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I report an innovation that provides a compelling demonstration of rocket propulsion, appropriate for students of physics and other physical sciences. An electrical spark is initiated from a distance to cause the deflagration of a combustible vapor mixed with air in a lightweight plastic bottle that is consequently propelled as a rocket by the release of combustion products, i.e., a “whoosh rocket.” My recommendation is that the standard fuel for pedagogical whoosh demonstrations be isopropanol, and the recommended vessel is the 3.8-L high-density polyethylene (HDPE) bottle.

The 1.3-m telescope at Kitt Peak National Observatory was originally commissioned in 1964 as the “Remotely Controlled Telescope”, a pioneering project in unattended, remote observing. Forty years of technological advances later, the 1.3-m has been refurbished, automated and reborn as the “Robotically Controlled Telescope”. The RCT is used to pursue a variety of research programs which incorporate techniques to achieve extremely high precision photometric monitoring of stars and AGN, as well as to search for transits of extrasolar planets. Since spring of 2003 the RCT has been controlled through pre-scheduled scripts, without interactive human control, to collect imaging data. The work on automation of the observatory system is continuing, with the ultimate goal being that the computer will control the telescope through semiintelligent software to make observations as efficiently as a well-trained human astronomer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We identify 16 optical counterparts of blazars that have been suggested as sources of high-energy gamma-ray emission detected by the EGRET instrument on board the Compton Gamma-Ray Observatory. Nine new redshifts are obtained, as well one contradiction and two confirmations of published redshifts ranging from z = 0.566 to z = 3.00. The optical spectra of four objects are featureless, including high signal-to-noise spectra of the likely counterparts of 3EG J0433+2908 and GeV J0508+0540, which, if at low redshift, would be attractive targets to search for TeV emission using atmospheric Cerenkov telescopes, because they emit above 10 GeV. However, the combination of spectroscopy and CCD imaging of those objects shows no evidence for their underlying host galaxies, which probably means that z > 0.3, diminishing their prospects as TeV sources.

We present the results of deep X-ray and gamma-ray observations of the Geminga pulsar obtained in the final years of the ASCA and CGRO missions, and an upper limit from RXTE. A phase-connected ephemeris from the gamma-rays is derived that spans the years 1973-2000, after allowing for a minor glitch in frequency of Delta f/f = 6.2 x 10^-10 in late 1996. ASCA observations of the hard X-ray pulse profile in 1994 and 1999 confirm this glitch. An improved characterization of the hard X-ray pulse profile and spectrum from the long ASCA observation of 1999 confirms that there is a non-thermal X-ray component that is distinct from the gamma-ray spectrum as measured by EGRET. It can be parameterized as a power-law of photon index Gamma = 1.72 +/- 0.10 with a flux of 2.62 x 10^-13 ergs/cm^2/s in the 0.7-5 keV band and pulsed fraction 0.54 +/- 0.05, similar to, but more precise than values measured previously. An extrapolation of this spectrum into the energy band observed by the RXTE PCA is consistent with the non-detection of pulsed emission from Geminga with that instrument. These results are interpreted in the context of outer-gap models, and motivations for future X-ray observations of Geminga are given., Comment: 22 pages including 7 figures

We present Very Long Baseline Array images of 42 γ-ray bright blazars, including 36 with polarization vectors, obtained during the course of a multiepoch monitoring program. Each object was observed at either 43 or 22 GHz, with some objects observed at both frequencies and/or at 15 or 8.4 GHz. The morphologies are varied, with some of the blazars displaying long, thin jets, others short, broad jets, and still others containing cores with only very weak features that are probably knots in faint jets. The polarization of the cores ranges from less than 1% to 8.6%, with electric vector position angles (EVPAs) that are split between nearly parallel and nearly transverse to the jet axis. The polarization of knots in the jets covers a much broader range, from less than 2% to tens of percent. The EVPA of the brightest compact feature in each jet ranges from 0° to 80° from the jet position angle, with roughly half measuring less than 20°. The distribution is consistent with intrinsically oblique magnetic fields whose observed directions are altered by relativistic aberration.

We examine the coincidence of times of high γ-ray flux and ejections of superluminal components from the core in EGRET blazars based on a Very Long Baseline Array (VLBA) monitoring program at 22 and 43 GHz from 1993 November to 1997 July. In 23 cases of γ-ray flares for which sufficient VLBA data exist, 10 of the flares (in eight objects) fall within 1 σ uncertainties of the extrapolated epoch of zero separation from the core of a superluminal radio component. In each of two sources (0528+134 and 1730-130), two successive γ-ray flares were followed by the appearance of new superluminal components. We carried out statistical simulations that show that if the number of coincidences is ≥10, the radio and γ-ray events are associated with each other at greater than 99.999% confidence. Our analysis of the observed behavior, including variability of the polarized radio flux, of the sources before, during, and after the γ-ray flares suggests that the γ-ray events occur in the superluminal radio knots. This implies that the γ-ray flares are caused by inverse Compton scattering by relativistic electrons in the parsec-scale regions of the jet rather than closer to the central engine.

The method of Mattox et al. for identifying EGRET sources with 5 GHz radio sources has been applied to the 3EG EGRET catalog of Hartman et al. Complete results are tabulated. We tabulate separately 46 EGRET sources with radio identifications which we expect to have a high probability of being correct. We suggest that these sources are appropriate for most studies of the properties of γ-ray blazars as a class. All but one of these 46 sources were classified by Hartman et al. as high-confidence identifications; and the additional source was classified by Hartman et al. as a plausible identification. We also tabulate separately 37 additional "plausible identifications of EGRET sources with radio sources." These less secure possibilities include the remaining 21 "high-confidence identifications" of Hartman et al., three of the 27 "lower confidence potential blazar identifications" of Hartman et al., and an additional 15 plausible identifications which have not been suggested previously. Many of these sources require new radio and optical observations to establish them as blazars. We suggest that the 23 "lower-confidence potential blazar identifications" of Hartman et al. which we do not find plausible should not be used in studies of the properties of the EGRET blazars. For this analysis, we have made elliptical fits to the 95% confidence contours of the position uncertainty regions of the 3EG sources which are tabulated in an Appendix.

Most Galactic point sources of gamma rays remain unidentified. The few (extrasolar) sources that have been identified are all young, rotation-powered pulsars, all but one of which were identified using radio ephemerides. The radio-quiet Geminga pulsar was identified only after pulsations were discovered in a coincident X-ray source. Observational evidence indicates that many of the unidentified Galactic sources are likely to be pulsars, and some theoretical models predict a potentially large population of radio-quiet gamma-ray pulsars. We present a new method for performing sensitive gamma-ray pulsar searches. We used this method to search several of the strongest EGRET sources for pulsations. This was a blind search for new pulsars, covering a frequency and a frequency-derivative phase space large enough to detect Crab-like pulsars as well as lower frequency, high magnetic field "magnetars." No new pulsars were discovered, and we report upper limits constraining the characteristics of any signals contained in the data sets searched.

We present the results of a program to monitor the structure of the radio emission in 42 $\gamma$-ray bright blazars (31 quasars and 11 BL Lac objects) with the VLBA at 43, 22, and occasionally 15 and 8.4 GHz, over the period from November 1993 to July 1997. We determine proper motions in 33 sources and find that the apparent superluminal motions in $\gamma$-ray sources are much faster than for the general population of bright compact radio sources. This follows the strong dependence of the $\gamma$-ray flux on the level of relativistic beaming for both external-radiation Compton and synchrotron self-Compton emission. There is a positive correlation (correlation coefficient $r$=0.45) between the flux density of the VLBI core and the $\gamma$-ray flux and a moderate correlation (partial correlation coefficient $r$=0.31) between $\gamma$-ray apparent luminosity and superluminal velocities of jet components, as expected if the $\gamma$-ray emission originates in a very compact region of the relativistic jet and is highly beamed. In 43% of the sources the jet bends by more than 20$^\circ$ on parsec scales, which is consistent with amplification by projection effects of modest actual changes in position angle. In 27 of the sources in the sample there is at least one non-core component that appears to be stationary during our observations. Different characteristics of stationary features close to and farther from the core lead us to suggest two different classes of stationary components: those within about 2 milliarcseconds (mas) of the core, probably associated with standing hydrodynamical compressions, and those farther down the jet, which tend to be associated with bends in the jet.

During the first 3 years of the Compton Gamma Ray Observatory mission, the blazar CTA 26 was observed 10 times by EGRET and not significantly detected. We report an observation in 1995 when CTA 26 flared to a peak γ-ray flux of (4.9 ± 1.5) × 10-6 cm-2 s-1 (E > 100 MeV), the third brightest of all EGRET blazars. Following the γ-ray flare, extensive VLBA and single-dish radio observations were obtained. We find two components of a milliarcsecond jet moving with apparent transverse velocities of 12 ± 1 h-1 c, and 5 ± 2 h-1 c (H0 = 100 h km s-1 Mpc-1, q0 = 0.1). The position angle of VLBI components appears to change with time. The slowest VLBI component's motion is consistent with ejection at the time of the 1995 γ-ray flare. A weak radio flare is also seen in Metsahovi millimeter radio monitoring data, peaking within weeks of the γ-ray flare.

Light concentrators to be used by the camera of a telescope to view gamma-ray-induced Cherenkov light, are analyzed from the point of view of optical efficiency, background rejection capability and manufacturability. A small decrease in the optical efficiency due to multiple reflections undergone by rays incident at small angles in a compound parabolic concentrator is observed. The influence of the angle of incidence on the reflectivity of the wall is analyzed and found to be inconsequential. A closed-packed matrix of concentrators with hexagonal entrance apertures is considered and the light spread in the adjacent pixels introduced by the removal of portions of the surface of concentrators is evaluated.

VSOPシンポジウム(2000年1月19日-21日. 宇宙科学研究所(ISAS)）, 相模原市, 神奈川県, VSOP Symposium (January 19-21, 2000. Institute of Space and Astronautical Science(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000155010

We present the COS-B/EGRET 1997 ephemeris for the rotation of the Geminga pulsar. This ephemeris is derived from high-energy gamma-ray observations that span 24 yr. The recently obtained accurate position and proper motion are assumed. A cubic ephemeris predicts the rotational phase of Geminga with errors smaller than 50 milliperiods for all existing high-energy gamma-ray observations that span a 24.2 yr timing baseline. The braking index obtained is 17 +/- 1. Further observation is required to ascertain whether this high value truly reflects the rotational energy loss mechanism, or whether it is a manifestation of timing noise. The ephemeris parameters are sufficiently constrained so that timing noise will be the limitation on forward extrapolation. If Geminga continues to rotate without a glitch, as it has for at least 23 yr, we expect this ephemeris to continue to describe the phase, with an error of less than 100 milliperiods, until 2008. Statistically significant timing residuals are detected in the EGRET data that depart from the cubic ephemeris at a level of 30 milliperiods. Although this could simply be an additional manifestation of timing noise, the EGRET timing residuals appear to have a sinusoidal modulation that is consistent with a planet of mass 1.7/sin i solar mass, orbiting Geminga at a radius of 3.3 AU.

Assuming that supernova shocks accelerate nonthermal particles, we model the temporally evolving nonthermal particle and photon spectra at different stages in the lifetime of a standard shell-type supernova remnant (SNR). A characteristic νFν spectrum of an SNR consists of a peak at radio through optical energies from nonthermal electron synchrotron emission and another high-energy gamma-ray peak due primarily to secondary pion production, nonthermal electron bremsstrahlung, and Compton scattering. We find that supernova remnants are capable of producing maximum gamma-ray luminosities 1035 ergs s-1 if the density of the local interstellar medium is 10 cm-3. This emission will persist for 105 yr after the supernova explosion because of the long energy loss timescales for electrons with kinetic energy ~1 GeV. This long gamma-ray lifetime implies that SNRs with a wide range of ages could be gamma-ray sources and could constitute some of the unidentified EGRET sources.

The COS B source 2CG 135+01 has been observed by the EGRET instrument on 10 different occasions during the first ~52 months of the Compton Gamma Ray Observatory mission. The source is detected in all but one of the observations. For that one, the exposure was inadequate. The only likely source that is spatially coincident with the gamma-ray position is the radio source GT 0236+610/LS I +61°303. However, there is no compelling evidence for time variations in the gamma-ray emission associated with the radio outbursts from GT 0236+610. Spectral determinations on a timescale of a few days also give no strong evidence for a spectral variation associated with the radio emission of GT 0236+610. Such fluctuations might be expected based on models involving a compact object in an elliptical binary orbit about a massive star. The search for correlations simultaneous with the 8.4 GHz radio outbursts were supported by coordinated observations with the Madrid Deep Space Network during one of the exposures and by Green Bank Interferometer observations on two others. Although there is some possible variability in the gamma-ray flux, it is not clear that it is related to the radio phasing.

We describe observations of the quasi-stellar object (QSO) NRAO 190 during a gamma-ray flare from 1994 August 9 to 1994 August 29. This QSO was serendipitously detected by the EGRET instrument on the Compton Gamma Ray Observatory in a gamma-ray flare with a luminosity at least 10 times that of its quiescent state. Optical, radio, and microwave data were obtained during or near the gamma-ray observations. The historical behavior of this object places it in the category of bright, flat-spectrum radio sources with strong optical variability that appear to form the largest class of non-Galactic high-energy gamma-ray sources. During the gamma-ray flare the source is observed with l(E > 100 MeV) = 8.4 ± 1.2 × 10-7 photons s-1 cm-2. A single power-law model gives a best-fit photon index of γ = -1.83 ± 0.14. Little evidence for major radio variability is seen during the flare or immediately afterward, although there is some increase in the 10-100 GHz flux over the next several months. There may be a slight hardening of the radio spectrum. In the optical region there are significant fluctuations on timescales of 1 day or less, although the overall optical luminosity is within the range of previous measurements. Optical observations a few weeks after the gamma-ray observations show a drop of about 60% and reduced variability. A contemporary optical spectrum shows that the source may be slightly harder than seen in a previously published spectrum. Radio monitoring of the source over the year subsequent to the flare has shown a very substantial drop in the flux at many frequencies.

0!rQ1The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory observed the Cygnus region in 14 different viewing periods during 1991 May to 1994 July. We present here our results on unpulsed and pulsed emissions of gamma rays at E > 50 MeV from Cyg X-3. While we detect a gamma-ray source consistent with the position of Cyg X-3, there was no evidence for the characteristic ~4.79 hr periodicity observed in X-rays and infrared.

In the course of the Compton Gamma Ray Observatory mission, the EGRET telescope has detected 14 BL Lacertae objects in high-energy gamma rays through Phase 4. According to the BL Lac sample in Ciliegi, Bassani, & Caroli, two of these 14 sources are X-ray selected (XBL) and 10 are radio-selected (RBL); two are not listed in this sample. An examination of the radio fluxes and the X-ray fluxes for the BL Lac objects detected by EGRET reveals that it seems a strong radio flux must be present if high-energy gamma rays are to be detected in a BL Lac object, while detection is independent of the X-ray flux of the source. This result is in agreement with the picture of the coaligned radio jet and X-ray jet model of the broadband properties of BL Lac objects. For the BL Lac objects listed in Ciliegi et al. that are not detected by EGRET, co-adding of the EGRET data for the undetected RBLs in such a way that the source positions coincide with each other yields a flux excess at a 3.5 σ level, but similar co-adding of the EGRET data for the undetected XBLs yields no flux excess.

We have developed a method for quantifying the flux variability of EGRET high-energy gamma-ray sources. We apply this method to all sources in the Second EGRET Catalog except for the one solar flare. Allowing for a small systematic uncertainty, the phase-averaged flux densities of the pulsars are consistent with being nonvariable. Many identified active galactic nuclei are variable, as expected, and it is likely that the apparent nonvariability of some identified active galactic nuclei results from decreased sensitivity to variability at low fluxes and low latitudes. Populations of both variable and nonvariable unidentified sources are found to be in excess at low Galactic latitudes. While low-flux, nonvariable, unidentified sources could result from errors in the Galactic diffuse model, some higher flux, nonvariable, unidentified sources are likely to be Galactic pulsars. The excess of variable, unidentified sources at low latitudes suggests that either pulsars can produce variable gamma rays under special circumstances, or that a new class of Galactic gamma-ray sources exists.

We report on the γ-ray variability of Mrk 421 at Eγ > 300 GeV during the 1995 season, and concentrate on the results of an intense multiwavelength observing campaign in the period April 20 to May 5, which included >100 MeV γ-ray, X-ray, extreme-ultraviolet, optical, and radio observations, some of which show evidence for correlated behavior. Rapid variations in the TeV γ-ray light curve with doubling and decay times of 1 day require a compact emission region and significant Doppler boosting. The TeV data reveal that the γ-ray emission is best characterized by a succession of rapid flares with a relatively low baseline level of steady emission.

The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory has detected more than 20 Active Galactic Nuclei (AGN) at photon energies above 30 MeV.

The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO) covers the high energy gamma ray energy range, approximately 30 MeV to 30 GeV, with a sensitivity considerably greater than earlier high energy gamma-ray satellites. Thus far, 4 pulsars have been detected and their properties measured, including in 3 cases the energy spectrum as a function of phase. The details of the galactic plane are being mapped and a spectra of the center region has been obtained in good agreement with that expected from cosmic ray interactions. The Magellanic clouds have been examined with the Large Magellanic Cloud (LMC) having been detected at a level consistent with it having a cosmic ray density compatible with quasi-stable equilibrium. Sixteen Active Galactic Nuclei (AGN's) have been seen thus far with a high degree of certainty including 12 quasars and 4 BL Lac objects, but no Seyferts. Time variation has been detected in some of these AGN's

We are proposing to operate a Network of Automatic Telescopes (ATN) for CCD imaging to conduct diverse astrophysical investigations and as a resource for science education. Coordinated utilization of telescopes at diverse sites provides the possibility of obtaining continuous photometry without diurnal interruption. We describe this project and discuss how it is impacted by light pollution, and conversely, how it might mitigate the growth of light pollution.

A Monte Carlo simulation shows that the EGRET gamma-ray telescope aboard the GRO satellite does not have sufficient sensitivity to detect linear polarization, even for 100% polarized gamma-ray sources. This is confirmed by analysis of calibration data. Several data selection techniques suggested to enhance polarization sensitivity have been evaluated and found to not significantly improve sensitivity.

The EGRET instrument on board the Compton Gamma Ray Observatory has detected about 150 sources above 100 MeV. Slightly less than half of these sources have been identified either as active galactic nuclei (AGNs) associated with spectrally flat radio-loud sources of the blazar type or as isolated young/intermediate-age pulsars. Except for rotational modulation, the gamma-ray flux of pulsars does not display significant variation, whereas blazars show variability on timescales as short as ~7 hr. We show here that one of the most prominent unidentified gamma-ray sources near the Galactic plane, 2CG 135+01 (first discovered by the COS B satellite), does not fit into either of these two classes. By comparing different EGRET observations, we establish with 98.8% confidence that the gamma-ray flux from 2CG 135+01 is time variable. This is inconsistent with the constant flux observed from isolated gamma-ray pulsars. No potential spectrally flat radio-loud AGN counterpart exists for this source. We show that 2CG 135+01 belongs to a new class of variable gamma-ray emitters in the Galactic plane, a class that also includes the recently discovered nonblazar gamma-ray transient GRO J1838-04.

Aims. A huge multiwavelength campaign targeting the blazar AO 0235+164 was organized by the Whole Earth Blazar Telescope (WEBT) in 2003-2005 to study the variability properties of the source. Methods. Monitoring observations were carried out at cm and mm wavelengths, and in the near-IR and optical bands, while three pointings by the XMM-Newton satellite provided information on the X-ray and UV emission. Results. We present the data acquired during the second observing season, 2004-2005, by 27 radio-to-optical telescopes. The ∼2600 data points collected allow us to trace the low-energy behaviour of the source in detail, revealing an increased near-IR and optical activity with respect to the previous season. Increased variability is also found at the higher radio frequencies, down to ∼15 GHz, but not at the lower ones. While the X-ray (and optical) light curves obtained during the XMM-Newton pointings reveal no significant short-term variability, the simultaneous intraday radio observations with the 100 m telescope at Effelsberg show flux-density changes at 10.5 GHz, which are more likely due to a combination of intrinsic and extrinsic processes. Conclusions. The radio (and optical) outburst predicted to peak around February-March 2004 on the basis of the previously observed 5-6 yr quasi-periodicity did not occur. The analysis of the optical light curves reveals now a longer characteristic time scale of variability of ∼8 yr, which is also present in the radio data. The spectral energy distributions corresponding to the XMM-Newton observations performed during the WEBT campaign are compared with those pertaining to previous pointings of X-ray satellites. Bright, soft X-ray spectra can be described in terms of an extra component, which appears also when the source is faint through a hard UV spectrum and a curvature of the X-ray spectrum. Finally, there might be a correlation between the X-ray and optical bright states with a long time delay of about 5 yr, which would require a geometrical interpretation., La lista completa de autores que integran el documento puede consultarse en el archivo., Facultad de Ciencias Astronómicas y Geofísicas

The EGRET (Energetic Gamma Ray Experiment Telescope) detector has been calibrated at SLAC (Stanford Linear Accelerator) and, to a lesser degree, at the MIT (Massachusetts Institute of Technology) Bates Linear Accelerator Center. To monitor the photon beams for the calibration, a plastic scintillator block, 5 cm*5 cm in cross section, 15 cm in length, and viewed by a single photomultiplier tube, was used for the entire beam energy range of 15 MeV to 10 GeV. The design operation, and method of analysis of the beam intensity are presented. A mathematical framework has been developed to treat the general case of a beam with multiphoton beam pulses and with a background component. A procedure to deal with the fluctuations of the beam intensity over a data-taking period was also developed. The photon beam monitor is physically sturdy, electronically steady, simple to construct, and easy to operate. Its major merits lie in its sheer simplicity of construction and operation and in the wide energy range it can cover. >

BL Lacertae has been the target of four observing campaigns by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we present UBVRI light curves obtained by theWEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have been collected, to be added to the ∼15 600 observations of the BL Lac Campaign 2000. All these data allow one to follow the source optical emission behaviour with unprecedented detail. The analysis of the colour indices reveals that the flux variability can be interpreted in terms of two components: longer-term variations occurring on a fewday time scale appear as mildly-chromatic events, while a strong bluer-when-brighter chromatism characterizes very fast (intraday) flares. By decoupling the two components, we quantify the degree of chromatism inferring that longer-term flux changes imply moving along a ∼0.1 bluerwhen- brighter slope in the B − R versus R plane; a steeper slope of ∼0.4 would distinguish the shorter-term variations. This means that, when considering the long-term trend, the B-band flux level is related to the R-band one according to a power law of index ∼1.1. Doppler factor variations on a “convex” spectrum could be the mechanism accounting for both the long-term variations and their slight chromatism. Reig Torres, Pablo, Pablo.Reig@uv.es

We report EGRET upper limits on the high-energy gamma-ray emission from clusters of galaxies. EGRET observations between 1991 and 2000 were analyzed at positions of 58 individual clusters from a flux-limited sample of nearby X-ray bright galaxy clusters. Subsequently, a coadded image from individual galaxy clusters has been analyzed using an adequately adapted diffuse gamma-ray foreground model. The resulting 2 sigma upper limit for the average cluster is \~ 6 x 10^{-9} cm^{-2} s^{-1} for E > 100 MeV. Implications of the non--detection of prominent individual clusters and of the general inability to detect the X-ray brightest galaxy clusters as a class of gamma-ray emitters are discussed. We compare our results with model predictions on the high-energy gamma-ray emission from galaxy clusters as well as with recent claims of an association between unidentified or unresolved gamma-ray sources and Abell clusters of galaxies and find these contradictory., 13 pages, 6 figures, 2 tables (emulateapj), accepted for publication in ApJ

Observations of the Small Magellanic Cloud using the Energetic Gamma Ray Experiment Telescope on the Compton Observatory yield an upper limit (95% confidence) for gamma-ray emission g100 MeV of 0.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ photon/${\mathrm{cm}}^{2}$ s. The expected flux if the cosmic rays are universal rather than galactic in origin, is (2.4-0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ photon/${\mathrm{cm}}^{2}$ s, only a third of which arise from cosmic ray electron interactions. Hence, the bulk of the cosmic ray energy density is almost certainly not metagalactic, and therefore galactic in origin.

The optical light curve of the energetic gamma-ray burst GRB 991216 is consistent with jet-like behavior in which a power-law decay steepens from t**(-1.22 +/- 0.04) at early times to t**(-1.53 +/- 0.05) in a gradual transition at around 2 d. The derivation of the late-time decay slope takes into account the constant contribution of a host or intervening galaxy which was measured 110 d after the event at R = 24.56 +/- 0.14, although the light curve deviates from a single power law whether or not a constant term is included. The early-time spectral energy distribution of the afterglow can be described as F_nu ~ nu**(-0.74 +/- 0.05) or flatter between optical and X-ray, which, together with the slow initial decay, is characteristic of standard adiabatic evolution in a uniformly dense medium. Assuming that a reported absorption-line redshift of 1.02 is correct, the apparent isotropic energy of 6.7 x 10**53 erg is reduced by a factor of ~ 200 in the jet model, and the initial half-opening angle is ~ 6 deg. GRB 991216 is the third good example of a jet-like afterglow (following GRB 990123 and GRB 990510), supporting a trend in which the apparently most energetic gamma-ray events have the narrowest collimation and a uniform ISM environment. This, plus the absence of evidence for supernovae associated with jet-like afterglows, suggests that these events may originate from a progenitor in which angular momentum plays an important role but a massive stellar envelope or wind does not, e.g., the coalescence of a compact binary., 19 pages, accepted by The Astrophysical Journal

We report some of the statistical results from our multi-epoch VLBA study of motions in the jets of 42 γ-ray bright blazars. The apparent velocities are high, which agrees with the expectations of inverse Compton models in which the γ rays are more highly beamed than is the radio synchrotron radiation. We find evidence that the apparent speeds are higher farther from the core, which can be explained best by bending from a viewing angle near zero to one closer to sin−1(Γ−1), rather than by increasing Lorentz factors. In 25 of the sources in the sample, there is at least one non-core component that appears to be stationary during our observations. We offer explanations for these results.

We compare the extrapolated epochs of zero separation of apparent superluminal components from the cores in γ-ray bright blazars with the EGRET light curves. In 10 out of 20 superluminal components with sufficient γ-ray data, the epochs of zero separation coincide with times of global or local maxima of the γ-ray light curves within the 1-σ uncertainties of the epochs of zero separation. If we focus only on the γ-ray peaks, nine out of ten with sufficient VLBA data are accompanied by superluminal ejections. The γ-ray flares are therefore associated with energetic events in the jets rather than with minor episodes of enhanced particle acceleration.

One of the most exciting recent developments in astrophysics is the detection of members of the blazar class of AGN at ∼1 GeV by the EGRET instrument aboard the Cdmpton Observatory. Although a weak detection of 3C 273 was obtained by the COS B mission, the very strong detection of 3C 279 by EGRET (Hartman et al 1992) two months after launch was not anticipated.

We model the temporally evolving nonthermal particle and photon spectra at different stages in the lifetime of a standard shell-type supernova remnant. A characteristic νFν spectrum of a SNR consists of a peak at radio-through-optical energies from nonthermal electron synchrotron emission and another high-energy gamma-ray peak due primarily to nonthermal electron bremsstrahlung, Compton scattering, and secondary pion production. We find that SNRs are capable of producing maximum gamma-ray luminosities ≳1034 erg s−1 if the density of the local ISM is ≳1 cm−3. This emission will persist for ≳105 years after the supernova explosion. This long gamma-ray lifetime suggests that SNRs with a wide range of ages could be gamma-ray sources and could constitute some of the unidentified EGRET sources.

We have identified a site at an elevation of 3,900 meters on the Barcroft Plateau in the White Mountains of California which would be a good site for Cerenkov γ-ray astronomy. The atmospheric conditions are conducive. There is ample infrastructure. And the site is large enough to accommodate an array of telescopes which at this altitude is expected to provide impressive performance.

A new bright gamma-ray source was detected in June 1995 near the Galactic plane (GRO J1838−04). Subsequent EGRET observations did not detect significant flux from this source. The gamma-ray error box of GRO J1838−04 does not contain any spectrally-flat radio-loud source. GRO J1838−04 provides strong evidence for the existence of a new class of variable gamma-ray sources.

We derive an ephemeris for the Geminga pulsar using all available EGRET, COS–B, and SAS–2 data spanning 24 yr. A cubic ephemeris predicts the rotational phase of Geminga with errors smaller than 50 milliperiods. The braking index obtained is 17±1. If Geminga continues to rotate without glitch as it has for at least 23 yr, we expect this ephemeris to continue to describe the phase with an error less than 100 milliperiods until the year 2008. Statistically significant timing residuals are detected in the EGRET data with an RMS value ∼20 milliperiods. The addition of a sinusoidal term to the ephemeris reduces the residuals to an RMS value of less than 6 milliperiods. This sinusoid corresponds to a planet of mass 1.7/sin i M⊕ orbiting Geminga at a radius of 3.3 AU, although these residuals could be caused by timing noise rather than a planet.

We present a method to assess the reliability of the identification of EGRET sources with extragalactic radio sources. We verify that EGRET is detecting the blazar class of AGN. However, many published identifications are found to be questionable. We provide a table of 42 blazars which we expect to be robust identifications of EGRET sources. This includes one previously unidentified EGRET source, the lensed AGN PKS 1830-210 near the direction of the Galactic center. We provide the best available positions for 16 more radio sources which are also potential identifications for previously unidentified EGRET sources. All high Galactic latitude EGRET sources (b>3 degrees) which demonstrate significant variability can be identified with flat spectrum radio sources. This suggests that EGRET is not detecting any type of AGN other than blazars. This identification method has been used to establish with 99.998% confidence that the peak gamma-ray flux of a blazar is correlated with its average 5 GHz radio flux. An even better correlation is seen between gamma-ray flux and the 2.29 GHz flux density measured with VLBI at the base of the radio jet. Also, using high confidence identifications, we find that the radio sources identified with EGRET sources have larger correlated VLBI flux densities than the parent population of flat radio spectrum sources., To be published in Ap J, May 20, 1997 issue, Vol. 481. The complete paper is available at http://bu-ast.bu.edu/~mattox/src_id.html

We report the observation by the Compton Gamma Ray Observatory of a spectacular flare of radio source PKS 1622-297. A peak flux of 17E-6 cm^-2 s^-1 (E > 100 MeV) was observed. The corresponding isotropic luminosity is 2.9E49 erg/s. We find that PKS 1622-297 exhibits gamma-ray intra-day variability. A flux increase by a factor of at least 3.6 was observed to occur in less than 7.1 hours (with 99% confidence). Assuming an exponential rise, the corresponding doubling time is less than 3.8 hours. A significant flux decrease by a factor of ~2 in 9.7 hours was also observed. Without beaming, the rapid flux change and large isotropic luminosity are inconsistent with the Elliot-Shapiro condition (assuming that gas accretion is the immediate source of power for the gamma-rays). This inconsistency suggests that the gamma-ray emission is beamed. A minimum Doppler factor of 8.1 is implied by the observed lack of pair-production opacity (assuming x-rays are emitted co-spatially with the gamma-rays). Simultaneous observation by EGRET and OSSE finds a spectrum adequately fit by a power law with photon index of -1.9. Although the significance is not sufficient to establish this beyond doubt, the high-energy gamma-ray spectrum appears to evolve from hard to soft as a flare progresses., 14 pages, 4 figures, 1 table

One of the key programs on the 1.3 m Robotically Controlled Telescope (RCT) located at Kitt Peak National Observatory and the 0.6 m telescope at the Bell Observatory operated by Western Kentucky University is a study of the variability of the class of Active Galactic Nuclei (AGN) known as Blazars. Blazars are highly variable on timescales of minutes to decades and this variability is seen across the electromagnetic spectrum. In addition, they display a featureless spectrum, thus continuum variability provides the only diagnostic of these objects. Variability provides information on the size of the emission region responsible for the observed variations and when observations are obtained at multiple wavelengths, it can be used to discriminate between emission models. However, traditional ground based observations are limited in a variety of ways. We will discuss how an automated facility, with time dedicated to this astrophysically interesting problem, can overcome many of these limitations, and we show results from the Bell Observatory as well as some of the first results of Blazar observations from the RCT. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report simultaneous observations of the optically violent variable (OVV) quasar PKS 1406-076 in the optical and gamma-ray regime. Gamma-ray emission is detected with very high significance. Both the gamma-ray and optical properties of PKS 1406-076 are typical for the group of gamma-bright active galactic nuclei detected by EGRET. During 1993 January the source was unusually bright in both frequency ranges. During this period we observed a rapid, symmetrical flare in the optical wavelength range which lasted for about 4 days. EGRET detected a similar rapid flare peaking about 22 hr after the optical outburst. Because such rapid flares are rare events, it is likely that the outbursts in the two frequency regimes are correlated. Correlated outbursts with similar profiles and a lag between the optical and gamma-ray maxima of 22 hr are inconsistent with simple versions of models suggested for the emission of high-energy radiation from blazars.

The EGRET instrument aboard the Compton Gamma Ray Observatory (CGRO) has completed the first all-sky survey in high-energy gamma rays and has repeatedly viewed selected portions of the sky. Analysis of the region with galactic latitude $+10\arcdeg < b < +40\arcdeg$ indicates the presence of nineteen point sources, including nine which can be identified as active galactic nuclei, some of which have been reported previously, as well as ten other sources with no definite counterparts. Using the combined exposures from Phase 1 and Phase 2 of the CGRO viewing program, the spectra, time variability, and positions of all detected sources in this region are determined. It is tentatively suggested that one of the unidentified sources might be associated with the radio galaxy Centaurus A., Comment: 18 pages, 3 Postscript figures (one of 3 pages) Uses aaspp4.sty

We detected a sixth high-energy gamma-ray pulsar, PSR B1951+32, pulsating in gamma rays at E ≥ 100 MeV with the same 39.5 ms periodicity as in radio, using the data obtained during 1991 May to 1994 July by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory. Although seen only as a weak source amidst the high background of galactic disk emission, the pulsation in high-energy gamma rays is clearly seen. The pulsed radiation has a photon spectral index of -1.74 ± 0.11. There is no evidence as yet for unpulsed emission from the object. The pulsar appears to have an efficiency of ~0.004 for converting its rotational energy loss into gamma rays at E ≥ 100 MeV.

The EGRET instrument on the Compton Gamma Ray Observatory, which detects photons in the energy range 30 MeV to 30 GeV, has detected about 40 sources of gamma rays (>100 MeV) at high galactic latitudes. Most of these appear to be associated with bright, flat-spectrum radio sources, many of which have been previously classified as optically violent variable (OVV) quasars or BL Lac objects (together often referred to as blazars). The remaining sources are presently unidentified, although some of them are positionally compatible with flat-spectrum radio sources which are somewhat less bright and less well-studied.

The use of EGRET data from the SSC Archive using programs developed by the Instrument Team, and the SSC is disccussed. The EGRET team delivers maps, photon event lists, and the exposure history for each viewing period. The QUICKLOOK program (see Macomb et al., these proceedings) can be used to browse the event lists, make selection, and do simple plots. The PULSAR program uses these event lists for pulsar analysis. The MAPGEN program generates counts maps, which can be used by INTMAP to create intensity maps. The SHOW program can be used for simple analysis of these maps. The LIKE program can be used for maximum likelihold point source analysis. The IDL procedures FITSMAP and SKYMAP can be used to look at these maps.

This paper provides a summary of the data reduction and analysis procedures used by the Energetic Gamma Ray Experimental Telescope (EGRET) team. The steps are summarized beginning with the extensive calibration, proceeding to the basic data reduction, and finishing with the data analysis techniques, including a brief description of the source determination, the intensity calculation, the spectral evaluation, the pulsar program, and time variations. References are provided for the detailed discussions of the major portions of the work. The types of data and the software available to Guest Investigators are also reviewed with guides to more detailed descriptions. In this way, the overview is given in one place with references for those wishing to see parts in detail.

EGRET onboard the Compton Gamma Ray Observatory observed four energetic X‐type solar flares during June 1991. Two of these flares were in the EGRET spark chamber field of view and were observed to have high energy gamma ray emission lasting hours after the impulsive phase of the flare. Measurements of all four flares were obtained by the EGRET large NaI spectrometer.