An unidentified TeV source in the vicinity of Cygnus OB2

Abstract

Abstract. Deep observation (∼113 hrs) of the Cygnus region at TeV energies using the HEGRA stereoscopic system of aiř Cerenkov telescopes has serendipitously revealed a signal positionally inside the core of the OB association Cygnus OB2, at the edge of the 95% error circle of the EGRET source 3EG J2033+4118, and ∼0.5• north of Cyg X-3. The source centre of gravity is RA α J2000 : 20 hr 32 m 07 s ± 9.2 s stat ± 2.2 s sys , Dec δ J2000 : +41• 30 30 ± 2.0 stat ± 0.4 sys . The source is steady, has a post-trial significance of +4.6σ, indication for extension with radius 5.6 at the ∼3σ level, and has a differential power-law flux with hard photon index of −1.9 ± 0.3 stat ± 0.3 sys . The integral flux above 1 TeV amounts ∼3% that of the Crab. No counterpart for the TeV source at other wavelengths is presently identified, and its extension would disfavour an exclusive pulsar or AGN origin. If associated with Cygnus OB2, this dense concentration of young, massive stars provides an environment conducive to multi-TeV particle acceleration and likely subsequent interaction with a nearby gas cloud. Alternatively, one could envisage γ-ray production via a jet-driven termination shock.

Astrophysical origins of ultrahigh energy cosmic rays

“…reported by HEGRA Collaboration [152] in the vicinity of Cygnus OB2 is likely due to hadronic processes. Since π 0 's, π + 's, and π − 's are produced in equal numbers, 48 This experiment observes microwaveČerenkov pulses from electromagnetic showers induced by neutrinos interacting in the Moon's rim [520] 49 A balloon-borne payload that will circle the continent of Antartica at 35,000 meters, scanning the vast expanses of ice for telltale pulses of radio emission generated by the neutrino collisions [http://www.ps.uci.edu/∼anita/].…”

Galactic discrete sources of high energy neutrinos

“…Torres et al (2004) propose that TeV γ-rays and neutrinos can be produced by CRs through interactions with the nuclei in the innermost parts of the winds of massive O and B stars. This model would explain the TeV emission observed by HEGRA in the vicinity of Cygnus OB2 (Aharonian et al 2002). The main acceleration region of CRs would be the outer boundary of the supper-bubble produced by the core of the association of OB stars.…”

“…8). Most of the models considered in this review predict neutrino event rates above the sensitivity limit of the future cubic-kilometer size detector IceCube (Ahrens et al 2004b) and of a possible km 3 (Montaruli 2003). Ten neutrino events were measured inside a 3 • half-width cone (that is expected to include 90% of an E −2 neutrino signal) around the plerion PSR1509-58, while 2 are expected from atmospheric ν's.…”

“…Recently, Cygnus OB2 became also an interesting high energy source due to the reports of detection of a few γ-ray EGRET sources (e.g. Mori et al 1997, Lamb & Macomb 1997), a TeV γ-ray source by HEGRA (Aharonian et al 2002), and an excess of CR particles at energies ∼ 10 18 eV by AGASA (Hayashida et al 1999). Therefore, it is also an interesting potential source of high energy neutrinos.…”

Pulsar Wind Nebulae and Cosmic Rays: A Bedtime Story

“…The serendipitous detection of the gamma-ray source TeV J2032+4130, based on observations made by the HEGRA IACT system, was reported in 2002 [54,55]. Subsequent observations by the IACT observatories MAGIC and VERITAS have confirmed the extension of the source and provided more precise measurements of its spectrum.…”