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Observation Date (UT) Observation Lat

Canonical Name:HESS J1826-130
TeVCat Name:TeV J1826-130
Other Names:PSR J1826-1256
PWN G018.5-00.4
2HWC J1825-134
Source Type:UNID
R.A.:18 26 02.16 (hh mm ss)
Dec.:-13 04 00 (dd mm ss)
Gal Long: 18.43 (deg)
Gal Lat: -0.41 (deg)
Distance: 4 kpc
Flux:0.049 (Crab Units)
Energy Threshold:1000 GeV
Spectral Index:1.7
Extended:Yes
Size (X):0.21 (deg)
Size (Y):0.21 (deg)
Discovery Date:2015-07
Discovered By: H.E.S.S.
TeVCat SubCat:Default Catalog

Source Notes:
TeVCat:
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 J1826-130
Source Class: Unid
Identified Object: None
R.A. (J2000): 276.51 deg (18 26 02)
Dec. (J2000): -13.02 deg (-13 01 02)
Positional uncertainty: 0.060 deg
Spatial Model: Gaussian
Size: 0.152 +/- 0.021 deg
Spectral Model: power law
Integral Flux > 1 TeV: 1.14e-12 +/- 1.60e-13 cm-2 s-1
Pivot Energy, E0: 2.06 TeV
Diff. Flux at E0: 2.73e-13 +/- 3.78e-14 cm-2 s-1 TeV-1
Spectral Index: 2.04 +/- 0.10
HGPS Source Notes:
The following is the text from the HGPS paper:

The HGPS catalog analysis reveals a distinct new source of VHE gamma rays, HESS J1826-130, in what was previously considered extended emission from the nearby PWN HESS J1825-137 (Aharonian et al. (2006)). Because of the very close proximity to its bright neighbor, the spectral measurementis highly contaminated (41%). Anguner et al. (2017) reported preliminary findings for this new source.

HESS J1826-130 is associated with the “Eel” PWN11 (PWN G18.5-0.4), an elongated, nonthermal, X-ray source observed with Chandra (Roberts et al. 2007), and the energetic pulsar PSR J1826-1256 (Abdo et al. 2009), on the basis of a spatial coincidence. The best-fit VHE centroid is compatible with the Eel, while the pulsar is somewhat offset (0.09 deg ) from the centroid but well within the VHE emission region(size 0.15 +/- 0.02 deg ). The pulsar is now notable for being one of the brightest radio-quiet γ-ray pulsars (3FGL J1826.1-1256; Acero et al. 2015). The distance of the pulsar is unfortunately not known, which precludes conclusions on the energetics, but its position, Edot = 3.6 x 10e36 erg s-1 , and Tchar = 14 kyr suggest it is probably powering the Eel. The PWN is not detected in HE gamma rays (Ackermann et al. 2011, 2016). Finally, we note that dense molecular gas was also found overlapping HESS J1826-130 at a distance matching that of the dispersion measure of the pulsar (Voisin et al. 2016), suggesting a possible hadronic origin for this VHE source.

The SNR G18.6-0.2 (Brogan et al. 2006) is also coincident with the VHE emission region, although it is significantly smaller in size (0.1 deg diameter). Very little is known about this SNR, except that a partial shell-type morphology has been observed so far only in radio and IR and that its distance is estimated to be 4.0–5.2 kpc (Johanson & Kerton 2009).

A firm identification of the VHE source as a PWN is not possible at this time, in part resulting from the unknown distance to the Eel PWN and PSR system and the poorly studied SNR. We are currently preparing more advanced VHE spectral analysis methods that can account for contamination in crowded FoVs. These methods will enable more accurate modeling of the SED.

Four 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":
- G18.5-0.4 (PWN)
- J1826-1256 (PSR)
- 3FGL J1826.1-1256 (3FGL)
- G18.6-0.2 (SNR)

This detection was announced by C. Deil at the 34th ICRC.

Source position:
On 210129 the position was updated from that given in Anguner et al. (2017) to that in H.E.S.S. Collaboration (2020).
From H.E.S.S. Collaboration (2020):
- R.A. (J2000): 18h 26m 02.16s +/- 3.38s (stat) +/- 1.30s (sys)
- Dec. (J2000): -13d 04' +/- 1.0' (stat) +/- 0.3' (sys)
From Anguner et al. (2017):
- The position in TeVCat was updated to this position on 170911
- R.A. (J2000): 18h 26m 00.2s
- Dec. (J2000): -13f 02' 01.8''
From Angüner et al. (2017):
- The position in TeVCat was updated to this position on 170131
- R.A. (J2000): 18h 26m 0.2s +/- 7.0s(stat) +/- 1.3s(syst)
- Dec. (J2000): -13d 02' +/- 1.8'(stat) +/- 0.3'(syst)
From Deil et al. (2015):
- Lat.: 18.48 deg
- Lon.: -0.39 deg
=> Convert this position to J2000 coordinates:
- R.A. (J2000): 18h 26m 02.59s
- Dec. (J2000): -13d 00' 55.0''
- no positional uncertainty is quoted

Source extent:
On 210129 the extent was updated from that given in Anguner et al. (2017) to that in H.E.S.S. Collaboration (2020).
From H.E.S.S. Collaboration (2020):
- "The extension (radius) of the source is estimated to be:
0.21 deg +/- 0.02 deg (stat) +/- 0.05 deg (sys)
... which is significantly larger than the HESS PSF."
From Anguner et al. (2017):
- 0.17 +/- 0.02
From Angüner et al. (2017):
- 0.17deg +/- 0.02deg(stat) +/- 0.05deg(syst)
From Deil et al. (2015):
- 0.15 deg

Flux:
From H.E.S.S. Collaboration (2020):
- "The integral flux level above 1 TeV is:
... F (> 1 TeV) = (10.2 +/- 0.5 (stat) +/- 2.0(sys) ) x 10e-13 cm-2 s-1
... and corresponds to 4.9% of the Crab Nebula flux at the same energies."
From Anguner et al. (2017):
- the flux >1TeV is 4.0% of the Crab Nebula
From Deil et al. (2015):
- 3.3% Crab

Spectral properties:
From H.E.S.S. Collaboration (2020):
- The authors describe that a "circular region with a radius of 0.22
deg centered at the best-fit position of HESS J1826-130 was used as
the integration region for measuring the differential VHE gamma-ray
spectrum of the source"
- "Several spectral models were used to fit the data, including a
simple power-law model, a broken power-law model, and a power-law
model with an exponential cutoff. The spectral fit is performed
between 0.42 and 56.2 TeV. The best-fit model is found to be the
power-law model with an exponential cutoff , with a p-value = 0.41 and
a likelihood ratio test (LLRT) against the power-law model providing a
statistical improvement at the ∼3.2 sigma level."
- The differential VHE emission is thus best represented by:
... dN/dE = F0 (E/1 TeV)^-A exp(-E/Ec) with
... F0: (10.10 +/- 0.69stat +/- 2.02 (sys) x 10e-13 cm-2s-1 TeV-1
... A: 1.78 +/- 0.10 (stat) +/- 0.20 (sys)
... Ec: 15.2 +5.5 −3.2 TeV
The integral flux level above 1 TeV is:
... F (> 1 TeV) = (10.2 +/- 0.5 (stat) +/- 2.0(sys) ) x 10e-13 cm-2 s-1
... and corresponds to 4.9% of the Crab Nebula flux at the same energies.
- "A 2 sigma lower limit on the cut-off energy of the source is
derived at ∼10 TeV."
- "The integration region used to measure the VHE spectrum of HESS J1826-130
is strongly contaminated, especially at lower energies, by the
relatively softer spectrum of HESS J1825-137. Therefore, the obtained
spectrum is affected by this contamination. Taking into account the
relatively softer contribution from the contaminating source, the
intrinsic spectrum of HESS J1826−130 is expected to be even harder
with respect to the spectral results discussed above."
- "Although the contamination from HESS J1825-137 could potentially
affect the spectrum of HESS J1826-130, our studies demonstrate that
the effects on the spectral parameters are at the level of our analysis
systematic uncertainties. The intrinsic spectrum of HESS J1826-130,
corrected for this contamination, is found to be well described by an
ECPL model where
... F0 = 9.2 x 10e-13 cm-2 s-1 TeV-1
... A = 1.7
... Ec = 16 TeV"
From Anguner et al. (2017):
- "HESS J1826−130 spectral parameters are updated with respect to
previously published results Angüner et al. (2017) taking into account the updated value
of the mirror reflection modelling in H.E.S.S. telescopes"
- the spectrum is best fit by a power law with an exponential cut off
at an energy of 13.5 +4.7 -2.7
- spectral index: 1.66 +/- 0.11(stat) +/- 0.20(syst)
- "The intrinsic (uncontaminated) spectrum of HESS J1826−130 is
expected to be even harder (or having a cut-off at higher energies),
given the relatively softer spectrum of contaminating emission from
HESS J1825−137. Our preliminary results provide an intrinsic spectrum
of HESS J1826−130 with a spectral index of 1.57 +/- 0.15(stat) and a
cut-off at 15.2 +8.9 -4.1 TeV."
From Angüner et al. (2017):
- the spectrum is best fit by a power law with an exponential cut off
at an energy of 12.5 TeV +4.0 TeV -2.4 TeV
- spectral index: 1.61 +/- 0.11(stat) +/- 0.20(syst)

Distance:
On 210129 the distance was updated from that given in Karpova, Zyuzin & Shibanov (2019) to that in H.E.S.S. Collaboration (2020).
From H.E.S.S. Collaboration (2020):
- "HESS J1826-130 is located at VLSR = 45-60 km s-1, corresponding to
a kinematic distance of 4.0 kpc, and VLSR = 60–80 km s−1,
corresponding to a kinematic distance of 4.6 kpc."
From Karpova, Zyuzin & Shibanov (2019):
- the authors perform a distance estimate based on "the empirical
relation between the distance and the interstellar reddening E(B-V)".
- they obtained a value of E(B-V) of 2.45 +/- 0.19 (1 sigma errors),
which is "much smaller than the total Galactic value and implies that
the pulsar is much closer than the Galactic disk edge in its
direction"
- "We compared the obtained E(B-V) with the extinction map by
Marshall et al. (2006), which is based on Two-Micron All-Sky Survey (2MASS)
stars photometry along with the Besancon model of population
synthesis. The E(B-V)-distance relation was constructed using the
python package mwdust (Bovy et al. 2016). The resulting D lies in the
range of 3.4-3.6 kpc. This is compatible with the distance estimate of
3 kpc based on the pulsar X-ray luminosity, though such estimate is
very uncertain (Roberts 2009)."
- "We adopt 3.5 kpc as a reasonable value in our following estimates."

Source Association:
From Cao et al. (2021):
- HESS J1826-130 may be associated with LHAASO J1825-1326
From H.E.S.S. Collaboration (2020):
- "The deep observation campaign on the source reported
in this paper provides several constraints to its spectral and
morphological properties, although its origin is still uncertain"
- The presence of nearby SNRs found in the region and/or another yet
unresolved accelerator, together with the gas density properties of
the surroundings, could make hadronic interactions responsible for the
observed emission. If protons are delivered with energies up to
hundreds of TeV, HESS J1826-130 could point to the existence of a
distinct population of CR sources that, along with the GC,
significantly contribute to the Galactic CR flux around the knee
feature.
- In a leptonic scenario, HESS J1826-130 has been proposed as
the counterpart of the Eel Nebula powered by the pulsar PSR J1826-1256.
Our observations reveal VHE emission above several tens of TeV that
comes from the vicinity of the pulsar.
- Regarding the association of HESS J1826-130 with the recently
discovered >100 TeV emitter, 2HWC J1825-13, it is worth noting that
the spectrum extends at least up to ∼43 TeV. Therefore, it could be
possible that a fraction of the emission reported from eHWC J1825-134
could be partially contributed by HESS J1826-130
From Karpova, Zyuzin & Shibanov (2019):
- The authors analysed archival XMM-Newton and Chandra data to study
this gamma-ray pulsar and its PWN.
- "The TeV source HESS J1826−130 overlaps with the PSR J1826−1256+PWN
system as well as with G18.45−0.42 and the open star cluster Bica 3.
Comparing the Eel X-ray and HESS J1826−130 gamma-ray luminosities with
those of other X-gamma-ray PWNe suggests the TeV source is the relic
PWN of PSR J1826−1256. However, we cannot exclude the possibility that
G18.45−0.42 can be the HESS J1826−130 counterpart (or partially
contribute to TeV emission)."
From Duvidovich et al. (2019):
- "To investigate the nature of HESS J1826-130, we reprocessed
unpublished archival data obtained with XMM-Newton."
- " ... the XMM-Newton study of the region including PSR J1826-1256 reveals
an elongated non-thermal X-ray emitting nebula with the pulsar located
in the northern border and a tail towards the peak of the very high
energy source. The spectrum is characterized by a power law with a
photon index going from 1.6 around the pulsar to 2.7 in the borders of
the nebula, a behaviour consistent with synchrotron cooling of
electrons. From our X-ray analysis we propose that HESS J1826-130 is
likely produced by the PWN powered by PSR J1826-1256 via the inverse
Compton mechanism."
From Anguner et al. (2017):
- this source was one of three included in a study of H.E.S.S. sources
"with spectra extending beyond 10 TeV and relatively hard spectral
indices compared with the average spectral index of H.E.S.S. sources"
-"Although the nature of these VHE γ-ray sources is still open, their
spectra suggest that the astrophysical objects producing such emission
must be capable of accelerating the parental particle population up to
energies of at least several hundreds of TeV"
From Abeysekara et al. (2017):
- this is one of three sources potentially associated with 2HWC J1825-134
From Angüner et al. (2017):
- "HESS J1826−130 shows one of the hardest spectra ever observed in
VHE gamma rays, extending up to at least few tens of TeV. The
shell-type supernova remnants, G018.1−00.1 and G018.6−00.2, are
located in the vicinity of the source along with the gamma-ray pulsar
PSR J1826−1256."
- "A proton or electron population extending up to several hundred TeV
is needed to produce the TeV emission."
- "The emission from HESS J1826−130 is characterized by a very hard
spectrum with an exponential cut-off at about 12 TeV. Such a spectrum,
together with a spatial coincidence of a dense molecular hydrogen
region, suggests that the radiation could be produced by several
hundred TeV protons colliding with the gas. To explain the very hard
spectrum, one can think of a hadronic scenario in which runaway
protons accelerated by the close shell-type SNRs G018.1−00.1 or
G018.6−00.2 are emitting TeV photons when interacting with the dense
ambient gas found along the line of sight."
- "A leptonic scenario, where electrons accelerated by the pulsar PSR
J1826−1256 are up-scattering CMB or IR photons, can also explain the
VHE emission."
From Voisin et al. (2016):
"From our ISM study, we identify a few plausible origins of the HESS
J1826-130 emission, including the progenitor SNR of PSR J1826-1334 and
the PWN G018.5-0.4 powered by PSR J1826-1256. A deeper TeV study
however, is required to fully identify the origin of this mysterious
TeV source."
From Deil et al. (2015):
- PSR J1826-1256 is within the extension of this source.
- PWN G018.5-00.4 is within the extension of this source.
- no further details are available in the PDF
- the source is classified as UNID in TeVCat for now


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