895 research outputs found
Analisis Kesalahan Siswa dalam Menyelesaikan Soal Sistem Persamaan Linear Dua Variabel pada Siswa Kelas VIII Mts di Kabupaten Bandung Barat
This study aims to describe the mistakes made by students and analyze the factors that cause student errors in completing in SPLDV material. The method used in this study is descriptive qualitative. This research took place in the eighth grade Al Barry MTs cikalong wetan in the 2018/2019 academic year. The population of this study was all eighth grade students of junior high / MTs in the western Bandung regency who had studied SPLDV material. The research subjects were class VIII A students at MTs Al Barry cikalong wetan. Data collection techniques using test and interview methods. The steps of analysis include data reduction, data presentation, and verification. Based on the results of data analysis it can be concluded that in solving SPLDV problems making mistakes; (1) Concept errors, (2) errors in understanding questions, (3) calculation errors. The causative factor is the students\u27 understanding ability which is low in mastering the concept, lack of training in completing varied questions, hurrying and not being careful in solving problems
Implications of the Visible and X-Ray Counterparts to GRB970228
The gamma-ray burst source GRB970228 has been observed after a delay of 8--12
hours in X-rays and after one day in visible and near infrared light. This
marks the first detection of emission at lower frequencies following the
gamma-ray observation of a GRB and the first detection of any visible
counterpart to a GRB. We consider possible delayed visible and X-ray emission
mechanisms, and conclude that the intrinsic gamma-ray activity continued at a
much reduced intensity for at least a day. There are hints of such continued
activity in other GRB, and future observations can decide if this is true of
GRB in general. The observed multi-band spectrum of GRB970228 agrees with the
predictions of relativistic shock theory when the flux is integrated over a
time longer than that required for a radiating electron to lose its energy.Comment: 5 pp., tex, 1 figur
GRB as explosions with standard power
We show that the distribution of observed energies of GRB with known
redshifts can be explained by the hypothesis of the standard energy release
E_0=5 10^51 ergs. Two situations are possible, either the beaming angle differs
from burst to burst, or there is a universal emssion diagram in each burst, the
observed difference being due to different viewing angles.Comment: 4 pages, 3 figures, use A&A styl
The redshift and afterglow of the extremely energetic gamma-ray burst GRB 080916C
The detection of GeV photons from gamma-ray bursts (GRBs) has important
consequences for the interpretation and modelling of these most-energetic
cosmological explosions. The full exploitation of the high-energy measurements
relies, however, on the accurate knowledge of the distance to the events. Here
we report on the discovery of the afterglow and subsequent redshift
determination of GRB 080916C, the first GRB detected by the Fermi Gamma-Ray
Space Telescope with high significance detection of photons at >0.1 GeV.
Observations were done with 7-channel imager GROND at the 2.2m MPI/ESO
telescope, the SIRIUS instrument at the Nagoya-SAAO 1.4m telescope in South
Africa, and the GMOS instrument at Gemini-S. The afterglow photometric redshift
of z=4.35+-0.15, based on simultaneous 7-filter observations with the Gamma-Ray
Optical and Near-infrared Detector (GROND), places GRB 080916C among the top 5%
most distant GRBs, and makes it the most energetic GRB known to date. The
detection of GeV photons from such a distant event is rather surprising.
The observed gamma-ray variability in the prompt emission together with the
redshift suggests a lower limit for the Lorentz factor of the
ultra-relativistic ejecta of Gamma > 1090. This value rivals any previous
measurements of Gamma in GRBs and strengthens the extreme nature of GRB
080916C.Comment: 6 pages, 5 figures; subm. to A&
Detection of a supernova signature associated with GRB 011121
Using observations from an extensive monitoring campaign with the Hubble
Space Telescope we present the detection of an intermediate-time flux excess
which is redder in color relative to the afterglow of GRB 011121, currently
distinguished as the gamma-ray burst with the lowest known redshift. The red
``bump,'' which exhibits a spectral roll-over at ~7200 Angstrom, is well
described by a redshifted Type Ic supernova that occurred approximately at the
same time as the gamma-ray burst event. The inferred luminosity is about half
that of the bright supernova 1998bw. These results serve as compelling evidence
for a massive star origin of long-duration gamma-ray bursts. Models that posit
a supernova explosion weeks to months preceding the gamma-ray burst event are
excluded by these observations. Finally, we discuss the relationship between
spherical core-collapse supernovae and gamma-ray bursts.Comment: Published in the Astrophysical Journal (Letters) on 20 May 2002.
Seven LaTeX pages, three Postscript figures, one tabl
Spectra and Light Curves of GRB Afterglows
We performed accurate numerical calculations of angle-, time-, and
frequency-dependent radiative transfer for the relativistic motion of matter in
gamma-ray burst (GRB) models. Our technique for solving the transfer equation,
which is based on the method of characteristics, can be applied to the motion
of matter with a Lorentz factor up to 1000. The effect of synchrotron
self-absorption is taken into account. We computed the spectra and light curves
from electrons with a power-law energy distribution in an expanding
relativistic shock and compare them with available analytic estimates. The
behavior of the optical afterglows from GRB 990510 and GRB 000301c is discussed
qualitatively.Comment: 8 pages, 7 figure
Observational Constraints on the Angular and Spectral Distributions of Photons in Gamma-Ray Burst Sources
The typical spectra of gamma-ray bursts (GRBs) are discussed in the context
of the compactness problem for GRB sources and how it is resolved in the
popular fireball model. In particular, observational (model-independent)
constraints on the collimation of the gamma-rays and the dependence of the
collimation angle on the photon energy are considered. The fact that the
threshold for the creation of pairs depends on the angle between
the momenta of the annihilating photons in the GRB source provides an
alternative solution to the compactness problem. A new approach to explaining
GRBs, taking into account the angular dependence for pair creation, is
proposed, and the main features of a scenario describing a GRB source with a
total (photon) energy smaller or of the order of erg are laid out.
Thus, we are dealing with an alternative to an ultra-relativistic fireball, if
it turns out (as follows from observations) that all "long" GRBs are associated
with normal (not peculiar) core-collapse supernovae. The effects of radiation
pressure and the formation of jets as a consequence of even a small amount of
anisotropy in the total radiation field in a (compact) GRB source are examined
in this alternative model. Possible energy release mechanisms acting in regions
smaller or of the order of cm in size (a compact model for a GRB) are
discussed. New observational evidence for such compact energy release in the
burst source is considered.Comment: 15 pages, no figures, no table
The exceptionally extended flaring activity in the X-ray afterglow of GRB 050730 observed with Swift and XMM-Newton
We present the results of a detailed spectral and temporal analysis of Swift
and XMM-Newton observations of the high redshift (z=3.969) GRB 050730. The
X-ray afterglow of GRB 050730 was found to decline with time with superimposed
intense flaring activity that extended over more than two orders of magnitude
in time. Seven distinct re-brightening events starting from 236 s up to 41.2 ks
after the burst were observed. The underlying decay of the afterglow was well
described by a double broken power-law model with breaks at t_1= 237 +/- 20 s
and t_2 = 10.1 (-2.2) (+4.6) ks. The temporal decay slopes before, between and
after these breaks were alpha_1 = 2.1 +/- 0.3, alpha_2 = 0.44 (-0.08) (+0.14)
and alpha_3 = 2.40 (+0.07) (-0.09), respectively. The spectrum of the X-ray
afterglow was well described by a photoelectrically absorbed power-law with an
absorbing column density N_H=(1.28 +/- 0.26) 10^22 cm^-2 in the host galaxy.
Strong X-ray spectral evolution during the flaring activity was present. In the
majority of the flares (6/7) the ratio Delta_t/t_p between the duration of the
event and the time when the flare peaks was nearly constant and about 0.6-0.7.
We showed that the observed spectral and temporal properties of the first three
flares are consistent with being due both to high-latitude emission, as
expected if the flares were produced by late internal shocks, or to refreshed
shocks, i.e. late time energy injections into the main afterglow shock by slow
moving shells ejected from the central engine during the prompt phase. The
event fully satisfies the E_p-E_iso Amati relation while is not consistent with
the E_p-E_jet Ghirlanda relation.Comment: 12 pages, 5 figures, accepted for publication in A&
Swift XRT Observations of the Breaking X-ray Afterglow of GRB 050318
We report the results of Swift X-Ray Telescope (XRT) observations of GRB
050318. This event triggered the Burst Alert Telescope (BAT) aboard Swift and
was followed-up with XRT and UVOT for 11 consecutive orbits starting from 54
minutes after the trigger. A previously unknown fading X-ray source was
detected and accurately monitored. The source was found to decrease in
intensity with time and a clear temporal break occurring at ~18000 s after the
trigger was observed. The X-ray light curve was found to be consistent with a
broken power-law with decay indices -1.17 +/- 0.08 and -2.10 (+0.22) (-0.24)
before and after the break. The spectrum of the X-ray afterglow was well
described by a photoelectrically absorbed power-law with energy index of -1.09
+/-0.09. No evidence of spectral evolution was found. We compare these results
with those obtained with UVOT and separately reported and refine the data
analysis of BAT. We discuss our results in the framework of a collimated
fireball model and a synchrotron radiation emission mechanism. Assuming the GRB
redshift derived from the farthest optical absorption complex (z = 1.44), the
event is fully consistent with the E_p-E_iso correlation.Comment: Accepted for publication in A&A Letters (5 pages, 3 figures
Comparative study of electroabsorption in InGaN/GaN quantum zigzag heterostructures with polarization-induced electric fields
Cataloged from PDF version of article.We present a comparative study on InGaN/GaN quantum zigzag structures embedded in p-i-n diode architecture that exhibit blue-shifting electroabsorption in the blue when an electric field is externally applied to compensate for the polarization-induced electric field across the wells. With the polarization breaking their symmetry, the same InGaN/GaN quantum structures redshift their absorption edge when the external field is applied in the same direction as the well polarization. Both computationally and experimentally, we investigate the effects of polarization on electroabsorption by varying compositional content and structural parameters and demonstrate that electroabsorption grows stronger with weaker polarization in these multiple quantum well modulators. (c) 2008 American Institute of Physics
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