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Observation Date (UT) Observation Lat

Canonical Name:2HWC J1953+294
TeVCat Name:TeV J1953+294
Other Names:VER J1952+293
DA 495
G65.7+1.2
3FGL J1951.6+2926
1WGA J1952.2+2925
1LHAASO J1952+2922
Source Type:PWN
R.A.:19 53 02.4 (hh mm ss)
Dec.:+29 28 48 (dd mm ss)
Gal Long: 65.85 (deg)
Gal Lat: 1.07 (deg)
Distance:
Flux: (Crab Units)
Energy Threshold: GeV
Spectral Index:2.78
Extended:No
Discovery Date:2017-02
Discovered By: HAWC
TeVCat SubCat:Default Catalog

Source Notes:

Source Position:
From Abeysekara et al. (2018):
VERITAS position:
- R.A. (J2000): 19h 52m 15s +/- 9s(stat)
- Dec. (J2000): 29d 23' +/- 01'(stat)
- "assuming that the spatial distribution of the emission follows a
simple 2D-Gaussian distribution"
From Abeysekara et al. (2017):
HAWC position:
- R.A. (J2000): 298.26 deg (= 19h 53m 02.4s)
- Dec. (J2000): +29.48 deg (= +29d 28' 48'')
- the statistical uncertainty on the position is 0.24 deg
- the systematic uncertainty on the position is 0.1 deg

Distance:
From Abeysekara et al. (2018):
- "The distance to DA 495 is estimated to be 1.0 +/- 0.4 kpc based on
H I absorption measurements (Kothes et al. 2008)."

Source Extent:
From Abeysekara et al. (2018):
The best-fit sigma value of the 2D-Gaussian:
- 0.14 +/- 0.02 deg (stat)
- "The extension of the PWN is 25′ (Kothes et al. 2008) in radio and
approx. 40′′ in X-ray (Arzoumanian et al. 2008). The detected TeV
extension by VERITAS matches well with the radio extension."
From Abeysekara et al. (2017):
- "This source is found in the point search with a TS value of 30.1."

Spectral Properties:
From Abeysekara et al. (2018):
The flux measured by VERITAS is well described by a power-law distribution:
- spectral index: 2.65 +/- 0.49(stat)
... which is in good agreement with the index measured by HAWC (below)
From Abeysekara et al. (2017):
- spectral index: 2.78 +/- 0.15(stat) +/- 0.2(syst)

Flux:
From Abeysekara et al. (2018):
- "the flux normalization value at 1 TeV measured by VERITAS is
2.84 +/- 0.54(stat) x10e-13 cm-2 s-1 TeV-1, about seven times lower
than the extrapolated flux value of HAWC's measurement to 1 TeV,
1.86 e10-12 cm-2 s-1 TeV-1. The difference between the two
measurements is significant at the level of 2.4 sigma when considering
only statistical errors."
- "Drawing firm conclusions about the discrepancy between the VERITAS
and HAWC observations in this field of view is challenging because of
the relatively weak signals (TS of 25-30) of the sources reported in
the 2HWC catalog. Further detailed study with larger HAWC exposure and
advanced analysis including multi-source likelihood analysis will be
necessary to understand the discrepancy"
- "We did not detect gamma-ray emission from 2HWC J1953+294 with the
Fermi-LAT analysis. The upper limit was obtained by assuming the
source extension to be similar to the extension of radio emission from
DA 495. The upper limt at the 99% confidence level is:"
- 8.17 x10e-11 cm-2 s-1 with an assumption of spectral index of 2.78
- 8.00 x10e-11 cm-2 s-1 with an assumption of spectral index of 2
"Assuming that the spectral index measured by HAWC will not change
down to 10 GeV, the upper limit we calculated disagrees with HAWC's
flux estimation at a confidence level of 85%."

Source Association:
From Coerver et al. (2019):
- The authors present high-energy X-ray observations of this source
from NuSTAR combined with archival Chandra and XMM-Newton
observations.
- They performed analytical modeling to test leptonic and hadronic
emission scenarios.
- "The leptonic models can explain the broadband emission, but also
imply a diffuse X-ray nebula of similar extent to the radio and TeV
nebulae, which cannot be confirmed by our observations."
- "The hadronic models can simultaneously explain the spectrum and the
spatial extent in all wavelengths; however, we need a very high
magnetic field strength pervading the radio and TeV nebulae and a
surprisingly high particle kinetic energy."
- "These requirements deepen the mystery of the physical nature of DA 495.
Future observations in radio to infrared bands and spatially resolved
gamma-rays can further constrain the physical conditions and radiation
mechanisms in DA 495."
From Abeysekara et al. (2018):
- "The likely counterpart of 2HWC J1953+294 and VER J1952+293 is the
PWN DA 495."
- "The implied blackbody temperature and luminosity, measured by
Chandra, suggest that the central object is an isolated neutron
star. Together with the extended emission surrounding the compact
object, this confirms the PWN interpretation of the source
(Arzoumanian et al. 2004, 2008)."
From Abeysekara et al. (2017):
"In this region, two sources are found nearby in the point source
search: 2HWC J1953+294 and 2HWC J1955+285, none of which has previous
TeV detection. After the HAWC discovery of 2HWC J1953+294, VERITAS
observed this source for 37 hours and confirmed the existence of the
TeV source. The VERITAS observations of this source will be continued
during the 2016–2017 season (Holder et al. 2017). 2HWC J1953+294 is
located at 0.2 deg from the pulsar wind nebula DA 495, which is
associated with the supernova remnant G65.7+1.2. It is likely that the
3FGL J1951.6+2926 is associated with the central pulsar of this system
(Karpova et al. 2015). A joint analysis of this region with Fermi-LAT,
VERITAS, and HAWC data is ongoing"
From Holder et al. (2017)
- "Dedicated VERITAS observations have also been performed this summer
of another of the preliminary HAWC source candidates, 2HWC J1953+294.
The VERITAS dataset in this case totals 37 hours, and reveals a
statistically significant gamma-ray source located within the HAWC
source contours. The emission is coincident with the PWN DA 495 (G65.7+1.2)
and its central object, WGA J1952.2+2925. Karpova et al. (2015)
have argued that, despite the lack of observed pulsations, the
Fermi-LAT source 3FGL J1951.6+2926 is likely the counterpart of the
pulsar in this system, and not of the PWN. The addition of VHE
measurements from HAWC and VERITAS to the broadband SED will soon help
to determine the nature of the high energy emission from this
interesting object."


Seen by: HAWC, VERITAS, LHAASO
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