INTEGRAL Picture Of the Month
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The INTEGRAL view of TeV sources
There is a significant correlation between INTEGRAL-detected hard X-ray
(or soft gamma-ray) sources and TeV sources. By comparing the
INTEGRAL/IBIS 1000 orbit catalogue
Bird et al. 2016, ApJS 223, 15) with the
online TeV source list, it has
been shown that 39 objects (about 20% of the very-high energy gamma-ray
catalogue) have emission in both the soft gamma-ray and TeV wavelength
bands. This provides an indication of the usefulness of combining
information at these frequencies and preparing a legacy program for
future very-high energy observations (such as with the Cherenkov
Telescope Array, CTA).
The central panel of the image shows the Galactic Plane as observed by
INTEGRAL/IBIS at 20-100 keV, with TeV sources superimposed.
The objects found by the cross-correlation analysis belong to various
classes, both galactic and extra-galactic, but also contains
In the galactic realm, compact objects, such as binary systems, pulsars,
as well as extended objects, like Supernova Remnants (SNR) and Pulsar
Wind Nebulae (PWN), have been found to emit in both wavelength bands.
In the bottom-left panel of the image the Spectral Energy Distribution
(SED) of the gamma-ray binary system LS 5039 is shown, which is
constructed using non-simultaneous data. The sensitivities expected from
the Southern (black line) and Northern (orange line) CTA observatories
in a 50-hour observation (from
https://www.cta-observatory.org/science/cta-performance/) show how
future CTA observations will help to discriminate between models
proposed to reproduce the observed data.
In the top-left panel of the image, a 20-100 keV IBIS/ISGRI image of a
complex region known as the "Kookaburra" is shown. In this region, the
High Energy Stereoscopic System (H.E.S.S.) telescope detected two
distinct TeV sources, one coincident with a PWN surrounding the pulsar
PSR J1420–607, the other coincident with the "Rabbit" nebula. INTEGRAL
detected IGR J14193–6048 in between these two TeV objects, although its
position is shifted towards PSR J1420–607. Analysis of low energy X-ray
data from the Chandra X-ray observatory suggests that the most likely
identification for the INTEGRAL source is indeed PSR J1420-6048, the
pulsar that powers one of the two H.E.S.S. sources.
The top central panel of the image, shows the unfolded IBIS/ISGRI
spectra as well as the data-to-model ratio of two SNRs, i.e., Tycho
(black) and Cas A (red), between 20 and 150 keV. It is evident that a
simple power law fits well the spectrum of Tycho but it is not
sufficient to describe that of Cas A. For the latter, an excess around
70–90 keV is clearly detected; this excess can be attributed to the
presence of Titanium-44 decay lines.
In the extra-galactic case, active galaxies of various flavours have
been found such as types of Blazars (both of the BL Lac and FSRQ
classes) as well as radio galaxies. The bottom-right panel of the image
shows the SED of the blazar candidate IGR J20569+4940, recently
classified as a high peaked BL Lac object.
Finally, the identification of objects that are still lacking a definite
counterpart at TeV energies can benefit from information at soft
gamma-ray energies. The top-right panel of the image shows the sky
region surrounding HESS J1844-030 as seen by IBIS/ISGRI. HESS J1844-030
is still an unidentified object; it has, however, been largely covered
by INTEGRAL observations, which have revealed only one persistent
source, AX J1844.7-0305, spatially associated with the TeV object.
back to the POM archive
- "INTEGRAL View of TeV Sources: A Legacy for the CTA Project",
A. Malizia, M. Fiocchi, L. Natalucci, V. Sguera, J.B. Stephen, L. Bassani,
A. Bazzano, P. Ubertini, E. Pian, A.J. Bird,
2021, in: Special Issue "High-Energy Gamma-Ray Astronomy: Results on Fundamental
Questions after 30 Years of Ground-Based Observations", Universe 7(5), 135