| Canonical Name: | VER J0521+211 |
| TeVCat Name: | TeV J0521+211 |
| Other Names: | RGB J0521.8+211 |
| Source Type: | IBL |
| R.A.: | 05 21 45 (hh mm ss) |
| Dec.: | +21 12 51.4 (dd mm ss) |
| Gal Long: | 183.60 (deg) |
| Gal Lat: | -8.71 (deg) |
| Distance: | |
| Flux: | 0.092 (Crab Units) |
| Energy Threshold: | 200 GeV |
| Spectral Index: | 3.44 |
| Extended: | No |
| Discovery Date: | 2009-10 |
| Discovered By: | VERITAS |
| TeVCat SubCat: | Default Catalog |
Source Notes:
Source position and its uncertainty:
The source position was updated on 131002.
From
The VERITAS Collaboration (2013):
- R.A. (J2000): 05h 21m 45s
- Dec. (J2000): +21d 12' 51.4"
- Statistical uncertainty of 14"
- Systematic uncertainty of 25"
From
Ong et al. (2009):
- R.A. (J2000): 80.48
- Dec. (J2000): +21.19
- Positional uncertainty: about 0.05 deg
The observations were motivated by the identification of a high energy (>30 GeV)
source at this position in the public Fermi-LAT data. This position is also consistent, within
errors, with the position of the radio-loud active galaxy RGB J0521.8+2112, detected in
the ROSAT all-sky X-ray survey and included in the RASS-Green Bank catalog, for which the
redshift is unknown.
Spectral Properties:
From
The VERITAS Collaboration (2013):
- Spectral index: 3.44 +/- 0.20(stat) +/- 0.30(syst)
From
Errando et al. (2011):
- Spectral index: 3.44 +/- 0.20
From
Benbow et al. (2011):
- Spectral index: 3.47 +/- 0.19
Flux:
From
The VERITAS Collaboration (2013):
- The source is strongly variable on a daily timescale across all wavebands from optical to TeV
- The time-averaged photon flux above 200 GeV corresponds to 0.092 +/- 0.006 Crab
- The peak flux corresponds to approx. 0.3 times that of the steady Crab Nebula flux
The flux from this object has been found to be variable (see references).
Classification:
Initially, this source was classified as an AGN of unknown type in
TeVCat. It has been updated (121113) to an IBL based on its
classification in the
Fermi
2nd AGN Catalog (Ackermann et al. 2012)
Distance:
On 180206 the redshift quoted in TeVCat was changed from z = 0.108 to unknown due
to the results of
Paiano et al. (2016) and
Archambault et al. (2013).
From
Sahu et al. (2023):
- "In the framework of the photohadronic model and using three
different extragalactic background light (EBL) models, we analyse
seven independent VHE spectra of VER J0521+211 and determine the
limiting values on its redshift."
- "It is observed that the photohadronic scenario provides excellent
fits to the reported observations."
- "It is further observed that the photohadronic scenario, along with
the EBL model of
Domínguez et al. (2011), puts the most restrictive limits on
the redshift z of VER J0521+211: 0.29 ≤ z ≤ 0.31 from the confidence
level (CL) intervals at 2 sigma, or a more conservative 0.28 ≤ z ≤ 0.33
at 3 sigma."
From
Paiano et al. (2016):
The authors report on a spectroscopic campaign carried out at the 10 m
Gran Telescopio Canarias for a sample of 22 BL Lac objects detected
(or candidates) at TeV energies, aimed at determining or constraining
their redshifts.
- "On the basis on a weak emission line at 5940˚A attributed to
[N II] 6583 Ang,
Shaw et al. (2013) proposed this source to be at
z = 0.108. This feature was not confirmed by
Archambault et al. (2013)
that reports a featureless spectrum. We do not confirm the redshift
of the source, which therefore is still unknown, setting a lower limit
of z > 0.18."
From
The VERITAS Collaboration (2013):
- "Optical spectroscopic observations were made on three occasions at
the 2.4 m Hiltner telescope of the MDM Observatory, using three
different CCD spectrographs. The optical spectra are devoid of
intrinsic emission or absorption lines and stellar continuum emission
in the wavelength range 4000–7500 Angstroms, classifying the source as
a BL Lac-type blazar but not revealing its redshift."
- "Recently published observations with the Low Resolution Imaging
Spectrograph at the W. M. Keck Observatory (
Shaw et al. 2013) show a
weak emission feature identified as [N II]lambda lambda 6548, 6583,
which would indicate a redshift of z = 0.108."
- "Although this feature cannot be identified in the MDM spectra, the
measurements are not in conflict given the lower level of continuum
emission present in the spectrum by
Shaw et al. 2013 and the higher
sensitivity of Keck."
Seen by: VERITAS
-
Constraining the redshift of BL Lac VER J0521+211
Sahu, Sarira et al., MNRAS 522 p5840-5847 (2023) [LINK]
-
Multiwavelength Observations of the Blazar VER J0521+211 during an Elevated TeV Gamma-Ray State
Adams, C.B. et al., ApJ 932 p129 (2022) [LINK]
-
Axion effects on gamma-ray spectral irregularities with AGN redshift uncertainty
Li, Hai-Jun and Chao, Wei, arXiv e-prints parXiv:2211.00524 (2022) [LINK]
-
VERITAS detection of unprecedented gamma-ray flare from the blazar VER J0521+211
Quinn, J. for the VERITAS Collaboration, The Astronomer's Telegram 13522 p1 (2020) [LINK]
-
Testing two-component models on very-high-energy gamma-ray emitting BL Lac objects
MAGIC Collaboration et al., arXiv e-prints parXiv:2006.04493 (2020) [LINK]
-
Search for Magnetically Broadened Cascade Emission From Blazars with VERITAS
VERITAS Collaboration et al., ArXiv e-prints p (2017) [LINK]
-
On the redshift of TeV BL Lac objects
Paiano, S. et al., ArXiv e-prints p (2017) [LINK]
-
Time-resolved multiwavelength observations of the blazar VER J0521+211 from radio to gamma-ray energies
Prokoph, H. et al., ArXiv e-prints p (2015) [LINK]
-
Discovery of a new TeV gamma-ray source: VER J0521+211
VERITAS Collaboration et al., ArXiv e-prints p (2013) [LINK]
-
Fermi LAT Detection of a Bright GeV Flare from VER 0521+211
Buson, S. on behalf of the Fermi LAT Collaboration, The Astronomer's Telegram 5472 p1 (2013) [LINK]
-
Observations of low- and intermediate-frequency-peaked BL Lacs above 100 GeV with VERITAS
Errando, M. for the VERITAS Collaboration, ArXiv e-prints p (2013) [LINK]
-
VHE Blazar Discoveries with VERITAS
Wystan Benbow for the VERITAS Collaboration, ArXiv e-prints p (2011) [LINK]
-
Discovery and identification of two gamma-ray blazars at low galactic latitude with VERITAS
Errando et al., ArXiv e-prints p (2011) [LINK]
-
VERITAS discovery of a new VHE Gamma-ray Source, VER J0521+211
Ong, R. A. on behalf of the VERITAS Collaboration, ATel 2260 [LINK]
-
VERITAS reports a High Gamma-ray Flux from VER J0521+211
Ong, R. A. on behalf of the VERITAS Collaboration, ATel 2309 [LINK]
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