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Observation Date (UT) Observation Lat

Canonical Name:HESS J1848-018
TeVCat Name:TeV J1848-017
Other Names:WR121a/W43
1HWC J1849-017c
2HWC J1847-018
1LHAASO J1848-0153u
Source Type:Massive Star Cluster
R.A.:18 48 29 (hh mm ss)
Dec.:-01 47 32.3 (dd mm ss)
Gal Long: 31.00 (deg)
Gal Lat: -0.16 (deg)
Distance: 5.3 kpc
Flux:0.02 (Crab Units)
Energy Threshold:1000 GeV
Spectral Index:2.8
Extended:Yes
Size (X):0.32 (deg)
Size (Y):0.32 (deg)
Discovery Date:2008-07
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 J1848-018
Source Class: Unid
Identified Object: None
R.A. (J2000): 282.12 deg (18 48 29)
Dec. (J2000): -1.89 deg (-01 53 14)
Positional uncertainty: 0.076 deg
Spatial Model: Gaussian
Size: 0.248 +/- 0.032 deg
Spectral Model: power law
Integral Flux > 1 TeV: 1.11e-12 +/- 1.53e-13 cm-2 s-1
Pivot Energy, E0: 0.87 TeV
Diff. Flux at E0: 2.51e-12 +/- 2.64e-13 cm-2 s-1 TeV-1
Spectral Index: 2.57 +/- 0.11
HGPS Source Notes:
The following is the text from the HGPS paper:

For the new source HESS J1848-018 preliminary H.E.S.S. source properties were previously shown (Chaves et al. 2008). These properties are compatible with the HGPS results except for the source size and flux; these were overestimated because the earlier analysis did not include a model for the diffuse emission, which is particularly bright in this region.

The origin of the VHE gamma-ray emission of HESS J1848-018 is not yet firmly identified. No SNR or energetic pulsar is currently detected in the proximity, although we have associated the VHE source with 3FGL J1848.4-0141 (Acero et al. (2015). This unidentified HE gamma-ray point source is significantly offset from the VHE gamma-ray centroid (by approximately 0.2 deg) but well within the VHE emission region. Studies attempting to relate the HE with the (preliminary) VHE morphology and spectra remained inconclusive (Tam et al. 2010; Acero et al. 2013). A potential PSR and PWN scenario cannot be confirmed due to the lack of a detected pulsar (at any wavelength), although the HE spectrum does exhibit curvature typical of pulsars (Acero et al. 2015). Furthermore, there is no known PWN nearby, although one study has shown marginal statistical evidence for an extension of the HE source (Lemoine-Goumard et al. 2011), which is expected if the HE emission is from a PWN or the combination of a pulsar and PWN.

An extensive search for other MWL counterparts found the VHE gamma-ray emission to be in the direction of the massive star-forming region W 43, a very active mini-starburst located at a distance of 6.2 +/- 0.6 kpc (Russeil 2003). It is one of the closest and most luminous star-forming regions in the Galaxy (Motte et al. 2003), hosting a giant H II region (G30.8-0.2), a giant molecular cloud, and the Wolf-Rayet binary star system WR 121a in the central stellar cluster together with O-type stars. The massive stars in the dense central cluster exhibit strong stellar winds with extreme mass loss rates, in particular the WN7-subtype WR 121a (Blum et al. 1999).

This unique MWL environment is of interest because the central cluster of W 43 could be the site of efficient particle acceleration in various plausible hadronic scenarios involving the high-velocity (up to 2000 km s-1 ) stellar winds (e.g., Reimer et al. 2006; Romero 2010). Furthermore, the very large amount of molecular gas present in W 43 (approx. 7×106 M_sun Nguyen Luong et al. 2011) provides a natural target for accelerated cosmic rays (regardless of their potential acceleration site), which would lead to gamma-ray production via hadronic p-p collisions (e.g., Aharonian 1991).

It is not yet possible to confirm the W 43 hadronic scenario for the origin of the VHE emission, in part because of the very complex morphologies present and the challenges in correlating features observed in radio and infrared observations at arcsecond scales with the approx. 5 arcsecond resolution in VHE. The VHE centroid, in particular, is significantly offset from the central cluster by approximately 0.2 deg, although the extended VHE emission is generally coincident with the W 43 complex. This scenario remains under investigation, especially in light of the recent detection of the superbubble 30 Dor C in the LMC (H.E.S.S. Collaboration 2015), which suggests that particle acceleration occurring in the collective winds of massive stars can indeed produce VHE emission.

Two 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 J1848.4-0141 (3FGL)
- W43 (EXTRA)
"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 (J2000):
From Chaves et al. (2008):
- l: 3.10 deg (= 18h 48m 29s R.A.)
- b: -0.16 deg (= -01d 47m 32.3s)

Source Extent:
From Chaves et al. (2008):
- radius: 0.32 +/- 0.02 deg

Source Association:
From Abeysekara et al. (2017):
- "Source 2HWC J1847-018 was previously detected by HAWC as 1HWC J1849-017c.
It is associated with the unidentified TeV gamma-ray source HESS J1848-018
(approx. 0.2 deg distance). HESS J1848-018 was discovered by the
H.E.S.S. experiment in the extended Galactic plane Survey. It is
located in the direction of, but slightly offset from, the
star-forming region W 43 and hence a possible association with it was
suggested in Chaves et al. (2008). However, the association with the
star-forming region has not been further confirmed, and this source is
now considered to be a candidate PWN following recent observations by
Fermi-LAT (Acero et al. 2013). Further multi-wavelength studies are
needed to properly identify the source."
From Abeysekara et al. (2015):
- "1HWC J1849-017c is detected at 3.7 sigma post trials and is
positionally coincident with the extended source HESS J1848-018, which
is possibly associated with the star forming region W43. The
differential flux normalization at 6 TeV from this dataset is
approx. 3.5 times the flux reported by H.E.S.S. Chaves et al. (2008)
reported an index of 2.8 and the spectral index assumption of 2.3 in
this analysis would result in a different flux normalization by
20%. More importantly, diffuse emission from this star forming region
that contains a molecular cloud could contribute more to the
differential flux normalization derived from the Pass 1 dataset than
that measured by IACTs, which have a smaller angular integration
region."
From Acero et al. (2013):
- Analysis of the LAT data from this source leads to its
classification as a PWN candidate
From Chaves et al. (2008):
- Associated with star forming region W43, which hosts Wolf-Rayet
star WR121a, Giant H-II region G30.8+0.2 and 10^6 solar masses of
molecular gas
From de Naurois (2011):
- a massive star cluster is mentioned as a possible association

Source Distance:
From Chaves et al. (2008):
- distance of 5.3 kpc is based on that of WR 121a

A PeVatron:

From Cao et al. (2024):
- This source is listed as being a UHE source in Table 2. This means
that it has a detection above 100 TeV at a significance level
corresponding to a test statistic of greater than 20.


Seen by: H.E.S.S., HAWC, LHAASO
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