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Fermi LAT Observations of the Cygnus Region

ATEL # 1850; J.E. Grove (NRL), J. Knödlseder (CESR), A. Tramacere (CIFS Torino/SLAC Stanford), on behalf of the Fermi Large Area Telescope Collaboration
on 21 Nov 2008; 19:01 UT
Password Certification: Elizabeth Hays (

Subjects: Gamma Ray, >GeV, Binaries, Transients

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has been observing the Cygnus region regularly since 3 August 2008 as part of its on-going sky survey, which covers ~20% of the sky at any instant and all points in the sky every 3 hours. The LAT has detected two persistent, bright sources within or near the error circle of the gamma-ray source AGL J2030+4043 reported by AGILE in ATEL #1827. These source positions are not consistent with gamma-ray emission from Cyg X-3.

The first source is within the AGILE error circle and is positionally consistent with the EGRET source 3EG J2033+4118 (R. Hartman et al. 1999, ApJS, 123, 79). The LAT measures a persistent integral flux of about 50 x 10-8 ph cm-2 s-1 above 100 MeV when the object is modeled as a point source. The second, nearby but outside the AGILE error circle, is the bright source 3EG J2020+4017, for which the LAT measures a persistent integral flux of about 170 x 10-8 ph cm-2 s-1 above 100 MeV when it is modeled as a point source. These fluxes have an uncertainty of about 30% and should be considered preliminary.

Firm locations, fluxes, and associated uncertainties of the LAT-detected sources will be reported in the forthcoming release of a LAT high-confidence source list.

During the interval reported by AGILE in ATEL #1827 (MJD 54773), the LAT can place a preliminary 95%-confidence upper limit on >100 MeV gamma flux from Cyg X-3 of 80 x 10-8 ph cm-2 s-1, including systematic uncertainty. Similar limits are observed on neighboring days. Given the proximity of the other bright sources, and the unexceptional level of the flux upper limit on this particular day, we conclude that the emission reported by AGILE from this region is unlikely to be from Cyg X-3.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this region will continue.

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R. E. Rutledge , Editor
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