EGRET Error Box Research Articles

A high-frequency search for radio pulsars in three EGRET error boxes

We present a new survey for pulsars in the error boxes of the low-latitude EGRET sources 3EG J1027−5817, 3EG J1800−2338 and 3EG J1810−1032. Although all of these sources have been covered by previous pulsar surveys, the recent discovery of the young, energetic pulsar PSR J1410−6132 at 6.7 GHz has shown that pulsars of this type can be hidden from low-frequency surveys. Using an observing frequency of 3.1 GHz, we discovered a 91-ms pulsar, PSR J1028−5819, which observations made at the Parkes telescope and the Australia Telescope Compact Array have shown to be young and energetic. We believe this pulsar is likely to be powering the unidentified EGRET source 3EG J1027−5817. Like other energetic pulsars, PSR J1028−5819 is highly linearly polarized, but astonishingly has a pulse duty cycle of only 0.4 per cent, one of the smallest in the entire pulsar catalogue.

Microquasar Models for 3EG J1828+0142 and 3EG J1735-1500

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box.

A Survey of Unidentified EGRET Sources at Very High Energies

The Whipple Observatory 10 m γ-ray telescope has been used to survey the error boxes of EGRET unidentified sources in an attempt to find counterparts at energies of 350 GeV and above. Twenty-one unidentified sources detected by EGRET (more than 10% of the total number) have been included in this survey. In no case is a statistically significant signal found in the EGRET error box, which implies that, at least for this sample, the γ-ray spectra of these sources steepen between 100 MeV and 350 GeV. For each EGRET source location, we list candidate associations and derive upper limits on the integral γ-ray flux above 350 GeV.

Is 3C 111, an apparently normal radio galaxy, the counterpart of 3EG J0416+3650?

The Third EGRET Catalog (3EG) lists 66 high-confidence identifications of sources with Active Galactic Nuclei (AGN). All are classified as belonging to the blazar class, with the only exception of the nearby radio galaxy Centaurus A. We report and strengthen the association of another radio galaxy, 3C 111, with the EGRET source 3EG J0416+3650. At the time of the compilation of the 3EG catalogue, 3C 111 has been considered as a low-confidence counterpart of 3EG J0416+3650, being located outside the 99% γ-ray probability contour. Since this first suggestion, no other counterparts have been reported nor the EGRET error box has been searched for likely candidates. 3C 111 has never been considerated or cited in literature as a radiogalaxy counterpart of an EGRET source. We report a detailed multiwavelength study of the EGRET error box as well as for the first time the overall spectral energy distribution of 3C 111, which appears to be intriguingly similar to those of blazars, suggesting that the radiogalaxy 3C 111 is the likely counterpart of 3EG J0416+3650.

Pulsars and their nebulae as EGRET sources

At the end of the EGRET mission, only 6–8 Galactic sources had been identified as young pulsars. Since then, several energetic pulsars have been detected in EGRET error boxes along the Galactic plane, as well as several pulsar wind nebulae from which pulsations have not yet been discovered. Some of these nebulae are associated with moderately variable EGRET sources, suggesting that the γ-ray emission might be coming from the nebula rather than from the pulsar magnetosphere. There is also a population of unidentified EGRET sources at mid-Galactic latitudes which have been proposed to be either nearby middle-aged pulsars or millisecond pulsars. I review the current status of observational studies of pulsars associated with EGRET sources and what they suggest the upcoming AGILE and GLAST γ-ray missions might observe.

Multiwavelength Examination of theCOS BField 2CG 075+00 Yields a Blazar Identification for 3EG J2016+3657

We present a high-energy study of the intriguing COS B gamma-ray field, 2CG 075+00, in order to search for possible counterparts. New EGRET data show that the COS B emission probably corresponds to two localized gamma-ray sources, 3EG J2016+3657 and 3EG J2021+3716. Spectral fits to these EGRET sources, assuming a power-law model, yield photon indices of approx. 2 for each object. We examine archival ROSAT and ASCA X-ray data that overlap both EGRET error boxes and find several point sources in the region to a flux limit of approximately 6.5 x 10(exp -13) ergs/sq cm s. We conclude that the most probable candidate for 3EG J2016+3657 is the compact, variable, flat-spectrum radio and millimeter source B2013+370 (G74.87+1.22), which has blazar like properties. The other source, 3EG J2021+3716, remains unidentified.

BeppoSAX and ASCA observations of the field containing the γ-ray transient GRO J1838-04

We present preliminary results of BeppoSAX and ASCA observations of the Galactic field containing the unidentified γ-ray transient GRO J1838-04. Several weak X-ray sources are detected within the EGRET error box. No obvious counterpart of GRO J1838-04 is evident from these observations. More multiwavelength observations are necessary to identify the nature of this non-blazar γ-ray transient.

ASCAObservations of the Unidentified EGRET Source 2EGS J1418−6049

In a 40 ks ASCA exposure of the GeV EGRET error box of the unidentified source 2EGS J1418-6049, we observe diffuse emission surrounding several unusual hard spectrum X-ray sources. Two of these sources have plausible identifications as absorbed active galactic nuclei (AGNs). Our best candidate for the EGRET source counterpart is an extended nonthermal object, which we argue to be a wind nebula surrounding a pulsar with characteristic age τ ~ 104.5 yr. We also discuss optical and radio data supporting the proposal that the GeV source is a young energetic pulsar. This analysis demonstrates how hard X-ray observations can significantly constrain the nature of GeV γ-ray sources.

Optical studies of gamma-ray bursts. 2: The superbowl burst GRB 930131

view Abstract Citations (4) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Studies of gamma-Ray Bursts. II. The Superbowl Burst GRB 930131 McNamara, Bernard ; Harrison, Thomas E. Abstract We report CCD observations of the central region of the COMPTEL error box for the 1993 January 31 γ-ray burst. One optical transient was found. Its distance from the IPN track and EGRET error box make the association of this object with GRB 930131 doubtful. We present new CCD observations of two objects identified by Schaefer et al. [preprint (1993)] that are located within a few arcminutes of the IPN that were reported to be possibly variable. We also report observations on the ROSAT All-Sky Survey EUV source noted by those investigators and the RS CVn star HD 106255. The ROSAT All-Sky Survey EUV source is suggested to arise from a faint, but relatively rich cluster of galaxies. HD 106255 is located approximately 7' from the IPN. Our CCD results show that this star was bluer than previously reported, but these observations were obtained significantly after the occurrence of GRB 930131. It is not possible to estimate the color of HD 106255 when the burst occurred. Publication: The Astronomical Journal Pub Date: May 1994 DOI: 10.1086/116991 Bibcode: 1994AJ....107.1825M Keywords: Astronomical Photometry; Blue Stars; Cataclysmic Variables; Gamma Ray Astronomy; Gamma Ray Bursts; Optical Measurement; Charge Coupled Devices; Images; Optical Filters; Rosat Mission; Telescopes; Astronomy; GAMMA-RAYS: BURSTS; GAMMA-RAYS: OBSERVATIONS full text sources ADS | data products SIMBAD (50) NED (1) HEASARC (1) Related Materials (2) Part 1: 1994AJ....107..254H Part 3: 1994AJ....108..600H