66 research outputs found
Core-collapse astrophysics with a five-megaton neutrino detector
The legacy of solar neutrinos suggests that large neutrino detectors should be sited underground. However, to instead go underwater bypasses the need to move mountains, allowing much larger water Čerenkov detectors. We show that reaching a detector mass scale of ~5 Megatons, the size of the proposed Deep-TITAND, would permit observations of neutrino “mini-bursts” from supernovae in nearby galaxies on a roughly yearly basis, and we develop the immediate qualitative and quantitative consequences. Importantly, these mini-bursts would be detected over backgrounds without the need for optical evidence of the supernova, guaranteeing the beginning of time-domain MeV neutrino astronomy. The ability to identify, to the second, every core collapse in the local Universe would allow a continuous “death watch” of all stars within ~5 Mpc, making practical many previously-impossible tasks in probing rare outcomes and refining coordination of multiwavelength/multiparticle observations and analysis. These include the abilities to promptly detect otherwise-invisible prompt black hole formation, provide advance warning for supernova shock-breakout searches, define tight time windows for gravitational-wave searches, and identify “supernova impostors” by the nondetection of neutrinos. Observations of many supernovae, even with low numbers of detected neutrinos, will help answer questions about supernovae that cannot be resolved with a single high-statistics event in the Milky Way
An Unexpectedly Swift Rise in the Gamma-ray Burst Rate
The association of long gamma-ray bursts with supernovae naturally suggests
that the cosmic GRB rate should trace the star formation history. Finding
otherwise would provide important clues concerning these rare, curious
phenomena. Using a new estimate of Swift GRB energetics to construct a sample
of 36 luminous GRBs with redshifts in the range z=0-4, we find evidence of
enhanced evolution in the GRB rate, with ~4 times as many GRBs observed at z~4
than expected from star formation measurements. This direct and empirical
demonstration of needed additional evolution is a new result. It is consistent
with theoretical expectations from metallicity effects, but other causes remain
possible, and we consider them systematically.Comment: 4 pages, 4 figures; minor changes to agree with published versio
Potential for Supernova Neutrino Detection in MiniBooNE
The MiniBooNE detector at Fermilab is designed to search for oscillation appearance at and to make a
decisive test of the LSND signal. The main detector (inside a veto shield) is a
spherical volume containing 0.680 ktons of mineral oil. This inner volume,
viewed by 1280 phototubes, is primarily a \v{C}erenkov medium, as the
scintillation yield is low. The entire detector is under a 3 m earth
overburden. Though the detector is not optimized for low-energy (tens of MeV)
events, and the cosmic-ray muon rate is high (10 kHz), we show that MiniBooNE
can function as a useful supernova neutrino detector. Simple trigger-level cuts
can greatly reduce the backgrounds due to cosmic-ray muons. For a canonical
Galactic supernova at 10 kpc, about 190 supernova
events would be detected. By adding MiniBooNE to the international network of
supernova detectors, the possibility of a supernova being missed would be
reduced. Additionally, the paths of the supernova neutrinos through Earth will
be different for MiniBooNE and other detectors, thus allowing tests of
matter-affected mixing effects on the neutrino signal.Comment: Added references, version to appear in PR
New Signal of Atmospheric Tau Neutrino Appearance: Sub-GeV Neutral-Current Interactions in JUNO
We propose the first practical method to detect atmospheric tau neutrino
appearance at sub-GeV energies, which would be an important test of oscillations and of new-physics scenarios. In the
Jiangmen Underground Neutrino Observatory (JUNO; starts in 2024), active-flavor
neutrinos eject neutrons from carbon via neutral-current quasielastic
scattering. This produces a two-part signal: the prompt part is caused by the
scattering of the neutron in the scintillator, and the delayed part by its
radiative capture. Such events have been observed in KamLAND, but only in small
numbers and were treated as a background. With
oscillations, JUNO should measure a clean sample of 55 events/yr; with simple
disappearance, this would instead be 41 events/yr, where the latter
is determined from Super-Kamiokande charged-current measurements at similar
neutrino energies. Implementing this method will require precise laboratory
measurements of neutrino-nucleus cross sections or other developments. With
those, JUNO will have sensitivity to tau-neutrino appearance in 5
years exposure, and likely sooner.Comment: 12 pages, 8 figure
(Not as) Big as a Barn: Upper Bounds on Dark Matter-Nucleus Cross Sections
Critical probes of dark matter come from tests of its elastic scattering with
nuclei. The results are typically assumed to be model-independent, meaning that
the form of the potential need not be specified and that the cross sections on
different nuclear targets can be simply related to the cross section on
nucleons. For point-like spin-independent scattering, the assumed scaling
relation is , where the comes from coherence and the from kinematics for . Here we calculate where model
independence ends, i.e., where the cross section becomes so large that it
violates its defining assumptions. We show that the assumed scaling relations
generically fail for dark matter-nucleus cross sections , significantly below the geometric sizes of
nuclei, and well within the regime probed by underground detectors. Last, we
show on theoretical grounds, and in light of existing limits on light
mediators, that point-like dark matter cannot have , above which many claimed constraints originate
from cosmology and astrophysics. The most viable way to have such large cross
sections is composite dark matter, which introduces significant additional
model dependence through the choice of form factor. All prior limits on dark
matter with cross sections with
must therefore be re-evaluated and reinterpreted.Comment: 17 pages, 7 figures, comments are welcom
The Star Formation Rate in the Reionization Era as Indicated by Gamma-ray Bursts
High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to
study aspects of the early Universe, including the cosmic star formation rate
(SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z = 6.7 and
GRB 090423 at z = 8.1, and more than four years of Swift observations, we first
confirm that the GRB rate does not trace the SFR in an unbiased way. Correcting
for this, we find that the implied SFR to beyond z = 8 is consistent with
LBG-based measurements after accounting for unseen galaxies at the faint end of
the UV luminosity function. We show that this provides support for the
integrated star formation in the range 6 < z < 8 to have been alone sufficient
to reionize the Universe.Comment: 4 pages, 4 figures; modified to match version accepted for
publication in ApJ Letter
Revealing the High-Redshift Star Formation Rate with Gamma-Ray Bursts
While the high-z frontier of star formation rate (SFR) studies has advanced
rapidly, direct measurements beyond z ~ 4 remain difficult, as shown by
significant disagreements among different results. Gamma-ray bursts, owing to
their brightness and association with massive stars, offer hope of clarifying
this situation, provided that the GRB rate can be properly related to the SFR.
The Swift GRB data reveal an increasing evolution in the GRB rate relative to
the SFR at intermediate z; taking this into account, we use the highest-z GRB
data to make a new determination of the SFR at z = 4-7. Our results exceed the
lowest direct SFR measurements, and imply that no steep drop exists in the SFR
up to at least z ~ 6.5. We discuss the implications of our result for cosmic
reionization, the efficiency of the universe in producing stellar-mass black
holes, and ``GRB feedback'' in star-forming hosts.Comment: 4 pages, 2 figures; ApJ Letters, in pres
Guaranteed and Prospective Galactic TeV Neutrino Sources
Recent observations, particularly from the HESS Collaboration, have revealed
rich Galactic populations of TeV gamma-ray sources, including a collection
unseen in other wavelengths. Many of these gamma-ray spectra are well measured
up to ~10 TeV, where low statistics make observations by air Cerenkov
telescopes difficult. To understand these mysterious sources, especially at
much higher energies--where a cutoff should eventually appear--new techniques
are needed. We point out the following: (1) For a number of sources, it is very
likely that pions, and hence TeV neutrinos, are produced; (2) As a general
point, neutrinos should be a better probe of the highest energies than gamma
rays, due to increasing detector efficiency; and (3) For several specific
sources, the detection prospects for km^3 neutrino telescopes are very good,
about 1-10 events/year, with low atmospheric neutrino background rates above
reasonable energy thresholds. Such signal rates, as small as they may seem,
will allow neutrino telescopes to powerfully discriminate between models for
the Galactic TeV sources, with important consequences for our understanding of
cosmic-ray production.Comment: 12 pages, 5 figures; minor changes to match published versio
The Advanced Compton Telescope
The Advanced Compton Telescope (ACT), the next major step in gamma-ray astronomy, will probe the fires where chemical elements are formed by enabling high-resolution spectroscopy of nuclear emission from supernova explosions. During the past two years, our collaboration has been undertaking a NASA mission concept study for ACT. This study was designed to (1) transform the key scientific objectives into specific instrument requirements, (2) to identify the most promising technologies to meet those requirements, and (3) to design a viable mission concept for this instrument. We present the results of this study, including scientific goals and expected performance, mission design, and technology recommendations
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