Study of the γ-ray source 1AGL J2022+4032 in the Cygnus region

¹ INAF/IASF-Roma, 00133 Roma, Italy
² Dip. di Fisica, Univ. Tor Vergata, 00133 Roma, Italy
³ INAF/IASF-Milano, 20133 Milano, Italy
e-mail: chen@iasf-milano.inaf.it
⁴ CIFS-Torino, 10133 Torino, Italy
⁵ INAF/IASF-Bologna, 40129 Bologna, Italy
⁶ Dip. Fisica and INFN Trieste, 34127 Trieste, Italy
⁷ INFN-Pavia, 27100 Pavia, Italy
⁸ ENEA-Bologna, 40129 Bologna, Italy
⁹ INFN-Roma La Sapienza, 00185 Roma, Italy
¹⁰ CNR-IMIP, Roma, Italy
¹¹ INFN-Roma Tor Vergata, 00133 Roma, Italy
¹² Dip. di Fisica, Univ. Dell’Insubria, 22100 Como, Italy
¹³ ENEA Frascati, 00044 Frascati, Roma, Italy
¹⁴ ASI Science Data Center, 00044 Frascati,Roma, Italy
¹⁵ Agenzia Spaziale Italiana, 00198 Roma, Italy
¹⁶ INAF-Osservatorio Astron. di Roma, Monte Porzio Catone, Italy
¹⁷ INAF-IASF-Palermo, via U. La Malfa 15, 90146 Palermo, Italy
¹⁸ Dip. Fisica, Universitá di Torino, Turin, Italy
¹⁹ INAF-Osservatorio Astronomico di Cagliari, localita’ Poggio dei Pini, strada 54, 09012 Capoterra, Italy
²⁰ Institute of Astronomy and Space Physics, University of Buenos Aires, Ciudad Universitaria, (1428), Ciudad de Buenos Aires, Argentina

Received: 24 June 2010
Accepted: 20 September 2010

Abstract

Context. Identification of γ-ray-emitting Galactic sources is a long-standing problem in astrophysics. One such source, 1AGL J2022+4032, coincident with the interior of the radio shell of the supernova remnant Gamma Cygni (SNR G78.2+2.1) in the Cygnus region, has recently been identified by Fermi as a γ-ray pulsar, LAT PSR J2021+4026.

Aims. We present long-term observations of 1AGL J2022+4032 with the AGILE γ-ray telescope, measuring its flux and light curve.

Methods. We compare the light curve of 1AGL J2022+4032 with that of 1AGL J2021+3652 (PSR J2021+3651), showing that the flux variability of 1AGL J2022+4032 appears to be greater than the level predicted from statistical and systematic effects and producing detailed simulations to estimate the probability of the apparent observed variability.

Results. We evaluate the possibility that the γ-ray emission may be due to the superposition of two or more point sources, some of which may be variable, considering a number of possible counterparts.

Conclusions. We consider the possibility of a nearby X-ray quiet microquasar contributing to the flux of 1AGL J2022+4032 to be more likely than the hypotheses of a background blazar or intrinsic γ-ray variabilty of LAT PSR J2021+4026.