| Canonical Name: | LHAASO J2108+5157 |
| TeVCat Name: | TeV J2108+519 |
| Other Names: | 1LHAASO J2108+5153u |
| Source Type: | DARK |
| R.A.: | 21 08 36 (hh mm ss) |
| Dec.: | +51 57 00 (dd mm ss) |
| Gal Long: | 92.28 (deg) |
| Gal Lat: | 2.87 (deg) |
| Distance: | |
| Flux: | 0.38 (Crab Units) |
| Energy Threshold: | 100000 GeV |
| Spectral Index: | |
| Extended: | Yes |
| Size (X): | 0.00 (deg) |
| Size (Y): | 0.00 (deg) |
| Discovery Date: | 2021-05 |
| Discovered By: | LHAASO |
| TeVCat SubCat: | Default Catalog |
Source Notes:
Details of the source detection:
From
Cao et al. (2021):
- "In absence of VHE gamma-ray counterparts, this is the first
gamma-ray source directly discovered in the UHE band."
From
Cao et al. (2021):
- "At 100 TeV, the angular and energy resolutions are about 15–20 arcmin
and better than 20%, respectively, allowing adequate spectroscopic and
morphological studies."
- "The statistical significance of the detection above 100 TeV is calculated
using a 0.3deg extension template"
- "Crab Units (CU), flux of the Crab Nebula at 100 TeV; 1 CU = 6.1 x 10-17 photons TeV-1 cm-2 s-1)"
- Significance above 100 TeV: 8.3 sigma
- E_max (PeV): 0.43 +/- 0.05
- Differential photon flux at 100 TeV (CU): 0.38 +/-0.09
- On-source events/Off-source events: 30/6.4
- Exposure (hr): 2525.8
Source Position:
From
Cao et al. (2021):
- R.A. (J2000): 317.17 +/- 0.07 (stat) = 21h 08m 40.8s +/- 15s
- Dec. (J2000): +51.95 +/- 0.05 (stat) = +51d 57m 00s +/- 180s
- The authors report: "which is coincident with the location of events
with E_rec > 100 TeV (
Cao et al., 2021))."
From
Cao et al. (2021):
- This is the position reported in TeVCat.
- R.A. (J2000): 317.15 = 21h 08m 36s
- Dec. (J2000): +51.95 = +51d 57m 00s
Source Extension:
From
Cao et al. (2021):
- "The source is found to be point-like (TS = 118.79), but a slightly
extended morphology (TS = 121.48) cannot be ruled out due to the
limited statistics and the KM2A PSF. An upper limit on the extension
of the source is calculated to be 0.26 deg at 95% confidence level."
Distance:
From
Kar & Gupta (2021):
- "This source is located near the center of a GMC [MML2017]4607
(
Miville-Deschenes et al. (2017)), which is within the upper limit of
the extension of LHAASO J2108+5157. The average angular radius of the
GMC [MML2017]4607 is 0.236 deg with a mass of 8469 M_solar at a distance of
3.28 kpc."
Spectral Information:
From
Cao et al. (2021):
- "The total number of photon-like events detected above 25 TeV and 100
TeV is 140 and 18, respectively. There is one photon-like event with
energy of 434 +/- 49 TeV in the last bin."
- "Assuming a single power-law form, the differential energy spectrum
of gamma-ray emission from LHAASO J2108+5157 is derived. It can be
described by a single power law from 20 TeV to 500 TeV"
- dN/dE = N0*(E/E0)^(-A) with ...
- N0 = 1.59 +/- 0.35 (stat) × 10e-15 TeV-1 cm-2 s-1
- E0 = 20 TeV
- A = 2.83 +/- 0.18
Possible Origin:
From
de la Fuente et al. (2023):
- "PeVatrons are the most powerful naturally occurring particle
accelerators in the Universe. The identification of counterparts
associated to astrophysical objects such as dying massive stars,
molecular gas, star-forming regions, and star clusters is essential
to clarify the underlying nature of the PeV emission, i.e., hadronic
or leptonic."
- "We present 12,13 CO(J=2 ->1) observations made with the 1.85~m
radio-telescope of the Osaka Prefecture University toward the Cygnus
OB7 molecular cloud, which contains the PeVatron candidate LHAASO
J2108+5157."
- "We propose this cloud as a new candidate to produce the sub-PeV
emission observed in LHAASO J2108+5157. Considering a distance of 1.7
kpc, we estimate a nucleon (HI+H 2 ) density of 37 +/- 14cm-3, and a
total nucleon mass(HI+H 2 ) of 1.5 +/-0.6 x10e4 M_sun."
- "On the other hand, we confirm that Kronberger 82 is a molecular
clump with an angular size of 0.1 deg. a nucleon density ∼ 10e3
cm-3−3, and a mass ∼ 10e3 M_sun."
- "Although Kronberger 82 hosts the physical conditions to produce the
observed emission of LHAASO J2108+5157, [FKT-MC]2022 is located
closer to it, suggesting that the latter could be the one associated
to the sub-PeV emission. Under this scenario, our results favour a
hadronic origin for the emission."
From
De Sarkar (2023):
- "We present a simple phenomenological model of hadronic interaction
between protons accelerated in an old supernova remnant (SNR) and
cold protons situated within the associated molecular clouds
(MCs)."
- "We use the model discussed in this letter to explain the
multiwavelength spectral energy distribution of unidentified
Galactic ultra-high-energy gamma-ray source LHAASO J2108+5157. We
also discuss the feasibility of applying this model in other cases
as well. Future observations can test the viability of the model
discussed in this letter, which will in turn confirm that the SNRs
can, in fact, accelerate particles up to PeV energies."
From
Abe et al. (2022):
- "We observed LHAASO J2108+5157 in the X-ray band with XMM-Newton in
2021 for a total of 3.8 hours and at TeV energies with the
Large-Sized Telescope prototype (LST-1), yielding 49 hours of good
quality data. In addition, we analyzed 12 years of Fermi-LAT data,
to better constrain emission of its High-Energy (HE) counterpart
4FGL J2108.0+5155."
- "We did not find any significant extended emission which could be
related to a Supernova Remnant (SNR) or Pulsar Wind Nebula (PWN) in
the XMM-Newton data, which puts strong constraints on possible
synchrotron emission of relativistic electrons. The LST-1 and LHAASO
observations can be explained as inverse Compton dominated leptonic
emission of relativistic electrons with cutoff energy of 100+70-30
TeV. The low magnetic field in the source imposed by the X-ray upper
limits on synchrotron emission is compatible with a hypothesis of a
TeV halo. Furthermore, the spectral properties of the HE counterpart
are consistent with a hypothesis of Geminga-like pulsar, which would
be able to power the VHE-UHE emission. LST-1 and Fermi-LAT upper
limits impose strong constraints on hadronic scenario of pi-0 decay
dominated emission from accelerated protons interacting with nearby
molecular clouds, requiring hard spectral index, which is
incompatible with the standard diffusive acceleration scenario."
From
Cao et al. (2021):
- "The position of the gamma-ray emission is correlated with a giant
molecular cloud, which favors a hadronic origin. No obvious counterparts
have been found, and deeper multiwavelength observations will help to
cast new light on this intriguing UHE source."
- "In the fourth Fermi-LAT Source Catalog (4FGL, Abdollahi et al. 2020),
a HE point source 4FGL J2108.0+5155 is spatially coincident with
LHAASO J2108+5157 at an angular distance of ∼ 0.13 deg. The coincidence
possibility of a HE point source being found in the region of LHAASO
J2108+5157 is about 0.006."
- "We dedicated an analysis to 4FGL J2108.0+5155 using ∼ 12.2 years
Fermi-LAT data. At a high significance level (7.8sigma), 4FGL J2108.0+5155
is spatially extended (namely 4FGL J2108.0+5155e) and the extension of
a 2DGaussian model is ∼ 0.48 deg."
- "The extrapolation of the spectrum of 4FGL J2108.0+5155e predicts a
differential flux of 4.4 × 10e-13 erg cm-2 s-1 at 10 TeV, a factor of
10 lower than that of LHAASO J2108+5157."
- "Considering the angular size of 4FGL J2108.0+5155e is about two
times larger than the 95% upper limit extension (UL_ext_95% = 0.26 deg )
of LHAASO J2108+5157, the physical coincidence between the two sources
can not be clearly identified."
- "Therefore, we derived the upper limit flux with the same spatial
template as LHAASO J2108+5157 (r_extent = 0.26deg) centered at the
position of LHAASO J2108+5157 above 10 GeV, which is used to limit the
10 GeV-1 TeV emission associated with LHAASO J2108+5157."
From
Kar & Gupta (2021):
- "In this paper we have selected two ultra-high energy photon sources
LHAASO J2108+5157 and LHAASO J0341+5258 which are associated with
giant molecular clouds, but no powerful pulsar or supernova remnant
has been detected in their vicinity. We have proposed a scenario
where shock accelerated electrons and protons are injected in the
local environment of these sources from past explosions, which
happened thousands of years ago. We show that the observed ultra-high
energy photon flux can be explained with the secondary gamma rays
produced by the time evolved relativistic electron and proton spectra"
From
Cao et al. (2021):
- No source is identified as a possible origin.
Potential TeV Counterparts:
From
Cao et al. (2021):
- There are no nearby TeV sources (i.e. within 1 deg of the centre of the LHAASO source).
Pevatron:
From
Mitchell (2021):
- this source is included in a list of Galactic sources currently known
to produce gamma-ray emission above 100 TeV.
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: LHAASO
-
Are Kronberger 80 and/or Kronberger 82 regions PeVatron candidates for LHAASO J2108+5157?
Gupta, Akash et al., arXiv e-prints parXiv:2504.15446 (2025) [LINK]
-
uGMRT observation of the unidentified PeVatron candidate LHAASO J2108+5157
Krishna Mahanta, Gunindra et al., arXiv e-prints parXiv:2412.14224 (2024) [LINK]
-
The First LHAASO Catalog of Gamma-Ray Sources
Cao, Zhen et al., ApJS 271 p25 (2024) [LINK]
-
Detection of a new molecular cloud in the LHAASO J2108+5157 region supporting a hadronic PeVatron scenario
de la Fuente, Eduardo et al., arXiv e-prints parXiv:2303.05712 (2023) [LINK]
-
Supernova connection of unidentified ultra-high-energy gamma-ray source LHAASO J2108+5157
De Sarkar, Agnibha, MNRAS 521 pL5-L10 (2023) [LINK]
-
Multi-wavelength study of the galactic PeVatron candidate LHAASO J2108+5157
Abe, S. et al., arXiv e-prints parXiv:2210.00775 (2022) [LINK]
-
Observation of the galactic PeVatron candidate LHAASO J2108+5157 with the Large-Sized Telescope for Cherenkov Telescope Array
Jurysek, Jakub et al., arXiv e-prints parXiv:2212.02123 (2022) [LINK]
-
Ultrahigh-energy photons up to 1.4 petaelectronvolts from 12 gamma-ray Galactic sources
Cao, Z., Aharonian, F. A., An, Q., et al., Nature 594, pages 33–36 (2021) [LINK]
-
Strong constraints on Lorentz violation using new gamma-ray observations around PeV
Chen, Liang et al., arXiv e-prints parXiv:2105.07927 (2021) [LINK]
-
Constraints on Hadronic Contribution to LHAASO Sources with Neutrino Observations
Huang, Tian-Qi and Li, Zhuo, arXiv e-prints parXiv:2105.09851 (2021) [LINK]
-
Ultrahigh-energy photons from LHAASO as probes of Lorentz symmetry violations
Li, Chengyi and Ma, Bo-Qiang, arXiv e-prints parXiv:2105.07967 (2021) [LINK]
-
Discovery of the Ultra-high energy gamma-ray source LHAASO J2108+5157
The LHAASO collaboration, arXiv e-prints parXiv:2106.09865 (2021) [LINK]
-
Status of Ground-based and Galactic Gamma-ray Astronomy
Mitchell, A.M.W., arXiv e-prints parXiv:2109.13753 (2021) [LINK]
-
The Hunt for Pevatrons: The Case of Supernova Remnants
Cristofari, P., arXiv e-prints parXiv:2110.07956 (2021) [LINK]
-
Ultra-high Energy Gamma-rays from Past Explosions in our Galaxy
Kar, Alokanananda and Gupta, Nayantara, arXiv e-prints parXiv:2112.08757 (2021) [LINK]
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