13 research outputs found
High-energy neutrinos from reverse shocks in choked and successful relativistic jets
Highly relativistic jets are a key element of current gamma-ray burst models,
where the jet kinetic energy is converted to radiation energy at optically thin
shocks. High-energy neutrinos are also expected, from interactions of protons
accelerated in the same shocks. Here we revisit the early evolution of a
relativistic jet, while the jet is still inside the star, and investigate its
neutrino emission. In particular we study propagation of mildly relativistic
and ultrarelativistic jets through a type Ib progenitor, and follow reverse
shocks as the jets cross the star. We show that protons can be accelerated to
10^4-10^5 GeV at reverse shocks, and efficiently produce mesons. The mesons
experience significant cooling, suppressing subsequent neutrino emission. We
show, however, that the neutrino yield from the reverse shock is still
reasonably large, especially for low-luminosity and long-duration jets, where
meson cooling is less severe. We discuss implications of our results in the
context of neutrinos from choked jets, which are completely shock heated and do
not break out of the star. From a choked jet with isotropic equivalent energy
of 10^{53} erg at 10 Mpc, we expect ~20 neutrino events at IceCube.Comment: 11 pages, 7 figures, 2 tables; accepted for publication in Physical
Review
Dark matter annihilation from intermediate-mass black holes: Contribution to the extragalactic gamma-ray background
We investigate contributions to the extragalactic gamma-ray background (EGB)
due to neutralino dark matter (DM) pair-annihilation into photons, from DM
density enhancements (minispikes) surrounding intermediate-mass black holes
(IMBHs). We focus on two IMBH formation scenarios; our conservative scenario
where IMBHs are remnants of Population-III stars, and our optimistic scenario
here IMBHs are formed in protogalactic disks. In both scenarios, their
formation in pregalactic halos at high redshift lead to the formation of
minispikes that are bright sources of gamma-ray photons. Taking into account
minispike depletion processes, we only sum contributions from a cosmological
distribution of IMBHs with maintained minispikes. Our conservative scenario (BH
mass 10^2 M_sun with a r^{-3/2} minispike) predicts gamma-ray fluxes that are
an order larger than the equivalent flux, using the same DM parameters (mass
100 GeV and annihilation cross-section 3 \times 10^{-26} cm^3 s^{-1}, from the
host halo without IMBH minispikes. Our optimistic scenario (BH mass 10^5 M_sun
with a r^{-7/3} minispike) predicts fluxes that are three orders larger, that
can reach current EGB observations taken by EGRET (DM parameters as above).
This fact may serve interesting consequences for constraining DM parameters and
elucidating the true nature of IMBHs. Additionally, we determine the spectra of
DM annihilation into monochromatic gamma-rays, and show that its flux can be
within observational range of GLAST, providing a potential `smoking-gun'
signature of DM.Comment: 11 pages, 6 figures, 2 tables, accepted for publication in Phys.Rev.
Diffuse neutrino background from past core-collapse supernovae
Core-collapse supernovae are among the most powerful explosions in the
universe, emitting thermal neutrinos that carry away the majority of the
gravitational binding energy released. These neutrinos create a diffuse
supernova neutrino background (DSNB), one of the largest energy budgets among
all radiation backgrounds. Detecting the DSNB is a crucial goal of modern
high-energy astrophysics and particle physics, providing valuable insights in
both core-collapse modeling, neutrino physics, and cosmic supernova rate
history. In this review, we discuss the key ingredients of DSNB calculation and
what we can learn from future detections, including black-hole formation and
non-standard neutrino interactions. Additionally, we provide an overview of the
latest updates in neutrino experiments, which could lead to the detection of
the DSNB in the next decade. With the promise of this breakthrough discovery on
the horizon, the study of DSNB holds enormous potential for advancing our
understanding of the Universe.Comment: 21 pages, 8 figures. Invited review article submitted to Proceedings
of the Japan Academy, Series B. Figures are made using the numerical codes
that accompany this paper; see
https://github.com/shinichiroando/PyDSNB/tree/mai
Non-thermal neutrinos from supernovae leaving a magnetar
Under the fossil field hypothesis of the origin of magnetar magnetic fields, the magnetar inherits its magnetic field from its progenitor. We show that during the supernova of such a progenitor, protons may be accelerated to ∼10^4 GeV as the supernova shock propagates in the stellar envelope. Inelastic nuclear collisions of these protons produce a flash of high-energy neutrinos arriving a few hours after thermal (10 MeV) neutrinos. The neutrino flash is characterized by energies up to O(100) GeV and durations seconds to hours, depending on the progenitor: those from smaller Type Ibc progenitors are typically shorter in duration and reach higher energies compared to those from larger Type II progenitors. A Galactic Type Ib supernova leaving behind a magnetar remnant will yield up to ∼160 neutrino-induced muon events in Super-Kamiokande, and up to ∼7000 in a km^3 class detector such as IceCube, providing a means of probing supernova models and the presence of strong magnetic fields in the stellar envelope
Cross Correlation of the Extragalactic Gamma-ray Background with Thermal Sunyaev-Zel'dovich Effect in the Cosmic Microwave Background
Cosmic rays in galaxy clusters are unique probes of energetic processes
operating with large-scale structures in the Universe. Precise measurements of
cosmic rays in galaxy clusters are essential for improving our understanding of
non-thermal components in the intracluster-medium (ICM) as well as the accuracy
of cluster mass estimates in cosmological analyses. In this paper, we perform a
cross-correlation analysis with the extragalactic gamma-ray background and the
thermal Sunyaev-Zel'dovich (tSZ) effect in the cosmic microwave background. The
expected cross-correlation signal would contain rich information about the
cosmic-ray-induced gamma-ray emission in the most massive galaxy clusters at
. We analyze the gamma-ray background map with 8 years of data
taken by the Large Area Telescope onboard Fermi satellite and the publicly
available tSZ map by Planck. We confirm that the measured cross-correlation is
consistent with a null detection, and thus it enables us to put the tightest
constraint on the acceleration efficiency of cosmic ray protons at shocks in
and around galaxy clusters. We find the acceleration efficiency must be below
5\% with a confidence level when the hydrostatic mass bias of
clusters is assumed to be 30\%, and our result is not significantly affected by
the assumed value of the hydrostatic mass bias. Our constraint implies that the
non-thermal cosmic-ray pressure in the ICM can introduce only a level
of the hydrostatic mass bias, highlighting that cosmic rays alone do not
account for the mass bias inferred by the Planck analyses. Finally, we discuss
future detectability prospects of cosmic-ray-induced gamma rays from the
Perseus cluster for the Cherenkov Telescope Array.Comment: 19 pages, 15 figures, 1 table. Accepted for publication in Phys. Rev.
The Andromeda Gamma-Ray Excess: Background Systematics of the Millisecond Pulsars and Dark Matter Interpretations
Since the discovery of an excess in gamma rays in the direction of M31, its
cause has been unclear. Published interpretations focus on a dark matter or
stellar related origin. Studies of a similar excess in the Milky Way center
motivate a correlation of the spatial morphology of the signal with the
distribution of stellar mass in M31. However, a robust determination of the
best theory for the observed excess emission is very challenging due to large
uncertainties in the astrophysical gamma-ray foreground model. Here we perform
a spectro-morphological analysis of the M31 gamma-ray excess using
state-of-the-art templates for the distribution of stellar mass in M31 and
novel astrophysical foreground models for its sky region. We construct maps for
the old stellar populations of M31 based on observational data from the PAndAS
survey and carefully remove the foreground stars. We also produce improved
astrophysical foreground models by using novel image inpainting techniques
based on machine learning methods. We find that our stellar maps, taken as a
proxy for the location of a putative population of millisecond pulsars in the
bulge of M31, reach a statistical significance of , making them as
strongly favoured as the simple phenomenological models usually considered in
the literature, e.g., a disk-like template with uniform brightness. Our
detection of the stellar templates is robust to generous variations of the
astrophysical foreground model. Once the stellar templates are included in the
astrophysical model, we show that the dark matter annihilation interpretation
of the signal is unwarranted. Using the results of a binary population
synthesis model we demonstrate that a population of about one million
unresolved MSPs could naturally explain the observed gamma-ray luminosity per
stellar mass, energy spectrum, and stellar bulge-to-disk flux ratio.Comment: 15 pages, 11 figures, comments are welcom
Cherenkov Telescope Array sensitivity to the putative millisecond pulsar population responsible for the Galactic center excess
The leading explanation of the Galactic center -ray
excess is the extended emission from a unresolved population of millisecond
pulsars (MSPs) in the Galactic bulge. Such a population would, along with the
prompt rays, also inject large quantities of electrons/positrons
() into the interstellar medium. These could potentially
inverse-Compton (IC) scatter ambient photons into rays that fall
within the sensitivity range of the upcoming Cherenkov Telescope Array (CTA).
In this article, we examine the detection potential of CTA to this signature by
making a realistic estimation of the systematic uncertainties on the Galactic
diffuse emission model at TeV-scale -ray energies. We forecast that, in
the event that injection spectra are harder than , CTA has the
potential to robustly discover the IC signature of a putative Galactic bulge
MSP population sufficient to explain the GCE for injection efficiencies
in the range , or higher, depending on the level of
mismodeling of the Galactic diffuse emission components. On the other hand, for
spectra softer than , a reliable CTA detection would require an
unphysically large injection efficiency of . However,
even this pessimistic conclusion may be avoided in the plausible event that MSP
observational and/or modeling uncertainties can be reduced. We further find
that, in the event that an IC signal were detected, CTA can successfully
discriminate between an MSP and a dark matter origin for the radiating .Comment: 21+6 pages, 12+5 figures. Updated to match version soon to be
published by MNRA
Non-Universal Stellar Initial Mass Functions: Large Uncertainties in Star Formation Rates at and Other Astrophysical Probes
We explore the assumption, widely used in many astrophysical calculations,
that the stellar initial mass function (IMF) is universal across all galaxies.
By considering both a canonical Salpeter-like IMF and a non-universal IMF, we
are able to compare the effect of different IMFs on multiple observables and
derived quantities in astrophysics. Specifically, we consider a non-universal
IMF which varies as a function of the local star formation rate, and explore
the effects on the star formation rate density (SFRD), the extragalactic
background light, the supernova (both core-collapse and thermonuclear) rates,
and the diffuse supernova neutrino background. Our most interesting result is
that our adopted varying IMF leads to much greater uncertainty on the SFRD at
than is usually assumed. Indeed, we find a SFRD (inferred using
observed galaxy luminosity distributions) that is a factor of lower
than canonical results obtained using a universal Salpeter-like IMF. Secondly,
the non-universal IMF we explore implies a reduction in the supernova
core-collapse rate of a factor of , compared against a universal IMF.
The other potential tracers are only slightly affected by changes to the
properties of the IMF. We find that currently available data do not provide a
clear preference for universal or non-universal IMF. However, improvements to
measurements of the star formation rate and core-collapse supernova rate at
redshifts may offer the best prospects for discernment.Comment: 15 pages, 11 figures, 1 appendi