ISDC Data Centre for Astrophysics

HESS J1632-478: An Energetic Relic

The unidentified very high energy source HESS J1632-478 is very likely an old (10⁴ years) Pulsar Wind Nebula with a size of several parsecs containing very high energy electrons cooling slowly mostly through Inverse Compton scattering. Its spectrum is made of a faint synchrotron component (from the radio to the X-rays) emitted by electrons accelerated up to very high energies and of a bright high-energy gamma-ray component emitted by inverse Compton scatering against infrared photons.

Balbo et al. 2010, A&A 520, A111

ABSTRACT

HESS J1632-478 is an extended and still unidentified TeV source in the galactic plane. In order to identify the source of the very high energy emission and to constrain its spectral energy distribution, we used a deep observation of the field obtained with XMM-Newton together with data from Molonglo, Spitzer and Fermi to detect counterparts at other wavelengths. The flux density emitted by HESS J1632-478 peaks at very high energies and is more than 20 times weaker at all other wavelengths probed. The source spectrum features two large prominent bumps with the synchrotron emission peaking in the ultraviolet and the external inverse Compton emission peaking in the TeV. HESS J1632-478 is an energetic pulsar wind nebula with an age of the order of 10⁴ years. Its bolometric (mostly GeV-TeV) luminosity reaches 10% of the current pulsar spin down power. The synchrotron nebula has a size of 1 pc and contains an unresolved point-like X-ray source, probably the pulsar with its wind termination shock.

XMM-Newton MOS mosaic
This MOS image (10'x10') in the 0.2-12 keV energy range shows the extended shape of our source, with a white continuous ellipse.
Credits: ISDC

Enlarged XMM image
In this enlarged image form the MOS1 camera, around our extended source, we have shown with a black circle the region used to analyze the point-like source, and with the dashed white circle its relative background.
Credits: ISDC

X-ray spectra
Best power-law fit of the spectra of the extended X-ray source obtained from the three EPIC cameras.
Credits: ISDC

Molonglo radio excess
This image (15'x11') from the second epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz shows the radio excess from the PWN. For comparison is reported also the white ellipse that represents the region used to extract the XMM-Newton diffuse source.
Credits: ISDC

Neighborhood of the PWN
An extraction from the MIPSGAL survey at 24 μm (45′ × 30′). The small ellipse shows the position of the diffuse X-ray source, the dashed ellipse shows the HESS source extension (as in Fig. 11 of Aharonian et al. 2006a) and the two large dashed circles indicates the 95% confidence region for the FERMI detections. The crosses indicate (A) XMMU J163219.9-474731, (B) AXJ1632.8- 4746, (C) IGR J16320-4751, (D) the nearby radio pulsar PSR J1632-4757 and (F) an unidentified 24 μm circular structure.
Credits: ISDC

SED
Spectral energy distribution of HESS J1632-478, including the upper limits from PARKES (magenta) and GLIMPSE (cyan), the probable detection from MGPS-2 (green), and the detections by XMM-Newton (red) and HESS (purple). The Fermi spectrum of the nearby source 1FGL 1632.7-4733 is also shown (in blue). The continuous line indicates the prediction of the model used to represent the emission. At low energy the dotted line represents the synchrotron emission from the electron distribution, the dotted-dashed and the dashed lines show the CMB and IR dust photons components respectively. At high energy, the dotted line represents the SSC component, the dotted-dashed and the dashed lines show the external Compton emission on the CMB and dust photons components respectively.
Credits: ISDC