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Observation Date (UT) Observation Lat

Canonical Name:PG 1553+113
TeVCat Name:TeV J1555+111
Other Names:1ES 1553+113, HESS J1555+111
Source Type:HBL
R.A.:15 55 44.7 (hh mm ss)
Dec.:+11 11 41 (dd mm ss)
Gal Long: 21.92 (deg)
Gal Lat: 43.96 (deg)
Distance: z=0.5
Flux:0.034 (Crab Units)
Energy Threshold:300 GeV
Spectral Index:4.5
Discovery Date:2006-03
Discovered By: H.E.S.S.
TeVCat SubCat:Default Catalog

Source Notes:

Source position and its uncertainty:
From Aharonian et al. (2008):
- RA (J2000): 15 55 44.7 +/- 3.0s(stat) +/- 1.3s(syst)
- Dec (J2000): +11 11 41 +/- 53"(stat) +/- 20"(syst)

The distance quoted for this source in TeVCat is the mean of the
values proposed by Danforth et al. (2010), which is also in good
agreement with the value obtained by Abramowski et al. (2015).
Details below.
From Nicastro (2018):
- "In this contribution we first summarize the fidings from our recent
discovery of two intervening OVII-bearing absorption systems along the
line of sight to the blazar 1ES 1553+113, at redshifts z = 0.3551 and
z = 0.4339"
From Abramowski et al. (2015):
- "The most probable redshift found with this method is z = 0.49 +/- 0.04,
in good agreement with the independent measure of Danforth
et al. (2010)
From Aliu et al. (2014):
- "When accounting for EBL evolution using the approach described (in
reference above), the 95% confidence level upper limit on the redshift
of PG 1553+115 is z<=0.62"
From Landoni et al. (2014):
- "We secured optical and near-infrared medium-resolution spectra of
four bright BL Lac objects of unknown redshift using the spectrograph
X-Shooter at the ESO-VLT."
- "In spite of the high quality of the spectra and the extended
spectral range of the observations, we have not detected intrisic
spectral features for these sources. However, we are able to provide
strigent lower limits to their redshift." (For two TeV sources: PG
1553+113 and H 1722+119)
- For PG 1553+113 they inferred z > 0.30
From Danforth et al. (2010):
- This distance estimate constrains the redshift to z > 0.400,
specifically putting it in the range: 0.43 - 0.58. We quote the mean
of this z for this source's distance in TeVCat.
From Yang & Wang (2010):
- an upper limit of 0.78 is placed on the redshift of this object.

Spectral Properties:
From Abramowski et al. (2015):
- Spectral index: 4.8 +/- 0.2 (stat) +/- 0.2 (syst) (power law; pre-flare)
... a log-parabola model was also fit to the pre-flare data
- Spectral index: 4.9 +/- 0.3 (stat) +/- 0.2 (syst) (power law; flare)
From Aliu et al. (2014):
- Spectral index: 4.33 +/- 0.09
From Benbow et al. (2011):
- Spectral index: 4.41 +/- 0.14
From Aharonian et al. (2008):
- Spectral index: 4.5 +/- 0.3(stat) +/- 0.1(syst)
From Albert et al. (2008):
- Spectral index: 4.1 +/- 0.3

From Aliu et al. (2014):
- Fluxes of between 5.5% and 10.3% of the Crab are reported
From Benbow et al. (2011):
- a flux of 10% that of the Crab is reported
From Aharonian et al. (2008):
- a flux of 3.4% that of the Crab is reported

Information on the jet:
From Lister et al. (2019):
- "We were unable to identify any robust jet features in this BL Lac object."

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