Unidentified TeV Source Research Articles

TeV Analysis of a Source-rich Region with the HAWC Observatory: Is HESS J1809-193 a Potential Hadronic PeVatron?

HESS J1809-193 is an unidentified TeV source, first detected by the High Energy Stereoscopic System (H.E.S.S.) collaboration. The emission originates in a source-rich region that includes several supernova remnants (SNRs) and pulsars including SNR G11.1+0.1, SNR G11.0-0.0, and the young radio pulsar PSR J1809-1917. Originally classified as a pulsar wind nebula candidate, recent studies show the peak of the TeV region overlapping with a system of molecular clouds. This resulted in the revision of the original leptonic scenario to look for alternate hadronic scenarios. Marked as a potential PeVatron candidate, this region has been studied extensively by H.E.S.S. due to its emission extending up to several tens of TeV. In this work, we use 2398 days of data from the High Altitude Water Cherenkov (HAWC) observatory to carry out a systematic source search of the HESS J1809-193 region. We were able to resolve emission detected as an extended component (modelled as a symmetric Gaussian with a 1σ radius of 0.°21) with no clear cutoff at high energies and emitting photons up to 210 TeV. We model the multiwavelength observations for the region around HESS J1809-193 using a time-dependent leptonic model and a lepto-hadronic model. Our model indicates that both scenarios could explain the observed data within the region of HESS J1809-193.

GeV Gamma-Ray Emission and Molecular Clouds toward Supernova Remnant G35.6–0.4 and the TeV Source HESS J1858+020

It is difficult to distinguish the hadronic process from the leptonic one in γ-ray observation, which is however crucial in revealing the origin of cosmic rays. As an endeavor in this regard, we focus in this work on the complex γ-ray emitting region, which partially overlaps with the unidentified TeV source HESS J1858+020 and includes supernova remnant (SNR) G35.6−0.4 and H ii region G35.6−0.5. We reanalyze CO line, H i, and Fermi-LAT GeV γ-ray emission data of this region. The analysis of the molecular and H i data suggests that SNR G35.6−0.4 and H ii region G35.6−0.5 are located at different distances. The analysis of the GeV γ-rays shows that GeV emission arises from two point sources: one (SrcA) coincident with the SNR, and the other (SrcB) coincident with both HESS J1858+020 and H ii region G35.6−0.5. The GeV emission of SrcA can be explained by the hadronic process in the SNR–molecular cloud association scenario. The GeV-band spectrum of SrcB and the TeV-band spectrum of HESS J1858+020 can be smoothly connected by a power-law function, with an index of ∼2.2. The connected spectrum is well explained with a hadronic emission, with the cutoff energy of protons above 1 PeV. It thus indicates that there is a potential PeVatron in the H ii region and should be further verified with ultrahigh-energy observations with, e.g., LHAASO.

Investigating the Nature of MGRO J1908+06 with Multiwavelength Observations

Abstract The unidentified TeV source MGRO J1908+06, with emission extending from hundreds of GeV to beyond 100 TeV, is one of the most intriguing sources in the Galactic plane. MGRO J1908+06 spatially associates with an IceCube hotspot of neutrino emission. Although the hotspot is not significant yet, this suggests a possible hadronic origin of the observed gamma-ray radiation. Here we describe a multiwavelength analysis on MGRO J1908+06 to determine its nature. We identify, for the first time, an extended GeV source as the counterpart of MGRO J1908 + 06, discovering possibly associated molecular clouds (MCs). The GeV spectrum shows two well-differentiated components: a soft spectral component below ∼10 GeV, and a hard one (Γ ∼ 1.6) above these energies. The lower-energy part is likely associated with the dense MCs surrounding the supernova remnant (SNR) G40.5−0.5, whereas the higher-energy component, which connects smoothly with the spectrum observed in TeV range, resembles the inverse Compton emission observed in relic pulsar wind nebulae. This simple scenario seems to describe the data satisfactorily, but raises questions about the interpretation of the emission at hundreds of TeV. In this scenario, no detectable neutrino flux would be expected.

Lightning black holes as unidentified TeV sources

Imaging Atmospheric Cherenkov Telescopes have revealed more than 100 TeV sources along the Galactic Plane, around 45% of them remain unidentified. However, radio observations revealed that dense molecular clumps are associated with 67% of 18 unidentified TeV sources. In this paper, we propose that an electron-positron magnetospheric accelerator emits detectable TeV gamma-rays when a rapidly rotating black hole enters a gaseous cloud. Since the general-relativistic effect plays an essential role in this magnetospheric lepton accelerator scenario, the emissions take place in the direct vicinity of the event horizon, resulting in a point-like gamma-ray image. We demonstrate that their gamma-ray spectra have two peaks around 0.1 GeV and 0.1 TeV and that the accelerators become most luminous when the mass accretion rate becomes about 0.01% of the Eddington accretion rate. We compare the results with alternative scenarios such as the cosmic-ray hadron scenario, which predicts an extended morphology of the gamma-ray image with a single power-law photon spectrum from GeV to 100 TeV.

GeV Emission in the Region of HESS J1809−193 and HESS J1813−178: Is HESS J1809−193 a Proton Pevatron?

Abstract HESS J1809−193 is an unidentified TeV source discovered by the High Energy Stereoscopic System and originally classified as a pulsar wind nebula (PWN) candidate associated with the pulsar PSR J1809−1917. However, a recent study of deep radio observations and the interstellar medium near the source has found evidence for a hadronic scenario for the gamma-rays. Here, a detailed study of the GeV emission in the region using data from the Fermi-LAT is presented. The GeV emission has an extended morphology in the region of the TeV emission and the overall spectrum can be accounted for by a cosmic-ray population having a simple power-law spectrum with energies extending up to 1 PeV. However, the spectrum at tens of TeV should be observed more deeply in the future to confirm its hadronic nature, and other scenarios involving combinations of leptonic and hadronic emission from several of the known supernova remnants in the region cannot be ruled out. The nearby TeV source HESS J1813−178, thought to be a PWN, is also studied in detail at GeV energies and we find a region of significant emission that is much more extended than the TeV emission and whose spectrum is softer than expected from a PWN but similar to those seen in several star-forming regions that are believed to accelerate protons. There is marginal evidence for a GeV point source at the location of the X-ray PWN, beside the extended emission.

Dense molecular gas at 12 mm towards Galactic TeV gamma-ray sources

The High Energy Stereoscopic System (H.E.S.S.) has revealed many TeV (10 12 eV) gamma-ray sources along the Galactic Plane and around 30 percent of these sources remain unidentified. The morphology and dynamics of dense gas coincident and surrounding the gamma-ray emission can provide clues about the nature of the TeV emission. The H2O Southern Galactic Plane Survey (HOPS) undertaken with the Mopra radio telescope, includes several dense gas tracers, such as NH3 (n,n) transitions and HC3N (3-2), star formation tracers including H2O masers, and radio recombination lines which trace ionised gas. A search for dense gas, traced by NH3 (1,1) emission seen in HOPS and additional observations, towards Galactic TeV sources has been undertaken. Of the 49 Galactic TeV sources covered by 12 mm observations, NH3 (1,1) is detected towards or adjacent to 38 of them. Dense gas counterparts have been detected near several unidentified Galactic TeV sources which display morphology pointing to a hadronic origin to the TeV gamma-rays. The dense gas detected towards some TeV sources displays unusual emission characteristics, including very broad linewidths and enhanced ortho-to-para NH3 abundance ratios towards HESS J1745-303 and HESS J1801-233, which reflects previous shock activity within the gas.

HESS J1943+213: A NON-CLASSICAL HIGH-FREQUENCY-PEAKED BL LAC OBJECT

ABSTRACT HESS J1943+213 is an unidentified TeV source that is likely a high-frequency-peaked BL Lac (HBL) object, but that is also compatible with a pulsar wind nebula (PWN) nature. Each of these enormously different astronomical interpretations is supported by some of the observed unusual characteristics. In order to finally classify and understand this object, we took a three-pronged approach, through time-domain, high angular resolution, and multi-frequency radio studies. First, our deep time-domain observations with the Arecibo telescope failed to uncover the putative pulsar powering the proposed PWN. We conclude with ∼70% certainty that HESS J1943+213 does not host a pulsar. Second, long-baseline interferometry of the source with e-MERLIN at 1.5 and 5 GHz shows only a core, that is, a point source at –100 mas resolution. Its 2013 flux density is about one-third lower than that detected in the 2011 observations with similar resolution. This radio variability of the core strengthens the HBL object hypothesis. Third, additional evidence against the PWN scenario comes from the radio spectrum we compiled. The extended structure follows a power-law behavior with spectral index while the core component displays a flat spectrum ( ). In contrast, the radio synchrotron emission of PWNe predicts a single power-law distribution. Overall, we rule out the PWN hypothesis and conclude that the source is a BL Lac object. The consistently high fraction (70%) of the flux density from the extended structure then leads us to conclude that HESS J1943+213 must be a non-classical HBL object.

ISM gas studies towards the TeV PWN HESS J1825−137 and northern region

HESS J1825-137 is a pulsar wind nebula (PWN) whose TeV emission extends across ~1 deg. Its large asymmetric shape indicates that its progenitor supernova interacted with a molecular cloud located in the north of the PWN as detected by previous CO Galactic survey (e.g Lemiere, Terrier & Djannati-Ata\"i 2006). Here we provide a detailed picture of the ISM towards the region north of HESS J1825-137, with the analysis of the dense molecular gas from our 7mm and 12mm Mopra survey and the more diffuse molecular gas from the Nanten CO(1-0) and GRS $^{13}$CO(1-0) surveys. Our focus is the possible association between HESS J1825-137 and the unidentified TeV source to the north, HESS J1826-130. We report several dense molecular regions whose kinematic distance matched the dispersion measured distance of the pulsar. Among them, the dense molecular gas located at (RA, Dec)=(18.421h,-13.282$^{\circ}$) shows enhanced turbulence and we suggest that the velocity structure in this region may be explained by a cloud-cloud collision scenario. Furthermore, the presence of a H$\alpha$ rim may be the first evidence of the progenitor SNR of the pulsar PSR J1826-1334 as the distance between the H$\alpha$ rim and the TeV source matched with the predicted SNR radius R$_{\text{SNR}}$~120 pc. From our ISM study, we identify a few plausible origins of the HESS J1826-130 emission, including the progenitor SNR of PSR J1826-1334 and the PWN G018.5-0.4 powered by PSR J1826-1256. A deeper TeV study however, is required to fully identify the origin of this mysterious TeV source.

Observing two dark accelerators around the Galactic Centre withFermiLarge Area Telescope

We report the results from a detailed $\gamma-$ray investigation in the field of two "dark accelerators", HESS J1745-303 and HESS J1741-302, with $6.9$ years of data obtained by the Fermi Large Area Telescope. For HESS J1745-303, we found that its MeV-GeV emission is mainly originated from the "Region A" of the TeV feature. Its $\gamma-$ray spectrum can be modeled with a single power-law with a photon index of $\Gamma\sim2.5$ from few hundreds MeV to TeV. Moreover, an elongated feature, which extends from "Region A" toward northwest for $\sim1.3^{\circ}$, is discovered for the first time. The orientation of this feature is similar to that of a large scale atomic/molecular gas distribution. For HESS J1741-302, our analysis does not yield any MeV-GeV counterpart for this unidentified TeV source. On the other hand, we have detected a new point source, Fermi J1740.1-3013, serendipitously. Its spectrum is apparently curved which resembles that of a $\gamma-$ray pulsar. This makes it possibly associated with PSR B1737-20 or PSR J1739-3023.

Estimating Galactic gas content using different tracers: Compatibility of results, dark gas, and unidentified TeV sources

A large fraction of Galactic very-high energy (VHE; E≳100 GeV) γ-ray sources is cataloged as unidentified. In this work we explore the possibility that these unidentified sources are located in environment particularly rich in material content unaccounted by traditional tracers. In a scenario where the VHE emission is due to the interaction of the accelerated particles with a target mass, a large mass of untraced material could be substantially contributing to the VHE emission from these regions. Here, we use three tracers for the commonly explored components: intensity of the 12CO(1→0) line to trace the molecular material, HI hyperfine transition at 21 cm to trace atomic hydrogen, and dust emission to trace the total hydrogen content. We show that the estimates of material content from these three tracers are compatible if the uncertainty on the respective conversion factors is taken into account. No additional gas component is found in these regions. However, a simple mass estimation from the 12CO(1→0) line intensity might underestimate the total mass component in some locations.

Nature of the Unidentified TeV Source HESS J1614−518, Revealed by Suzaku and XMM-Newton Observations

Abstract We report on new Suzaku and XMM-Newton results concerning HESS J1614 $-$ 518, which is one of the brightest extended TeV $\gamma$ -ray sources and has two regions with intense $\gamma$ -ray emission. We newly observed the south and center regions of HESS J1614 $-$ 518 with Suzaku, since the north region, including the position of the 1st brightest peak of the TeV $\gamma$ -ray emission, has already been observed. No X-ray counterpart was found at the position of the 2nd brightest peak of the TeV $\gamma$ -ray emission; we estimated the upper limit of the X-ray flux to be 1.6 $\times$ 10 $^{-13}$ erg cm $^{-2}$ s $^{-1}$ in the 2–10 keV band. The soft X-ray source Suzaku J1614 $-$ 5152, which was found at the edge of the field of view in a previous observation, was also detected at the middle of HESS J1614 $-$ 518. Analyzing the XMM-Newton archival data, we revealed that Suzaku J1614 $-$ 5152 consists of multiple point sources. The X-ray spectrum of the brightest point source, XMMU J161406.0 $-$ 515225, can be described by a power-law model with a photon index of $\Gamma$$=$ 5.2 $^{+0.6}_{-0.5}$ , or a blackbody model with temperature $kT$$=$ 0.38 $^{+0.04}_{-0.04}$ keV. In the blackbody model, the hydrogen-equivalent column density is almost the same as that of the hard extended X-ray emission, Suzaku J1614 $-$ 5141, which was found at the 1st peak position. If true, XMMU J161406.0 $-$ 515225 may be physically related to Suzaku J1614 $-$ 5141 and HESS J1614 $-$ 518.

A new study of the supernova remnant G344.7-0.1 located in the vicinity of the unidentified TeV source HESS J1702-420

Context. The identification of counterparts of dark gamma-ray sources adds greatly to our understanding of their underlying astrophysical processes. Aims. We investigate the physical properties of the supernova remnant (SNR) G344.7−0.1, to clarify whether it hosts a pulsar wind nebula (PWN), and the possible physical relationship between the SNR and the gamma-ray source HESS J1702−420. Methods. The research was carried out based on new high-resolution radio images produced from archival ATCA and VLA data in combination with X-ray archival XMM-Newton data. The ambient interstellar medium was investigated in HI, 12 CO and mid IR (λ 24 μm) with data from the public SGPS, CfA CO and MIPSGAL surveys, respectively. Results. Based on the radio images and the comparison with X-ray and IR observations, we confirm that there is no PWN within G344.7−0.1; the observed emission highlights sites where the SN blast wave is encountering dense material. No radio counterpart is found for the X-ray object CXOU J170357.8-414302. The X-ray radiation completely fills in the interior of the SNR, being thermal in nature and originating in heated ejecta. From the spectral analysis it is inferred that G344.7−0.1 is the result of a core-collapse SN that exploded about 3000 yr ago. On the basis of HI absorption and emission we redetermined its distance in (6.3 ± 0.1) kpc. From the study of the surrounding gas, we conclude that G344.7−0.1 has evolved within an HI bubble created by the SN precursor. This bubble is, in turn, part of a larger HI/IR ring created by the stellar wind of prior-generation stars, about 2.6 × 10 6 yr ago. A second generation of stars formed in this compressed gas and about 3000 yr ago one of these stars exploded, creating the SNR G344.7−0.1. This study suggests that G344.7−0.1 and its turbulent environment is a plausible counterpart for HESS J1702−420.

A new SNR with TeV shell-type morphology: HESS J1731-347

Aims. The recent discovery of the radio shell-type supernova remnant (SNR), G353.6-0.7, in spatial coincidence with the unidentified TeV source HESS J1731−347 has motivated further observations of the source with the High Energy Stereoscopic System (HESS) Cherenkov telescope array to test a possible association of the γ-ray emission with the SNR.

HESS J1632-478: an energetic relic

HESS J1632-478 is an extended and still unidentified TeV source in the galactic plane. In order to identify the source of the very high energy emission and to constrain its spectral energy distribution, we used a deep observation of the field obtained with XMM-Newton together with data from Molonglo, Spitzer and Fermi to detect counterparts at other wavelengths. The flux density emitted by HESS J1632-478 peaks at very high energies and is more than 20 times weaker at all other wavelengths probed. The source spectrum features two large prominent bumps with the synchrotron emission peaking in the ultraviolet and the external inverse Compton emission peaking in the TeV. HESS J1632-478 is an energetic pulsar wind nebula with an age of the order of 10^4 years. Its bolometric (mostly GeV-TeV) luminosity reaches 10% of the current pulsar spin down power. The synchrotron nebula has a size of 1 pc and contains an unresolved point-like X-ray source, probably the pulsar with its wind termination shock.

PROBING THE NATURE OF THE UNIDENTIFIED TeV GAMMA-RAY SOURCE HESS J0632+057 WITHSWIFT

New generation TeV gamma-ray telescopes have discovered many new sources, including several enigmatic unidentified TeV objects. HESS J0632+057 is a particularly interesting unidentified TeV source since: it is a point source, it has a possible hard-spectrum X-ray counterpart and a positionally consistent Be star, it has evidence of long-term VHE flux variability, and it is postulated to be a newly detected TeV/X-ray binary. We have obtained Swift X-ray telescope observations of this source from MJD 54857 to 54965, in an attempt to ascertain its nature and to investigate the hypothesis that it's a previously unknown X-ray/TeV binary. Variability and spectral properties similar to those of the other 3 known X-ray/TeV binaries have been observed, with measured flux increases by factors of approximately 3. X-ray variability is present on multiple timescales including days to months; however, no clear signature of periodicity is present on the timescales probed by these data. If binary modulation is present and dominating the measured variability, then the period of the orbit is likely to be more than 54 days (half of this campaign), or it has a shorter period with a variable degree of flux modulation on successive high states. If the two high states measured to date are due to binary modulation, then the favored period is approximately 35-40 days. More observations are required to determine if this object is truly a binary system and to determine the extent that the measured variability is due to inter-orbit flaring effects or periodic binary modulation.

Broad-band non-thermal emission from molecular clouds illuminated by cosmic rays from nearby supernova remnants

Molecular clouds are expected to emit non-thermal radiation due to cosmic ray interactions in the dense magnetized gas. Such emission is amplified if a cloud is located close to an accelerator of cosmic rays and if energetic particles can leave the accelerator site and diffusively reach the cloud. We consider here the situation in which a molecular cloud is located in the proximity of a supernova remnant which is efficiently accelerating cosmic rays and gradually releasing them in the interstellar medium. We calculate the multiwavelength spectrum from radio to gamma rays which is emerging from the cloud as the result of cosmic ray interactions. The total energy output is dominated by the gamma ray emission, which can exceed the emission in other bands by an order of magnitude or more. This suggests that some of the unidentified TeV sources detected so far, with no obvious or very weak counterparts in other wavelengths, might be in fact associated with clouds illuminated by cosmic rays coming from a nearby source. Moreover, under certain conditions, the gamma ray spectrum exhibit a concave shape, being steep at low energies and hard at high energies. This fact might have important implications for the studies of the spectral compatibility of GeV and TeV gamma ray sources.

Discovery of Extended X-Ray Emission from an Unidentified TeV Source, HESS J1614$-$518, Using the Suzaku Satellite

Abstract We report Suzaku results concerning HESS J1614$-$518, which is the brightest extended TeV gamma-ray source discovered in the Galactic plane survey conducted using the H.E.S.S. telescope. We discovered three X-ray objects in the field of view of the X-ray Imaging Spectrometer, which were designated as Suzaku J1614$-$5141 (src A), Suzaku J1614$-$5152 (src B), and Suzaku J1614$-$5148 (src C). Src A is an extended source located at the peak position of HESS J1614$-$518, and is therefore a plausible counterpart to HESS J1614$-$518. The X-ray flux in the 2-10keV band is 5$\times 10^{-13}$ergs$^{-1}$cm$^{-2}$, which is an order of magnitude smaller than the TeV flux. The photon index is 1.7, which is smaller than the canonical value of synchrotron emissions from high-energy electrons found in some supernova remnants. These findings present a challenge to models in which the origin of TeV emission is inverse Compton scattering of the cosmic microwave background by accelerated electrons that emit X-rays via synchrotron emission. Src B is located at a relatively dim region in the TeV band image; however, its hydrogen column density is the same as that of src A. Therefore, src B may also be physically related to HESS J1614$-$518. Src C is a foreground late-type B star. We also discovered soft extended X-ray emission near HESS J1614$-$518.

X‐Ray Emission from PSR J1809−1917 and Its Pulsar Wind Nebula, Possibly Associated with the TeV Gamma‐Ray Source HESS J1809−193

We detected X-ray emission from the 50-kyr-old pulsar J1809‐1917 and resolved its pulsar wind nebula (PWN) with the Chandra X-ray Observatory. The pulsar’s observed flux is Fpsr = (1: 8� 0: 2)� 10 -14 ergs cm -2 s -1 in the 1‐6 keV band. A two-component blackbody+power-law (BB+PL) fit of the pulsar’s spectrum yields the photon index psr = 1: 2� 0: 6 and luminosity L psr = (4� 1)� 10 31 ergs s -1 of the PL component, in the 0.5‐8 keV band, for a plausible distance d = 3: 5 kpc and nH = 0: 7� 10 22 cm -2 . The BB component corresponds to the temperature T � 2 MK, and bolometric luminosity L bol � 1� 10 32 ergs s -1 . The bright inner PWN component of a 3 00 � 12 00 size is elongated in the north-south direction, with the pul sar close to its south end. This component is immersed in a larger (� 20 00 � 40 00 ), similarly elongated outer PWN component of lower surface brightness. The elongated shape of the compact PWN can be explained by the ram pressure confinement of the pulsar wind due to the supersonic motion of the pulsar. The observed flux of the compact PWN, including both components, is Fpwn ’ (1: 5� 0: 1)� 10 -13 ergs cm -2 s -1 in the 1‐6 keV band. The PWN spectrum can be fitted with a PL model with nH � 0: 7� 10 22 cm -2 and photon index pwn = 1: 4� 0: 1, corresponding to the 0.5‐8 keV luminosity Lpwn � 4� 10 32 ergs s -1 . The compact PWN appears to be inside a more extended (� 4 0 � 4 0 ) emission with the total observed flux Fext � 5� 10 -13 ergs s -1 in the 0.8‐7 keV band. This large-scale emission is more extended to the south of the pulsar, i.e. in the direction of the alleged pulsar motion. To explain the extended X-ray emission ahead of the moving pulsar, one has to invoke strong intrinsic anisotropy of the pulsar wind or assume that this e mission comes from a relic PWN swept by the asymmetrical reverse SNR shock. The pulsar and its PWN are located within the extent of the unidentified TeV source HESS J1809‐193. The brightest part of the TeV source is offset by � 8 0 to the south of the pulsar, i.e. in the same direction as the large-scale X-ray emission. Altho ugh the association between the PSR J1809‐1917 and HESS J1809‐193 is plausible, an alternative source of relativistic electrons powering HESS J1809‐193 might be the serendipitously discovered X-ray source CXOU J180940.7-192544. In addition to the CMBR or Galactic starlight background, the low-frequency seed p hotons for Compton upscattering to TeV energies might be supplied by bright infrared emission from dust-molecular clouds seen within HESS J1809‐193. Subject headings: pulsars: individual (PSR J1809‐1917) — X-rays: individual (CXOU J180940.7-192544, CXOU 180933.3-192959) — gamma-rays: individual (HESS J1809‐193) — ISM: individual (IRAS 18067‐1927, IRAS 18067‐1921)

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.

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.