Deep radio images of the HEGRA and Whipple TeV sources in the Cygnus OB2 region

Abstract

Context. The modern generation of Cherenkov telescopes has revealed a new population of gamma-ray sources in the Galaxy. Some of them have been identified with previously known X-ray binary systems while other remain without clear counterparts a lower energies. Our initial goal here was reporting on extensive radio observations of the first extended and yet unidentified source, namely TeV J2032+4130. This object was originally detected by the HEGRA telescope in the direction of the Cygnus OB2 region and its nature has been a matter of debate during the latest years. The situation has become more complex with the Whipple and MILAGRO telescopes new TeV detections in the same field which could be consistent with the historic HEGRA source, although a different origin cannot be ruled out. Aims. We aim to pursue our radio exploration of the TeV J2032+4130 position that we initiated in a previous paper but taking now into account the latest results from new Whipple and MILAGRO TeV telescopes. The data presented here are an extended follow up of our previous work. Methods. Our investigation is mostly based on interferometric radio observations with the Giant Metre Wave Radio Telescope (GMRT) close to Pune (India) and the Very Large Array (VLA) in New Mexico (USA). We also conducted near infrared observations with the 3.5 m telescope and the OMEGA2000 camera at the Centro Astronómico Hispano Alemán (CAHA) in Almería (Spain).Results. We present deep radio maps centered on the TeV J2032+4130 position at different wavelengths. In particular, our 49 and 20 cm maps cover a field of view larger than half a degree that fully includes the Whipple position and the peak of MILAGRO emission. Our most important result here is a catalogue of 153 radio sources detected at 49 cm within the GMRT antennae primary beam with a full width half maximum (FWHM) of 43 arc-minute. Among them, peculiar sources inside the Whipple error ellipse are discussed in detail, including a likely double-double radio galaxy and a one-sided jet source of possible blazar nature. This last object adds another alternative counterpart possibility to be considered for both the HEGRA, Whipple and MILAGRO emission. Moreover, our multi-configuration VLA images reveal the non-thermal extended emission previously reported by us with improved angular resolution. Its non-thermal spectral index is also confirmed thanks to matching beam observations at the 20 and 6 cm wavelengths.

MAGIC Observations of the Unidentified γ-Ray Source TeV J2032+4130

“…The question of whether the result reported by Horns et al can be interpreted as a truly diffuse background, or whether it could be a result of unresolved X-ray sources, remains disputable. Paredes et al (2007) and Martí et al (2007) have provided deep radio observations covering the TeV J2032ϩ4130 vicinity using the Giant Metrewave Radio Telescope and discovered a population of radio sources, some in coincidence with X-ray detections by Butt et al (2006) and with optical/IR counterparts. At least three of these sources are nonthermal, and one has a hard X-ray energy spectrum.…”

“…Among them, those related to extragalactic counterparts, e.g., a radio galaxy (Butt et al 2006) or a proton blazar (Mukherjee et al 2003), face the difficulty of explaining the extended appearance of the source. Gammaray production in hypothetical jet termination lobes of Cyg X-3 was explored (Aharonian et al 2002), but the putative northern lobe of Cyg X-3 (now considered a mere thermal H ii region; Martí et al 2006) is far from the location of the TeV source. A yet unknown pulsar wind nebula (PWN) was proposed by Bednarek (2003), although no clear PWN signal was observed.…”

A pulsar wind nebula associated with PSR J2032+4127 as the powering source of TeV J2032+4130

“…They also used archival VLA D configuration observations at 1.4 and 5 GHz and archival Chandra X-ray observations. [6,7] identified several possible point-like sources and extended structures that could be related to TeV J2032+4130, although at that time no conclusive results could be obtained.…”

“…The authors in [6,7] conducted a detailed multi-wavelength study of TeV J2032+4130. In particular, they performed radio interferometric observations with the Giant Metrewave Radio Telescope (GMRT) at 610 MHz, with the Very Large Array (VLA) in C configuration at 1.4 and 5 GHz, and obtained near infrared K s observations with the CAHA 3.5 m telescope.…”

The Molecular Environment of the Gamma-Ray Source TeV J2032+4130

“…TeV J2032ϩ4130 is spatially extended and steady in intensity indicating it is likely of Galactic origin, yet still has no firmly identified counterparts at lower energies. Although follow-up observations using Chandra and the VLA were inconclusive (Butt et al 2003(Butt et al , 2006(Butt et al , 2008Mukherjee et al 2003Mukherjee et al , 2007Paredes et al 2007;Marti et al 2007), the low X-ray and radio emission indicates that the TeV flux is likely hadronic, as opposed to leptonic, in origin. 4 Recently, the HESS collaboration detected TeV gamma-ray emission from the Westerlund 2 stellar association in the southern sky (Aharonian et al 2007), which may also indicate turbulent particle acceleration induced by stellar shocks, perhaps with a contribution from "hidden" supernova remnants expanding in low-density media (e.g., Bykov 2001;Tang & Wang 2005).…”