1,246 research outputs found
Chandra Observations of the X-ray Environs of SN 1998bw/GRB 980425
(Abrigded) We report X-ray studies of the environs of SN 1998bw and GRB
980425 using the Chandra X-Ray Observatory 1281 days after the GRB. Combining
our observation of the supernova with others of the GRB afterglow, a smooth
X-ray light curve, spanning ~1300 days, is obtained by assuming the burst and
supernova were coincident at 35.6 Mpc. When this X-ray light curve is compared
with those of the X-ray ``afterglows'' of ordinary GRBs, X-ray Flashes, and
ordinary supernovae, evidence emerges for at least two classes of lightcurves,
perhaps bounding a continuum. By three to ten years, all these phenomena seem
to converge on a common X-ray luminosity, possibly indicative of the supernova
underlying them all. This convergence strengthens the conclusion that SN 1998bw
and GRB 980425 took place in the same object. One possible explanation for the
two classes is a (nearly) standard GRB observed at different angles, in which
case X-ray afterglows with intermediate luminosities should eventually be
discovered. Finally, we comment on the contribution of GRB afterglows to the
ULX source population.Comment: 26 pages, 5 figues, submitted to Ap
Protention and retention in biological systems
This paper proposes an abstract mathematical frame for describing some
features of cognitive and biological time. We focus here on the so called
"extended present" as a result of protentional and retentional activities
(memory and anticipation). Memory, as retention, is treated in some physical
theories (relaxation phenomena, which will inspire our approach), while
protention (or anticipation) seems outside the scope of physics. We then
suggest a simple functional representation of biological protention. This
allows us to introduce the abstract notion of "biological inertia".Comment: This paper was made possible only as part of an extended
collaboration with Francis Bailly (see references), a dear friend and
"ma\^itre \'a penser", who contributed to the key ideas. Francis passed away
in february 2008: we continue here our inspiring discussions and joint wor
The dark GRB080207 in an extremely red host and the implications for GRBs in highly obscured environments
[Abridged] We present comprehensive X-ray, optical, near- and mid-infrared,
and sub-mm observations of GRB 080207 and its host galaxy. The afterglow was
undetected in the optical and near-IR, implying an optical to X-ray index <0.3,
identifying GRB 080207 as a dark burst. Swift X-ray observations show extreme
absorption in the host, which is confirmed by the unusually large optical
extinction found by modelling the X-ray to nIR afterglow spectral energy
distribution. Our Chandra observations obtained 8 days post-burst allow us to
place the afterglow on the sky to sub-arcsec accuracy, enabling us to pinpoint
an extremely red galaxy (ERO). Follow-up host observations with HST, Spitzer,
Gemini, Keck and the James Clerk Maxwell Telescope (JCMT) provide a photometric
redshift solution of z ~1.74 (+0.05,-0.06) (1 sigma), 1.56 < z < 2.08 at 2
sigma) for the ERO host, and suggest that it is a massive and morphologically
disturbed ultra-luminous infrared galaxy (ULIRG) system, with L_FIR ~ 2.4 x
10^12 L_solar. These results add to the growing evidence that GRBs originating
in very red hosts always show some evidence of dust extinction in their
afterglows (though the converse is not true -- some extinguished afterglows are
found in blue hosts). This indicates that a poorly constrained fraction of GRBs
occur in very dusty environments. By comparing the inferred stellar masses, and
estimates of the gas phase metallicity in both GRB hosts and sub-mm galaxies we
suggest that many GRB hosts, even at z>2 are at lower metallicity than the
sub-mm galaxy population, offering a likely explanation for the dearth of
sub-mm detected GRB hosts. However, we also show that the dark GRB hosts are
systematically more massive than those hosting optically bright events, perhaps
implying that previous host samples are severely biased by the exclusion of
dark events.Comment: 13 pages, 6 figures, accepted for publication in MNRA
Saturated Fat Intake Is Associated with Lung Function in Individuals with Airflow Obstruction: Results from NHANES 2007⁻2012
Nutritional status is a well-recognized prognostic indicator in chronic obstructive pulmonary disease (COPD); however, very little is known about the relationship between lung function and saturated fat intake. We used data from the cross-sectional National Health and Nutrition Examination Surveys (NHANES) to assess the relationship between saturated fatty acid (SFA) intake and lung function in the general US adult population. Adults in NHANES (2007⁻2012) with pre-bronchodilator spirometry measurements and dietary SFA intake were included. Primary outcomes were lung function including forced expiratory volume in one second (FEV₁
The first Swift X-ray Flash: The faint afterglow of XRF 050215B
We present the discovery of XRF 050215B and its afterglow. The burst was
detected by the Swift BAT during the check-out phase and observations with the
X-ray telescope began approximately 30 minutes after the burst. These
observations found a faint, slowly fading X-ray afterglow near the centre of
the error box as reported by the BAT. Infrared data, obtained at UKIRT after 10
hours also revealed a very faint K-band afterglow. The afterglow appear unusual
since it is very faint, especially in the infrared with K>20 only 9 hours post
burst. The X-ray and infrared lightcurves exhibit a slow, monotonic decay with
alpha=0.8 and no evidence for steepening associated with the jet break to 10
days post burst. We discuss possible explanations for the faintness and slow
decay in the context of present models for the production of X-ray Flashes.Comment: 8 pages, 5 figures, accepted for publication in Ap
GRB 070201: A possible Soft Gamma Ray Repeater in M31
The gamma-ray burst (GRB) 070201 was a bright short-duration hard-spectrum
GRB detected by the Inter-Planetary Network (IPN). Its error quadrilateral,
which has an area of 0.124 sq. deg, intersects some prominent spiral arms of
the nearby M31 (Andromeda) galaxy. Given the properties of this GRB, along with
the fact that LIGO data argues against a compact binary merger origin in M31,
this GRB is an excellent candidate for an extragalactic Soft Gamma-ray Repeater
(SGR) giant flare, with energy of 1.4x10^45 erg. Analysis of ROTSE-IIIb visible
light observations of M31, taken 10.6 hours after the burst and covering 42% of
the GRB error region, did not reveal any optical transient down to a limiting
magnitude of 17.1. We inspected archival and proprietary XMM-Newton X-ray
observations of the intersection of the GRB error quadrilateral and M31,
obtained about four weeks prior to the outburst, in order to look for periodic
variable X-ray sources. No SGR or Anomalous X-ray Pulsar (AXP) candidates
(periods in range 1 to 20 s) were detected. We discuss the possibility of
detecting extragalactic SGRs/AXPs by identifying their periodic X-ray light
curves. Our simulations suggest that the probability of detecting the periodic
X-ray signal of one of the known Galactic SGRs/AXPs, if placed in M31, is about
10% (50%), using 50 ks (2 Ms) XMM-Newton exposures.Comment: 7 pages, submitted to ApJ (Fig. 2 resolution reduced
VLT/X-shooter spectroscopy of the afterglow of the Swift GRB 130606A: Chemical abundances and reionisation at
The reionisation of the Universe is thought to have ended around z~6, as
inferred from spectroscopy of distant bright background sources, such as
quasars (QSO) and gamma-ray burst (GRB) afterglows. Furthermore, spectroscopy
of a GRB afterglow provides insight in its host galaxy, which is often too dim
and distant to study otherwise. We present the high S/N VLT/X-shooter spectrum
of GRB130606A at z=5.913. We aim to measure the degree of ionisation of the IGM
between 5.02<z<5.84 and to study the chemical abundance pattern and dust
content of its host galaxy. We measured the flux decrement due to absorption at
Ly, and wavelength regions. The hydrogen and metal
absorption lines formed in the host galaxy were fitted with Voigt profiles to
obtain column densities. Our measurements of the Ly-forest optical
depth are consistent with previous measurements of QSOs, but have a much
smaller uncertainty. The analysis of the red damping wing yields a neutral
fraction (3). We obtain column density measurements of
several elements. The ionisation corrections due to the GRB is estimated to be
negligible (<0.03 dex), but larger corrections may apply due to the
pre-existing radiation field (up to 0.4 dex based on sub-DLA studies). Our
measurements confirm that the Universe is already predominantly ionised over
the redshift range probed in this work, but was slightly more neutral at z>5.6.
GRBs are useful probes of the ionisation state of the IGM in the early
Universe, but because of internal scatter we need a larger statistical sample
to draw robust conclusions. The high [Si/Fe] in the host can be due to dust
depletion, alpha-element enhancement, or a combination of both. The very high
value of [Al/Fe]=2.40+/-0.78 might connected to the stellar population history.
We estimate the host metallicity to be -1.7<[M/H]<-0.9 (2%-13% of solar).
(trunc.)Comment: 15 pages, 12 figure
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