| Canonical Name: | Westerlund 1 |
| TeVCat Name: | TeV J1647-458 |
| Other Names: | Wd1, HESS J1646-458 |
| Source Type: | Massive Star Cluster |
| R.A.: | 16 46 50 (hh mm ss) |
| Dec.: | -45 49 12 (dd mm ss) |
| Gal Long: | 339.55 (deg) |
| Gal Lat: | -0.35 (deg) |
| Distance: | 3.2 kpc |
| Flux: | (Crab Units) |
| Energy Threshold: | 680 GeV |
| Spectral Index: | |
| Extended: | Yes |
| Size (X): | 1.10 (deg) |
| Size (Y): | 1.10 (deg) |
| Discovery Date: | 2009-06 |
| Discovered By: | H.E.S.S. |
| TeVCat SubCat: | Default Catalog |
Source Notes:
| H.E.S.S. Galactic Plane Survey (HGPS, 2018): |
| A selection of information for each of the 78 sources in the HGPS is provided in TeVCat. For full details, visit the HGPS website. |
| Name: | HESS J1646-458 |
| Source Class: | Unid |
| Identified Object: | None |
| R.A. (J2000): | 251.98 deg (16 47 54) |
| Dec. (J2000): | -46.26 deg (-46 15 30) |
| Positional uncertainty: | 0.091 deg |
| Spatial Model: | Gaussian |
| Size: | 0.503 +/- 0.030 deg |
| Spectral Model: | power law |
| Integral Flux > 1 TeV: | 5.81e-12 +/- 7.32e-13 cm-2 s-1 |
| Pivot Energy, E0: | 1.05 TeV |
| Diff. Flux at E0: | 7.87e-12 +/- 7.90e-13 cm-2 s-1 TeV-1 |
| Spectral Index: | 2.54 +/- 0.13 |
| HGPS Source Notes: | |
| | |
This source is one of the twelve source whose HGPS results differed from those published in previous publications.
"HESS J1646−458 is a complex emission region located in the vicinity of the stellar cluster Westerlund 1. Its morphology suggests it consists of multiple sources.
Abramowski et al. (2012) separated the emission into at least two distinct features
(with radii 0.35 deg and 0.25 deg, respectively) as well as some structured extended
emission, distributed over the signal region of 2.2 deg diameter, and even extending beyond. A flux above 1 TeV in the signal region of 7.6 +/- 1.3 +/- 1.5 × 10e−12 cm−2 s−1
was derived, and a spectral index of 2.19 +/- 0.08 +/- 0.20. An ON-OFF background estimation technique was used to cope with the large source size. In the HGPS analysis,
this complex emission is modeled by a single Gaussian component of 0.5 deg size shifted by 0.47 deg from the center of the region used in Abra\
mowski et al. (2012),
with a
lower flux above 1 TeV of 5.48 +/- 0.46 × 10e-12 cm-2 s-1, and steeper index of 2.54 +/- 0.13. Given the complex morpology and the large scale of the spectral extraction
region used in Abramowski et al. (2012), significant differences in source parameters are to be expected;
in the HGPS analysis part of the flux is absorbed in the large-scale
diffuse background."
" ... the HGPS analysis for this source is not very reliable, because the source size is similar to the H.E.S.S. field of view and a more careful individual study and background
estimation is needed ... "
Three possible associations are listed in Table A.9. "This is a list of astronomical objects, extracted from catalogs of plausible counterparts,
which are are found to be spatially coincident with the HGPS source":
- 3FGL J1648.3−4611 (3FGL)
- J1648−4611 (PSR)
- 3FGL J1650.3−4600 (3FGL)
Source position and its uncertainty:
From
Abramowski et al. (2011):
- R.A. (J2000): 16h 46m 50s +/- 27s
- Dec. (J2000): -45d 49m 12s +/- 7m
Up until Nov. 2011:
- no information available
- the source position provided by
SIMBAD was used:
- R.A. (J2000): 16h 47m 04.0s
- Dec. (J2000): -45d 51m 04.9s
Source Association:
From
Ohm, Hinton & White (2013):
- "Acceleration of electrons in a Pulsar Wind Nebula provides a
reasonably natural interpretation of the GeV emission, but leaves the
TeV emission unexplained. A scenario in which protons are accelerated
in or near Wd 1 in supernova explosion(s) and are diffusing away and
interacting with molecular material, seems consistent with the
observed GeV and TeV emission, but requires a very high energy input
in protons, ~10^51 erg, and rather slow diffusion."
From
Abramowski et al. (2011):
- "Four objects coincident with HESS J1646–458 are discussed in the search of a
counterpart, namely the magnetar CXOU J164710.2-455216, the X-ray binary
4U 1642-45, the pulsar PSR J1648-4611 and the massive stellar cluster Wd 1.
In a single-source scenario, Wd 1 is favoured as site of VHE particle acceleration"
From
de Naurois (2011):
- collective winds scenario is attractive due to large number
of Wolf-Rayet stars harboured by Westerlund 1
From
Sakai et al. (2113):
- "These results imply that HESS J1646−458 seems unlikely to be
explained only as a PWN powered by PSR J1648−4611. However, it is
conceivable that parts of the VHE gamma-ray emission of HESS J1646−458
are powered by the pulsar."
Source Extent:
From
Abramowski et al. (2011):
- "The studies presented here show some evidence for a multisource morphology
and a separation into multiple VHE gamma-ray sources." ... "In order to
investigate the multi-source hypothesis two emission regions A and B
are considered."
- radius of full source: 1.1deg
- radius of Region A: 0.35deg
- radius of Region B: 0.25deg
From
Ohm et al. (2009):
- diameter: 2 deg - no uncertainty provided
Spectral Information:
From
Abramowski et al. (2011):
- Spectral index:
- Full source: 2.19 +/- 0.08(stat) +/- 0.20(syst)
- Region A: 2.11 +/- 0.12(stat)
- Region B: 2.29 +/- 0.17(stat)
Distance:
From
Davies & Beasor (2019):
- The authors "present distance estimates for three star clusters rich in
Red Supergiants" including Westerlund 1.
- these distance measures are " based on their average astrometric
parallaxes in Gaia Data Release 2, where the measurement of the
astrometric parrallax is obtained from a proper-motion screened sample
of spectroscopically-confirmed cluster members."
- for Westerlund 1 a distance of We determine distances of:
3.87 +0.95 -0.64 kpc is obtained
- "We find that the dominant source of error is that in Gaia's
zero-point parallax offset and we argue that more precise distances
cannot be determined without an improved characterization of this
quantity."
From
Aghakhanloo et al. (2019):
- "Westerlund 1 (Wd1) is potentially the largest star cluster in the
Galaxy. That designation critically depends upon the distance to the
cluster, yet the cluster is highly obscured, making luminosity-based
distance estimates difficult. Using Gaia Data Release 2 parallaxes
and Bayesian inference, we infer a parallax of 0.31 +/- 0.04 mas
corresponding to a distance of 3.2 +/- 0.04 kpc."
- "Previous estimates for the distance to Wd1 ranged from 1.2 to 5.5
kpc, although values around 5 kpc have usually been adopted. The Gaia
DR2 parallaxes reduce the uncertainty from a factor of 3 to 15% and
rules out the most often quoted value of 5 kpc with 99%
confidence. This new distance allows for more accurate mass and age
determinations for the stars in Wd1."
Seen by: H.E.S.S.
-
Cosmic rays from massive star clusters : A close look at Westerlund 1
Bhadra, Sourav et al., arXiv e-prints parXiv:2201.00529 (2022) [LINK]
-
A deep spectromorphological study of the gamma-ray emission surrounding the young massive stellar cluster Westerlund 1
Aharonian, F. et al., arXiv e-prints parXiv:2207.10921 (2022) [LINK]
-
Using Interstellar Clouds to Search for Galactic PeVatrons: Gamma-ray Signatures from Supernova Remnants
Mitchell, A.M.W. et al., arXiv e-prints parXiv:2103.01787 (2021) [LINK]
-
The young massive stellar cluster Westerlund 1 in gamma rays as seen with H.E.S.S
Mohrmann, Lars et al., arXiv e-prints parXiv:2108.03003 (2021) [LINK]
-
Inferring the distance to Westerlund 1 from Gaia DR2
Aghakhanloo, M. et al., arXiv e-prints p (2019) [LINK]
-
The distances to star-clusters hosting Red Supergiants: chi Per, NGC 7419, and Westerlund 1
Davies, B. and Beasor, E., arXiv e-prints p (2019) [LINK]
-
Asymmetric Ejecta of Cool Supergiants and Hypergiants in the Massive Cluster Westerlund 1
Andrews, H. et al., ArXiv e-prints p (2018) [LINK]
-
Massive Stars as Major Factories of Galactic Cosmic Rays
Aharonian, F. et al., ArXiv e-prints p (2018) [LINK]
-
An ALMA 3mm continuum census of Westerlund 1
Fenech, D.M. et al., ArXiv e-prints p (2018) [LINK]
-
Dense molecular gas at 12 mm towards Galactic TeV gamma-ray sources
de Wilt, P. et al., MNRAS 468 p2093-2113 (2017) [LINK]
-
Discovery of Diffuse Hard X-Ray Emission from the Vicinity of PSR J1648-4611 with Suzaku
Sakai, M. et al., ArXiv e-prints p (2013) [LINK]
-
Gamma-ray emission from the Westerlund 1 region
Ohm, S. et al., ArXiv e-prints p (2013) [LINK]
-
Discovery of extended VHE gamma-ray emission from the vicinity of the young massive stellar cluster Westerlund 1
Hess Collaboration et al., A&A p (2011) [LINK]
-
The Discovery of a Molecular Cavity in the Norma Near Arm Associated with H.E.S.S Gamma-ray Source Located in the Direction of Westerlund 1
Luna, A. et al., ApJ 713 pL45-L49 (2010) [LINK]
-
H.E.S.S. observations of massive stellar clusters
Ohm, S. et al., ArXiv e-prints p (2009) [LINK]
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