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Astrophysics, Galaxy Astrophysics, astro-ph.GA
Abstract:
Supernova remnants (SNRs) have emerged as one of the largest source classes
in very-high-energy (VHE; E>0.1,TeV) astronomy. Many of the now known VHE
gamma-ray emitting SNRs have been discovered by the H.E.S.S. imaging Cherenkov
telescope array, thanks to its unique access to the inner galaxy.
Statistically-significant emission of VHE gamma rays has now been detected from
the direction of the supernova remnant G15.4+0.1. While the centroids of the
H.E.S.S. source and the shell-type SNR are compatible, the VHE morphology
suggests a center-dominated source at TeV energies, something which is at odds
with the shell-like morphology observed at radio frequencies. This suggests
that H.E.S.S. may be observing TeV emission from a previously unknown pulsar
wind nebula (PWN) located within the boundaries of the radio shell. If this
interpretation is correct, G15.4+0.1 would in fact be a composite SNR, the
first case in which an SNR is identified as a composite on the basis of VHE
gamma-ray observations. Archival data from MAGPIS gives exciting hints that
there is radio emission from the central parts of the remnant, giving support
to this hypothesis. Unfortunately, image artefacts from a nearby strong radio
source produce considerable uncertainties in the radio analysis. Additional
observations in both the radio and X-ray are needed to confirm the composite
nature of G15.4+0.1 suggested by H.E.S.S.
