Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPossible New Identifications for EGRET Sources
303
0
0.0
(
0
)
Authors
S. D. Bloom
Ask ChatGPT about the research
No Arabic abstract
We have conducted a multiwavelength study of several radio sources within or near the error boxes of EGRET unidentified sources at mid to high Galactic latitude, under the hypothesis that the radio sources are blazars and are thus the best identification candidates for the EGRET objects. We show that one of these radio sources, PMN 0850-12, has a flux of 1.5 Jy at 22 GHz and a nearly flat spectrum up to 230 GHz and is thus very likely to be the correct identification for for the EGRET source 2EG J0852-1237.
rate research
Read More
We study the $gamma$-ray emission from the pulsar magnetosphere based on outer gap models, and the TeV radiation from pulsar wind nebulae (PWNe) through inverse Compton scattering using a one-zone model. We showed previously that GeV radiation from the magnetosphere of mature pulsars with ages of $sim 10^5-10^6$ years old can contribute to the high latitude unidentified EGRET sources. We carry out Monte Carlo simulations of $gamma$-ray pulsars in the Galaxy and the Gould Belt, assuming the pulsar birth rate, initial position, proper motion velocity, period, and magnetic field distribution and evolution based on observational statistics. We select from the simulation a sample of mature pulsars in the Galactic plane ($|b|leq 5^circ$) and in the high latitude ($|b|> 5^circ$) which could be detected by EGRET. The TeV flux from the pulsar wind nebulae of our simulated sample through the inverse Compton scattering by relativistic electrons on the microwave cosmic background and synchrotron seed photons are calculated. The predicted fluxes are consistent with the present observational constraints. We suggest that strong EGRET sources can be potential TeV source candidates for present and future ground-based TeV telescopes.
We present the results of our analysis devoted to the research of sources emitting in the energy bands surveyed by both the Swift-BAT and the Fermi-LAT telescopes. We cross-correlate the Fermi-LAT 1-year point source catalogue (1FGL) of {gamma}-ray sources and the second Palermo BAT catalogue (2PBC) of hard X-ray sources, establishing a correspondence between sources when their error boxes overlap. We also extract the significance value in the BAT 15-150 keV map, obtained using a dedicated software for the reduction of BAT data, in the direction of the 1FGL sources and take into account those above the significance threshold {sigma} = 3. We obtain a sample of common sources emitting in both the hard X- and the {gamma}-ray energy bands and evaluate its content in galactic and extragalactic objects. We assess the fraction of unidentified sources and describe in greater detail the properties of two of them, 1FGL J0137.8+5814 and 1FGL J2056.7+4938, supporting their classification as blazars after the analysis of their broad-band spectral energy distribution. We discuss the blazar content of the collected 1FGL-2PBC sources: we build its redshift distibution and compare it with that of the whole blazar population as reported in the second edition of the BZCAT blazar catalogue.
3EG J1835+5918 is the brightest of the so-called unidentified EGRET sources at intermediate galactic latitude (l,b)=(89,25). We obtained complete radio, optical, and X-ray coverage of its error box, discovering a faint ultrasoft X-ray source in the ROSAT All-Sky Survey. Deep optical imaging at the location of this source, as pinpointed by an observation with the ROSAT HRI, reveals a blank field to a limit of V > 25.2. The corresponding lower limit on f_X/f_V is 300, which signifies that the X-ray source 3EG J1835+5918 is probably a thermally emitting neutron star. Here we report on recent Chandra and HST observations that strengthen this identification. 3EG J1835+5918 may thus become the prototype of an hypothesized population of older pulsars, born in the Gould belt, that can account for as many as 40 local EGRET sources. In addition to 3EG 1835+5918, we review the ongoing multiwalength effort by members of our group to study other unidentified EGRET sources using X-ray, optical, and radio data.
The variability of the high-energy gamma ray sources in the Third EGRET catalog is analyzed by a new method. We re-analyze the EGRET data to calculate a likelihood function for the flux of each source in each observation, both for detections and upper limits. These functions can be combined in a uniform manner with a simple model of the flux distribution to characterize the flux variation by a confidence interval for the relative standard deviation of the flux. The main result is a table of these values for almost all the cataloged sources. As expected, the identified pulsars are steady emitters and the blazars are mostly highly variable. The unidentified sources are heterogeneous, with greater variation at higher Galactic latitude. There is an indication that pulsar wind nebulae are associated with variable sources. There is a population of variable sources along the Galactic plane, concentrated in the inner spiral arms.
Context. A considerable fraction of the gamma-ray sources discovered with the Energetic Gamma-Ray Experiment Telescope (EGRET) remain unidentified. The EGRET sources that have been properly identified are either pulsars or variable sources at both radio and gamma-ray wavelengths. Most of the variable sources are strong radio blazars.However, some low galactic-latitude EGRET sources, with highly variable gamma-ray emission, lack any evident counterpart according to the radio data available until now. Aims. The primary goal of this paper is to identify and characterise the potential radio counterparts of four highly variable gamma-ray sources in the galactic plane through mapping the radio surroundings of the EGRET confidence contours and determining the variable radio sources in the field whenever possible. Methods. We have carried out a radio exploration of the fields of the selected EGRET sources using the Giant Metrewave Radio Telescope (GMRT) interferometer at 21 cm wavelength, with pointings being separated by months. Results. We detected a total of 151 radio sources. Among them, we identified a few radio sources whose flux density has apparently changed on timescales of months. Despite the limitations of our search, their possible variability makes these objects a top-priority target for multiwavelength studies of the potential counterparts of highly variable, unidentified gamma-ray sources.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
