1,758 research outputs found
Simulations of Astrophysical Fluid Instabilities
We present direct numerical simulations of mixing at Rayleigh-Taylor unstable
interfaces performed with the FLASH code, developed at the ASCI/Alliances
Center for Astrophysical Thermonuclear Flashes at the University of Chicago. We
present initial results of single-mode studies in two and three dimensions. Our
results indicate that three-dimensional instabilities grow significantly faster
than two-dimensional instabilities and that grid resolution can have a
significant effect on instability growth rates. We also find that unphysical
diffusive mixing occurs at the fluid interface, particularly in poorly resolved
simulations.Comment: 3 pages, 1 figure. To appear in the proceedings of the 20th Texas
Symposium on Relativistic Astrophysic
Large-Scale Simulations of Clusters of Galaxies
We discuss some of the computational challenges encountered in simulating the
evolution of clusters of galaxies. Eulerian adaptive mesh refinement (AMR)
techniques can successfully address these challenges but are currently being
used by only a few groups. We describe our publicly available AMR code, FLASH,
which uses an object-oriented framework to manage its AMR library, physics
modules, and automated verification. We outline the development of the FLASH
framework to include collisionless particles, permitting it to be used for
cluster simulation.Comment: 3 pages, 3 figures, to appear in Proceedings of the VII International
Workshop on Advanced Computing and Analysis Techniques in Physics Research
(ACAT 2000), Fermilab, Oct. 16-20, 200
Swift and Suzaku Observations of the X-Ray Afterglow from the GRB 060105
Results are presented of early X-ray afterglow observations of GRB 060105 by
Swift and Suzaku. The bright, long gamma-ray burst GRB 060105 triggered the
Swift Burst Alert Telescope (BAT) at 06:49:28 on 5 January 2006. The Suzaku
team commenced a pre-planned target of opportunity observation at 19 ks (5.3
hr) after the Swift trigger. Following the prompt emission and successive very
steep decay, a shallow decay was observed from T_0+187 s to T_0+1287 s. After
an observation gap during T_0 +(1.5-3) ks, an extremely early steep decay was
observed in T_0+(4-30) ks. The lightcurve flattened again at T_0+30 ks, and
another steep decay followed from T_0+50 ks to the end of observations. Both
steep decays exhibited decay indices of 2.3 - 2.4. This very early break, if it
is a jet break, is the earliest case among X-ray afterglow observations,
suggesting a very narrow jet whose opening angle is well below 1 degree. The
unique Suzaku/XIS data allow us to set very tight upper limits on line emission
or absorption in this GRB. For the reported pseudo-redshift of z=4.0+/-1.3 the
upper limit on the iron line equivalent width is 50 eV.Comment: 8 pages, 5 figures, Accepted for publication in PASJ Suzaku Special
Issue (vol. 58
HETE-II and the Interplanetary Network
The FREGATE experiment aboard HETE-II has been successfully integrated into
the Third Interplanetary Network (IPN) of gamma-ray burst detectors. We show
how HETE's timing has been verified in flight, and discuss what HETE can do for
the IPN and vice-versa.Comment: To appear in the proceedings of the conference on Gamma-Ray Burst and
Afterglow Astronomy 2001: A Workshop Celebrating the First Year of the HETE
Mission, to be published by AIP. Figures must be downloaded and printed
separatel
In flight performance and first results of FREGATE
The gamma-ray detector of HETE-2, called FREGATE, has been designed to detect
gamma-ray bursts in the energy range [6-400] keV. Its main task is to alert the
other instruments of the occurrence of a gamma-ray burst (GRB) and to provide
the spectral coverage of the GRB prompt emission in hard X-rays and soft
gamma-rays. FREGATE was switched on on October 16, 2000, one week after the
successful launch of HETE-2, and has been continuously working since then. We
describe here the main characteristics of the instrument, its in-flight
performance and we briefly discuss the first GRB observations.Comment: Invited lecture at the Woods Hole 2001 GRB Conference, 8 pages, 15
figure
The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs
Between 1996 July and 2002 April, one or more spacecraft of the
interplanetary network detected 787 cosmic gamma-ray bursts that were also
detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera
experiments aboard the BeppoSAX spacecraft. During this period, the network
consisted of up to six spacecraft, and using triangulation, the localizations
of 475 bursts were obtained. We present the localization data for these events.Comment: 89 pages, 3 figures. Submitted to the Astrophysical Journal
Supplement Serie
Time-resolved X-ray spectral modeling of an intermediate burst from SGR1900+14 observed by HETE-2/FREGATE and WXM
We present a detailed analysis of a 3.5 s long burst from SGR 1900+14 that occurred on 2001 July 2. The 2-150 keV time-integrated energy spectrum is well described by the sum of two blackbodies whose temperatures are approximately 4.3 and 9.8 keV. The time-resolved energy spectra are similarly well fitted by the sum of two blackbodies. The higher temperature blackbody evolves with time in a manner consistent with a shrinking emitting surface. The interpretation of these results in the context of the magnetar model suggests that the two-blackbody fit is an approximation of an absorbed, multitemperature spectrum expected on theoretical grounds rather than a physical description of the emission. If this is indeed the case, our data provide further evidence for a strong magnetic field and indicate that the entire neutron star was radiating during most of the burst duration
WASP-4b Arrived Early for the TESS Mission
The Transiting Exoplanet Survey Satellite (TESS) recently observed 18
transits of the hot Jupiter WASP-4b. The sequence of transits occurred 81.6
11.7 seconds earlier than had been predicted, based on data stretching
back to 2007. This is unlikely to be the result of a clock error, because TESS
observations of other hot Jupiters (WASP-6b, 18b, and 46b) are compatible with
a constant period, ruling out an 81.6-second offset at the 6.4 level.
The 1.3-day orbital period of WASP-4b appears to be decreasing at a rate of
milliseconds per year. The apparent period change
might be caused by tidal orbital decay or apsidal precession, although both
interpretations have shortcomings. The gravitational influence of a third body
is another possibility, though at present there is minimal evidence for such a
body. Further observations are needed to confirm and understand the timing
variation.Comment: AJ accepte
- âŠ