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Register a new userCounterpart candidates to the unidentified Fermi source 0FGL J1848.6-0138
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Aims. We aim here to contribute to the identification of unassociated bright sources of gamma-rays in the recently released catalogue obtained by the Fermi collaboration. Methods. Our work is based on a extensive cross-identification of sources from different wavelength catalogues and databases. Results. As a first result, we report the finding of a few counterpart candidates inside the 95% confidence error box of the Fermi LAT unidentified gamma-ray source 0FGL J1848.6$-$0138. The globular cluster GLIMPSE-C01 remarkably stands out among the most peculiar objects consistent with the position uncertainty of the gamma-ray source and with a conceivable physical scenario for gamma-ray production. The Fermi observed spectrum is compared against theoretical predictions in the literature making the association plausible but not yet certain due to its low X-ray to gamma-ray luminosity ratio. Other competing counterparts are also discussed. In particular, we pay a special attention to a possible Pulsar Wind Nebula inside the Fermi error box whose nature is yet to be confirmed. Conclusions.Both a globular cluster and an infrared source resembling a Pulsar Wind Nebula have been found in positional agreement with 0FGL J1848.6$-$0138. In addition, other interesting objects in the field are also reported. Future gamma-ray observations will narrow the position uncertainty and we hope to eventually confirm one of the counterpart candidates reported here. If GLIMPSE-C01 is confirmed, together with the Fermi possible detection of the well known globular cluster 47 Tuc, then it would provide strong support to theoretical predictions of globular clusters as gamma-ray sources.
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Here we report the results of searching millisecond pulsar (MSP) candidates from the Fermi LAT second source catalog (2FGL). Seven unassociated $gamma-$ray sources in this catalog are identified as promising MSP candidates based on their $gamma$-ray properties. Through the X-ray analysis, we have detected possible X-ray counterparts, localized to an arcsecond accuracy. We have systematically estimated their X-ray fluxes and compared with the corresponding $gamma$-ray fluxes. The X-ray to $gamma$-ray flux ratios for 2FGL J1653.6-0159 and 2FGL J1946.4-5402 are comparable with the typical value for pulsars. For 2FGL J1625.2-0020, 2FGL J1653.6-0159 and 2FGL J1946.4-5402, their candidate X-ray counterparts are bright enough for performing a detailed spectral and temporal analysis to discriminate their thermal/non thermal nature and search for the periodic signal. We have also searched for possible optical/IR counterparts at the X-ray positions. For the optical/IR source coincident with the brightest X-ray object that associated with 2FGL J1120.0-2204, its spectral energy distribution is comparable with a late-type star. Evidence for the variability has also been found by examining its optical light curve. All the aforementioned 2FGL sources resemble a pulsar in one or more aspects, which make them as the promising targets for follow-up investigations.
Blazars and in particular the subclass of high synchrotron peaked Active Galactic Nuclei are among the main targets for the present generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) and will remain of great importance for very high-energy $gamma$-ray science in the era of the Cherenkov Telescope Array (CTA). Observations by IACTs, which have relatively small fields of view ($sim$ few degrees), are limited by viewing conditions; therefore, it is important to select the most promising targets in order to increase the number of detections. The aim of this paper is to search for unclassified blazars among known $gamma$-ray sources from the Fermi Large Area Telescope (LAT) third source catalog that are likely detectable with IACTs or CTA. We use an artificial neural network algorithm and updated analysis of Fermi-LAT data. We found 80 $gamma$-ray source candidates, and for the highest-confidence candidates, we calculate their potential detectability with IACTs and CTA based on an extrapolation of their energy spectra. Follow-up observations of our source candidates could significantly increase the current TeV source population sample and could ultimately confirm the efficiency of our algorithm to select TeV sources.
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 discuss the time-series behavior of 8 extragalactic 3FGL sources away from the Galactic plane (i.e., $mid bmid geq 10^{circ}$) whose uncertainty ellipse contains a single X-ray and one radio source. The analysis was done using the standard Fermi textit{ScienceTools}, package of version v10r0p5. The results show that sources in the study sample display a slight indication of flux variability in $gamma$-ray on monthly timescale. Furthermore, based on the object location on the variability index versus spectral index diagram, the positions of 4 objects in the sample were found to fall in the region of the already known BL Lac positions.
We report on the identification of the gamma-ray source 0FGL J20001.0+4352 listed in the Fermi bright source catalogue. This object, which has an observed 1-100 GeV flux of (7.8 +/- 1.2) x 10^{-9} ph cm^{-2} s^{-1} and is located close to the Galactic plane, is not associated with any previously known high energy source. We use archival XMM-Newton and Swift/XRT data to localise with arcsec accuracy the X-ray counterpart of this GeV emitter and to characterise its X-ray properties: the source is bright (the 0.2-12 keV flux is 1.9 x 10^{-12} erg cm^{-2} s^{-1}), variable (by a factor of ~2) and with a steep power law spectrum (Gamma = 2.7). It coincides with a radio bright (~200 mJy at 8.4 GHz) and flat spectrum object (MG4 J200112+4352 in NED). Broad-band optical photometry of this source suggests variability also in this waveband, while a spectroscopic follow-up observation provides the first source classification as a BL Lac object. The source SED, as well as the overall characteristics and optical classification, point to a high frequency peaked blazar identification for 0FGL J2001.0+4352.
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