High-energy Gamma-ray Sources Research Articles

Search for the Identification of 3EG J1835+5918: Evidence for a New Type of High‐Energy Gamma‐Ray Source

The EGRET source 3EG J1835+5918 is the brightest and most accurately positioned of the as-yet unidentified high-energy gamma-ray sources at high Galactic latitude (l,b=89,25). We present a multiwavelength study of the region around it, including X-ray, radio, and optical imaging surveys, as well as optical spectroscopic classification of most of the active objects in this area. The identified X-ray sources in or near the EGRET error ellipse are radio-quiet QSOs, a galaxy cluster, and coronal emitting stars. The radio sources inside the error ellipse are all fainter than 4 mJy at 1.4 GHz. In addition there are no flat-spectrum radio sources in the vicinity. Since no blazar-like or pulsar-like candidate has been found as a result of these searches, 3EG J1835+5918 must be lacking one or more of the physically essential attributes of these known classes of gamma-ray emitters. If it is an AGN it lacks the beamed radio emission of blazars by at least a factor of 100 relative to identified EGRET blazars. If it is an isolated neutron star, it lacks the steady thermal X-rays from a cooling surface and the magnetospheric non-thermal X-ray emission that is characteristic of all EGRET pulsars. If a pulsar, 3EG J1835+5918 must be either older or more distant than Geminga, and probably an even more efficient or beamed gamma-ray engine.

Discovery of a new population of high-energy gamma-ray sources in the Milky Way

One of the great mysteries of the high-energy gamma-ray sky is the group of approximately 170 unidentified point sources found along the Galactic plane. They are more numerous than all other high-energy gamma-ray sources combined and, despite 20 years of effort, no clear counterparts have been found at other wavelengths. Here we report a new population of such objects. A cluster of approximately 20 faint sources appears north of the Galactic Centre, which is part of a broader class of faint objects at mid-latitudes. In addition, we show in a model-independent way that the mid-latitude sources are distinct from the population of bright unidentified sources along the Galactic plane. The distribution on the sky indicates that the faint mid-latitude sources are associated with the Gould belt of massive stars and gas clouds at approximately 600 light years distance, as has been previously suggested.

Radio and Millimeter Spectral Properties of Newly Identified High‐Energy Gamma‐Ray Sources

We have conducted a variability study of several radio/millimeter sources that are possible counterparts of high-energy gamma-ray sources detected by EGRET. Some sources were possibly variable during this period. The radio source with the highest spectral and temporal coverage, PMN J0850-1213, behaves in a manner consistent with the shocked-jet models for extragalactic radio sources proposed in the literature. In addition, GB 105536.5+564424 is an X-ray-selected BL Lac object, and, if the identification with the EGRET source is correct, it would be the most distant such object detected at energies >100 MeV (z = 0.41). A future detection in the TeV range, as well, could provide an important constraint on absorption of very high energy gamma rays by the intergalactic infrared photon field. We also discuss the possibility that this object is a gravitationally microlensed active galactic nucleus, with the foreground lensing object at z = 0.144.

High‐Energy Gamma‐Ray Observations of Two Young, Energetic Radio Pulsars

We present results of Compton Gamma-Ray Observatory EGRET observations of the unidentified high-energy gamma-ray sources 2EG J1049-5847 (GEV J1047-5840, 3EG J1048-5840) and 2EG J1103-6106 (3EG J1102-6103). These sources are spatially coincident with the young, energetic radio pulsars PSRs B1046-58 and J1105-6107, respectively. We find evidence for an association between PSR B1046-58 and 2EG J1049-5847. The gamma-ray pulse profile, obtained by folding time-tagged photons having energies above 400 MeV using contemporaneous radio ephemerides, has probability of arising by chance of 1.2E-4 according to the binning-independent H-test. A spatial analysis of the on-pulse photons reveals a point source of equivalent significance 10.2 sigma. Off-pulse, the significance drops to 5.8 sigma. Archival ASCA data show that the only hard X-ray point source in the 95% confidence error box of the gamma-ray source is spatially coincident with the pulsar within the 1' uncertainty (Pivovaroff, Kaspi & Gotthelf 1999). The double peaked gamma-ray pulse morphology and leading radio pulse are similar to those seen for other gamma-ray pulsars and are well-explained in models in which the gamma-ray emission is produced in charge-depleted gaps in the outer magnetosphere. The inferred pulsed gamma-ray flux above 400 MeV, (2.5 +/- 0.6) x 10E-10 erg/cm^2/s, represents 0.011 +/- 0.003 of the pulsar's spin-down luminosity, for a distance of 3 kpc and 1 sr beaming. For PSR J1105-6107, light curves obtained by folding EGRET photons using contemporaneous radio ephemerides show no significant features. We conclude that this pulsar converts less than 0.014 of its spin-down luminosity into E > 100 MeV gamma-rays beaming in our direction (99% confidence), assuming a distance of 7 kpc, 1 sr beaming and a duty cycle of 0.5.

CAFNA/sup (R)/, coded aperture fast neutron analysis for contraband detection: preliminary results

We have developed a near field coded aperture imaging system for use with fast neutron techniques as a tool for the detection of contraband and hidden explosives through nuclear elemental analysis. The technique relies on the prompt gamma rays produced by fast neutron interactions with the object being examined. The position of the nuclear elements is determined by the location of the gamma emitters. For existing fast neutron techniques, in Pulsed Fast Neutron Analysis (PFNA), neutrons are used with very low efficiency; in Fast Neutron Analysis (FNA), the sensitivity for detection of the signature gamma rays is very low. For the Coded Aperture Fast Neutron Analysis (CAFNA(R)) we have developed, the efficiency for both using the probing fast neutrons and detecting the prompt gamma rays is high. Compared to PFNA, the improvement for neutron utilization is n/sup 2/, where the total number of voxels in the object being examined is n/sup 3/. Compared to FNA, the improvement for gamma-ray imaging is proportional to the total open area of the coded aperture plane; a typical value is n/sup 2//2, where n/sup 2/ is the number of total detector resolution elements or the number of pixels in an object layer. We have performed analysis, Monte Carlo simulations, and preliminary experiments using low and high energy gamma-ray sources. The results show that a high sensitivity 3-D contraband imaging and detection system can be realized by using CAFNA.

The pending GLAST mission

The Gamma-ray Large Area Space Telescope (GLAST) is a high-energy (20 MeV - 300 GeV) gamma-ray astronomy mission planned for launch in 2005. GLAST will be very useful for studies of particle acceleration in the Universe. Topics of interest include active galactic nuclei and their jets, extragalactic and Galactic diffuse emissions, dark matter, supernova remnants, pulsars, and the unidentified high-energy gamma-ray sources. The sensitivity is expected to be ∼2 × 10—9 photons cm—2 s—1 (> 100 MeV) for a 2-year all-sky survey, which is a factor of more than 30 improvement in sensitivity over the EGRET Telescope onboard the Compton Observatory.

The Third EGRET Catalog of High‐Energy Gamma‐Ray Sources

The third catalog of high-energy gamma-ray sources detected by the EGRET telescope on the Compton Gamma Ray Observatory includes data from 1991 April 22 to 1995 October 3 (cycles 1, 2, 3, and 4 of the mission). In addition to including more data than the second EGRET catalog and its supplement, this catalog uses completely reprocessed data (to correct a number of mostly minimal errors and problems). The 271 sources (E > 100 MeV) in the catalog include the single 1991 solar flare bright enough to be detected as a source, the Large Magellanic Cloud, five pulsars, one probable radio galaxy detection (Cen A), and 66 high-confidence identifications of blazars (BL Lac objects, flat-spectrum radio quasars, or unidentified flat-spectrum radio sources). In addition, 27 lower confidence potential blazar identifications are noted. Finally, the catalog contains 170 sources not yet identified firmly with known objects, although potential identifications have been suggested for a number of those. A figure is presented that gives approximate upper limits for gamma-ray sources at any point in the sky, as well as information about sources listed in the second catalog and its supplement, that do not appear in this catalog.

Milagro as a solar observatory

The Milagro Gamma Ray Observatory, a ground-based water Čherenkov detector designed primarily for observing very high energy gamma ray sources, can also be used to study the Sun. Measurements of high energy emission from solar flares can lead to an understanding of the solar energetic particle acceleration mechanism(s), and Milagro, with enhanced data acquisition electronics, will measure solar cosmic rays in the poorly studied energy range from 10 to 300 GeV. Monte Carlo simulations show that proton and neutron solar cosmic rays at these energies will be detectable at the ground level through the single muons and/or mini showers they produce. Milagro can detect these events in a scaler counting mode similar to that of a neutron monitor. Additionally, it can operate in a telescope mode that reduces background by pointing at the source region. We also report a preliminary detection, using the Milagro prototype, Milagrito, of a ground level event (GLE) on 6 November 1997 associated with an X-class solar flare.

GLAST: the next-generation high energy gamma-ray astronomy mission

The Gamma Ray Large Area Space Telescope (GLAST) is a high energy (20–300 GeV) gamma-ray astronomy mission planned for launch in 2005. The overarching scientific theme of the mission is studying sites of particle acceleration in the Universe. Topics of interest include active galactic nuclei and their jets, extragalactic and galactic diffuse emissions, dark matter, supernova remnants, pulsars, and the unidentified high energy gamma-ray sources. The sensitivity is 2 × 10 −9 photons cm −2 s −1 (>100 MeV) for a 2 year all-sky survey, which is a factor of >30 better than CGRO/EGRET. The GLAST program is currently in a high level of mission development activity.

A Model for Non High Energy Gamma Ray Bursts and Sources of Ultra High Energy Cosmic Rays: Super Strongly Magnetized Milli-Second Pulsar Formed from a (C+O) Star and a Neutron Star (Black Hole) Close Binary System

A Model for Non High Energy Gamma Ray Bursts and Sources of Ultra High Energy Cosmic Rays: Super Strongly Magnetized Milli-Second Pulsar Formed from a (C+O) Star and a Neutron Star (Black Hole) Close Binary System

A 7–9 MeV isotopic gamma-ray source for detector testing

An isotopic source of high-energy gamma rays has been constructed and tested. The source uses either a long-lived americium–beryllium neutron source or 252Cf to produce fast neutrons, which are moderated in paraffin and then absorbed in metallic nickel. The radiative capture of thermal neutrons in natural metallic Ni produced five prominent gamma-ray energies in the range 7.5–9 MeV, of which the 8.997 MeV line is the strongest by more than a factor of two. The source was optimized for counting rate by measuring gamma-ray energy spectra with a 76 mm diam. NaI detector, then used to test an imaging BGO detector with gamma rays in the energy range 7.5–9 MeV.

A candidate gamma-ray pulsar in the supernova remnant CTA 1

ABSTRA C T We present a detailed analysis of the high-energy gamma-ray source 2EG J0008+7307. The source has a steady flux and a hard spectrum, softening above 2 GeV. The properties of the gamma-ray source are suggestive of emission from a young pulsar in the spatially coincident CTA 1 supernova remnant, which has recently been found to have a non-thermal X-ray plerion. Our 95 per cent uncertainty contour around the> 1 GeV source position includes the point-like X-ray source at the centre of the plerion. We propose that this object is a young pulsar and is the most likely counterpart of 2EG J0008+7307.

A 5-GHz Southern Hemishere VLBI Survey of Compact Radio Sources.I.

We report the results of a 5 GHz southern hemisphere VLBI survey of compact extragalactic radio sources. These observations were undertaken with the SHEVE array plus Shanghai station in November 1992. A sample of 22 sources was observed and images of 20 of them were obtained. Of the 20 sources imaged, 15 showed core-jet structure, one had a two-sided jet and 4 had only single compact cores. Eleven of the 16 core-jet (including one two-sided jet) sources show some evidence of bent jets. No compact doubles were found. A comparison with previous images and the temporal variability of the radio flux density showed evidence for superluminal motion in 4 of the sources. Five sources were high energy (>100 MeV) gamma-ray sources. Statistical analysis showed the dominance of highly polarized quasars among the detected gamma-ray sources, which emphasizes the importance of beaming effect in the gamma-ray emission.

A Gamma‐Ray Flare in NRAO 190

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.

Variability ofCGRO/EGRET Gamma‐Ray Sources

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.

Supplement to the Second EGRET Catalog of High-Energy Gamma-Ray Sources

view Abstract Citations (123) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Supplement to the Second EGRET Catalog of High-Energy Gamma-Ray Sources Thompson, D. J. ; Bertsch, D. L. ; Dingus, B. L. ; Esposito, J. A. ; Etienne, A. ; Fichtel, C. E. ; Friedlander, D. P. ; Hartman, R. C. ; Hunter, S. D. ; Kendig, D. J. ; Mattox, J. R. ; McDonald, L. M. ; Mukherjee, R. ; Ramanamurthy, P. V. ; Sreekumar, P. ; von Montigny, C. ; Fierro, J. M. ; Jones, B. B. ; Lin, Y. C. ; Michelson, P. F. ; Nolan, P. L. ; Tompkins, W. ; Willis, T. D. ; Kanbach, G. ; Mayer-Hasselwander, H. A. ; Merck, M. ; Pohl, M. ; Kniffen, D. A. ; Schneid, E. J. Abstract This supplement extends the second EGRET catalog of high-energy gamma- ray sources (see recent paper by Thompson et al.), incorporating data from 1993 September to 1994 October. The second catalog contained 129 sources, based on data from 1991 April to 1993 September. An additional 28 sources are found, including three new identifications of active galactic nuclei. Publication: The Astrophysical Journal Supplement Series Pub Date: November 1996 DOI: 10.1086/192362 Bibcode: 1996ApJS..107..227T Keywords: CATALOGS; GALAXIES: ACTIVE; GAMMA RAYS: OBSERVATIONS full text sources ADS | data products SIMBAD (31) NED (28) CDS (2) HEASARC (1) Related Materials (1) Catalog: 1997yCat..21070227T

A search for diffuse sources of ultra high energy gamma-rays

We describe a search for diffuse emission from several candidate sources of gamma-rays with energieauthor00 TeV, using the Chicago Air Shower Array / Michigan Muon Array (CASA-MIA) experiment. Since March 1990, CASA-MIA has recorded over 2.0 × 10 9 air shower events. Searches for diffuse emission are based upon the muon content of air showers. Candidate source regions include molecular clouds in the galaxy and the galactic plane. Results from CASA-MIA are compared to predicted diffuse emission.

Variability of CGRO/EGRET Gamma Ray Sources

We have developed a method for quantifying the flux variabilities of high energy gamma ray sources. We have applied this method to 128 sources listed in the second catalog of sources detected with the Energetic Gamma Ray Experiment Telescope (EGRET) (Thompson et. al. 1995). These sources include the Large Magellanic Cloud, 5 pulsars, 41 active galactic nuclei (AGN), and 81 sources not yet identified with known objects.Our data include photon maps (E > 100 MeV) from 134 EGRET viewing periods spanning a roughly 3year period. Each source was observed in 3-20 viewing periods ranging from a few days to 3 weeks in length. For each observation, a source flux was calculated using the method of maximum likelihood (Mattoxet al. 1996) which simultaneously estimates the strength of the Galactic and isotropic diffuse emission, and that of a point source distributed as the EGRET point spread function.

The Second EGRET Catalog of High-Energy Gamma-Ray Sources

The Second EGRET Catalog of High-Energy Gamma-Ray Sources

The Evolution of Gamma-Ray--loud Active Galactic Nuclei

view Abstract Citations (86) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Evolution of Gamma-Ray--loud Active Galactic Nuclei Chiang, J. ; Fichtel, C. E. ; von Montigny, C. ; Nolan, P. L. ; Petrosian, V. Abstract During the period from the launch of the Compton Observatory in 1991 April through 1993 September, the Energetic Gamma-Ray Experiment Telescope (EGRET) has detected, with high significance (>5σ), 33 blazar-type QSOs which are sources of high-energy gamma-rays and another eight which show strong evidence for high-energy gamma-ray emission. Many of the gamma-ray loud blazars have redshifts z ∼ 1 with the most distant source having a redshift of z = 2.2. The V/VMAX test has been applied to the sample of gamma-ray loud AGNs seen during the phase I and II observing periods, and evidence for the evolution of these sources consistent with pure luminosity evolution is presented. The effects of observational biases due to gamma-ray flux-detection limits and optical identifications are considered. Using the Ve/Va test, we find the parameters describing the evolution, and by de-evolving the sample, we make an estimate of the luminosity function of these objects. Finally, using this luminosity function, we make an estimate of the gamma-ray loud AGN contribution to the diffuse extragalactic emission. Publication: The Astrophysical Journal Pub Date: October 1995 DOI: 10.1086/176287 Bibcode: 1995ApJ...452..156C Keywords: GALAXIES: ACTIVE; GAMMA RAYS: OBSERVATIONS; GALAXIES: QUASARS: GENERAL full text sources ADS | data products SIMBAD (41) NED (41) HEASARC (1) Related Materials (1) Erratum: 1996ApJ...465.1011C