Discovery and follow-up studies of the extended, off-plane, VHE gamma-ray source HESS J1507-622

Abstract

Context. The detection of gamma-rays in the very-high-energy (VHE) range (100 GeV−100 TeV) offers the possibility of studying the parent population of ultrarelativistic particles found in astrophysical sources, so it is useful for understanding the underlying astrophysical processes in nonthermal sources. Aims. The discovery of the VHE gamma-ray source HESS J1507-622 is reported and possibilities regarding its nature are investigated. Methods. The H.E.S.S. array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (∼1% of the Crab flux in 25 h observation time for a 5σ point-source detection) and has a large field of view (∼5 • in diameter). HESS J1507-622 was discovered within the ongoing H.E.S.S. survey of the inner Galaxy, and the source was also studied by means of dedicated multiwavelength observations. Results. A Galactic gamma-ray source, HESS J1507-622, located ∼3.5 • from the Galactic plane was detected with a statistical significance >9σ. Its energy spectrum is well fitted by a power law with spectral index Γ = 2.24 ± 0.16 stat ± 0.20 sys and a flux above 1 TeV of (1.5 ± 0.4 stat ± 0.3 sys ) × 10 −12 cm −2 s −1 . Possible interpretations (considering both hadronic and leptonic models) of the VHE gamma-ray emission are discussed in the absence of an obvious counterpart.

Ancient Pulsar Wind Nebulae as a natural explanation for unidentified gamma-ray sources

“…Even if the results shown here are still preliminary, the time-dependent model (described in [5]) is clearly a powerful tool to study PWNe, but not only; in fact, once more, it strengthen the idea that most of the unidentified VHE gamma-ray sources can be described within a PWN framework and this will more than double (as underlined in Table 1 and 2) the population of VHE PWNe. In particular it can confirm the hypothesis, suggested by [2] and [3], that the so-called "dark sources" are indeed ancient PWNe. Moreover strengthening the idea about the very long lifetime of inverse Compton emitting electrons in VHE gamma-ray PWNe could have strong implications, far beyond the interpretation of "dark sources".…”

“…After some earlier models (e.g. [2], [3], [4]]), we developed a leaky-box [6] PWN model [7] and finally a new spatially-independent model to calculate the temporal evolution of the electron/positron spectrum in a spherically expanding PWN [5]. As also described in [5], the magnetic field is decreasing with time (B ∝ t −1.3 ) as theoretical models predict [8].…”

“…It was suggested, that an evolved PWN can lead to a fairly bright gamma-ray source without any lower energy counterpart (e.g. [2], [3], [4]]). Especially the discovery of the very high energy (VHE,E> 10 11 eV) source HESS J1507-622, off-set from the Galactic plane without reasonable low energy counterparts, was important, since an ancient PWN model is the only reasonable scenario which can physically describe the VHE emission of this unique source (e.g.…”

“…Especially the discovery of the very high energy (VHE,E> 10 11 eV) source HESS J1507-622, off-set from the Galactic plane without reasonable low energy counterparts, was important, since an ancient PWN model is the only reasonable scenario which can physically describe the VHE emission of this unique source (e.g. [2], [4], [5]).…”

Search for PeV Gamma-Ray Emission from the Southern Hemisphere with 5 Yr of Data from the IceCube Observatory

“…The type of the source has not been established, and it has a uniquely high Galactic latitude (∼3°. 5;Acero et al 2011). This allows for the possibility of the source being nearby.…”