Spatially Resolving the Very High Energy Emission from MGRO J2019+37 with VERITAS
Fortin, P.; Reyes, L. C.; Aune, T.; Benbow, W.; Bird, R.; Bugaev, V.; Cui, W.; Falcone, A.; Feng, Q.; Finley, J. P.; Fleischhack, H.; Fortson, L.; Furniss, A.; Gotthelf, E. V.; Grube, J.; Hanna, D.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kertzman, M.; Kieda, D.; Lang, M. J.; Maier, G.; McArthur, S.; Moriarty, P.; Mukherjee, R.; Ong, R. A.; Otte, A. N.; Pandel, D.; Park, N.; Pohl, M.; Popkow, A.; Quinn, J.; Ragan, K.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Sembroski, G. H.; Shahinyan, K.; Tyler, J.; Wakely, S. P.; Weinstein, A.; Wilhelm, A.; Williams, D. A.; Zitzer, B.; Dwarkadas, V. V.; Beilicke, M.; Galante, N.; Aliu, E.; Chen, X.; Buckley, J. H.; Cerruti, M.; Ciupik, L.; Connolly, M. P.; Griffin, S.; McCann, A.; Nieto, D.; Staszak, D.; Telezhinsky, I.; Tucci, J. V.; Behera, B.; Kargaltsev, O.; Bouvier, A.; Dumm, J.; Errando, M.; Federici, S.; Gillanders, G. H.; Gyuk, G.; Khassen, Y.; Krennrich, F.; Madhavan, A. S.; O'Faoláin de Bhróithe, A.; Prokoph, H.; Roberts, M.; Smith, A. W.; Vincent, S.; Welsing, R.; Berger, K.; Griffiths, S. T.; Millis, J.; Rajotte, J.
United States, Germany, Ireland, Canada
Abstract
We present very high energy (VHE) imaging of MGRO J2019+37 obtained with the VERITAS observatory. The bright extended (~2°) unidentified Milagro source is located toward the rich star formation region Cygnus-X. MGRO J2019+37 is resolved into two VERITAS sources. The faint, point-like source VER J2016+371 overlaps CTB 87, a filled-center remnant (SNR) with no evidence of a supernova remnant shell at the present time. Its spectrum is well fit in the 0.65-10 TeV energy range by a power-law model with photon index 2.3 ± 0.4. VER J2019+378 is a bright extended (~1°) source that likely accounts for the bulk of the Milagro emission and is notably coincident with PSR J2021+3651 and the star formation region Sh 2-104. Its spectrum in the range 1-30 TeV is well fit with a power-law model of photon index 1.75 ± 0.3, among the hardest values measured in the VHE band, comparable to that observed near Vela-X. We explore the unusual spectrum and morphology in the radio and X-ray bands to constrain possible emission mechanisms for this source.