SEARCH FOR SPATIALLY EXTENDEDFERMILARGE AREA TELESCOPE SOURCES USING TWO YEARS OF DATA

Abstract

Spatial extension is an important characteristic for correctly associating γ -ray-emitting sources with their counterparts at other wavelengths and for obtaining an unbiased model of their spectra. We present a new method for quantifying the spatial extension of sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi). We perform a series of Monte Carlo simulations to validate this tool and calculate the LAT threshold for detecting the spatial extension of sources. We then test all sources in the second Fermi-LAT catalog for extension. We report the detection of seven new spatially extended sources.

Search for Extended Sources in the Galactic Plane Using Six Years of Fermi-Large Area Telescope Pass 8 Data above 10 GeV

“…The error quoted is only statistical. The sigma value for a disk is expected to be a factor of 1.85 larger than the sigma for a 2D Gaussian fit to the same source (Lande et al 2012 …”

“…As a last step, to address the ambiguity of detecting a source as spatially extended as opposed to a combination of point sources, we utilized the algorithm detailed in Lande et al (2012) to simultaneously fit the spectra and positions of two nearby point sources. To help with convergence, it begins by dividing the extended source into two spatially coincident pointlike sources and then fitting the sum and difference of the positions of the two sources without any limitations on the fit parameters.…”

Pulsar Wind Nebulae and Cosmic Rays: A Bedtime Story

“…It is interesting to note that this particularly challenging case of source confusion parallels the evolution of Fermi LAT's perspective on the SNR. A source co-located with VER J2019+407, reported in the 1FGL and 2FGL catalogs, was subsequently subsumed into the disk-like emission from the entire remnant [49].It should also be noted that this study makes somewhat pessimistic predictions. While a simple twodimensional Gaussian was used to describe the cocoon in [37], this assumed morphology is almost certainly more featureless and diffuse than the actual cocoon morphology, which should therefore be easier to resolve.…”

“…Simple power-law extrapolations are used for the cocoon and γ Cygni, based on the spectral parameters and fluxes reported in [37], [49], and the 1FHL catalog [40]. The spatial model used in all cases is a two-dimensional Gaussian of the appropriate extent.…”

“…It is interesting to note that this particularly challenging case of source confusion parallels the evolution of Fermi LAT's perspective on the SNR. A source co-located with VER J2019+407, reported in the 1FGL and 2FGL catalogs, was subsequently subsumed into the disk-like emission from the entire remnant [49].…”