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Observation Date (UT) Observation Lat

Canonical Name:1ES 0647+250
TeVCat Name:TeV J0650+250
Other Names:
Source Type:HBL
R.A.:06 50 46.5 (hh mm ss)
Dec.:+25 03 00 (dd mm ss)
Gal Long: 190.28 (deg)
Gal Lat: 11.00 (deg)
Distance:
Flux:0.03 (Crab Units)
Energy Threshold:100 GeV
Spectral Index:
Extended:No
Discovery Date:2011-09
Discovered By: MAGIC
TeVCat SubCat:Newly Announced

Source Notes:

Source position and its uncertainty:
- The source position is taken from NED:
- the reference for the position is Healey et al. (2007):
- R.A. (J2000): 06 50 46.5
- Dec. (J2000): +25 03 00
- the uncertainty ellipse has both semi-maj and semi-min dimensions of 0.15''

Distance:
On 180206 the redshift quoted in TeVCat was changed from z = 0.45 +/- 0.2
to unknown due to the results of Paiano et al. (2016).

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.
- "An optical spectrum of this source, with modest SNR was found
featureless by Schachter et al. (1993), a result later confirmed by a
better spectrum obtained with the Keck telescope by Shaw et al. (2013)."
- "Our GTC higher SNR (∼ 200) spectrum confirms this featureless
behaviour with absorptions at around 4400 Ang and 4880 Ang due to
Diffusing Interstellar bands and at ∼ 6500 ˚A due to water vapor.
On the basis of our spectrum we set a lower limit of z > 0.29."

From Massaro et al. (2015):
- the redshift is listed as uncertain in this paper and no value is
quoted (BZB J0650+2503)

From Shaw et al. (2013):
- the authors obtained spectroscopic measurements on a large sample of
gamma-ray selected BL Lacs
- a featureless spectrum was measured for 1ES 0647+250 (Figure 1.17,
lower right panel) and a redshift limit of z > 0.49 was set for this
object

From Kotilainen et al.(2011):
- the authors report a redshift estimate of z=0.41 +/- 0.06
- "We are able to detect the underlying host galaxy in the
near-infrared. The host galaxy has an H-band magnitude of 16.9 +/- 0.2
and an effective radius of 1.6 arcsec +/- 0.3 arcsec. Using the imaging
redshift method developed by Sbarufatti and collaborators (2005), we
estimate a redshift z = 0.41 +/- 0.06. This redshift is consistent with the
previously reported imaging redshift estimate from the optical i'-band
of z = 0.45 +/- 0.08, and with previously reported lower limits to the
redshift. It agrees with constraints from its gamma-ray emission. "

From Meisner & Romani (2010):
- the authors report a redshift estimate of:
z=0.45 +/- 0.02 (host) +0.09(disp) -0.08(disp)
as part of a search for imaging redshifts for a sample of BL Lac
objects. The estimations provided are based on the analysis of the
host galaxy of the BL Lac objects which the authors state "have been
argued to be standard candles".
Note on the uncertainties (summarised from the text of the paper):
There are two contributions to the full redshift uncertainty. The
first is host measurement uncertainty (denoted as "host" in TeVCat),
including both statistical and systematic photometry errors. In
addition, the claimed 0.5 mag dispersion in the host luminosity leads
to a redshift range. This nearly always completely dominates the
redshift uncertainty and is listed as the second error flag in our
tables (denoted as "disp" in TeVCat).
- the authors note that "while individual redshifts are doubtless
imprecise, the estimates can still be useful for statistical studies
of BL Lac evolution and as a guide to and comparison with other
methods of redshift estimation".

From Sbarufatti et al. (2005):
- the authors use the absolute brightness of the host galaxies of BL
Lacs to estimate their distances. For 1ES 0647+250 they derive a lower
limit on the redshift of z > 0.47. Since only an upper limit is
available for the absolute R magnitude of the nucelus, they assume a
host galaxy absolute magnitude of M_R = -22.9 in order to obtain a
redshift estimate.

From Nilsson et al. (2003):
- 1ES 0647+250 (0650+250) was observed for 900s with the ALFOSC
instrument on the Nordic Optical Telescope (NOT)1 on La Palma in
December 1998. The authors note:
- "As in all previous studies, this object remains unresolved." and
they reference the work of Falomo & Kotilainen (1999) saying that
those authors "note that the tentative redshift 0.203 would lead to a
relatively faint host galaxy."

From Falomo & Kotilainen (1999):
- the authors investigated the properties of the host galaxies of 52
BL Lac objects (HBLs) from the EMSS and Slew samples using a "large
and homogeneous data set of high spatial resolution R-band observations".
- as part of a list of lower limits on the redshift for unresolved BL
Lacs they quote z > 0.3 for 1ES 0647+250.
- they also state:
"A tentative redshift z = 0.203 has been derived for this BL Lac,
which is unresolved in the NOT images taken with very good seeing
(FWHM 0.65''). It is also unresolved in the HST snapshot survey
(Scarpa et al. 1999), who derived an upper limit m(host) >19.1. At
z = 0.203, this corresponds to M(host) >–21.7, i.e. 2 magnitudes
fainter than an average BL Lac host."

From Scarpa et al. (1999):
Our 10-minute HST exposure of this BL Lac shows a bright point-like
object. The image is well exposed and the radial profile can be traced
out to 6 arcsec, to a faint surface brightness, R 26 mag arcsec^2. The
agreement with the PSF model is very good, enabling us to put an
interesting lower limit to the host apparent magnitude m_R > 19.1 mag
Including 0.35 mag of K correction, and conservatively assuming the
host has m_R = 22.7mag, i.e., 1 mag fainter than the median for this
sample, our upper limit corresponds to a minimum distance for the
source of z > 0.3.

From Schachter et al. (1993):
- the authors present in Figure 2d a featureless spectrum for
1ES 0647+250 taken with the MDM 1.3 m and the MMT Red Channel


Seen by: MAGIC, VERITAS
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