CONSTRAINTS ON THE GALACTIC POPULATION OF TeV PULSAR WIND NEBULAE USINGFERMILARGE AREA TELESCOPE OBSERVATIONS

Abstract

Pulsar wind nebulae (PWNe) have been established as the most populous class of TeV γ-ray emitters. Since launch, the Fermi Large Area Telescope (LAT) has identified five high-energy (100 MeV < E < 100 GeV) γ-ray sources as PWNe and detected a large number of PWN candidates, all powered by young and energetic pulsars. The wealth of multi-wavelength data available and the new results provided by Fermi-LAT give us an opportunity to find new PWNe and to explore the radiative processes taking place in known ones. The TeV γ-ray unidentified (UNID) sources are the best candidates for finding new PWNe. Using 45 months of Fermi-LAT data for energies above 10 GeV, an analysis was performed near the position of 58 TeV PWNe and UNIDs within 5 • of the Galactic plane to establish new constraints on PWN properties and find new clues on the nature of UNIDs. Of the 58 sources, 30 were detected, and this work provides their γ-ray fluxes for energies above 10 GeV. The spectral energy distributions and upper limits, in the multi-wavelength context, also provide new information on the source nature and can help distinguish between emission scenarios, i.e., between classification as a pulsar candidate or as a PWN candidate. Six new GeV PWN candidates are described in detail and compared with existing models. A population study of GeV PWN candidates as a function of the pulsar/PWN system characteristics is presented.

Search for Extended Sources in the Galactic Plane Using Six Years of Fermi-Large Area Telescope Pass 8 Data above 10 GeV

“…Galactic Plane Survey revealed two sources in this region: HESS J1420−607 centered north of PSR J1420−6048 (near K3), and HESS J1418−609 coincident with the Rabbit nebula (Aharonian et al 2006c). In a previous analysis of the region above 10 GeV using Fermi-LAT data (Acero et al 2013), HESS J1420−607 and HESS J1418−609 were detected as two point sources with different spectral shapes: a hard spectrum for the first one (suggesting a PWN origin), and a soft spectrum with an energy cutoff at a few GeV for the second one, suggestive of pulsar emission and thus likely due to contamination from PSR J1418−6058. It was then detected as a very extended source 64 of 0°.33 covering both PWNe in Ackermann et al (2016).…”

“…Galactic Plane Survey , was previously analyzed assuming the published morphology, an elliptical Gaussian with extensions of 0°.41 and 0°.25 (Acero et al 2013). In this new work, it is detected as two separate disks whose origin and real separation remain unclear since both γ-ray components present the same spectral shape as can be seen in Figure 7 (left).…”

“…However, looking at the TS maps in Figure 16, one clearly sees two hot spots in the southeast Figure 19. Left: SEDs of the pulsar wind nebula Kookaburra with data points from this analysis (black stars and dashed butterfly), from a previous Fermi-LAT publication (Acero et al 2013), from the 2FHL catalog (blue diamonds and line), and from IACT data (red triangles and line; Aharonian et al 2006c). Middle and right: background-subtracted TS maps of Kookaburra using the same conventions as in Figure 3 and above-quoted references for the IACT contours shown in green.…”

“…They were both detected at GeV energies by Acero et al (2013): the source coincident with HESS J1634−472 was pointlike, whereas the source coincident with HESS J1632−478 was modeled with a Gaussian distribution with a size almost twice as large as the TeV size, showing that this source might suffer from contamination. In our new analysis, an extended source (FGES J1631.7−4756) is detected with a relatively good match to the position and size of the TeV source HESS J1632 −478 and a good spectral connection with the H.E.S.S.…”

Pulsar Wind Nebulae and Cosmic Rays: A Bedtime Story

“…Fermi LAT has only published upper limits on the flux from the PWN [24]. VERITAS likewise has no confirmed detection of the Geminga PWN [25,26].…”