We report on the spectral cross-calibration results of the Konus-Wind, the Suzaku/WAM, and the Swift/BAT instruments using simultaneously observed gamma-ray bursts (GRBs). This is the first attempt ...to use simultaneously observed GRBs as a spectral calibration source to understand systematic problems among the instruments. Based on these joint spectral fits, we find that (1) although a constant factor (a normalization factor) agrees within 20% among the instruments, the BAT constant factor shows a systematically smaller value by 10%–20% compared to that of Konus-Wind, (2) there is a systematic trend that the low-energy photon index becomes steeper by 0.1–0.2 and
$E_{\rm peak}$
becomes systematically higher by 10%–20% when including the BAT data in the joint fits, and (3) the high-energy photon index agrees within 0.2 among the instruments. Our results show that cross-calibration based on joint spectral analysis is an important step to understanding the instrumental effects that could be affecting the scientific results from the GRB prompt emission data.
Temporal and spectral information extracted from a stream of photons received from astronomical sources is the foundation on which we build understanding of various objects and processes in the ...Universe. Typically astronomers fit a number of models separately to light curves and spectra to extract relevant features. These features are then used to classify, identify, and understand the nature of the sources. However, these feature extraction methods may not be optimally sensitive to unknown properties of light curves and spectra. One can use the raw light curves and spectra as features to train classifiers, but this typically increases the dimensionality of the problem, often by several orders of magnitude. We overcome this problem by integrating light curves and spectra to create an abstract image and using wavelet analysis to extract important features from the image. Such features incorporate both temporal and spectral properties of the astronomical data. Classification is then performed on those abstract features. In order to demonstrate this technique, we have used gamma-ray burst (GRB) data from the NASA's Swift mission to classify GRBs into high- and low-redshift groups. Reliable selection of high-redshift GRBs is of considerable interest in astrophysics and cosmology.
We report on observations of correlated behavior between the prompt g-ray and optical emission from GRB 080319B, which (i) strongly suggest that they occurred within the same astrophysical source ...region and (ii) indicate that their respective radiation mechanisms were most likely dynamically coupled. Our preliminary results, based upon a new cross-correlation function (CCF) methodology for determining the time-resolved spectral lag, are summarized as follows. First, the evolution in the arrival offset of prompt g-ray photon counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic g-ray spectral lag) appears to be anti-correlated with the arrival offset between prompt 15-350 keV g-rays and the optical emission observed by TORTORA (extrinsic g-ray/optical lag), thus effectively partitioning the burst into two main episodes at ~T+28+/-2 sec. Second, prompt optical emission is nested within intervals of both (a) trivial intrinsic g-ray spectral lag (~T+12+/-2 and ~T+50+/-2 sec) with (b) discontinuities in the hard to soft evolution of the photon index for a power law fit to 15-150 keV Swift-BAT data (~T+8+/-2 and ~T+48+/-1 sec), both of which coincide with the rise (~T+10+/-1 sec) and decline (~T+50+/-1 sec) of prompt optical emission. This potential discovery, robust across heuristic permutations of BAT energy channels and varying temporal bin resolution, provides the first observational evidence for an implicit connection between spectral lag and the dynamics of shocks in the context of canonical fireball phenomenology.
We report on an investigation that confronts the lag-luminosity relation (LLR), i.e. a surrogate redshift parameterization based upon an empirically determined anti-correlation between the observed ...isotropic luminosity and the temporal lag between the arrivals of photon pulses in low (25-50 keV) and high (100-300 keV) energy bands, with observations of gamma-ray bursts (GRBs) with Swift's Burst Alert Telescope (BAT). Our initial methodology is based upon a cross-correlation function (CCF) analysis of 64 ms BAT light curves (temporal spectra), for a small subset of GRBs with observed spectroscopic redshift (zobs). Our preliminary results span 4 temporal decades and indicate an agreement with LLR, within the margins of error (excluding GRBs 980425 and 060218).
Gamma-ray bursts (GRBs) are thought to be the most concentrated and brightest explosions in the universe, making them observable to very great distances. Hence GRBs can be used to probe the early ...universe, including the re-ionization period as well as the intergalactic medium. GRBs may also be used to study the biggest mystery of our time: 'Dark Energy'. However, unlike Supernove 1a, GRBs as yet are not good standard candles. Hence, in order to use GRBs to connect luminosity and distance, we need GRB Luminosity Relations. Over the years people have proposed a number of GRB luminosity relations. Unfortunately, none of them are tight enough to be used individually to construct the GRB Hubble Diagram. However, by combining multiple GRB luminosity relations we can construct a GRB Hubble diagram that may be able to constrain cosmological parameters. Thus, it is important to study and improve existing GRB luminosity relations and perhaps discover new GRB luminosity relations. In addition to helping to improve our understanding of Dark Energy, these GRB luminosity relations are very useful to understand the underlying physics of GRBs. One major limiting factor in GRB luminosity relation studies is the low statistics. Before the Swift mission there were very few GRBs with measured redshifts. But now in the Swift era we have more than 150 GRBs with measured redshifts. In this work we have utilized this high-quality data set to study two GRB luminosity relations. In Part-I we extracted spectral lags and studied the lag-luminosity relation. The spectral lag is the time difference between the arrival of high-energy and low-energy photons. To quantify this lag we have developed an improved method based upon the cross correlation function. With this method we investigated the lag-luminosity relation over the entire Swift Burst Alert Telescope (BAT) energy range. Typically, a spectral lag is extracted in two arbitrary energy bands in the observer-frame. However, because of the redshift dependance of GRBs, the two energy bands can correspond to multiple energy bands in the source-frame. Thus, introducing a variable energy dependant factor into the lag-luminosity relation. We avoid this difficulty by defining two energy bands in the GRB source-frame and projecting these two bands into the observer-frame and extracting lags between them. This work has led to a significant improvement in the robustness of the lag-luminosity relation. In Part-II we studied the variability of GRBs using Fourier analysis and introduce a new GRB luminosity relation. We extract a maximum frequency at which there is still significant signal power and associate this threshold frequency with the isotropic luminosity of the burst. As a result of this study, we propose a potential correlation between isotropic peak luminosity and the extracted threshold frequency. In this investigation, we study in detail the potential observational biases in the frequency-luminosity relation. In Part-III we investigate long-term correlations and variability in GRB prompt emission light curves using the Hurst rescaled range analysis technique. As far as we know this is the first time this technique has been applied to GRBs. Based on this analysis, we present evidence indicating that the prompt emission of GRB light curves show anti-persistence.
The design and performance of the GPS Timing and Control (GTC) System of the High Altitude Water Cerenkov (HAWC) gamma ray observatory is described. The GTC system provides a GPS synchronized ...absolute timestamp, with an accuracy better than 1\(\mu\)s, for each recorded event in HAWC. In order to avoid any slack between the recorded data and the timestamp, timestamps are injected to the main data acquisition (DAQ) system after the Front-end Electronic Boards (FEBs). When HAWC is completed, the HAWC main DAQ will use 10 time to digital converters (TDCs). In order to keep all the TDCs in sync, the GTC system provides a synchronized clock signal, coordinated trigger signal, and control signals to all TDCs.
ABSTRACT The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able ...to explain such events. The final bursts of evaporating primordial black holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to GRBs using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short-duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 1013-1018 cm (7-105 au) range, which are consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Assuming that these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.
Primordial Black Holes MacGibbon, Jane H; Ukwatta, Tilan N; Linnemann, J T ...
arXiv.org,
03/2015
Paper, Journal Article
Open access
Primordial Black Holes (PBHs) are of interest in many cosmological contexts. PBHs lighter than about 1012 kg are predicted to be directly detectable by their Hawking radiation. This radiation should ...produce both a diffuse extragalactic gamma-ray background from the cosmologically-averaged distribution of PBHs and gamma-ray burst signals from individual light black holes. The Fermi, Milagro, Veritas, HESS and HAWC observatories, in combination with new burst recognition methodologies, offer the greatest sensitivity for the detection of such black holes or placing limits on their existence.
We report on observations of correlated behavior between the prompt gamma-ray and optical emission from GRB 080319B, which (i) strongly suggest that they occurred within the same astrophysical source ...region and (ii) indicate that their respective radiation mechanisms were most likely dynamically coupled. Our preliminary results, based upon a new cross-correlation function (CCF) methodology for determining the time-resolved spectral lag, are summarized as follows. First, the evolution in the arrival offset of prompt gamma-ray photon counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic gamma-ray spectral lag) appears to be anti-correlated with the arrival offset between prompt 15-350 keV gamma-rays and the optical emission observed by TORTORA (extrinsic optical/gamma-ray spectral lag), thus effectively partitioning the burst into two main episodes at ~T+28+/-2 sec. Second, prompt optical emission is nested within intervals of (a) trivial intrinsic gamma-ray spectral lag (~T+12+-2 and ~T+50+/-2 sec) with (b) discontinuities in the hard to soft evolution of the photon index for a power law fit to 15-150 keV Swift-BAT data (~T+8+/-2 and ~T+48+/-1 sec), both of which coincide with the rise (~T+10+/-1 sec) and decline (~T+50+/-1 sec) of prompt optical emission. This potential discovery, robust across heuristic permutations of BAT energy channels and varying temporal bin resolution, provides the first observational evidence for an implicit connection between spectral lag and the dynamics of shocks in the context of canonical fireball phenomenology.
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