HESS very-high-energy gamma-ray sources without identified counterparts

Abstract

Context. The detection of gamma rays in the very-high-energy (VHE) energy range (100 GeV-100 TeV) provides a direct view of the parent population of ultra-relativistic particles found in astrophysical sources. For this reason, VHE gamma rays are useful for understanding the underlying astrophysical processes in non-thermal sources. Aims. We investigate unidentified VHE gamma-ray sources that have been discovered with HESS in the most sensitive blind survey of the Galactic plane at VHE energies conducted so far. Methods. The HESS array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (∼0.01 Crab in 25 h observation time for a 5σ point-source detection), and with its large field of view, is well suited for scan-based observations. The on-going HESS survey of the inner Galaxy has revealed a large number of new VHE sources, and for each we attempt to associate the VHE emission with multi-wavelength data in the radio through X-ray wavebands. Results. For each of the eight unidentified VHE sources considered here, we present the energy spectra and sky maps of the sources and their environment. The VHE morphology is compared with available multi-wavelength data (mainly radio and X-rays). No plausible counterparts are found.

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

“…Within this scenario, the faint diffuse emission detected by Chandra assumes a particular importance. The morphology of HESS J1507-622 is similar to HESS J1702-420 (Aharonian et al 2008), where the pulsar PSR J1702-4128 could be powering an extremely asymmetric PWN visible in VHE gamma-rays, but it should be emphasized that the PWN association of HESS J1702-420 is not established. In the ancient PWN scenario therefore the faint diffuse emission in X-ray could be due to a younger population of electrons and reflect the proper motion of the pulsar within the nebula.…”

“…The search for counterparts was made following the procedure outlined in Aharonian et al (2008). At radio and infrared wavelengths, HESS J1507-622 is offset too far from the Galactic plane to be covered by the Southern Galactic Plane Survey (Haverkorn et al 2006) or by Spitzer GLIMPSE (Benjamin 2005).…”

“…survey of the Galactic plane (Aharonian et al 2005(Aharonian et al , 2006a of new sources have been discovered and many of them are still unidentified (Aharonian et al 2008). HESS J1507-622 is among the brightest (∼8% of Crab Flux) newly discovered sources, and it lacks plausible counterparts, as is the case for HESS J1427-608, HESS J1708-410 (Aharonian et al 2008), and HESS J1616-508 (Aharonian et al 2006a). While all unidentified VHE sources that have been discovered in the H.E.S.S.…”

A young supernova remnant illuminating nearby molecular clouds with cosmic rays

“…Shell-type emission from the SNR HESS J1731-347 is seen through TeV γ-ray emission (Aharonian et al 2008b;Abramowski et al 2011) and through radio synchrotron (Tian et al 2008) and X-ray synchrotron (Abramowski et al 2011;Bamba et al 2012) emission. In the GeV-(Fermi-LAT) band, only upper limits were derived (Yang et al 2014;Acero et al 2015); also, no thermal X-rays have been detected yet from the SNR (Abramowski et al 2011;Bamba et al 2012).…”

“…In the work presented in this paper, we focus on the TeV-emitting SNR HESS J1731-347 (Aharonian et al 2008b;Abramowski et al 2011). This SNR is very similar to the wellknown TeV SNRs RX J1713.7-3946 and Vela Jr., regarding their physical size and TeV luminosity, in displaying low surface brightness radio emission (Tian et al 2008) and exhibiting essentially pure nonthermal X-ray emission (Abramowski et al 2011;Bamba et al 2012).…”