3,193 research outputs found
Probing the birth of fast rotating magnetars through high-energy neutrinos
We investigate the high-energy neutrino emission expected from newly born
magnetars surrounded by their stellar ejecta. Protons might be accelerated up
to 0.1-100 EeV energies possibly by, e.g., the wave dissipation in the winds,
leading to hadronic interactions in the stellar ejecta. The resulting PeV-EeV
neutrinos can be detected by IceCube/KM3Net with a typical peak time scale of a
few days after the birth of magnetars, making the characteristic soft-hard-soft
behavior. Detections would be important as a clue to the formation mechanism of
magnetars, although there are ambiguities coming from uncertainties of several
parameters such as velocity of the ejecta. Non-detections would also lead to
useful constraints on the scenario.Comment: 5 pages, 3 figures, accepted for publication in PR
ALMA Observations of Ethyl Formate toward Orion KL
Orion KL is one of the prime templates of astrochemical and prebiotic
chemical studies. We wish to explore more organic molecules with increasing
complexity in this region. In particular, we have searched for one of the most
complex organic molecules detected in space so far, ethyl formate
(CHOCHO). This species is the next step in chemical complexity
after the simplest member of esters (methyl formate, CHOCHO). The
mechanisms leading to its formation are still poorly known. We have used high
angular resolution ( 1.5) ALMA observations covering a
large bandwidth from 214 to 247 GHz. We have detected 82 unblended lines of
CHOCHO (49 and 33 of the trans and gauche conformers,
respectively). The line images showed that CHOCHO arises mainly
from the compact ridge and the hot core-southwest regions. The derived
rotational temperatures and column densities are 122 34 K, (0.9
0.3) 10 cm for the hot core-SW, and 103 13 K, (0.6
0.3) 10 cm for the compact ridge. The comparison
of spatial distribution and abundance ratios with chemically related molecules
(methyl formate, ethanol and formic acid) indicates that CHOCHO is
likely formed on the surface of dust grains by addition of CH to
functional-group radicals (CHOCHO) derived from methyl formate
(CHOCHO)
Identification of Two categories of optically bright gamma-ray bursts
We present the results of a systematical analysis of the intrinsic optical
afterglow light curves for a complete sample of gamma-ray bursts (GRBs)
observed in the period from Feb. 1997 to Aug. 2005. These light curves are
generally well-sampled, with at least four detections in the band. The
redshifts of all the bursts in the sample are available. We derive the
intrinsic band afterglow lightcurves (luminosity versus time within the
cosmic proper rest frame) for these GRBs, and discover a fact that they
essentially follow two universal tracks after 2 hours since the GRB triggers.
The optical luminosities at 1 day show a clear bimodal distribution, peaking at
1.4*10^{46} ergs~s^{-1} for the luminous group and 5.3*10^{44} ergs~s^{-1} for
the dim group. About 75% of the GRBs are in the luminous group, and the other
25% belong to the dim group. While the luminous group has a wide range of
redshift distribution, the bursts in the dim group all appear at a redshift
lower than 1.1.Comment: 10 pages, 2 figures, emulateapj style, accepted for publication by
ApJ Letter
Late-Time Optical Afterglow Observations with LBT and MDM
Using the 2.4m MDM and 8.4m Large Binocular Telescope, we observed nine GRB
afterglows to systematically probe the late time behaviors of afterglows
including jet breaks, flares, and supernova bumps. In particular, the LBT
observations have typical flux limits of 25-26 mag in the Sloan r' band, which
allows us to extend the temporal baseline for measuring jet breaks by another
decade in time scale. We detected four jet breaks (including a "textbook" jet
break in GRB070125) and a fifth candidate, all of which are not detectable
without deep, late time optical observations. In the other four cases, we do
not detect the jet breaks either because of contamination from the host galaxy
light, the presence of a supernova bump, or the intrinsic faintness of the
optical afterglow. This suggests that the basic picture that GRBs are
collimated is still valid and that the apparent lack of Swift jet breaks is due
to poorly sampled afterglow light curves, particularly at late times. Besides
the jet breaks, we also detected late time flares, which could attribute to
late central engine activities, and two supernova bumps.Comment: 5 pages, 5 figures, 2008 NANJING GAMMA-RAY BURST CONFERENCE. AIP
Conference Proceedings, Volume 1065, pp. 93-97 (2008), Eds. Y.F. Huang, Z.G.
Dai, B. Zhan
Early photon-shock interaction in stellar wind: sub-GeV photon flash and high energy neutrino emission from long GRBs
For gamma-ray bursts (GRBs) born in a stellar wind, as the reverse shock
crosses the ejecta, usually the shocked regions are still precipitated by the
prompt MeV \gamma-ray emission. Because of the tight overlapping of the MeV
photon flow with the shocked regions, the optical depth for the GeV photons
produced in the shocks is very large. These high energy photons are absorbed by
the MeV photon flow and generate relativistic e^\pm pairs. These pairs
re-scatter the soft X-ray photons from the forward shock as well as the prompt
\gamma-ray photons and power detectable high energy emission, significant part
of which is in the sub-GeV energy range. Since the total energy contained in
the forward shock region and the reverse shock region are comparable, the
predicted sub-GeV emission is independent on whether the GRB ejecta are
magnetized (in which case the reverse shock IC and synchrotron self-Compton
emission is suppressed). As a result, a sub-GeV flash is a generic signature
for the GRB wind model, and it should be typically detectable by the future
{\em Gamma-Ray Large Area Telescope} (GLAST). Overlapping also influence
neutrino emission. Besides the 10^{15} \sim 10^{17} eV neutrino emission
powered by the interaction of the shock accelerated protons with the
synchrotron photons in both the forward and reverse shock regions, there comes
another eV neutrino emission component powered by protons interacting
with the MeV photon flow. This last component has a similar spectrum to the one
generated in the internal shock phase, but the typical energy is slightly
lower.Comment: 7 pages, accepted for publication in Ap
Nature and Nurture: a model for soft gamma-ray repeaters
During supernova explosions, strange stars with almost bare quark surfaces
may be formed. Under certain conditions, these stars could be rapidly spun down
by the torque exerted by the fossil disks formed from the fall-back materials.
They may also receive large kicks and hence, have large proper motion
velocities. When these strange stars pass through the spherical ``Oort'' comet
cloud formed during the pre-supernova era, they will capture some small-scale
comet clouds and collide with some comet-like objects occasionally. These
impacts can account for the repeating bursts as observed from the soft gamma
repeaters (SGRs). According to this picture, it is expected that SGR 1900+14
will become active again during 2004-2005.Comment: emulateapj, 5 pages, accepted by ApJ Letter
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