2,167 research outputs found
A mechanical coordinate converter
Mechanical converter for spherical coordinates used in polariscope balloon program
Polarimetry from high-altitude balloons
Polarimetry at 2850a and 2250a from high altitude balloon
Probes of Diffusive Shock Acceleration using Gamma-Ray Burst Prompt Emission
The principal paradigm for gamma-ray bursts (GRBs) suggests that the prompt
transient gamma-ray signal arises from multiple shocks internal to the
relativistic expansion. This paper explores how GRB prompt emission spectra can
constrain electron (or ion) acceleration properties at the relativistic shocks
that pertain to GRB models. The array of possible high-energy power-law indices
in accelerated populations is highlighted, focusing on how spectra above 1 MeV
can probe the field obliquity in GRB internal shocks, and the character of
hydromagnetic turbulence in their environs. When encompassing the MeV-band
spectral break, fits to BATSE/EGRET burst data indicate that the preponderance
of electrons responsible for the prompt emission reside in an intrinsically
non-thermal population. This differs markedly from typical populations
generated in acceleration simulations; potential resolutions of this conflict
such as the action of self-absorption are mentioned. Spectral modeling also
suggests that the synchrotron mechanism is favored over synchrotron
self-Compton scenarios due to the latter's typically broad curvature near the
peak. Such diagnostics will be enhanced by the broadband spectral coverage of
bursts by the Fermi Gamma-Ray Space Telescope; the GBM will provide key
information on the lower energy portions of the non-thermal particle
population, while the LAT will constrain the power-law regime of particle
acceleration.Comment: 6 pages, 1 embedded figure, to appear in Proc. of the 6th Huntsville
Gamma-Ray Burst Symposium, eds. C. A. Meegan, N. Gehrels, and C. Kouveliotou
(AIP Conf. Proc., New York
Spectrophotometry of planets, asteroids and satellites from the international ultraviolet explorer satellite
A total of 14 8 hour I.U.E. observing sessions resulted in 39 spectra of 11 asteroids and 9 solar type stars as well as 57 spectra at various locations on the disk of Jupiter. The Jupiter observations include a total of 5 center to limb series of spectra at various latitudes and a North South series along the central meridian. In the range from 2000-3000 A, the planet shows a striking decrease in brightness at latitudes greater than about 30 degrees, and exhibits limb brightening at low latitudes and limb darkening at high latitudes. Preliminary results indicate that about 6 km-amagats of clean hydrogen are required above a haze of absorbing aerosols to reproduce the limb brightening observed at 2500 A in the equatorial regions. At higher latitudes, the aerosols extend to even higher levels of the atmosphere. Comparison of the Jovian data with detailed model calculations and the analyses of the asteroid spectra are still in progress with other support
The First INTEGRAL AGN Catalog
We present the first INTEGRAL AGN catalog, based on observations performed
from launch of the mission in October 2002 until January 2004. The catalog
includes 42 AGN, of which 10 are Seyfert 1, 17 are Seyfert 2, and 9 are
intermediate Seyfert 1.5. The fraction of blazars is rather small with 5
detected objects, and only one galaxy cluster and no star-burst galaxies have
been detected so far. A complete subset consists of 32 AGN with a significance
limit of 7 sigma in the INTEGRAL/ISGRI 20-40 keV data. Although the sample is
not flux limited, the distribution of sources shows a ratio of obscured to
unobscured AGN of 1.5 - 2.0, consistent with luminosity dependent unified
models for AGN. Only four Compton-thick AGN are found in the sample. Based on
the INTEGRAL data presented here, the Seyfert 2 spectra are slightly harder
(Gamma = 1.95 +- 0.01) than Seyfert 1.5 (Gamma = 2.10 +- 0.02) and Seyfert 1
(Gamma = 2.11 +- 0.05).Comment: 17 pages, 12 figures, accepted for publication in Ap
The Progenitor of the New COMPTEL/ROSAT Supernova Remnant in Vela
We show that (1) the newly discovered supernova remnant (SNR), GRO
J0852--4642/RX J0852.0--4622, was created by a core-collapse supernova of a
massive star, and (2) the same supernova event which produced the Ti
detected by COMPTEL from this source is probably also responsible for a large
fraction of the observed Al emission in the Vela region detected by the
same instrument. The first conclusion is based on the fact that the remnant is
currently expanding too slowly given its young age for it to be caused by a
Type Ia supernova. If the current SNR shell expansion speed is greater than
3000 km/s, a Type II supernova with a moderate kinetic energy
exploding at about 150 pc away is favored. If the SNR expansion speed is lower
than 2000 km s, as derived naively from the X-ray data, a much more
energetic supernova is required to have occurred at pc away in a
dense environment at the edge of the Gum nebula. This progenitor has a
preferred ejecta mass of and therefore, it is probably a Type
Ib or Type Ic supernova. However, the required high ambient density of in this scenario is difficult to reconcile with the regional CO
data. A combination of our estimates of the age/energetics of the new SNR and
the almost perfect positional coincidence of the new SNR with the centroid of
the COMPTEL Al emission feature of the Vela region strongly favors a
causal connection. If confirmed, this will be the first case where both
Ti and Al are detected from the same young SNR and together they
can be used to select preferred theoretical core-collapse supernova models.Comment: Revised, 10 pages, 2 figures, to appear in ApJ Lett Vol.514 on April
1, 199
Anisotropy in the sky distributions of the short and intermediate gamma-ray bursts: Breakdown of the cosmological principle?
After the discovery of the anisotropy in the sky-distribution of intermediate
gamma-ray bursts recently also the distribution of the short gamma-ray bursts
is proven to be anisotropic. The impact of these behaviors on the validity of
the cosmological principle is shortly discussed.Comment: 3 pages, 1 figure, to appear in the proceedings of the Sixth
Huntsville Gamma-Ray Burst Symposium, edited by C.A. Meegan, N. Gehrels, and
C. Kouvelioto
Gamma-Ray Telescopes (in "400 Years of Astronomical Telescopes")
The last half-century has seen dramatic developments in gamma-ray telescopes,
from their initial conception and development through to their blossoming into
full maturity as a potent research tool in astronomy. Gamma-ray telescopes are
leading research in diverse areas such as gamma-ray bursts, blazars, Galactic
transients, and the Galactic distribution of aluminum-26.Comment: 11 pages, 6 figures/ in "400 Years of Astronomical Telescopes: A
Review of History, Science and Technology", ed. B.R. Brandl, R. Stuik, & J.K.
Katgert-Merkeli (Exp. Astron. 26, 111-122 [2009]
INTEGRAL and XMM-Newton Spectral Studies of NGC 4388
We present first INTEGRAL and XMM-Newton observations of a Seyfert galaxy,
the type 2 AGN NGC 4388. Several INTEGRAL observations performed in 2003 allow
us to study the spectrum in the 20 - 300 keV range. In addition two XMM-Newton
observations give detailed insight into the 0.2 - 10 keV emission. The
measurements presented here and comparison with previous observations by
BeppoSAX, SIGMA and CGRO/OSSE show that the overall spectrum from soft X-rays
up to the gamma-rays can be described by a highly absorbed (N_H = 2.7e23
1/cm^2) and variable non-thermal component in addition to constant non-absorbed
thermal emission (T = 0.8 keV) of low abundance (7% solar), plus a constant Fe
K-alpha and K-beta line. The hard X-ray component is well described by a simple
power law with a mean photon index of 1.7. During the INTEGRAL observations the
20 - 100 keV flux increased by a factor of 1.4. The analysis of XMM-Newton data
implies that the emission below 3 keV is decoupled from the AGN and probably
due to extended emission as seen in Chandra observations. The constant iron
line emission is apparently also decoupled from the direct emission of the
central engine and likely to be generated in the obscuring material, e.g. in
the molecular torus.Comment: 11 pages, 5 figures, accepted for publication in Ap
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