78 research outputs found
Hunting: Spear Flight Profiles
We build upon our previous work on prehistoric spear velocity and use Excel to calculate the velocity throughout the spear’s motion and therefore calculate the maximum range it could achieve with and without a launching aid such as an atlatl
Hunting: Prehistoric Spear Velocity
In this paper we outline a series of equations that describe a spear’s velocity profile, with respect to time, that is based on a simplified model of projectile launching techniques and drag forces
VISUAL IMAGES AS HOOKS FOR PROBLEM-BASED LEARNING
ABSTRACT In problem-based learning students are presented with a problem as the motivation for group research. The presentation of the problem attempts to address the issue of ownership of content by both providing a context for knowledge acquisition and requiring a transformation of material to address the problem. The transformational aspect in principle provides the opportunity for creativity. We present two case studies, with different outcomes, and the results of a workshop, in which visual imagery was used as the hook for a PBL problem with a view to encouraging creativity in the responses
GRB 050505: A high redshift burst discovered by Swift
We report the discovery and subsequent multi-wavelength afterglow behaviour
of the high redshift (z = 4.27) Gamma Ray Burst GRB 050505. This burst is the
third most distant burst, measured by spectroscopic redshift, discovered after
GRB 000131 (z = 4.50) and GRB 050904 (z = 6.29). GRB 050505 is a long GRB with
a multipeaked gamma-ray light curve, with a duration of T_90 = 63+/-2 s and an
inferred isotropic release in gamma-rays of ~4.44 x 10^53 ergs in the 1-10^4
keV rest frame energy range. The Swift X-Ray Telescope followed the afterglow
for 14 days, detecting two breaks in the light curve at 7.4(+/-1.5) ks and 58.0
(+9.9/-15.4) ks after the burst trigger. The power law decay slopes before,
between and after these breaks were 0.25 (+0.16/-0.17), 1.17 (+0.08/-0.09) and
1.97 (+0.27/-0.28) respectively. The light curve can also be fit with a
`smoothly broken' power law model with a break observed at ~ T+18.5 ks, with
decay slopes of ~0.4 and ~1.8 before and after the break respectively. The
X-ray afterglow shows no spectral variation over the course of the Swift
observations, being well fit with a single power law of photon index ~1.90.
This behaviour is expected for the cessation of continued energisation of the
ISM shock followed by a break caused by a jet, either uniform or structured.
Neither break is consistent with a cooling break. The spectral energy
distribution indeed shows the cooling frequency to be below the X-ray but above
optical frequencies. The optical -- X-ray spectrum also shows that there is
significant X-ray absorption in excess of that due to our Galaxy but very
little optical/UV extinction, with E(B-V) ~0.10 for a SMC-like extinction
curve.Comment: 9 pages, 6 figures. Accepted by MNRA
X-ray Spectroscopy of MXB 1728-34 with XMM-Newton
We have analysed an XMM-Newton observation of the low mass X-ray binary and
atoll source MXB 1728-34. The source was in a low luminosity state during the
XMM-Newton observation, corresponding to a bolometric X-ray luminosity of
5*10E36 d^2 erg/s, where d is the distance in units of 5.1 kpc. The 1-11 keV
X-ray spectrum of the source, obtained combining data from all the five
instruments on-board XMM-Newton, is well fitted by a Comptonized continuum.
Evident residuals are present at 6-7 keV which are ascribed to the presence of
a broad iron emission line. This feature can be equally well fitted by a
relativistically smeared line or by a self-consistent, relativistically
smeared, reflection model. Under the hypothesis that the iron line is produced
by reflection from the inner accretion disk, we can infer important information
on the physical parameters of the system, such as the inner disk radius, Rin =
25-100 km, and the inclination of the system, 44{\deg} < i < 60{\deg}.Comment: 7 pages, 3 figures, Accepted by A&A on 29.03.201
GRB 050717: A Long, Short-Lag Burst Observed by Swift and Konus
The long burst GRB 050717 was observed simultaneously by the Burst Alert Telescope (BAT) on Swift and the Konus instrument on Wind. Significant hard to soft spectral evolution was seen. Early gamma-ray and X-ray emission was detected by both BAT and the X-Ray Telescope (XRT) on Swift. The XRT continued to observe the burst for 7.1 days and detect it for 1.4 days. The X-ray light curve showed a classic decay pattern including evidence of the onset of the external shock emission at approx. 50 s after the trigger; the afterglow was too faint for a jet break to be detected. No optical, infrared or ultraviolet counterpart was discovered despite deep searches within 14 hours of the burst. The spectral lag for GRB 050717 was determined to be 2.5 +/- 2.6 ms, consistent, with zero and unusually short for a long burst. This lag measurement suggests that this burst has a high intrinsic luminosity and hence is at high redshift (z > 2.7). 050717 provides a good example of classic prompt and afterglow behavior for a gamma-ray burst
The early X-ray afterglows of optically bright and dark Gamma-Ray Bursts
A systematical study on the early X-ray afterglows of both optically bright
and dark gamma-ray bursts (B-GRBs and D-GRBs) observed by Swift has been
presented. Our sample includes 25 GRBs. Among them 13 are B-GRBs and 12 are
D-GRBs. Our results show that the distributions of the X-ray afterglow fluxes
(), the gamma-ray fluxes (), and the ratio ()
for both the D-GRBs and B-GRBs are similar. The differences of these
distributions for the two kinds of GRBs should be statistical fluctuation.
These results indicate that the progenitors of the two kinds of GRBs are the
same population. Their total energy explosions are comparable. The suppression
of the optical emissions from D-GRBs should results from circumburst but not
their central engine.Comment: 10 pages, 3 figures, 1 table; accepted by ChJA
The prompt to late-time multiwavelength analysis of GRB 060210
We present our analysis of the multiwavelength photometric & spectroscopic
observations of GRB 060210 and discuss the results in the overall context of
current GRB models. All available optical data underwent a simultaneous
temporal fit, while X-ray and gamma-ray observations were analysed temporally &
spectrally. The results were compared to each other and to possible GRB models.
The X-ray afterglow is best described by a smoothly broken power-law with a
break at 7.4 hours. The late optical afterglow has a well constrained single
power-law index which has a value between the two X-ray indices, though it does
agree with a single power-law fit to the X-ray. An evolution of the hardness of
the high-energy emission is demonstrated and we imply a minimum host extinction
from a comparison of the extrapolated X-ray flux to that measured in the
optical. We find that the flaring gamma-ray and X-ray emission is likely due to
internal shocks while the flat optical light curve at that time is due to the
external shock. The late afterglow is best explained by a cooling break between
the optical and X-rays and continued central engine activity up to the time of
the break. The required collimation corrected energy of ~ 2x10^52 erg, while at
the high end of the known energy distribution, is not unprecedented.Comment: 8 pages, 4 figures, accepted to Astronomy & Astrophysics after minor
change
An extended XMM-Newton observation of the Seyfert galaxy NGC 4051 - III. FeK emission and absorption
An extended XMM-Newton observation of the Seyfert 1 galaxy NGC 4051 in 2009
detected a photo-ionized outflow with a complex absorption line velocity
structure and a broad correlation of velocity with ionization parameter, shown
in Pounds et al (2011) to be consistent with a highly ionized, high velocity
wind running into the interstellar medium or previous ejecta, losing much of
its kinetic energy in the resultant strong shock. In the present paper we
examine the Fe K spectral region in more detail and find support for two
distinct velocity components in the highly ionized absorber, with values
corresponding to the putative fast wind (~ 0.12c) and the post-shock flow (v ~
5000-7000 km/s). The Fe K absorption line structure is seen to vary on a
orbit-to-orbit timescale, apparently responding to both a short term increase
in ionizing flux and - perhaps more generally - to changes in the soft X-ray
(and simultaneous UV) luminosity. The latter result is particularly interesting
in providing independent support for the existence of shocked gas being cooled
primarily by Compton scattering of accretion disc photons. The Fe K emission is
represented by a narrow fluorescent line from near-neutral matter, with a weak
red wing modelled here by a relativistic diskline. The narrow line flux is
quasi-constant throughout the 45-day 2009 campaign, but is resolved, with a
velocity width consistent with scattering from a component of the post-shock
flow. Evidence for a P Cygni profile is seen in several individual orbit
spectra for resonance transitions in both Fe XXV and Fe XXVI.Comment: submitted to MNRA
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