Hard X-Ray Emission from Sh 2-104: A NuSTAR Search for Gamma-Ray Counterparts

E. V. Gotthelf, K. Mori, E. Aliu, J. M. Paredes, J. A. Tomsick, S. E. Boggs, Finn Erland Christensen, W. W. Craig, C. J. Hailey, F. A. Harrison, J. S. Hong, F. Rahoui, D. Stern, W. W. Zhang

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We present NuSTAR hard X-ray observations of Sh 2–104, a compact H ii region containing several young massive stellar clusters (YMSCs). We have detected distinct hard X-ray sources coincident with localized VERITAS TeV emission recently resolved from the giant gamma-ray complex MGRO J2019+37 in the Cygnus region. Fainter, diffuse X-rays coincident with the eastern YMSC in Sh2-104 likely result from the colliding winds of a component star. Just outside the radio shell of Sh 2–104 lies 3XMM J201744.7+365045 and a nearby nebula, NuSTAR J201744.3+364812, whose properties are most consistent with extragalactic objects. The combined XMM-Newton and NuSTAR spectrum of 3XMM J201744.7+365045 is well-fit to an absorbed power-law model with cm−2 and a photon index . Based on possible long-term flux variation and the lack of detected pulsations (≤43% modulation), this object is likely a background active galactic nucleus rather than a Galactic pulsar. The spectrum of the NuSTAR nebula shows evidence of an emission line at E = 5.6 keV, suggesting an optically obscured galaxy cluster at z = 0.19 ± 0.02 (d = 800 Mpc) and LX = 1.2 × 1044 erg s−1. Follow-up Chandra observations of Sh 2–104 will help identify the nature of the X-ray sources and their relation to MGRO J2019+37. We also show that the putative VERITAS excess south of Sh 2–104, is most likely associated with the newly discovered Fermi pulsar PSR J2017+3625 and not the H ii region.
Original languageEnglish
Article number25
JournalThe Astrophysical Journal
Issue number1
Number of pages7
Publication statusPublished - 2016


  • ISM: individual objects (Sh 2-104, MGRO J2019+37, 3XMM J201744.7+365045, VER J2019+368)
  • Pulsars: individual (NuSTAR J201744.3+364812)
  • Stars: neutron


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