a projected distance of ~170 kpc from ESO
243-49. This amount of HI gas is ~10 times less than in spiral galaxies with
similar optical and near-infrared properties in the field, strengthening the
conclusion that the cluster environment indeed depletes the HI gas reservoir of
these two galaxies. Here we also report observations of AM 0108-462 in several
optical and near-infrared bands using the Magellan 6.5 m telescopes, and
archival X-ray and ultraviolet observations with XMM-Newton and Swift. These
data combined with the HI line data suggest it is likely that AM 0108-462 is
experiencing a merger event.Comment: 12 pages, 9 figures, accepted for publication in MNRA
The in-flight spectroscopic performance of the Swift XRT CCD camera during 2006-2007
The Swift X-ray Telescope focal plane camera is a front-illuminated MOS CCD,
providing a spectral response kernel of 135 eV FWHM at 5.9 keV as measured
before launch. We describe the CCD calibration program based on celestial and
on-board calibration sources, relevant in-flight experiences, and developments
in the CCD response model. We illustrate how the revised response model
describes the calibration sources well. Comparison of observed spectra with
models folded through the instrument response produces negative residuals
around and below the Oxygen edge. We discuss several possible causes for such
residuals. Traps created by proton damage on the CCD increase the charge
transfer inefficiency (CTI) over time. We describe the evolution of the CTI
since the launch and its effect on the CCD spectral resolution and the gain.Comment: 8 pages, 5 colour figures, submitted to SPI
Accurate early positions for Swift GRBS: enhancing X-ray positions with UVOT astrometry
Here we describe an autonomous way of producing more accurate prompt XRT
positions for Swift-detected GRBs and their afterglows, based on UVOT
astrometry and a detailed mapping between the XRT and UVOT detectors. The
latter significantly reduces the dominant systematic error -- the star-tracker
solution to the World Coordinate System. This technique, which is limited to
times when there is significant overlap between UVOT and XRT PC-mode data,
provides a factor of 2 improvement in the localisation of XRT refined positions
on timescales of less than a few hours. Furthermore, the accuracy achieved is
superior to astrometrically corrected XRT PC mode images at early times (for up
to 24 hours), for the majority of bursts, and is comparable to the accuracy
achieved by astrometrically corrected X-ray positions based on deep XRT PC-mode
imaging at later times (abridged).Comment: 12 pages, 8 figures, 1 table, submitted to Astronomy and
Astrophysics, August 7th 200
GRB 080319B: A Naked-Eye Stellar Blast from the Distant Universe
Long duration gamma-ray bursts (GRBs) release copious amounts of energy
across the entire electromagnetic spectrum, and so provide a window into the
process of black hole formation from the collapse of a massive star. Over the
last forty years, our understanding of the GRB phenomenon has progressed
dramatically; nevertheless, fortuitous circumstances occasionally arise that
provide access to a regime not yet probed. GRB 080319B presented such an
opportunity, with extraordinarily bright prompt optical emission that peaked at
a visual magnitude of 5.3, making it briefly visible with the naked eye. It was
captured in exquisite detail by wide-field telescopes, imaging the burst
location from before the time of the explosion. The combination of these unique
optical data with simultaneous gamma-ray observations provides powerful
diagnostics of the detailed physics of this explosion within seconds of its
formation. Here we show that the prompt optical and gamma-ray emissions from
this event likely arise from different spectral components within the same
physical region located at a large distance from the source, implying an
extremely relativistic outflow. The chromatic behaviour of the broadband
afterglow is consistent with viewing the GRB down the very narrow inner core of
a two-component jet that is expanding into a wind-like environment consistent
with the massive star origin of long GRBs. These circumstances can explain the
extreme properties of this GRB.Comment: 43 pages, 18 figures, 3 tables, submitted to Nature May 11, 200
The 2008 May burst activation of SGR 1627-41
In May 2008 the soft gamma-ray repeater SGR 1627-41 resumed its bursting
activity after nearly a decade of quiescence. After detection of a bright
burst, Swift pointed its X-ray telescope in the direction of the source in less
than five hours and followed it for over five weeks. In this paper we present
an analysis of the data from these Swift observations and an XMM-Newton one
performed when SGR 1627-41 was still in a quiescent state. The analysis of the
bursts detected with Swift/BAT shows that their temporal and spectral
properties are similar to those found in previous observations of SGR 1627-41
and other soft gamma-ray repeaters. The maximum peak luminosity of the bursts
was about 2E+41 erg/s. Our data show that the outburst was accompanied by a
fast flux enhancement and by a hardening of the spectrum with respect to the
persistent emission.Comment: 5 pages, 4 figures, 2 tables; accepted for publication in MNRAS
Letter
UVES/VLT high resolution spectroscopy of GRB 050730 afterglow: probing the features of the GRB environment
We analyze high resolution spectroscopic observations of the optical
afterglow of GRB050730, obtained with UVES@VLT about hours after the GRB
trigger. The spectrum shows that the ISM of the GRB host galaxy at z = 3.967 is
complex, with at least five components contributing to the main absorption
system. We detect strong CII*, SiII*, OI* and FeII* fine structure absorption
lines associated to the second and third component. For the first three
components we derive information on the relative distance from the site of the
GRB explosion. Component 1, which has the highest redshift, does not present
any fine structure nor low ionization lines; it only shows very high ionization
features, such as CIV and OVI, suggesting that this component is very close to
the GRB site. From the analysis of low and high ionization lines and fine
structure lines, we find evidences that the distance of component 2 from the
site of the GRB explosion is 10-100 times smaller than that of component 3. We
evaluated the mean metallicity of the z=3.967 system obtaining values about
0.01 of the solar metallicity or less. However, this should not be taken as
representative of the circumburst medium, since the main contribution to the
hydrogen column density comes from the outer regions of the galaxy while that
of the other elements presumably comes from the ISM closer to the GRB site.
Furthermore, difficulties in evaluating dust depletion correction can modify
significantly these values. The mean [C/Fe] ratio agrees well with that
expected by single star-formation event models. Interestingly the [C/Fe] of
component 2 is smaller than that of component 3, in agreement with GRB dust
destruction scenarios, if component 2 is closer than component 3 to the GRB
site.Comment: 11 pages, 15 postscript figures, accepted for pubblication in A&
Operational experience with the GEM detector assembly lines for the CMS forward muon upgrade
The CMS Collaboration has been developing large-area triple-gas electron multiplier (GEM) detectors to be installed in the muon Endcap regions of the CMS experiment in 2019 to maintain forward muon trigger and tracking performance at the High-Luminosity upgrade of the Large Hadron Collider (LHC); 10 preproduction detectors were built at CERN to commission the first assembly line and the quality controls (QCs). These were installed in the CMS detector in early 2017 and participated in the 2017 LHC run. The collaboration has prepared several additional assembly and QC lines for distributed mass production of 160 GEM detectors at various sites worldwide. In 2017, these additional production sites have optimized construction techniques and QC procedures and validated them against common specifications by constructing additional preproduction detectors. Using the specific experience from one production site as an example, we discuss how the QCs make use of independent hardware and trained personnel to ensure fast and reliable production. Preliminary results on the construction status of CMS GEM detectors are presented with details of the assembly sites involvement
The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy
We present the first reported case of the simultaneous metallicity
determination of a gamma-ray burst (GRB) host galaxy, from both afterglow
absorption lines as well as strong emission-line diagnostics. Using
spectroscopic and imaging observations of the afterglow and host of the
long-duration Swift GRB121024A at z = 2.30, we give one of the most complete
views of a GRB host/environment to date. We observe a strong damped Ly-alpha
absorber (DLA) with a hydrogen column density of log N(HI) = 21.88 +/- 0.10, H2
absorption in the Lyman-Werner bands (molecular fraction of log(f)~ -1.4;
fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular
emission lines H-alpha, H-beta, [O II], [O III] and [N II], as well as metal
absorption lines. We find a GRB host galaxy that is highly star-forming (SFR ~
40 solar masses/yr ), with a dust-corrected metallicity along the line of sight
of [Zn/H]corr = -0.6 +/- 0.2 ([O/H] ~ -0.3 from emission lines), and a
depletion factor [Zn/Fe] = 0.85 +/- 0.04. The molecular gas is separated by 400
km/s (and 1-3 kpc) from the gas that is photoexcited by the GRB. This implies a
fairly massive host, in agreement with the derived stellar mass of
log(M/M_solar ) = 9.9+/- 0.2. We dissect the host galaxy by characterising its
molecular component, the excited gas, and the line-emitting star-forming
regions. The extinction curve for the line of sight is found to be unusually
flat (Rv ~15). We discuss the possibility of an anomalous grain size
distributions. We furthermore discuss the different metallicity determinations
from both absorption and emission lines, which gives consistent results for the
line of sight to GRB 121024A.Comment: 20 pages, 11 figures, accepted by MNRA
Epidemiology and natural history of central venous access device use and infusion pump function in the NO16966 trial
Background: Central venous access devices in fluoropyrimidine therapy are associated with complications; however, reliable data are lacking regarding their natural history, associated complications and infusion pump performance in patients with metastatic colorectal cancer.<p></p>
Methods: We assessed device placement, use during treatment, associated clinical outcomes and infusion pump perfomance in the NO16966 trial.<p></p>
Results: Device replacement was more common with FOLFOX-4 (5-fluorouracil (5-FU)+oxaliplatin) than XELOX (capecitabine+oxaliplatin) (14.1% vs 5.1%). Baseline device-associated events and post-baseline removal-/placement-related events occurred more frequently with FOLFOX-4 than XELOX (11.5% vs 2.4% and 8.5% vs 2.1%). Pump malfunctions, primarily infusion accelerations in 16% of patients, occurred within 1.6–4.3% of cycles. Fluoropyrimidine-associated grade 3/4 toxicity was increased in FOLFOX-4-treated patients experiencing a malfunction compared with those who did not (97 out of 155 vs 452 out of 825 patients), predominantly with increased grade 3/4 neutropenia (53.5% vs 39.8%). Febrile neutropenia rates were comparable between patient cohorts±malfunction. Efficacy outcomes were similar in patient cohorts±malfunction.<p></p>
Conclusions: Central venous access device removal or replacement was common and more frequent in patients receiving FOLFOX-4. Pump malfunctions were also common and were associated with increased rates of grade 3/4 haematological adverse events. Oral fluoropyrimidine-based regimens may be preferable to infusional 5-FU based on these findings
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