2,082 research outputs found
The nature of GRB980425 and the search for off-axis GRB signatures in nearby type Ib/c supernovae emission
The identification of type Ib/c supernovae as GRB progenitors is motivated by
the association of GRB980425 with SN1998bw and of GRB030329 with SN2003dh.
While the gamma-ray luminosity of GRB030329 was typical to cosmological GRBs,
the luminosity of the nearby (40 Mpc) GRB980425 was ~5 orders of magnitude
lower. The large luminosity difference is commonly explained by hypothesizing
that either SNe Ib/c produce two different classes of GRBs, or that GRB980425
was a typical cosmological GRB jet viewed off-axis. In the latter scenario,
strong radio emission, ~10^{30} erg/s Hz, is expected at ~1 yr delay due to jet
deceleration to sub-relativistic speed, as observed from GRB970508. The radio
luminosity of SN1998bw was 3 orders of magnitude lower than this value. We show
that the low radio flux may be consistent with the off-axis jet interpretation,
if the density of the wind surrounding the progenitor is lower than typically
expected, \dot{m}=(\dot{M}/10^{-5} M_sun/yr)/(v/10^3 km/s)~0.1 instead of
\dot{m}>=1. The lower value of \dot{m} is consistent with the observed radio
emission from the supernova shock driven into the wind. This interpretation
predicts transition to sub-relativistic expansion at ~10 yr delay, with current
\~1 mJy 10GHz flux and m_V~23 optical flux, and with ~10 mas angular source
size. It also implies that in order to search for the signature of off-axis
GRBs associated with nearby Ib/c supernovae, follow up observations should be
carried on a multi-yr time scale.Comment: 13 pages, 1 figure; 2 references added; ApJ, in pres
GeV Photons from Ultra High Energy Cosmic Rays accelerated in Gamma Ray Bursts
Gamma-ray bursts are produced by the dissipation of the kinetic energy of a
highly relativistic fireball, via the formation of a collisionless shock. When
this happens, Ultra High Energy Cosmic Rays up to 10^20 eV are produced. I show
in this paper that these particles produce, via synchrotron emission as they
cross the acceleration region, photons up to 300 GeV which carry away a small,
~0.01, but non-negligible fraction of the total burst energy. I show that, when
the shock occurs with the interstellar medium, the optical depth to
photon-photon scattering, which might cause energy degradation of the photons,
is small. The burst thusly produced would be detected at Earth simultaneoulsy
with the parent gamma-ray burst, although its duration may differ significantly
from that of the lower energy photons. The expected fluences, ~10^{-5}-10^{-6}
erg/cm^2 are well within the range of planned detectors. A new explanation for
the exceptional burst GRB 940217 is discussed.Comment: Accepted for publication in The Physical Review Letters. 4 pages,
RevTeX needed, no figure
Orphan GRB radio afterglows: Candidates and constraints on beaming
The number of orphan radio afterglows associated with gamma-ray bursts (GRBs)
that should be detected by a flux limited radio survey, is calculated. It is
shown that for jetted GRBs this number is smaller for smaller jet opening angle
(theta), contrary to naive expectation. For a beaming factor
f_b^{-1}=(theta^2/2)^{-1} = 500, roughly the value inferred by Frail et al.
(2001) from analysis of afterglow light curves, we predict that between several
hundreds to several thousands orphan radio afterglows should be detectable
(over all sky) above 1 mJy at GHz frequencies at any given time. This orphan
population is dominated by sources lying at distances of a few hundred Mpc, and
having an age of ~1 yr. A search for point-like radio transients with flux
densities greater than 6 mJy was conducted using the FIRST and NVSS surveys,
yielding a list of 25 orphan candidates. We argue that most of the candidates
are unlikely to be radio supernovae. However, the possibility that they are
radio loud AGNs cannot be ruled out without further observations. Our analysis
sets an upper limit for the all sky number of radio orphans, which corresponds
to a lower limit f_b^{-1}>10 on the beaming factor. Rejection of all candidates
found in our search would imply f_b^{-1}>100. This, and the fact that some
candidates may indeed be radio afterglows, strongly motivate further
observations of these transients.Comment: 18 pages, including 2 figure
Neutrino afterglow from Gamma-Ray Bursts: ~10^{18} eV
We show that a significant fraction of the energy of a gamma-ray burst(GRB)
is probably converted to a burst of 10^{17}-10^{19} eV neutrinos and multiple
GeV gammas that follow the GRB by > 10 s . If, as previously suggested, GRB's
accelerate protons to ~10^{20} eV, then both the neutrinos and the gammas may
be detectable.Comment: Accepted ApJ; added sentence re: sterile neutrinos; related material
at http://www.sns.ias.edu/~jn
High Energy Neutrinos from Astrophysical Sources: An Upper Bound
We show that cosmic-ray observations set a model-independent upper bound to
the flux of high-energy, > 10^14 eV, neutrinos produced by photo-meson (or p-p)
interactions in sources of size not much larger than the proton photo-meson (or
pp) mean-free-path. The bound applies, in particular, to neutrino production by
either AGN jets or GRBs. This upper limit is two orders of magnitude below the
flux predicted in some popular AGN jet models, but is consistent with our
predictions from GRB models. We discuss the implications of these results for
future km^2 high-energy neutrino detectors.Comment: Added discussion showing bound cannot be evaded by invoking magnetic
fields. Accepted Phys Rev
Constraints on the Local Sources of Ultra High-Energy Cosmic Rays
Ultra high-energy cosmic rays (UHECRs) are believed to be protons accelerated
in magnetized plasma outflows of extra-Galactic sources. The acceleration of
protons to ~10^{20} eV requires a source power L>10^{47} erg/s. The absence of
steady sources of sufficient power within the GZK horizon of 100 Mpc, implies
that UHECR sources are transient. We show that UHECR "flares" should be
accompanied by strong X-ray and gamma-ray emission, and that X-ray and
gamma-ray surveys constrain flares which last less than a decade to satisfy at
least one of the following conditions: (i) L>10^{50} erg/s; (ii) the power
carried by accelerated electrons is lower by a factor >10^2 than the power
carried by magnetic fields or by >10^3 than the power in accelerated protons;
or (iii) the sources exist only at low redshifts, z<<1. The implausibility of
requirements (ii) and (iii) argue in favor of transient sources with L>10^{50}
erg/s.Comment: 7 pages, 1 figure, submitted to JCA
High energy neutrinos from magnetars
Magnetars can accelerate cosmic rays to high energies through the unipolar
effect, and are also copious soft photon emitters. We show that young,
fast-rotating magnetars whose spin and magnetic moment point in opposite
directions emit high energy neutrinos from their polar caps through photomeson
interactions. We identify a neutrino cut-off band in the magnetar
period-magnetic field strength phase diagram, corresponding to the photomeson
interaction threshold. Within uncertainties, we point out four possible
neutrino emission candidates among the currently known magnetars, the brightest
of which may be detectable for a chance on-beam alignment. Young magnetars in
the universe would also contribute to a weak diffuse neutrino background, whose
detectability is marginal, depending on the typical neutrino energy.Comment: emulateapj style, 6 pages, 1 figure, ApJ, v595, in press. Important
contributions from Dr. Harding added. Major revisions made. More conservative
and realistic estimates about the neutrino threshold condition and emission
efficiency performed. More realistic typical beaming angle and magnetar birth
rate adopte
A Search for Correlation of Ultra-High Energy Cosmic Rays with IRAS-PSCz and 2MASS-6dF Galaxies
We study the arrival directions of 69 ultra-high energy cosmic rays (UHECRs)
observed at the Pierre Auger Observatory (PAO) with energies exceeding 55 EeV.
We investigate whether the UHECRs exhibit the anisotropy signal expected if the
primary particles are protons that originate in galaxies in the local universe,
or in sources correlated with these galaxies. We cross-correlate the UHECR
arrival directions with the positions of IRAS-PSCz and 2MASS-6dF galaxies
taking into account particle energy losses during propagation. This is the
first time that the 6dF survey is used in a search for the sources of UHECRs
and the first time that the PSCz survey is used with the full 69 PAO events.
The observed cross-correlation signal is larger for the PAO UHECRs than for 94%
(98%) of realisations from an isotropic distribution when cross-correlated with
the PSCz (6dF). On the other hand the observed cross-correlation signal is
lower than that expected from 85% of realisations, had the UHECRs originated in
galaxies in either survey. The observed cross-correlation signal does exceed
that expected by 50% of the realisations if the UHECRs are randomly deflected
by intervening magnetic fields by 5 degrees or more. We propose a new method of
analysing the expected anisotropy signal, by dividing the predicted UHECR
source distribution into equal predicted flux radial shells, which can help
localise and constrain the properties of UHECR sources. We find that the 69 PAO
events are consistent with isotropy in the nearest of three shells we define,
whereas there is weak evidence for correlation with the predicted source
distribution in the two more distant shells in which the galaxy distribution is
less anisotropic.Comment: 23 pages, version published in JCA
High Energy Neutrinos from Cosmological Gamma-Ray Burst Fireballs
Observations suggest that -ray bursts (GRBs) are produced by the
dissipation of the kinetic energy of a relativistic fireball. We show that a
large fraction, , of the fireball energy is expected to be converted
by photo-meson production to a burst of neutrinos. A km^2
neutrino detector would observe at least several tens of events per year
correlated with GRBs, and test for neutrino properties (e.g. flavor
oscillations, for which upward moving 's would be a unique signature, and
coupling to gravity) with an accuracy many orders of magnitude better than is
currently possible.Comment: Submitted to PRL (4 pages, LaTeX
Ultra high energy neutrinos from gamma ray bursts
Protons accelerated to high energies in the relativistic shocks that generate
gamma ray bursts photoproduce pions, and then neutrinos in situ. I show that
ultra high energy neutrinos (> 10^19 eV) are produced during the burst and the
afterglow. A larger flux, also from bursts, is generated via photoproduction
off CMBR photons in flight but is not correlated with currently observable
bursts, appearing as a bright background. Adiabatic/synchrotron losses from
protons/pions/muons are negligible. Temporal and directional coincidences with
bursts detected by satellites can separate correlated neutrinos from the
background.Comment: Adiabatic/synchrotron losses from protons/pions/muons shown to be
negligible. Accepted for publication in Phys. Rev. Letters. RevTe
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