 "H.E.S.S. Supernova Überreste (i)"
 MIV
(ii)
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H.E.S.S. Supernova Überreste
The Crab Nebula — a famous standard candle for astronomy
Catalog
Observations of the Crab Nebula with H.E.S.S
GeV-TeV Emissions Quellen
K1
Catalog
Observations of the Crab Nebula with H.E.S.S
GeV-TeV Emissions Quellen
SNR G0.9+0.1 mit CXOU J174722.8-280915
Helfand and Becker
Radio map of the supernova remnant G0.9+0.1, showing a bright core region and a partial shell.
G0.9+0.1 is a well known composite supernova remnant, recognised as such from its radio morphology.
H.E.S.S. collaboration, F. Aharonian
Fig. 1.— Gamma-ray point source significance map for the region around the
GC. The position of G0.9+0.1 is marked with a
triangle. SgrA* is marked with a star. The circles
show the integration regions contributing to the quoted
significance at the positions of these two objects. The six
telescope pointings are shown as crosses.
Fig. 1a.—
Smoothed map of the VHE gamma-ray counts detected by H.E.S.S.
(Color scale), with radio contours superimposed. The cross indicates the best
estimate for the location of the TeV source, the dashed circle the limit on
the (rms) source size (assuming a Gaussian source distribution).
H.E.S.S. collaboration, F. Aharonian
VHE gamma-ray. / Radio data (triangles) are taken from (Helfand & Becker),
X-ray data (shaded box) from Porquet et al./ XMM.
Fig. 2.—
Wide-band spectral energy distribution of G0.9+0.1, interpreted as synchrotron radiation at lower
energies and as Inverse Compton upscattering of starlight, dust and microwave background photons
at higher energies.
The circles show the H.E.S.S. data from this work.
The solid curve shows a fit of a one-zone inverse
Compton model to all data. Contributions of the CMBR, IR from dust and starlight photon fields to the
IC emission are shown.
Fig. 2a.— Energy spectra of VHE gamma rays detected with H.E.S.S., using the regular
cuts to select gamma rays (closed symbols) and special cuts to improve the signal-to-noise at
high energies (open symbols).
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SNRs in the Galactic Center region
Radio images of the Galactic Center region include a number of shell-type supernova remnants. G0.9+0.1 is a composite remnant, showing a partial shell - about 8' in diameter - surrounding a bright core (see image). Assuming that the object is located at a similar distance as the Galactic Center, one can deduce an age of several 1000 years.
The radio emission from the shell is presumably caused by electrons accelerated in the supernova shock wave. The bright core - which is also resolved as an extended structure in X-ray observations with Chandra and XMM - is identified as a pulsar wind nebula, akin to the Crab Nebula.
A highly relativistic flow of electrons and positrons accelerated by the fields of the pulsar provides the energy source feeding a termination shock, where particles are accelerated to even higher energies in turbulent magnetic fields. A pulsar candidate (CXOU J174722.8-280915) is seen in Chandra images as a point source near the center of the nebula, however no pulsed emission has been detected.
It exhibits a bright compact core (~2' across) surrounded by an 8' diameter shell.
The radio spectrum of the core is significantly harder (alpha ~ 0.12) than that of the shell (alpha ~ -0.77). X-ray observations of the nebula with BeppoSAX, Chandra and XMM-Newton have unambiguously identified the core region as a pulsar wind nebula (PWN).
A plausible candidate for the central pulsar is the hard spectrum point source CXOU J174722.8-280915; however no pulsed emission has been detected.
Observations with XMM have revealed a softening of the X-ray spectrum with increasing distance from the centre of the PWN, a signature of energy loss of electrons within the nebula. The location of G0.9+0.1 in the Galactic Centre (GC) region suggests a distance of ~ 8.5 kpc.
At this distance the size of the shell implies an age of a few thousand years for the SNR. At gamma-ray energies G0.9+0.1 has not been detected previously.
It is not associated with any EGRET source and the only published observation in the TeV domain is an unconstraining upper limit from the HEGRA collaboration.
Already the first observations of the Galactic Center region with two H.E.S.S. telescopes in 2003 showed a faint signal at the location of G0.9+0.1. In 60 h of follow-up observations between March and September 2004 - now with all four H.E.S.S. telescopes - a highly significant signal is detected (13 s), consistent with the position of the core of the supernova remnant (Fig. 1). Within the angular resolution of H.E.S.S., the source is point-like, with an emission region smaller than 1.3' (rms). The location of the source and the size limit strongly suggest the pulsar wind nebula as the source of the VHE gamma-ray signal, rather than the supernova shock wave. Over more than a decade in energy - between 200 GeV and 6 TeV - the energy spectrum of gamma rays follows a power law with a spectral index of 2.4 (Fig. 2a). At a flux corresponding to 2% of the flux from the Crab Nebula and assuming a distance of 8.5 kpc, the total power radiated in VHE gamma rays is 2 × 1034 erg s-1, roughly half of the power output of the Crab Nebula, the only other established VHE source of this type.
Indeed, the wide-band energy spectra (Fig. 2) are well modeled assuming a primary population of electrons, which emits synchrotron radiation in the radio- and X-ray bands, and which creates the VHE gamma-rays by scattering ambient low-energy photons to high energies. Close to the Galactic Center, starlight photons represent to dominant source of target photons. At higher gamma-ray energies, the Klein-Nishina effect starts to suppress interactions with the (eV) starlight, and the photons of the cosmic microwave background take over, effectively adding up to a smooth power low spectrum in the H.E.S.S. energy range.
Using the stereoscopic technique the instrument reaches an angular resolution of ~0°.1 and a point source sensitivity of 1% of the flux from the Crab Nebula (5s in 25 hours).
The detection of VHE gamma-ray emission from G0.9+0.1 provides the first direct evidence for the acceleration of very energetic particles in this object. The position and point-like nature of the gamma-ray emission, combined with the broad band SED of G0.9+0.1, strongly suggest an origin of the VHE emission in the compact central source (previously identified as a pulsar wind nebula).
This detection represents the first step towards the study of an emerging population of VHE gamma-ray emitting PWN. The detection of new PWN with accurate TeV spectra and with morphological measurements will provide information key to understanding particle acceleration in the vicinity of pulsars.
Lit.
Helfand, D.J., Becker, R.H., 1987, Astrophys. J., 314, 203.
Porquet, D., Decourchelle, A., Warwick, R.S., 2003, Astron. & Astrophys., 401, 197.
K2.1
MSH 15-52 with PSR B1509-58
Zum Thema | |
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Smoothed excess map from MSH 15-52 in arbitrary units (a.u.).
The white contour lines denote the X-ray (0.6–2.1 keV) count rate measured by
ROSAT (Trussoni et al. 1996). The black point and black star lie at the pulsar position and
at the excess centroid, respectively. The right-bottom inset shows the simulated PSF smoothed
identically.
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The Supernova Remnant (SNR) MSH 15-52 (G320.4–1.2), first observed as an extended non-thermal radio source by Mills et al. (1961), is a complex object with an unusual morphology. Radio observations by Caswell et al. (1981) reveal a roughly circular SNR 30' in diameter with a bright feature in the NW rim and a fainter one in the SE. The 10' diameter NW source (G320.4–1.0) coincides with the HI nebula RCW89.
Einstein X-ray observations of MSH 15-52 by Seward and Harnden (1982) led to the discovery of the 150 ms pulsar PSRB1509–58 located within the SNR shell, surrounded by a diffuse extended non-thermal component. The existence of a pulsar wind nebula (PWN) was later confirmed by ROSAT (Trussoni et al. 1996; Brazier & Becker 1997) and ASCA (Tamura et al. 1996) as an extended emission region surrounding the pulsar with a power-law photon index of 2.0.
The PWN morphology is clearly visible in the ROSAT PSPC data (Trussoni et al. 1996) which show an elongated structure roughly centered on the pulsar with two arms extending several arcminutes along the NW and SE directions. These features were more recently confirmed by detailed Chandra observations.
Gaensler et al. (1999), comparing X-ray and radio observations, concluded that the radio SNR MSH 15-52 and the pulsar PSRB1509–58 are parts of a single system interacting via a pair of opposed collimated outflows (i.e. the PWN). The distance to the object and the pulsar spindown age were estimated to 5.2±1.4 kpc and 1700 years, respectively.
A differential flux at 1TeV of 5.7×10-12 TeV-1 cm-2 s-1 is detected. The corresponding integral flux above 280 GeV represents 15% of the Crab Nebula flux above the same threshold.
The total power, L, radiated by MSH 15-52 in the energy band 0.3–40TeV is 1.0×1035 erg s-1 (here we adopt a distance of 5 kpc) compared to 8.0×1034 erg s-1 for the Crab Nebula (assuming a distance of 2 kpc). Thus, the efficiency of VHE g-ray production relative to the spin-down rate (L/E') of PSRB1509–58 (0.6%) is much larger than that of the Crab pulsar (0.016%). Such high efficiency has been proposed previously (Aharonian et al. 1997).
K2.2
MSH 15-52 with PSR B1509-58
K3
HESS J1813-178 & SNR G12.82-0.02
Zum Thema | |
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Authors: P. Ubertini, L. Bassani, A. Malizia, A. Bazzano, A.J. Bird, A.J. Dean, A. De Rosa, F. Lebrun, L. Moran, M. Renaud, J. Stephen, R. Terrier, R. Walter | |
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Journal-ref: ApJ 629 (2005) L109-L112 [astro-ph/0505191  ] | |
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Title: INTEGRAL IGR J18135-1751=HESS J1813-178: A new cosmic high energy accelerator from keV to TeV | |
Abstract:
We report the discovery of a soft gamma ray source, namely IGR J18135-1751, detected with the IBIS imager on board the INTEGRAL satellite. The source is persistent and has a 20-100 keV luminosity of ~5.7·10^{34} erg s-1 (assuming a distance of 4kpc). This source is coincident with one of the ten objects recently reported by the HESS collaboration as part of the first TeV survey of the inner part of the Galaxy. Two out of those new sources along the Galactic Plane, HESS J1813-178 and HESS J1614-518, have been reported to have no known radio or X-ray counterpart, suggestive of a possible new dark nucleonic cosmic ray nature. In this letter, we also show that HESS J1813-178 has a strongly absorbed X-ray counterpart, the ASCA source AGPS273.4-17.8, showing a power law spectrum with photon index ~1.8 and an intrinsic absorption corresponding to N_H=5·10^{22} cm-2. The source Spectral Energy Distribution (SED) is consistent with a power law spectrum with photon index of ~2.1 from 1 keV up to several TeV. We hypothesize that the source is a pulsar wind nebula embedded in its supernova remnant or, alternatively a pulsar in a high mass binary system like PSRB1259-63. The lack of X/gamma-ray variability favours the first interpretation. In either case we rule out the hypothesis that HESS J1813-178 belongs to a new class of TeV objects or that it is a cosmic "dark particle" accelerator. | ||
| HESS J1813-178 — | ||
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Authors: D.J. Helfand, R.H. Becker, R.L. White | |
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Journal-ref: arxiv (2005) [astro-ph/0505392 ] | |
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Title: A Radio Counterpart for the Unidentified TeV Source HESS J1813-178: The Radio-Gamma-Ray Connection | |
1. Introduction
The sites of cosmic ray acceleration in the Galaxy are widely believed to be supernova remnants (SNRs), although
the evidence for this belief has been largely indirect. Over the last twenty years, nonthermal X-ray emission
has been detected in several remnants, allowing us to infer that electrons
with energies up to at least 100 TeV are present
(e.g., Cas A – Allen et al. 1997; SN1006 – Becker et al. 1980; Koyama et al.
1995; G347.3 - 0.5 – Slane et al. 1999).
Recently, the commissioning of the High Energy Stereoscopic System (HESS) for the detection of TeV gamma rays (Benbow et al. 2005) has opened a new window on high energy processes in the Galaxy, providing a tool to locate directly hadronic CR acceleration sites. A HESS survey of the innermost 60 degrees of Galactic longitude has recently been published (Aharonian et al. 2005a), and the results suggest we have much to learn about the details of CR acceleration in SNRs. References Aharonian, F., et al. 2005a, Science 307, 1938 | ||
K3.1
HESS J1813-178 — no longer an unidentified TeV source
| MAGIC confirms— HESS J1813-178 | |
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Authors: J. Albert, et al, MAGIC collaboration |
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Journal-ref: ApJ 637 (2006) L41-L44 [astro-ph/0512283 ] |
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Title: MAGIC observations of very high energy gamma-rays from HESS J1813-178 |
| Abstract: Recently, the HESS collaboration has reported the detection of
gamma-ray emission above a few hundred GeV from eight new sources located
close to the Galactic Plane. The source HESS J1813-178 has sparked particular
interest, as subsequent radio observations imply an association with SNR
G12.82-0.02. Triggered by the detection in VHE gamma-rays, a positionally
coincident source has also been found in INTEGRAL and ASCA data. In this
Letter we present MAGIC observations of HESS J1813-178, resulting in the
detection of a differential gamma-ray flux consistent with a hard-slope power law, described as
dN/(dA dt dE) = (3.3 ± 0.5) × 10-12 (E/TeV)-2.1 ± 0.2 cm-2 s-1TeV-1. We briefly discuss the observational technique used, the procedure implemented for the data analysis, and put this detection in the perspective of multifrequency observations. | |
H.E.S.S.
Lupe 1: Angular distribution of VHE gamma rays relative to the fitted source position. The red dashed line
indicates the experimental resolution, the full black line the best fit obtained for an intrinsic source size
of 2' rms.
Fig. 1: The new TeV gamma-ray source HESS J1813-178 and its surrounding field. The inset illustrates the H.E.S.S. "beam size" governed both by the experimental resolution and a certain amount of smoothing applied to the image. The white contours show the smoothed X-ray count map obtained by the ASCA satellite and the black contours show 20 cm radio emission as observed by the VLA |
For two of these sources, HESS J1813-178 and HESS J1614-518, no counterparts in other wavelength regimes were found in the literature. In many sources of high-energy radiation, gamma ray production is related to the acceleration of electrons to high energies. These electrons will emit synchrotron X-rays and radio waves.
A source not visible in X-rays or radio could either be a proton accelerator, or be immersed in a rather small magnetic field, reducing losses by synchrotron radiation. Previously, two sources of VHE gamma rays without counterpart were known, the HEGRA-discovered TeV J2032+4130 and HESS J1303-631 .
HESS J1813-178 is located within a fraction of a degree from the Galactic plane and is slightly extended, with about 2' (rms) size. Therefore, it is most probably a Galactic object.
The flux of VHE gamma rays is about 6% of the flux from the Crab nebula, the energy spectrum extends to multi-TeV energies.
Shortly after the discovery of HESS J1813-178 was published, counterparts were located in existing but unpublished multiwavelength data.
At the location of HESS J1813-178, X-ray emission is seen in ASCA data (Brogan et al. 2005, Ubertini et al. 2005).
The ASCA source is termed AX J1813-178 or also AGPS273.4-17.8, the latter referring to the ASCA scan of the Galactic plane.
In radio data, both Brogan et al. (2005) and Helfand et al. (2005) located a shell-type supernova remnant where a section of the shell coincides with the gamma-ray source.
Finally, data from the INTEGRAL satellite (Ubertini et al. 2005) show in the 20-100 keV range a soft gamma-ray source at the same location (Fig. 3). The distance to the supernova shell is estimated to more than 4 kpc (Brogan et al. 2005), from the size of the shell they estimate an age between 285 and 2500 years. Based on the available data, it is hard to identity the exact source mechanism - particle acceleration in the supernova shock wave as in RXJ 1713.7-3946, or emission from a pulsar wind nebula such as MSH 15-52 or the Crab Nebula.
Ubertini et al. (2005) also speculate about a possible binary system in analogy to the PSR B1259-63/SS2883 system. In either case, HESS J1813-178 is clearly a more or less "classical" TeV source, rather than a "dark accelerator", as initially thought.
K3.2
HESS J1813-178 — a composite Supernova remnant
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Authors: S. Funk, J. A. Hinton, Y. Moriguchi, F. A. Aharonian, Y. Fukui, W. Hofmann, D. Horns, G. Puehlhofer, O. Reimer, G. Rowell, R. Terrier, J. Vink, S. Wagner |
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Journal-ref: A&A 470 (2007) 249 [astro-ph/0611646 ] |
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Title: XMM-Newton observations of HESS J1813-178 reveal a composite Supernova remnant |
| Abstract:
We present X-ray and 12CO(J=1-0) observations of the very-high-energy (VHE)
gamma-ray source HESS J1813-178 with the aim of understanding the origin of the
gamma-ray emission.
Using this dataset we are able to undertake spectral and morphological studies of the X-ray emission from this object with greater precision than previous studies. NANTEN 12CO(J=1-0) data are used to search for correlations of the gamma-ray emission with molecular clouds which could act as target material for gamma-ray production in a hadronic scenario. The NANTEN 12CO(J=1-0) observations show a giant molecular cloud of mass M = 2.5 × 105M 
at a distance of 4 kpc in the vicinity of HESS J1813-178. Even
though there is no direct positional coincidence, this giant cloud might have
influenced the evolution of the gamma-ray source and its surroundings.
The X-ray data show a highly absorbed non-thermal X-ray emitting object coincident with the previously known ASCA source AX J1813-178 showing a compact core and an extended tail towards the north-east, located in the centre of the radio shell-type Supernova remnant (SNR) G12.82-0.2. This central object shows morphological and spectral resemblance to a Pulsar Wind Nebula (PWN) and we therefore consider that the object is very likely to be a composite SNR. We discuss the scenario in which the gamma-rays originate in the shell of the SNR and the one in which they originate in the central object. We demonstrate, that in order to connect the core X-ray emission to the VHE gamma-ray emission electrons have to be accelerated to energies of at least 1 PeV. | |
K3.3
HESS J1813-178 — Discovery of the Putative Pulsar and Wind Nebula
| CXOU J181335.1-174957 — LPSR = 3.2 × 1033 erg s-1 | |
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Authors: D.J. Helfand, E.V. Gotthelf, J. P. Halpern, F. Camilo, D. R. Semler, R. H. Becker, R. L. White |
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Journal-ref: ApJ 665 (2007) 1297 [0705.0065 ] |
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Title: Discovery of the Putative Pulsar and Wind Nebula Associated with the TeV Gamma-ray Source HESS J1813-178 |
| Abstract:
We present a Chandra X-ray observation of G12.82-0.02, a shell-like radio supernova
remnant coincident with the TeV gamma-ray source HESS J1813-178.
We resolve the X-ray emission from the co-located ASCA source into a point source surrounded by structured diffuse emission that fills the interior of the radio shell. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula. The spectrum of the compact source is well-characterized by a power-law with index Gamma approx 1.3, typical of young and energetic rotation-powered pulsars. For a distance of 4.5 kpc, consistent with the X-ray absorption and an association with the nearby star formation region W33, the 2-10 keV X-ray luminosities of the putative pulsar and nebula are LPSR = 3.2 × 1033 erg s-1 and LPWN = 1.4 × 1034 erg s-1, respectively. Both the flux ratio of LPWN/LPSR = 4.3 and the total luminosity of this system predict a pulsar spin-down power of E' > 1 × 1037 erg s-1, placing it within the ten most energetic young pulsars in the Galaxy. A deep search for radio pulsations using the Parkes telescope sets an upper-limit of approx 0.07 mJy at 1.4 GHz for periods >~ 50 ms. We discuss the energetics of this source, and consider briefly the proximity of bright H2 regions to this and several other HESS sources, which may produce their TeV emission via inverse Compton scattering. 1. Introduction
The HESS observatory has revolutionized the field of TeV gamma-ray astronomy, opening a new window onto
the highest energy processes occurring in our Galaxy and
beyond. Of the 21 Galactic TeV sources detected by HESS during the first two years of four-telescope
operation, firm identifications have been made for only seven objects (HESS “A” class sources – Funk et al.
2006a).
Of these sources, nearly all are associated with supernova products: four with bright pulsar wind nebula (PWNe – three of which contain detected young, energetic pulsars), and two with non-thermal shell-type supernova remnants (SNRs); the remaining object is associated with a high-mass X-ray binary system. There are five less secure associations with SNRs/PWNe (HESS “B/C” class sources). The remaining nine HESS sources have yet to be identified with a known object at any other wavelength. An opportunity to study the origin of SNR TeV emission is provided by the coincidence of the unidentified TeV source HESS J1813-178 with a previously uncatalogued shell-type radio supernova remnant G12.82-0.02 (Helfand et al. 2005). This low-surface-brightness, small-diameter (~ 2') remnant lies within the 1s extent of HESS J1813-178 and is coincident with a bright ASCA X-ray source. The possibility that this source represented a third example of a shell-type SNR producing non-thermal X-rays along with TeV gamma rays raised considerable interest; however, as noted by the above authors, the source of the high-energy emission could also be an energetic pulsar associated with this apparently young remnant. Helfand et al. (2005) noted the proximity of the star forming region W33 as a source of ambient photons for producing gamma-rays from inverse Compton scattering. References
Helfand, D. J., Becker, R. H., & White, R. L. 2005 (astro-ph/0505392
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IGR J18135-1751/HESS J1813-178 — d ~ 4.5 kpc
— LPWN ~ 1.4 × 1034 erg s-1
theoretical properties — LPSR(2–10 keV) ~ 3.2 × 1033 erg s-1 — P = 0.55 s — B ~ 1014 G | |
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Authors: A.J. Dean, A.B. Hill |
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Journal-ref: A&A (2008) [0804.3420 ] |
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Title: The properties of the putative pulsar associated with IGR J18135-1751/HESS J1813-178 |
| Abstract:
• Context: We investigate the possible theoretical properties of the putative pulsar associated with the pulsar wind nebula IGR J18135-1751/HESS J1813-178 based upon recent gamma-ray observations and archival multi-wavelength observations. • Aims: We show that when using the standard equations for magnetic dipole radiation with recent soft gamma-ray observations leads to deriving an extreme set of parameters (magnetic field, period and spin down rate) for the putative pulsar. Alternative scenarios that generate more typical parameter values are explored. • Methods: The properties of the putative pulsar are calculated assuming that the 20-100 keV luminosity corresponds to 1% of Edot, that the source is 4.5 kpc away, and that the pulsar age is 300 yrs. This gives P = 0.55 s, P' = 3 × 10-11 s/s, and B = 1.28 × 1014 G. This is a very extreme set compared to the population of known pulsars in PWN systems. Using the equations for magnetic dipole losses makes it possible to adjust the initial assumptions to see what is required for a more reasonable set of pulsar parameters. • Results: The current measured properties for IGR J18135-1751/HESS J1813-178 (i.e. luminosity, distance, and age) result in extreme properties of the unseen pulsar within the PWN. The simplest method for achieving more reasonable properties for the pulsar is to decouple the spin-down age of the pulsar from the actual age for the system. 1. Introduction
HESS J1813-178 was discovered in the HESS galactic plane
survey (Aharonian et al., 2006) and was seen to be one of the
more compact TeV sources, with a radius of ~2'.
XMM-Newton observations (Funk et al., 2007) have revealed
a highly absorbed (NH ~ 1023 cm-2) non-thermal pointlike
object coincident with the ASCA source inside the radio
shell and having a faint tail towards the north-east resembling a
PWN system. The basic scenario is essentially confirmed by recent
Chandra observations of HESS J1813-178 (Helfand et al.,
2007). The Chandra image resolves the ASCA source into diffuse
X-ray emission and a point source. The diffuse emission
generally fills the radio shell and peaks towards the point source
emission, which lies within, but slightly offset from the centroid
of the SNR by about 20''. Spectra from each morphological region
are well characterized by an absorbed power law model
associated with non-thermal emission. The best fit photon index
for the nebular flux is G ~ 1.3 with NH = 9.8 × 1022 cm-2, and the
point source having a similar spectrum, also at G ~ 1.3. These
values are typical of other energetic young pulsars. For a distance
of 4.5 kpc the Chandra results correspond to a
LPSR(2–10 keV) ~ 3.2 × 1033 erg s-1
luminosities of the putative pulsar and PWN of
LPWN ~ 1.4 × 1034 erg s-1.
References Aharonian F., et al., 2006, ApJ, 636, 777 Funk S., et al., 2007, A&A, 470, 249 | |
K4
Supernova Remnant RX J0852.0-4622
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Authors: F. Aharonian, et al (H.E.S.S. collaboration) |
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Journal-ref: A&A 437 (2005) L7-L10 [astro-ph/0505380 ] |
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Title: Detection of TeV gamma-ray Emission from the Shell-Type Supernova Remnant RX J0852.0-4622 with H.E.S.S |
| Abstract:
We report the detection of TeV gamma-rays from the shell-type supernova remnant
RX J0852.0-4622 with data of 3.2 h of live time recorded with H.E.S.S. in February 2004.
An excess of 700 events from the whole remnant with a significance of 12 s was found.
The observed emission region is clearly extended with a radius of the order of 1 degree and
the spatial distribution of the signal correlates with X-ray observations.
The spectrum in the energy range between 500 GeV and 15 TeV is well described by
a power law with a photon index of 2.1 and a differential flux at 1 TeV of
2.1·10-11 cm-2 s-1 TeV-1.
The integral flux above 1 TeV was measured to be
1.9·10-11 cm-2 s-1,
which is at the level of the flux of the Crab nebula at these energies.
More data are needed to draw firm conclusions on the magnetic field in the remnant
and the type of the particle population creating the TeV gamma-rays.
INTRODUCTION
earlier work :
HESS: ("Vela Junior")
Gamma-rays around 1TeV (CANGAROO)
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Count map of g-rays from the direction of RX J0852.0-4622 after
background subtraction. The data are smoothed with a Gaussian
representing the angular resolution of the
instrument. The point spread function (PSF) is indicated by a
circle. g-ray features smaller than the PSF should not be
considered as real. The lines denote equidistant contours of smoothed
X-ray data from the ROSAT All Sky Survey, with
energies restricted to above 1.3 keV. The position of the neutron
star candidate is marked with an asterisk. The axes show J2000.0
equatorial coordinates.
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This source has been suggested to be a neutron star, supported by the detection of an coincident Ha nebula. An association of the neutron star candidate with RX J0852.0-4622 would point to a core-collapse supernova. However, recent X-ray observations suggest that RX J0852.0-4622 is the result of a sub-Chandrasekhar type Ia supernova explosion, which would imply that the compact object is not related to RX J0852.0-4622. Radio observations show only weak emission from the shell and no emission from the centre.
The age and distance of RX J0852.0-4622 were calculated from the diameter seen in X-rays and the flux of 44Ti lines to be 680 ± 100 years and ~ 200 pc with upper limits of 1100 years and 500 pc, respectively. An age between 630 and 970 years was estimated by Tsunemi based on the observation of Ca lines. These estimates for distance and age would imply that RX J0852.0-4622 is one of the closest supernovae in recent history, whereas Slane et al. (2001) argue that RX J0852.0-4622 might be located near the Vela Molecular Ridge at a much larger distance of 1—2 kpc.
Shell-type SNRs with non-thermal X-ray emission are prime candidates for accelerating cosmic rays up to very high energies.
Their detection in VHE g-rays is expected to be possible with modern atmospheric Cherenkov telescopes, and to provide insight into the underlying acceleration mechanisms. So far, only one of these SNRs, RX J1713.7-3946, was detected by two independent experiments employing the imaging atmospheric Cherenkov technique.
The CANGAROO collaboration detected g-ray emission from the north-western part of the RX J0852.0-4622 SNR. Here we report on the detection of the entire SNR RX J0852.0-4622 by H.E.S.S. in a short observation campaign.
Spectrum of gamma rays:
Differential photon flux spectrum of the g-rays from the
direction of the whole SNR. The solid line is the result of a power law fit.
The solid line shows a power law fit with a spectral index of 2.1.
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RX J0852.0-4622 is the second shell-type SNR which has been spatially resolved at TeV energies, following the H.E.S.S. detection of RX J1713.7-3946. Similar to RX J1713.7-3946, RX J0852.0-4622 is a weak radio source and was initially discovered in X-ray observations. There are some other similarities between these two SNRs, in particular:
(i) in both sources the non-thermal X-ray component strongly dominates over the thermal component and
(ii) both are strong sources of extended TeV emission spatially correlated with X-rays.
There are two basic mechanisms for TeV g-ray production in young SNRs — inverse Compton scattering (IC) of multi-TeV electrons on photons of the cosmic microwave background (CMB) and other target photon fields, and po-decay g-rays from inelastic interactions of accelerated protons with ambient gas. The measured g-ray flux spectrum of RX J0852.0-4622 translates into an energy flux between 1 and 10 TeV of wg (1-10 TeV), which is quite close to the X-ray energy flux of the entire remnant of wX (0.5-10 keV) ~ 10-10 erg cm-2 s-1.
The TeV flux can be easily explained in terms of interactions of accelerated protons with the ambient gas. The total energy in accelerated protons in the range 10-100 TeV required to provide the observed TeV flux is estimated to be 1049 erg. For distances to the SNR in the order of d ~ 200 pc the conversion of several percent of the assumed mechanical explosion energy of 1051 erg to the acceleration of protons up to > 100 TeV would be sufficient to explain the observed TeV g-ray flux by nucleonic interactions in a medium of density comparable to the average density of the interstellar medium, n ~ 1 cm-3. For larger distances a correspondingly higher fraction of the explosion energy would have to be converted into the acceleration of protons.
K4.1
Vela X nebula
Zum Thema | |
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| Vela X nebula — | |
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Authors: F. Aharonian, et al (H.E.S.S. collaboration) |
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Journal-ref: A&A 448 (2006) L43-L47 [astro-ph/0601575 ] |
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Title: First detection of a VHE gamma-ray spectral maximum from a Cosmic source: H.E.S.S. discovery of the Vela X nebula |
| Abstract:
The Vela supernova remnant (SNR) is a complex region containing a
number of sources of non-thermal radiation. The inner section of this SNR,
within 2 degrees of the pulsar PSR B0833-45, has been observed by the H.E.S.S.
gamma-ray atmospheric Cherenkov detector in 2004 and 2005.
A strong signal is seen from an extended region to the south of the pulsar, within an integration region of radius 0.8 deg. around the position (RA = 08h 35m 00s, dec = -45 deg. 36' J2000.0). The excess coincides with a region of hard X-ray emission seen by the ROSAT and ASCA satellites. The observed energy spectrum of the source between 550 GeV and 65 TeV is well fit by a power law function with photon index = 1.45 and an exponential cutoff at an energy of 13.8 TeV. The integral flux above 1 TeV is fHE = 1.28 × 10-11 cm-2 s-1. This result is the first clear measurement of a peak in the spectral energy distribution from a VHE gamma-ray source, likely related to inverse Compton emission. A fit of an Inverse Compton model to the H.E.S.S. spectral energy distribution gives a total energy in non-thermal electrons of ~ 2 x 1045 erg between 5 TeV and 100 TeV, assuming a distance of 290 parsec to the pulsar. The best fit electron power law index is 2.0, with a spectral break at 67 TeV. | |
| Vela X - a Cosmic Accelerator 290 pc from Earth | ||
Image credit: ROSAT / H.E.S.S. / F. Aharonian et al.
Three views of the Vela region:
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 (left)
the ROSAT image in the 0.1-2.4 keV range shows the huge Vela supernova remnant, with the smaller Puppis
supernova remnant in the upper corner.
(middle, Aschenbach et al. 1998)
the image in high-energy photons >1.3 keV reveals yet another supernova
remnant, Vela Junior or RX J0852.0-4622, and exposes the Vela pulsar more clearly, near the center of the image.
The enhanced X-ray emission south of the pulsar is known as the Vela X nebula.
(right)
The sky image was taken at TeV energies with H.E.S.S.; the old Vela supernova remnant does
not show up at the these energies, but the circular young Vela Junior remnant is clearly visible
(see also March 05), an extended emission region south of the pulsar, coincident with Vela X.
The two gamma ray sources in Vela are the nearest known cosmic "Tevatrons". | ||
Image credit: Chandra
Fig. 1
Chandra view of the Vela pulsar (small inset) and of the Vela X nebula south of the pulsar.
The high-resolution Chandra image shows clearly that - contrary to earlier assumptions - the X-ray nebula
does not line up with the pulsar axis, which is indicated by the dashed line.
Image credit: ROSAT
Fig. 2
Intensity of very high energy gamma rays (color scale), with superimposed ROSAT X-ray contours.
The gamma ray emission extends over roughly 1 degree. While the Vela pulsar is clearly visible in X-rays,
no excess is seen in gamma rays.
Image credit: H.E.S.S.
Fig. 3
Spectral energy distribution of the VHE gamma rays from Vela X. Most of the energy is emitted in the interval
around 10 TeV. Vela X is the first source where the spectral energy distribution peaks at TeV energies.
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The resulting supernova remnant, well over 30 pc in diameter, is best seen in X-ray images (top left), but is also visible in optical images.
At the center of the remnant is the left-over stellar core, collapsed into a 25 km diameter, a rapidly spinning neutron star - the Vela pulsar.
ROSAT hard X-ray images revealed extended X-ray emission south of the pulsar, most likely of nonthermal origin (see also middle image above), and coincident with a bright radio feature labeled Vela X (other radio features being called Vela Y and Vela Z by Risbeth, 1958).
Later observations with Chandra (Fig. 1) resolved the detailed structure in the vicinity of the pulsar and show that Vela X cannot be associated with a jet emerging along the pulsar's spin axis;
the asymmetric X-ray emission could result from a pulsar wind nebula offset from the pulsar due to ambient pressures,
or reflect enhanced magnetic fields and therefore increased synchrotron radiation.
H.E.S.S. observed the Vela X region in 2004 and 2005 for a total of 16 h, resulting in a strong gamma ray signal of about 2000 events (about 16 s) from an extended source south of the Vela pulsar, coincident with Vela-X (Fig. 2). The source region is elongated, and well described by a Gaussian profile of major axis 0.48 degr. and minor axis 0.36 degr.; its orientation is almost perpendicular to the pulsar's jet.
The spectrum of gamma rays is among the hardest detected so far, with a spectral index of 1.45, meaning that the spectral energy distribution (SED) - the amount of energy radiated per logarithmic interval of energy - rises with gamma-ray energy (Fig. 3).
At high energies, the spectrum turns over, resulting in a peak of the SED around 10 TeV.
Such a peak is characteristic for gamma-rays produced by inverse-Compton up-scattering of ambient photons by high-energy electrons, but for all other known gamma-ray sources, the peak is below the energy range covered by Cherenkov telescopes, and it's existence can only be inferred indirectly.
The gamma-ray data demonstrate conclusively that Vela X is indeed a nonthermal phenomenon, and that high-energy particles are confined to the region of the Vela X nebula. In the inverse-Compton model, to maintain the gamma-ray flux which is equivalent to 50% of the flux from the Crab Nebula, the primary electrons must have a spectral index of 2.0, and contain about 2 x 1045 ergs of energy, in electrons between 5 and 100 TeV.
1. Introduction
The region surrounding the Vela supernova remnant (SNR) is very well studied across the electromagnetic spectrum
and contains a number of complex objects, including the SNR RX J0852.0-4622, which has been previously detected
in the very high energy ?-ray (VHE) range.
The Vela SNR itself, at a distance estimated to be ~290 pc, extends over a diameter of ~8°.
It is the nearest SNR to contain a young active pulsar, PSR B0833-45, with a period of 89 ms and a period derivative P' of 1.25 × 10-13 s s-1.
This implies a spin-down luminosity of 7 × 1036 erg s-1 and age of 11,000 years.
Observations by Chandra clearly show the torus-like morphology of the compact X-ray nebula surrounding the pulsar and have allowed its rotation axis to be inferred. The plane of the torus (i.e. pulsar equator) appears to intersect the plane of the sky at a position angle of 40.6° relative to North, and its X-ray spectral index of ~ 1.5 is typical of pre-cooled pulsar wind torii.
The SNR also contains a number of regions of non-thermal emission, including those labelled by Rishbeth (1958) from radio observations as Vela X, Vela Y and Vela Z (which is part of the shell of RX J0852.0-4622).
A diffuse emission feature has been detected by ROSAT (1995) in hard X-rays (0.9–2.0 keV), coinciding with the centre of the Vela X region. It was first suggested that this feature, which is aligned closely with a filament detected at radio wavelengths, corresponds to the outflow jet from the pole of the pulsar (Frail et al. 1997). However, the Chandra observations showed that this feature lies along the extension of the pulsar equator, although bending to the southwest.
4. Discussion
The new VHE source reported here, HESS J0835–455, is situated to the south of the pulsar and the compact X-ray
nebula (as seen by Chandra). The integral flux is estimated to be
~ 50% of that of the Crab nebula above 1 TeV. As the distance
to the pulsar is well measured, one can estimate the size of
the emission region seen by H.E.S.S. to be 5.1 parsec (full
length for 68% containment) along the major axis by 3.8 parsec
(full width). The luminosity of the emission region in the
energy range from 550 GeV to 65 TeV can be estimated to be
Lo = 9.9 × 1032 erg s-1, using the power law fit to the spectrum
with the exponential cutoff.
HESS J0835–455 appears to be spatially coincident with
the X-ray (0.4–2.4 keV) emission as seen by ROSAT (shown
in Figure 1). It has been suggested (Blondin et al. 2001) that
the Vela X feature corresponds to the pulsar wind nebula, displaced
to the south by the unequal pressure of the reverse shock
from the SNR. This hypothesis is consistent with the H.E.S.S. observations which demonstrate conclusively
for the first time that this feature emits non-thermal radiation. A similar explanation
has been proposed for the emission seen by H.E.S.S.
(HESS J1825–137) close to the pulsar wind nebula G18.0–0.7
(Aharonian et al. 2005c).
K5
HESS J1837-069 & AX J1838-0655
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Authors: A. Malizia, L. Bassani, J. B. Stephen, A. Bazzano, P. Ubertini, A. J. Bird, A. J. Dean, V. Sguera, M. Renaud, R. Walter, F. Gianotti |
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Journal-ref: ApJ 630 (2005) L157 [astro-ph/0507660
 ] ] |
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Title: The INTEGRAL/IBIS source AXJ1838.0-0655: a soft X-ray to TeV gamma-ray broad band emitter |
| Abstract:
We report on INTEGRAL observations of AX J1838.0-0655, one of the unidentified objects listed in the first IBIS/ISGRI survey catalogue and located in the Scutum arm region. This object, detected in the 20-300 keV band at a confidence level of 15.3 s (9 x 10^-11 erg cm-2 s-1) is the likely counterpart of the still unidentified TeV source HESS J1837-069. It has been detected in the past by various X-ray telescopes, including ASCA, implying that it is a persistent rather than a transient source; the ASCA image is compatible with the source not being resolved. The broad 1-300 keV spectrum is characterized by an absorbed (NH = 6.7 ± 1.3 x 10^22 cm-2) and hard (Gamma =1.5 ± 0.2) power law continuum. Possible counterparts (radio and infrared) present within the X-ray error box are discussed, even if no clear association can be identified. The broad band spectrum together with the TeV detection suggests that AX J1838.0-0655 maybe a supernova remnant or a pulsar wind nebula, which has so far eluded detection in the radio band. This is the second unidentified HESS source that shows a substantial soft gamma-ray emission. | |
| PSR J1838-0655 — Prot = 70.5 ms — tc = 23 kyr — Bs = 1.9 × 1012G — E'rot = 5.5 × 1036 erg s-1 | |
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Authors: E.V. Gotthelf, J.P. Halpern |
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Journal-ref: ApJ 681 (2008) 515 [0803.1361 ] |
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Title: Discovery of a Young, Energetic 70.5 ms Pulsar Associated with the TeV Gamma-ray Source HESS J1837-069 |
| Abstract:
We report the discovery of 70.5 ms pulsations from the X-ray source AX J1838.0-0655 using the Rossi X-ray
Timing Explorer} (RXTE).
PSR J1838-0655 is a rotation-powered pulsar with spin-down luminosity E'rot = 5.5 × 1036 erg s-1, characteristic age tc = P/2P' = 23 kyr, and surface dipole magnetic field strength Bs = 1.9 × 1012G. It coincides with an unresolved INTEGRAL source and the extended TeV source HESS J1837-069. At an assumed distance of 6.6 kpc by association with an adjacent massive star cluster, the efficiency of PSR J1838-0655 converting spin-down luminosity to radiation is 0.8% for the 2-10 keV ASCA flux, 9% for the 20-300 keV INTEGRAL flux and ~2% for the >200 GeV emission of HESS J1837-069, making it a plausible power source for the latter. A Chandra X-ray observation resolves AX J1838.0-0655 into a bright point source surrounded by a ~2' diameter, centrally peaked nebula. The spectra of the pulsar and nebula are each well fitted by power laws, with photon indices G = 0.5 and G = 1.6, respectively. The 2-10 keV X-ray luminosities of the pulsar and nebula are LPSR = 4.6 × 1034(d/6.6kpc)2 erg s-1 and LPWN = 5.2 × 1033(d/6.6kpc)2 erg s-1. A second X-ray source adjacent to the TeV emission, AX J1837.3-0652, is resolved into an apparent pulsar/PWN; it may also contribute to HESS J1837-069. The star cluster RSGC1 may have given birth to one or both pulsars, while fueling TeV emission from the extended PWN with target photons for inverse Compton scattering. 1. Introduction
Surveys of the Galactic plane (Aharonian et al. 2006a) by the High Energy Stereoscopic System (H.E.S.S.) find
that at least half of its sources (Funk 2007) can be identified with supernova remnants (SNRs) or pulsar wind
nebulae (PWNe). The sizes of those sources that are identified as PWNe are generally larger in
TeV g-rays than in X-rays, revealing a new view of the penetration of
high-energy particles into the surrounding medium.
The larger TeV nebulae are often displaced from the pulsar, possibly by the reverse shock of a supernova that exploded in an inhomogeneous medium. They may also contain relic electrons from the more energetic, younger phase of the pulsar spin-down. The characteristic mismatch between X-ray and g-ray sizes, together with the positional offsets of the X-ray and TeV emitting nebulae, are becoming familiar as new examples are found (Aharonian et al. 2006b, 2006c, 2007). Understanding exactly how the spin-down luminosity of a particular pulsar powers its TeV nebula requires time-dependent modeling and sometimes uncertain details of the local environment that must be determined at other wavelengths. The favored theoretical mechanisms, either inverse-Compton scattering of ambient photons, or decay of neutral pions produced in hadronic collisions of high-energy protons with a dense phase of the ISM, are being tested in several cases. For a recent review of these issues, see de Jager & Djannati-Atai (2008). A most instructive association is AX J1838.0-0655 with HESS J1837-069. One of the first extended sources detected by H.E.S.S. (Aharonian et al. 2005, 2006a), it was considered unidentified until now even though X-ray studies of the field pointed to a coincident hard, steady X-ray source detected up to 300 keV by INTEGRAL (Malizia et al. 2005). AX J1838.0-0655 was seen by X-ray satellites spanning decades, beginning with Einstein (1E 1835.3-0658; Hertz & Grindlay 1985), and including ASCA, BeppoSAX, XMM-Newton, and Swift , always with steady flux. Bamba et al. (2003) measured 1.1×10-11 ergs cm-2 s-1 from AX J1838.0-0655 in the 0.7-10 keV band, which is comparable to the > 200 GeV flux from HESS J1837-069, 2 × 10-11 ergs cm-2 s-1 (Aharonian et al. 2006a). The absence of variability is an important clue to the nature of AX J1838.0-0655, as is its hard spectrum. Malizia et al. (2005) fitted the combined INTEGRAL and ASCA spectrum with a power law of photon index G = 1.5, and conjectured that the source is a supernova product, more likely a PWN than a shell SNR. References Funk, S. 2007, Ap&SS 309, 11 | |
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Authors: T. Anada, K. Ebisawa, T. Dotani, A. Bamba | ||||||
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Journal-ref: PASJ (2008) [0810.3745 ] | ||||||
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Title: X-ray studies of HESS J1837-069 with Suzaku and ASCA: a VHE gamma-ray source originated from the pulsar wind nebula | ||||||
| Abstract:
We present the ASCA and Suzaku studies of the TeV source HESS J1837-069, which has not been identified in other
wave-lengths. We confirm the presence of two X-ray sources in the Suzaku XIS image,
AX J1838.0-0655 and AX J1837.3-0652, near both ends of the elongated TeV emission region.
The XIS spectra of the two sources are reproduced by an absorbed power-law model, whose parameters are all consistent with those determined by the ASCA data. Recently, 70.5 ms X-ray pulsation has been detected with RXTE in the sky region including HESS J1837-069 (2008, ApJ 681, 515). Using the ASCA GIS data which has both timing and imaging capabilities, we identified the pulsation source as AX J1838.0-0655. The pulse periods determined by ASCA and Suzaku, and that reported with RXTE indicate steady spin-down at P' = 4.917 × 10-14 s s-1. These results suggest that AX J1838.0-0655 is an intrinsically stable source, and presumably a pulsar wind nebula (PWN). We discuss the possibility that AX J1838.0-0655 is associated with HESS J1837-069 and the VHE gamma-ray emission is originated from the PWN. 1. Introduction
HESS J1837–069 is one of the VHE gamma-ray sources discovered by the Galactic survey with H.E.S.S. in 2004.
It has a significantly elongated shape with an extension of 7'×3' (Aharonian et al. 2005; Aharonian et al.
2006). No X-ray sources are known to be positionally coincident to the center of HESS J1837–
069, although AX J1838.0–0655, which is located at the Galactic south edge of the HESS source,
was suggested to be a possible counterpart (Gotthelf & Halpern 2008). ASCA observation
revealed that AX J1838.0–0655 has very hard and strongly absorbed spectrum (Bamba et
al. 2003). INTEGRAL (Malizia et al. 2005) observations also support this result. Recently,
Gotthelf & Halpern (2008) discovered a 70.5 ms pulsation with RXTE in the sky field including
AX J1838.0–0655, and also resolved a bright point source surrounded by diffuse emission with
Chandra. They concluded that AX J1838.0–0655 is a PWN. Here we report the results of
ASCA archival data analysis and the newly obtained Suzaku observation of HESS J1837–069/AX J1838.0–0655.
References Aharonian, F., et al. 2005, Science 307, 1938 | |||||||
| Literatur zu "H.E.S.S. SNR" | |||
| F. Aharonian, et al (H.E.S.S. collaboration) | 2005 | A&A 437, L7-L10 |
"Detection of TeV gamma-ray Emission from the Shell-Type Supernova Remnant RX J0852.0-4622"
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| A. Malizia, L. Bassani, J.B. Stephen, A. Bazzano, P. Ubertini, et al | 2005 | ApJ 630, L157 |
"The INTEGRAL/IBIS source AXJ1838.0-0655: a soft X-ray to TeV gamma-ray broad band emitter "
|
| F. Aharonian, et al (H.E.S.S. collaboration) | 2006 | A&A 448, L43-L47 |
"First detection of a VHE gamma-ray spectral maximum from a Cosmic source: ... the Vela X nebula"
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| F. Aharonian, et al (H.E.S.S. collaboration) | 2005 | A&A 432, L25-9 |
"Very high energy gamma rays from the composite SNR G0.9+0.1"
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| F. Aharonian, et al (H.E.S.S. collaboration) | 2005 | A&A 435, L17-L20 |
"Discovery of extended VHE from the asymmetric pulsar wind nebula in MSH 15-52 with H.E.S.S"
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| C. L. Brogan, B. M. Gaensler, J.D. Gelfand, J.S. Lazendic, et al. | 2005 | ApJ 629, L105-8 |
"Discovery of a Radio Supernova Remnant and Non-thermal X-rays Coincident with the TeV Source HESS J1813-178"
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| A. Malizia, L. Bassani, J. B. Stephen et al. | 2005 | ApJ 630, L157 |
"The INTEGRAL/IBIS source AXJ1838.0-0655: a soft X-ray to TeV gamma-ray broad band emitter"
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| P. Ubertini, L. Bassani, A. Malizia, et al. | 2005 | ApJ 629, L109-12 |
"INTEGRAL IGR J18135-1751=HESS J1813-178: A new cosmic high energy accelerator from keV to TeV"
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| J. Albert, et al, MAGIC collaboration | 2006 | ApJ 637, L41-L44 |
"MAGIC observations of very high energy gamma-rays from HESS J1813-178"
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| S. Funk, J.A. Hinton, Y. Moriguchi, F.A. Aharonian, et al. | 2007 | A&A 470, 249 |
"XMM-Newton observations of HESS J1813-178 reveal a composite Supernova remnant"
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| E.V. Gotthelf, J.P. Halpern | 2008 | ApJ 681, 515 |
"Discovery of a Young 70.5 ms Pulsar Associated with the TeV Source HESS J1837-069"
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 | H. Heintzmann | ( Eintrag vom 4.11.2008) |
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