21 research outputs found
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Monte Carlo Radiation Transfer Simulations of Gamma Ray Burst Prompt Emission
Gamma Ray Bursts (GRBs) are the most energetic explosions in the Universe, producing up to ergs of energy in the first few seconds of their emission -- the so-called prompt phase that is dominated by high energy X-ray and -ray photons. The very large luminosities released in these events make GRBs an ideal laboratory for exploring the interplay between matter and radiation under extreme conditions. The available GRB data has provided much insight on which models best explain observations, contributing to a general understanding of these events. However, there is still much more information hidden in the data. This information can shed light on the microphysical processes that are relevant to radiation from jets, the properties of both the GRB jet and the environment surrounding the jet, and how the jet imprints its signature on the resulting radiation. The Monte Carlo Radiation Transfer code (MCRaT) studies the interplay between matter and radiation by conducting radiative transfer calculations using the background of a realistic jet profile acquired from special relativistic hydrodynamic simulations (SRHD) of GRBs. MCRaT injects thermal photons into the jet and Compton scatters and propagates the photons through the outflow, taking their polarization into account. Using MCRaT we show that the radiation signatures from GRB SRHD simulations are able to reproduce the Yonetoku and Golenetskii observational relationships. Furthermore, we show that the expected polarization signatures are also in agreement with the observations made by the POLAR instrument. Our MCRaT simulations are additionally able to reproduce common features of observed GRB spectra. Due to the ability of MCRaT to conduct radiation transfer calculations using the background of a realistic jet profile, we are able to begin understanding the complex relationship between the progenitor material, the jet matter and the radiation signature. This work has resounding implications for understanding the GRB environment and properties through the detected electromagnetic signal
Optimizing the Resolution of Hydrodynamic Simulations for MCRaT Radiative Transfer Calculations
Despite their discovery about half a century ago, the Gamma-ray burst (GRB)
prompt emission mechanism is still not well understood. Theoretical modeling of
the prompt emission has advanced considerably due to new computational tools
and techniques. One such tool is the PLUTO hydrodynamics code, which is used to
numerically simulate GRB outflows. PLUTO uses Adaptive Mesh Refinement to focus
computational efforts on the portion of the grid that contains the simulated
jet. Another tool is the Monte Carlo Radiation Transfer (MCRaT) code, which
predicts electromagnetic signatures of GRBs by conducting photon scatterings
within a jet using PLUTO. The effects of the underlying resolution of a PLUTO
simulation with respect to MCRaT post-processing radiative transfer results
have not yet been quantified. We analyze an analytic spherical outflow and a
hydrodynamically simulated GRB jet with MCRaT at varying spatial and temporal
resolutions and quantify how decreasing both resolutions affect the resulting
mock observations. We find that changing the spatial resolution changes the
hydrodynamic properties of the jet, which directly affect the MCRaT mock
observable peak energies. We also find that decreasing the temporal resolution
artificially decreases the high energy slope of the mock observed spectrum,
which increases both the spectral peak energy and the luminosity. We show that
the effects are additive when both spatial and temporal resolutions are
modified. Our results allow us to understand how decreased hydrodynamic
temporal and spatial resolutions affect the results of post-processing
radiative transfer calculations, allowing for the optimization of hydrodynamic
simulations for radiative transfer codes.Comment: 12 pages, 10 figures, submitted to ApJ, for calculations, see:
https://github.com/jaritaes99/MCRaT-resolutio
BatAnalysis -- A Comprehensive Python Pipeline for Swift BAT Survey Analysis
The Swift Burst Alert Telescope (BAT) is a coded aperture gamma-ray
instrument with a large field of view that primarily operates in survey mode
when it is not triggering on transient events. The survey data consists of
eighty-channel detector plane histograms that accumulate photon counts over
time periods of at least 5 minutes. These histograms are processed on the
ground and are used to produce the survey dataset between and keV.
Survey data comprises of all BAT data by volume and allows for the
tracking of long term light curves and spectral properties of cataloged and
uncataloged hard X-ray sources. Until now, the survey dataset has not been used
to its full potential due to the complexity associated with its analysis and
the lack of easily usable pipelines. Here, we introduce the BatAnalysis python
package which provides a modern, open-source pipeline to process and analyze
BAT survey data. BatAnalysis allows members of the community to use BAT survey
data in more advanced analyses of astrophysical sources including pulsars,
pulsar wind nebula, active galactic nuclei, and other known/unknown transient
events that may be detected in the hard X-ray band. We outline the steps taken
by the python code and exemplify its usefulness and accuracy by analyzing
survey data from the Crab Pulsar, NGC 2992, and a previously uncataloged MAXI
Transient. The BatAnalysis package allows for 18 years of BAT survey to
be used in a systematic way to study a large variety of astrophysical sources.Comment: 13 pages, 6 figures; Submitted to ApJ; BatAnalysis github link is:
https://github.com/parsotat/BatAnalysis, comments/suggestions are welcome
A candidate relativistic tidal disruption event at 340 Mpc
We present observations of an extreme radio flare, VT J024345.70-284040.08,
hereafter VT J0243, from the nucleus of a galaxy with evidence for historic
Seyfert activity at redshift . Between NRAO VLA Sky Survey
observations in 1993 to VLA Sky Survey observations in 2018, VT J0243 rose from
a GHz radio luminosity of erg s to
erg s, and still continues to brighten. The
radio spectral energy distribution (SED) evolution is consistent with a nascent
jet that has slowed over days with an average . The jet is energetic ( erg), and had a radius
pc in Dec. 2021. X-ray observations suggest a persistent or
evolving corona, possibly associated with an accretion disk, and IR and optical
observations constrain any high-energy counterpart to be sub-Eddington. VT
J0243 may be an example of a young, off-axis radio jet from a slowly evolving
tidal disruption event. Other more mysterious triggers for the accretion
enhancement and jet launching are possible. In either case, VT J0243 is a
unique example of a nascent jet, highlighting the unknown connection between
supermassive black holes, the properties of their accretion flows, and jet
launching.Comment: 20 pages, 5 figures, 3 tables. Submitted to Ap
The cosipy library: COSI's high-level analysis software
The Compton Spectrometer and Imager (COSI) is a selected Small Explorer
(SMEX) mission launching in 2027. It consists of a large field-of-view Compton
telescope that will probe with increased sensitivity the under-explored MeV
gamma-ray sky (0.2-5 MeV). We will present the current status of cosipy, a
Python library that will perform spectral and polarization fits, image
deconvolution, and all high-level analysis tasks required by COSI's broad
science goals: uncovering the origin of the Galactic positrons, mapping the
sites of Galactic nucleosynthesis, improving our models of the jet and emission
mechanism of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs), and
detecting and localizing gravitational wave and neutrino sources. The cosipy
library builds on the experience gained during the COSI balloon campaigns and
will bring the analysis of data in the Compton regime to a modern open-source
likelihood-based code, capable of performing coherent joint fits with other
instruments using the Multi-Mission Maximum Likelihood framework (3ML). In this
contribution, we will also discuss our plans to receive feedback from the
community by having yearly software releases accompanied by publicly-available
data challenges
The Compton Spectrometer and Imager
The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX)
satellite mission in development with a planned launch in 2027. COSI is a
wide-field gamma-ray telescope designed to survey the entire sky at 0.2-5 MeV.
It provides imaging, spectroscopy, and polarimetry of astrophysical sources,
and its germanium detectors provide excellent energy resolution for emission
line measurements. Science goals for COSI include studies of 0.511 MeV emission
from antimatter annihilation in the Galaxy, mapping radioactive elements from
nucleosynthesis, determining emission mechanisms and source geometries with
polarization measurements, and detecting and localizing multimessenger sources.
The instantaneous field of view for the germanium detectors is >25% of the sky,
and they are surrounded on the sides and bottom by active shields, providing
background rejection as well as allowing for detection of gamma-ray bursts and
other gamma-ray flares over most of the sky. In the following, we provide an
overview of the COSI mission, including the science, the technical design, and
the project status.Comment: 8 page