Gamma-ray bursts (GRBs) are detectable out to very large distances and as such are potentially powerful cosmological probes. Historically, the angular distribution of GRBs provided important information about their origin and physical properties. As
a general population, GRBs are distributed isotropically across the sky. However, there are published reports that once binned by duration or redshift, GRBs display significant clustering. We have studied the redshift- and duration-dependent clustering of GRBs using proximity measures and kernel density estimation. Utilizing bursts detected by BATSE, Fermi/GBM and Swift/BAT, we found marginal evidence for clustering in very short duration GRBs lasting less than 100 ms. Our analysis provides little evidence for significant redshift-dependent clustering of GRBs.
Many early universe theories predict the creation of Primordial Black Holes (PBHs). The PBHs could have masses ranging from the Planck mass to 10^5 solar masses or higher depending on the formation scenario. Hawking showed that any Black Hole (BH) ha
s a temperature which is inversely proportional to its mass. Hence a sufficiently small BH will thermodynamically radiate particles at an ever-increasing rate, continually decreasing its mass and raising its temperature. The final moments of this evaporation phase should be explosive. In this work, we investigate the final few seconds of the BH burst using the Standard Model of particle physics and calculate the energy dependent burst time profiles in the GeV/TeV range. We use the HAWC (High Altitude Water Cherenkov) observatory as a case study and calculate PBH burst light curves which would be observed by HAWC.
Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects,
a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally. PBHs with initial masses of ~5.0 x 10^14 g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV - TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a range of PBH observation times. In addition, we report the sensitivity of the Milagro successor, the High Altitude Water Cherenkov (HAWC) observatory, to PBH evaporation events.
