TeV J2032 Research Articles

Transient X-ray sources in the field of the unidentified gamma-ray source TeV J2032+4130 in Cygnus

We present an analysis of Chandra ACIS observations of the field of TeV J2032+4130, the first unidentified TeV source, detected serendipitously by HEGRA. This deep (48.7 ks) observation of the field follows up on an earlier 5 ks Chandra director’s discretionary observation. Of the numerous point-like X-ray sources in the field, the brightest are shown to be a mixture of early and late-type stars. We find that several of the X-ray sources are transients, exhibiting rapid increases in count rates by factors 3–10, and similar in nature to the one, hard absorbed transient source located in the earlier Chandra observation of the field. None of these transient sources are likely to correspond to the TeV source. Instead, we identify a region of diffuse X-ray emission within the error circle of the TeV source and consider its plausible association.

Observations of the Unidentified TeV γ‐Ray Source TeV J2032+4130 with the Whipple Observatory 10 m Telescope

We report on observations of the sky region around the unidentified TeV γ-ray source (TeV J2032+4130) carried out with the Whipple Observatory 10 m atmospheric Cerenkov telescope for a total of 65.5 hr between 2003 and 2005. The standard two-dimensional analysis developed by the Whipple collaboration for a stand-alone telescope reveals an excess in the field of view at a pretrial significance level of 6.1 σ. The measured position of this excess is α = 20h32m27s, δ = 41°39'17'' (J2000.0). The estimated integral flux for this γ-ray source is about 8% of the Crab Nebula flux. The data are consistent with a pointlike source. Here we present a detailed description of the standard two-dimensional analysis technique used for the analysis of data taken with the Whipple Observatory 10 m telescope and the results for the TeV J2032+4130 campaign. We include a short discussion of the physical mechanisms that may be responsible for the observed γ-ray emission, based on possible association with known astrophysical objects, in particular, Cygnus OB2.

Superluminal cascade spectra of TeV γ-ray sources

Astrophysical radiation sources are scrutinized in search of superluminal γ-rays. The tachyonic spectral densities generated by ultra-relativistic electrons in uniform motion are fitted to the high-energy spectra of Galactic supernova remnants, such as RX J0852.0−4622 and the pulsar wind nebulae in G0.9+0.1 and MSH 15-52. The superluminal spectral maps of the unidentified TeV γ-ray sources HESS J1303−631, TeV J2032+4130 and HESS J1825−137 are inferred from EGRET, HEGRA and HESS data. Tachyonic cascade spectra are quite capable of generating the spectral curvature seen in double-logarithmic plots, as well as the extended spectral plateaus defined by EGRET flux points in the GeV band. The curvature of the TeV spectra is intrinsic, caused by the Boltzmann factor in the source densities. The spectral averaging with thermal and exponentially cut power-law electron densities can be done in closed form, and systematic high- and low-temperature expansions of the superluminal spectral densities are derived. Estimates on the electron/proton populations generating the tachyon flux are obtained from the spectral fits, such as power-law indices, temperature and source counts. The cutoff temperatures of the source densities suggest ultra-high-energy protons in MSH 15-52, HESS J1825−137 and TeV J2032+4130.

The Population of Radio Sources in the Field of the Unidentified Gamma-Ray Source TeV J2032+4130

TeV J2032+4130 is the first extended very high energy gamma-ray source and has remained enigmatic since its discovery because of the lack of identification. We report here deep radio observations covering the TeV J2032+4130 field and revealing for the first time an extended and diffuse radio emission, as well as a remarkable population of compact radio sources. Some of these radio sources are in positional coincidence with X-ray and optical/IR sources. Future follow-up studies of these new radio sources will likely contribute to solving the mystery of this extended unidentified TeV source.

Observations of 14 young open star clusters with the HEGRA system of Cherenkov telescopes

Context. A sample of 14 young open star clusters has been observed in the TeV energy regime with the stereoscopic system of the HEGRA (High Energy Gamma-Ray Astronomy) Cherenkov telescopes from 1997 to 2002, resulting in more than 300 h of observation time. Aims. Young open star clusters may contribute to the acceleration of cosmic rays. The detection of γ-rays (from decaying π 0 s produced in hadronic interactions) from these objects could be evidence for such a contribution. The results of our observations are compared to available γ-ray data and to a simple hadronic model in the framework of shock front acceleration of cosmic rays in the stellar winds of the cluster members to test the potential of the presently available data on young open star clusters to constrain this type of model. Methods. The stereoscopic system of HEGRA Cherenkov telescopes makes use of the atmospheric imaging technique. Air showers initiated by primary Gamma-Rays are recorded as elliptical images in the telescope cameras. The images from the different telescopes are then superimposed to reconstruct the parameters of the primary particle. This technique (stereoscopy) was pioneered by the HEGRA experiment. Results. No significant excess has been found in the analysed data set of young open star clusters. The derived upper limit on the TeV gamma-ray flux from Berkeley 87 and the available EGRET data from the same direction do not allow us to fully constrain the simple hadronic model used here. The comparison of the upper limits derived for all 14 objects with the flux detected from TeV J2032+4130 (under the assumption of an association of the TeV-signal with the compact stellar association Cyg OB2) suggests that γ-ray emission from young open star clusters as an object class cannot be ruled out.

DeeperChandraFollow‐up of Cygnus TeV Source Perpetuates Mystery

A 50 ks Chandra observation of the unidentified TeV source in Cygnus reported by the HEGRA collaboration reveals no obvious diffuse X-ray counterpart. However, 240 pointlike X-ray sources are detected within or nearby the extended TeV J2032+4130 source region, of which at least 36 are massive stars and two may be radio emitters. That the HEGRA source is a composite, having as a counterpart the multiple pointlike X-ray sources we observe, cannot be ruled out. Indeed, the distribution of pointlike X-ray sources appears nonuniform and concentrated broadly within the extent of the TeV source region. We offer a hypothesis for the origin of the very high energy gamma-ray emission in Cyg OB2 based on the local acceleration of TeV-range cosmic rays and the differential distribution of OB versus less massive stars in this association.

ChandraObservation of the Unidentified TeV Gamma‐Ray Source HESS J1303−631 in the Galactic Plane

The imaging atmospheric Cerenkov array HESS recently discovered an extended source in the 0.4-10 TeV energy range, HESS J1303-631. We obtained a 5 ks observation with the ACIS-I array on the Chandra X-Ray Observatory that does not reveal an obvious compact or diffuse X-ray counterpart. Archival ROSAT images are also blank in this region. Although there are several radio pulsars within the field of HESS J1303-631, none is detected in X-rays to a flux limit of <5 × 10-14 ergs cm-2 s-1, and none is a likely counterpart on energetic grounds. Over the entire 17' × 17' ACIS-I field, we place an upper limit of <5.4 × 10-12 ergs cm-2 s-1 on the excess diffuse flux in the 2-10 keV band. One hard point source with flux ≈4 × 10-14 ergs cm-2 s-1 lies within 05 of the centroid of the TeV emission. These exploratory observations suggest that deeper pointings with Chandra and XMM-Newton are needed before we can learn more about the nature of HESS J1303-631. Its similarity to the unidentified source TeV J2032+4130 indicates the probable existence of a new class of high-energy source in the Galactic plane that originates from young, massive stars or their supernova remnants.

Evidence for TeV gamma ray emission from TeV J2032+4130 in Whipple archival data

A reanalysis of data taken on the Cygnus region in 1989-90 using the Whipple Observatory atmospheric Cherenkov imaging telescope confirms the existence of the TeV J2032+4130 source reported by the Crimean Astrophysical Observatory and published by the HEGRA Collaboration. The significance at the a priori HEGRA position is 3.3sigma. The peak signal was found at RA=20hr32min, Dec=+41deg33min. This is 0.6deg north of Cygnus X-3 which was the original target of the observations. The flux level (12% of the level of the Crab Nebula) is intermediate between the two later observations and suggests that the TeV source is variable.

HEGRA discovery of the first unidentified TeV source

The first unidentified TeV source in the Cygnus region is confirmed by follow-up observations carried out in 2002 with the HEGRA stereoscopic system of air Cherenkov telescopes. Using the combined ∼279 h of data, this new source TeV J2032+4130, appears to be steady in flux over the four years of data taking, it shows an extension with radius 6.2 ′, and has a hard spectrum with photon index −1.9 between 1 and 10 TeV. Its location places it at the edge of the core of the extremely dense stellar OB association, Cygnus OB2. Its integral flux above energies E>1 TeV amounts to ∼3% of the Crab nebula flux. No counterpart at radio, optical, nor X-ray energies is as-yet seen, leaving TeV J2032+4130 presently unidentified. Summarized here are observational parameters of this source and brief astrophysical interpretation.

Recent results from HEGRA

The HEGRA collaboration has achieved outstanding results during the operation of the six imaging atmospheric Cherenkov telescopes from 1996 to 2002. The experimental work pioneered the field of TeV gamma-ray astronomy with observations during partial moon time and mainly by applying the stereoscopic observation mode using a system of five Cherenkov telescopes. Concerning Galactic objects the HEGRA observations have led to a precise measurement of the energy spectrum of the Crab nebula between 0.5 and 80 TeV, the detection of the first shell type supernova remnant in the Northern hemisphere (Cassiopeia A) and the investigation of the yet unidentified HEGRA TeV gamma-ray source TeV J2032+4130 in the Cygnus region. In addition, a large fraction of the Galactic plane has been studied during dedicated scans. Following the most precise measurements of the energy spectra of the well known extragalactic objects Mkn 421 and Mkn 501, the blazars H 1426+428 and 1ES 1959+650 have just been established as sources of TeV photons in the last two years. Extensive multi-wavelength campaigns have been successfully performed and spectroscopy of these four objects gives important clues for the understanding of the nonthermal emission processes and also on the optical to infrared part of the spectrum of the extragalactic background light. Recently, strong evidence for the nearby giant radio galaxy M 87 being a TeV gamma-ray emitter has been obtained. Some of these results are highlighted in this article.

Search for a Point‐Source Counterpart of the Unidentified Gamma‐Ray Source TeV J2032+4130 in Cygnus

We have made a multiwavelength study of the overlapping error boxes of the unidentified γ-ray sources TeV J2032+4130 and 3EG J2033+4118 in the direction of the Cygnus OB2 association (d = 1.7 kpc) in order to search for a point-source counterpart of the first unidentified TeV source. Optical identifications and spectroscopic classifications for the brighter X-ray sources in ROSAT PSPC and Chandra ACIS images are obtained, without finding a compelling counterpart. The classified X-ray sources are a mix of early- and late-type stars, with one exception. The brightest source in the Chandra observation is a new, hard absorbed source that is both transient and rapidly variable. It lies 7' from the centroid of the TeV emission, which places it outside of the claimed 2 σ location (r ≈ 48). A possible eclipse or "dip" transition is seen in its light curve. With a peak 1-10 keV luminosity of ≈7 × 1032(d/1.7 kpc)2 ergs s-1, this source could be a quiescent low-mass X-ray binary that lies beyond the Cyg OB2 association. A coincident, reddened optical object of R = 20.4, J = 15.4, H = 14.2, and K = 13.4 is observed but not yet classified as a result of the lack of obvious emission or absorption features in its spectrum. Alternatively, this Chandra and optical source might be a considered a candidate for a "proton blazar," a long hypothesized type of radio-weak γ-ray source. More detailed observations will be needed to determine the nature of this variable X-ray source and to assess the possibility of its connection with TeV J2032+4130.