| Canonical Name: | Westerlund 2 |
| TeVCat Name: | TeV J1023-577 |
| Other Names: | WR20a
RCW 49
HESS J1023-575
1FGL J1023.0-5746
PSR J1022-5746 |
| Source Type: | Massive Star Cluster |
| R.A.: | 10 23 24 (hh mm ss) |
| Dec.: | -57 47 24 (dd mm ss) |
| Gal Long: | 284.22 (deg) |
| Gal Lat: | -0.40 (deg) |
| Distance: | 8 kpc |
| Flux: | 0.09 (Crab Units) |
| Energy Threshold: | 380 GeV |
| Spectral Index: | 2.58 |
| Extended: | Yes |
| Size (X): | 0.18 (deg) |
| Size (Y): | 0.18 (deg) |
| Discovery Date: | 2007-06 |
| 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 J1023-575 |
| Source Class: | Unid |
| Identified Object: | None |
| R.A. (J2000): | 155.81 deg (10 23 15) |
| Dec. (J2000): | -57.78 deg (-57 46 34) |
| Positional uncertainty: | 0.030 deg |
| Spatial Model: | Gaussian |
| Size: | 0.166 +/- 0.009 deg |
| Spectral Model: | power law |
| Integral Flux > 1 TeV: | 2.41e-12 +/- 1.34e-13 cm-2 s-1 |
| Pivot Energy, E0: | 1.87 TeV |
| Diff. Flux at E0: | 7.50e-13 +/- 4.16e-14 cm-2 s-1 TeV-1 |
| Spectral Index: | 2.36 +/- 0.05 |
| HGPS Source Notes: | |
| | |
This source is listed as unidentified in the HGPS. Five 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 J1023.1−5745 (3FGL)
- J1023−5746 (PSR)
- Westerlund 2 (EXTRA)
- 2FHL J1022.0−5750 (2FHL)
- 3FGL J1024.3−5757 (3FGL)
"EXTRA associations: For completeness, in addition to the associations obtained through the catalog-based, automatic procedure, we add a list of 20 extra
associated objects that are plausible counterparts for some HGPS sources and are not covered by the limited set of catalogs we use."
Source position and its uncertainty:
From
Aharonian et al. (2007):
- RA (J2000): 10h 23m 18s +/- 12s(stat) +/-20s(syst)
- Dec (J2000): -57d 45' 50" +/- 1'30"(stat) +/- 20"(syst)
From
HESS Collaboration (2011):
- RA (J2000): 10h 23m 24s +/- 7.2s (stat) +/- 20"(syst)
- Dec (J2000): -57d 47m 24s +/- 1m12s (stat) +/- 20"(syst)
Source Association:
From
Asahina et al. (2017):
- "The formation mechanism of CO clouds observed with NANTEN2 and
Mopra telescope toward the stellar cluster Westerlund 2 is studied by
three-dimensional magnetohydrodynamic simulations taking into account
the interstellar cooling. These molecular clouds show a peculiar shape
composing of an arcshaped cloud in one side of a TeV gamma-ray source
HESS J1023-575 and a linear distribution of clouds (jet clouds) in
another side. We propose that these clouds are formed by the
interaction of a jet with interstellar neutral hydrogen (HI) clumps"
- "HESS J1023-575 is observed both at the high energy band (above 2.5
TeV) and the low energy band (0.7 − 2.5 TeV). The cooling by the
pp-interaction and diffusion time scales of the relativistic particles
are estimated to be about 5×10e6 yr and 2×10e4 yr, respectively, by
Furukawa et al. (2014). If the arc and the jet clouds and TeV
gamma-ray source are produced by a single object, a supernova remnant
or a pulsar wind nebulae is not likely as the origin for TeV gamma-ray
source since the diffusion time scale of the relativistic particles is
shorter than the age of the arc and jet clouds (∼ Myr). A microquasar
jet which is active over 1 Myr can explain both the age of the arc and
jet clouds and the lifetime of the relativistic particles."
From
Furukawa et al. (2014):
- "We have made new CO observations of two molecular clouds, which we
call "jet" and "arc" clouds, toward the stellar cluster Westerlund 2
and the TeV gamma-ray source HESS J1023-575. ... In addition, we have
found a new counter jet cloud on the west. ... A sign of star
formation is found at the edge of the jet cloud and gives a constraint
on the age of the jet cloud to be ~Myrs. An analysis with the multi CO
transitions gives temperature as high as 20 K in a few places of the
jet cloud, suggesting that some additional heating may be operating
locally. The new TeV gamma-ray images by H.E.S.S. correspond to the
jet and arc clouds spatially better than the giant molecular clouds
associated with Westerlund 2. We suggest that the jet and arc clouds
are not physically linked with Westerlund 2 but are located at a
greater distance around 7.5 kpc. A microquasar with long-term activity
may be able to offer a possible engine to form the jet and arc clouds
and to produce the TeV gamma-rays, although none of the known
microquasars have a Myr age or steady TeV gamma-rays. Alternatively,
an anisotropic supernova explosion which occurred ~Myr ago may be able
to form the jet and arc clouds, whereas the TeV gamma-ray emission
requires a microquasar formed after the explosion."
From
Acero et al. (2013):
- Analysis of the LAT data from this source leads to its
classification as a PWN candidate
From
de Naurois (2011):
- due to the extension of this source and the lack of apparent variability,
mechanisms involving collective stellar wind effects are preferred. The
recent discovery of 2 neighbouring bright pulsars by Fermi motivate the
consideration of pulsar wind nebula emission
From
HESS Collaboration (2011):
- "a clear identification of the object responsible for
the VHE emission from HESS J1023–575 is not yet possible, and
contribution from the nearby high-energy pulsar and/or the open
cluster remains a possibility"
Source Extent:
From
Aharonian et al. (2007):
- radius: 0.18 +/- 0.02 deg
From
HESS Collaboration (2011):
- radius: 0.18 +/- 0.02 deg
Spectral Properties:
From
Aharonian et al. (2007):
- Spectral index: 2.53 +/- 0.16 (stat) +/- 0.1 (syst)
From
HESS Collaboration (2011):
- Spectral Index: 2.58 +/- 0.19 (stat) +/- 0.2 (syst)
Seen by: H.E.S.S.
-
X-ray emission from Westerlund 2 detected by SRG/ART-XC and Chandra: search for radiation of TeV leptons
Bykov, A.M. et al., arXiv e-prints parXiv:2306.09960 (2023) [LINK]
-
Probing the hadronic nature of the gamma-ray emission associated with Westerlund 2
de Ona Wilhelmi, Emma et al., arXiv e-prints parXiv:2109.07823 (2021) [LINK]
-
Probing the hadronic nature of the gamma-ray emission associated with Westerlund 2
Mestre, Enrique et al., MNRAS p (2021) [LINK]
-
The young massive star cluster Westerlund 2 observed with MUSE. III. A cluster in motion -- the complex internal dynamics
Zeidler, Peter et al., arXiv e-prints parXiv:2101.01694 (2021) [LINK]
-
Search for PeV Gamma-Ray Emission from the Southern Hemisphere with 5 Yr of Data from the IceCube Observatory
Aartsen, M.G. et al., ApJ 891 p9 (2020) [LINK]
-
The Young Massive Star Cluster Westerlund 2 Observed with MUSE. II. MUSEpack - A Python Package to Analyze the Kinematics of Young Star Clusters
Zeidler, Peter et al., AJ 158 p201 (2019) [LINK]
-
The young massive star cluster Westerlund 2 observed with MUSE. I. First results on the cluster internal motion from stellar radial velocities
Zeidler, P. et al., ArXiv e-prints p (2018) [LINK]
-
Massive stars in the hinterland of the young cluster, Westerlund 2
Drew, J.E. et al., ArXiv e-prints p (2018) [LINK]
-
Constraining cosmic ray acceleration in young star clusters using multi-wavelength observations
Gupta, S. 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]
-
Dense molecular gas at 12 mm towards Galactic TeV gamma-ray sources
de Wilt, P. et al., MNRAS 468 p2093-2113 (2017) [LINK]
-
Magnetohydrodynamic Simulations of the Formation of Molecular Clouds toward the Stellar Cluster Westerlund 2: Interaction of a Jet with Clumpy Interstellar Medium
Asahina, Y. et al., ArXiv e-prints p (2017) [LINK]
-
Diffuse gamma-ray emission in the vicinity of young star cluster Westerlund 2
Yang, R. et al., ArXiv e-prints p (2017) [LINK]
-
Investigation of Dense Gas Towards Relativistic Outflow Sources
Hawkes, J. et al., 28 p1460198 (2014) [LINK]
-
The Jet and Arc Molecular Clouds toward Westerlund 2, RCW 49, and HESS J1023-575 12CO and 13CO (J = 2-1 and J = 1-0) observations with NANTEN2 and Mopra Telescope
Furukawa, N. et al., ApJ 781 p70 (2014) [LINK]
-
Constraints on the Galactic Population of TEV Pulsar Wind Nebulae Using Fermi Large Area Telescope Observations
Acero, F. et al., ArXiv e-prints p (2013) [LINK]
-
Fermi-LAT detection of gamma-ray emission in the vicinity of the star forming regions W43 and Westerlund 2
Lemoine-Goumard, M. et al., ArXiv e-prints p (2011) [LINK]
-
Revisiting the Westerlund 2 field with the HESS telescope array
HESS Collaboration et al., A&A 525 pA46+ (2011) [LINK]
-
Fermi-LAT Search for Pulsar Wind Nebulae Around Gamma-ray Pulsars
Ackermann, M. et al., ApJ 726 p35-+ (2011) [LINK]
-
Eight Gamma-ray Pulsars Discovered in Blind Frequency Searches of Fermi LAT Data
Saz Parkinson, P.M. et al., ApJ 725 p571-584 (2010) [LINK]
-
Temperature and Density Distribution in the Molecular Gas Toward Westerlund 2: Further Evidence for Physical Association
Ohama, A. et al., ApJ 709 p975-982 (2010) [LINK]
-
Fermi-LAT Search for Pulsar Wind Nebulae around gamma-ray Pulsars
The Fermi LAT Collaboration and Timing Consortium, P., ArXiv e-prints p (2010) [LINK]
-
Suzaku Observation of Diffuse X-Ray Emission from the Open Cluster Westerlund 2: a Hypernova Remnant?
Fujita, Y. et al., PASJ 61 p1229- (2009) [LINK]
-
A peculiar jet and arc of molecular gas toward the rich and young stellar cluster Westerlund 2 and a TeV gamma ray source
Fukui, Y. et al., ArXiv e-prints p (2009) [LINK]
-
H.E.S.S. observations of massive stellar clusters
Ohm, S. et al., ArXiv e-prints p (2009) [LINK]
-
Discovery of a Young Gamma-ray Pulsar Associated with an Extended TeV Gamma-ray Source
Dormody, M. and for the Fermi-LAT Collaboration, ArXiv e-prints p (2009) [LINK]
-
Molecular Clouds as a Probe of Cosmic-Ray Acceleration in a Supernova Remnant
Fujita, Y. et al., ApJ 707 pL179-L183 (2009) [LINK]
-
Molecular Clouds Toward RCW49 and Westerlund 2: Evidence for Cluster Formation Triggered by Cloud-Cloud Collision
Furukawa, N. et al., ApJ 696 pL115-L119 (2009) [LINK]
-
Discovery of a Young Gamma-ray Pulsar Associated with an Extended TeV Gamma-ray Source
Dormody, M. and for the Fermi-LAT Collaboration, ArXiv e-prints p (2009) [LINK]
-
Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund2
Naze, Y. et al., ArXiv e-prints 801 p (2008) [LINK]
-
Detection of extended very-high-energy gamma-ray emission towards the young stellar cluster Westerlund 2
Aharonian, F. et al., A&A 467 p1075-1080 (2007) [LINK]
-
On the Distance and Molecular Environment of Westerlund 2 and HESS J1023-575
Dame, T.M., ApJ 665 pL163-L166 (2007) [LINK]
-
HESS J1023-575: Non-thermal Particle Acceleration Associated with a Young Stellar Cluster
Reimer, O. et al., 921 p220-222 (2007) [LINK]
-
On the Distance and Molecular Environment of Westerlund 2 and HESS J1023-575
Dame, T.M., ArXiv e-prints 707 p (2007) [LINK]
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