6418107
A new search for primordial black hole evaporations using the Whipple gamma-ray telescope
Stephen Hawking's prediction that black holes should radiate like black bodies has several important consequences, including the possibility of the detection of small (~1015 g) black holes created in the very early universe. The detection of such primordial black holes (PBHs) would be an important discovery, not only confirming Hawking's theory, but also providing valuable insights into the history of the early universe. A search through 5.5 years of archival data from the Whipple Atmospheric Cerenkov Telescope is made for TeV gamma-ray bursts on 1, 3, and 5 s timescales. On the basis of a null result from this direct search for PBH evaporations, an upper limit of 1.08 × 106 pc−3 yr−1 (99% CL) is set on the PBH evaporation rate in the local region of the galaxy, assuming the Standard Model of particle physics. This is more than a factor of two better than the previous limit at this energy range and includes longer timescales than have previously been explored. Comparison of this result with previous limits on the fraction of the critical density comprised by PBHs, Ωpbh, depends strongly on assumptions made about PBH clustering; in models predicting strong PBH clustering, the limit in this work could be as many as ten orders of magnitude more stringently than those set by diffuse MeV gamma-ray observations.
121457285
INITIAL STEREO ANALYSIS OF MRK 421 FROM THE VERITAS TELESCOPES
VERITAS (Very Energetic Radiation Imaging Telescope Array System), an array of ground-based gamma-ray telescopes in southern Arizona, USA, has been taking data in hardware stereo mode since March, 2006. The April–May 2006 dark run provided a large set of data from two telescopes on the known blazar Markarian (Mrk) 421. An initial analysis produced a light curve and preliminary cuts showing the two telescope array's angular resolution to be 0.19°. The remaining two VERITAS telescopes will be brought online by January, 2007.
11717821
Multiwavelength observations of 1ES 1959+650, 1 year after the strong outburst of 2002
In 2003 April-May, the blazar 1ES 1959+650 showed an increased level of X-ray activity. This prompted a multiwavelength observation campaign with the Whipple 10 m γ-ray telescope, the Rossi X-Ray Timing Explorer, the Bordeaux Optical Observatory, and the University of Michigan Radio Astronomy Observatory. We present the multiwavelength data taken from 2003 May 2 to June 7 and compare the source characteristics with those measured during observations taken during the years 2000 and 2002. The X-ray observations gave a data set with high signal-to-noise ratio light curves and energy spectra; however, the γ-ray observations did not reveal a major TeV γ-ray flare. Furthermore, we find that the radio and optical fluxes do not show statistically significant deviations from those measured during the 2002 flaring periods. While the X-ray flux and X-ray photon index appear correlated during subsequent observations, the apparent correlation evolved significantly among the years 2000, 2002, and 2003. We discuss the implications of this finding for the mechanism that causes the flaring activity.
18693900
TeV Gamma-Ray Observations of the Perseus and Abell 2029 Galaxy Clusters
Galaxy clusters might be sources of TeV gamma rays emitted by high-energy protons and electrons accelerated by large-scale structure formation shocks, galactic winds, or active galactic nuclei. Furthermore, gamma rays may be produced in dark matter particle annihilation processes at the cluster cores. We report on observations of the galaxy clusters Perseus and A2029 using the 10 m Whipple Cerenkov telescope during the 2003-2004 and 2004-2005 observing seasons. We apply a two-dimensional analysis technique to scrutinize the clusters for TeV emission. In this paper we first determine flux upper limits on TeV gamma-ray emission from point sources within the clusters. Second, we derive upper limits on the extended cluster emission. We subsequently compare the flux upper limits with EGRET upper limits at 100 MeV and theoretical models. Assuming that the gamma-ray surface brightness profile mimics that of the thermal X-ray emission and that the spectrum of cluster cosmic rays extends all the way from thermal energies to multi-TeV energies with a differential spectral index of -2.1, our results imply that the cosmic-ray proton energy density is less than 7.9% of the thermal energy density for the Perseus Cluster.
121262274
The Whipple Observatory 10 m gamma-ray telescope, 1997–2006
Abstract Details are presented of the Whipple Observatory’s 10 m atmospheric Cherenkov telescope and camera, as it evolved during the period 1997 until 2006. The design of the telescope and camera’s optical and electronic systems is discussed together with a detailed description of the four-stage GRANITE (Gamma-RAy New Imaging TElescope) upgrade program, undertaken during the same time period. The objective of the upgrade was to improve the telescope’s sensitivity for the detection of very-high-energy gamma-rays. Results from the program are provided and are briefly discussed in the context of the design of VERITAS.
78089676
Spacetime and orbits of bumpy black holes
Our Universe contains a great number of extremely compact and massive objects which are generally accepted to be black holes. Precise observations of orbital motion near candidate black holes have the potential to determine if they have the spacetime structure that general relativity demands. As a means of formulating measurements to test the black hole nature of these objects, Collins and Hughes introduced ''bumpy black holes'': objects that are almost, but not quite, general relativity's black holes. The spacetimes of these objects have multipoles that deviate slightly from the black hole solution, reducing to black holes when the deviation is zero. In this paper, we extend this work in two ways. First, we show how to introduce bumps which are smoother and lead to better behaved orbits than those in the original presentation. Second, we show how to make bumpy Kerr black holes--objects which reduce to the Kerr solution when the deviation goes to zero. This greatly extends the astrophysical applicability of bumpy black holes. Using Hamilton-Jacobi techniques, we show how a spacetime's bumps are imprinted on orbital frequencies, and thus can be determined by measurements which coherently track the orbital phase of a small orbiting body. We find thatmore » in the weak field, orbits of bumpy black holes are modified exactly as expected from a Newtonian analysis of a body with a prescribed multipolar structure, reproducing well-known results from the celestial mechanics literature. The impact of bumps on strong-field orbits is many times greater than would be predicted from a Newtonian analysis, suggesting that this framework will allow observations to set robust limits on the extent to which a spacetime's multipoles deviate from the black hole expectation.« less
1891241
How black holes get their kicks: Radiation recoil in binary black hole mergers
Gravitational waves from the coalescence of binary black holes carry linear momentum, causing center of mass recoil. This ``radiation rocket'' has important implications for systems with escape speeds of order the recoil velocity. We describe new recoil calculations using high precision black hole perturbation theory to estimate the magnitude of the recoil for the slow ``inspiral'' coalescence phase; coupled with a cruder calculation for the final ``plunge'', we estimate the total recoil imparted to a merged black hole. We find that velocities of many tens to a few hundred km/sec can be achieved fairly easily. The recoil probably never exceeds about 500 km/sec.
4307974
Distance to the Virgo cluster galaxy M100 from Hubble Space Telescope observations of Cepheids
Accurate distances to galaxies are critical for determining the present expansion rate of the Universe or Hubble constant (H0). An important step in resolving the current uncertainty in H0 is the measurement of the distance to the Virgo cluster of galaxies. New observations using the Hubble Space Telescope yield a distance of 17.1 ± 1.8 Mpc to the Virgo cluster galaxy M100. This distance leads to a value of H0 = 80 ± 17 km s−1 Mpc−1. A comparable value of H0 is also derived from the Coma cluster using independent estimates of its distance ratio relative to the Virgo cluster.
28606941
Computing radiation from Kerr black holes: Generalization of the Sasaki-Nakamura equation
As shown by Teukolsky, the master equation governing the propagation of weak radiation in a black hole spacetime can be separated into four ordinary differential equations, one for each spacetime coordinate. (“Weak” means the radiation’s amplitude is small enough that its own gravitation may be neglected.) Unfortunately, it is difficult to accurately compute solutions to the separated radial equation (the Teukolsky equation), particularly in a numerical implementation. The fundamental reason for this is that the Teukolsky equation’s potentials are long ranged. For non-spinning black holes, one can get around this difficulty by applying transformations which relate the Teukolsky solution to solutions of the Regge-Wheeler equation, which has a short-ranged potential. A particularly attractive generalization of this approach to spinning black holes for gravitational radiation (spin weight s = −2) was given by Sasaki and Nakamura. In this paper, I generalize Sasaki and Nakamura’s results to encompass radiation fields of arbitrary integer spin weight, and give results directly applicable to scalar (s = 0) and electromagnetic (s = −1) radiation. These results may be of interest for studies of astrophysical radiation processes near black holes, and of programs to compute radiation reaction forces in curved spacetime.
16525828
Census of transient orbital resonances encountered during binary inspiral
Transient orbital resonances have recently been identified as potentially important to the inspiral of small bodies into large black holes. These resonances occur as the inspiral evolves through moments in which two fundamental orbital frequencies, $\Omega_\theta$ and $\Omega_r$, are in a small integer ratio to one another. Previous work has demonstrated that a binary's parameters are "kicked" each time the inspiral passes through a resonance, changing the orbit's characteristics relative to a model that neglects resonant effects. In this paper, we use exact Kerr geodesics coupled to an accurate but approximate model of inspiral to survey orbital parameter space and estimate how commonly one encounters long-lived orbital resonances. We find that the most important resonances last for a few hundred orbital cycles at mass ratio $10^{-6}$, and that resonances are almost certain to occur during the time that a large mass ratio binary would be a target of gravitational-wave observations. Resonances appear to be ubiquitous in large mass ratio inspiral, and to last long enough that they are likely to affect binary evolution in observationally important ways.