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Notes for object MRK 0421

17 note(s) found in NED.

1. 2004ApJ...607..309I
Re:MRK 0421
Markarian 421.-The closest HVC to this BL Lac sight line is Complex M,
several degrees away. N V column densities are low but not undetected.

2. 2003ApJS..146....1W
Re:MRK 0421
Mrk 421.-The high positive velocity wing on the O VI profile is not
clearly separated from the Galactic component. In several nearby
directions such a wing is also seen, but with a clearer separation:
at 95 km s^-1^ toward HS 1102+3441 (4deg away), at 100 km s^-1^ toward
PG 0947+396 (14deg away), and at 115 km s^-1^ toward PG 1116+215 (18deg
away). Toward Mrk 421 the wing extends rather far and the separation was
placed at 100 km s^-1^. The wing is rather weak, however: 37 +- 11 +- 29
Both the O VI {lambda}1031.926 and the O VI {lambda}1037.617 lines can
be measured. In the velocity range -130 to 100 km s^-1^ the ratio
N(1037)/N(1031) is 1.60 +- 0.18.
The Leo Spur (v = 620 +- 160 km s^-1^) is sampled by this sight line,
but no intergalactic absorption is apparent.

3. 2003A&A...400...95N
Re:RGB J1104+382
1104+382: This object is discussed in more detail by Nilsson et al.
(1999a). The bright companion galaxy was masked from the fit, but
its outer parts may still be affecting the results. Gorham et al.
(2000) find the companion to be a spiral with an unresolved nucleus.

4. 2002MNRAS.329..877C
Re:GB6 J1104+3812
74-spectrum in Marcha et al. (1996).

5. 2002AJ....124..675C
Re:UGC 06132
CfA BL Lac object (Huchra & Burg 1992), Mrk 421. Bent triple radio
source, 1.49 GHz C-array image in Machalski & Condon (1985).

6. 2001ApJ...552..508G
Re:MRK 0421
1101+38 (Mkn 421). - This BL Lac source was studied in detail by
Piner et al. (1999). We presented a VLBA image in Giovannini et al. (1999a)
and a more detailed paper is in preparation. The core dominance for this
source is low (to be a BL Lac) even if we take into account the core
variability (Piner et al. 1999). The presence of proper motion is
uncertain: from our data we derive a possible proper motion of ~1.5c
(Giovannini et al. 2001, in preparation), while Piner et al. (1999) found
subluminal proper motions (or no motion at all), and Marscher (1999) found
a proper motion with an apparent velocity of the order of 2c-3c.
Taking into account the jet/counterjet ratio and the core dominance,
we can have (1) a high-velocity jet, but in this case the angle with
respect to the line of sight should be near 20^deg^; and (2) a jet
oriented at a small angle (~5^deg^) with {beta} as low as 0.9. In either
case we have a low Doppler factor. If we want to reconcile this result
with the high Doppler factor requested by gamma-ray and variable emission,
we need (1) a large change in the jet orientation from the tetraelectron
volt to the radio emission region or (2) a large decrease of the jet
velocity from the tetraelectron volt to the radio emission region. Given
the radio morphology of the parsec-scale jet with its diffuse emission,
both cases 1 and 2 are probably present.

7. 2000MNRAS.318..827M
Re:MRK 0421
4.1.14 1101+3828 (Markarian 421)
Machalski & Condon (1985) give a VLA C-configuration map at 1.4 GHz, with
a resolution of 15 arcsec, which shows this source to have a compact core
surrounded by a faint envelope with a largest angular size of 3 arcmin at
a position angle of ~-60^deg^. Xu et al. (1995) give a 5 GHz tapered VLBI
map, with a resolution of 11 x 8 milliarcsec, showing a compact core with
a complex 0.1 arcsec jet at position angle ~-60^deg^.
Zhang & Baath (1990, 1991) present VLBI maps made at 5 and 22 GHz. The
5-GHz maps (resolution 1 milliarcsec) show a compact core with a smooth
jet of length 7 milliarcsec at a position angle of -45^deg^; the 22-GHz
maps (resolution 0.15 milliarcsec) show only an unresolved core. They also
give a 5-GHz Multi-Element Radio-Linked Interferometer Network (MERLIN)
map (resolution 65 milliarcsec), which shows knots up to 2.2 arcsec away
from the core, in the direction of the jet. The source is clearly resolved
by the CLFST at 151 MHz; its compact core is bright enough to be
responsible for the variability at this frequency. The core is also
variable at high frequencies (e.g. Seielstad et al. 1983).

8. 2000A&AS..143..357K
Re:MRK 0421
Mrk 421 (Markarian & Lipovetsky 1972) has shown strong and rapid
TeV-outbursts several times (e.g. Schubnell et al. 1996; Petry et al.
1996). Our data and analysis of the optical behaviour of Mrk 421 are
presented by Tosti et al. (1998a) and hence only the light curve is
shown (Fig. 10).

9. 2000A&A...362..871C
Re:MRK 0421
1101+38: This source is associated with the BL Lac object Mrk 421. Not
surprisingly it is dominated by its bright unresolved nucleus which
produces strong diffraction spikes. Nonetheless a smooth elliptical host
galaxy is clearly visible.

10. 1999ApJS..121..131F
Re:MRK 0421
This object is found to have nebulosity with a redshift of 0.0308 by
Ulrich et al. (1975). A large optical variation of 4.6 mag was observed
(Stein, O'Dell, & Strittmatter 1976).The observed optical, infrared, and
radio polarizations are, respectively, 0%-7.9% (Rieke et al. 1977),
2%-4%(CH84), and 3.7% (Wardle 1978). (J-K) is correlated with(J-H):
(J-K)=0.72(J-H)+0.69 with r=0.68 and p=6.1x10^-4^. (H-K) shows an
anticorrelation with (J-H): (H-K)=-0.68(J-H)+0.94 (p=6.0x10^-3^). For
(J-K) and (H-K), it is hard to draw a definite conclusion, as shown in
Figure 11i. No definite color index-magnitude relation can be obtained.
The infrared variation found here is much smaller than the variation in
the optical band.

11. 1998AJ....115.1295K
Re:MRK 0421
1101+384.--Mrk 421 is the closest known BL Lac object. It is one of the
brightest gamma-ray sources in the sky, which has also had a strong TeV flare in
1994 May (Macomb 1995) and again in 1996 May (Zweerink et al. 1997).

12. 1998A&AS..130..305V
Re:MRK 0421
3.3 Mkn 421
Star 1 of our photometric sequence corresponds to that calibrated in the UBV
bands by Veron & Veron (1976); while the V magnitudes are in agreement, we find
a B magnitude which is fainter by 0.10 mag.

13. 1997A&AS..121..119V
Re:MRK 0421
3.7. Mkn 421 (1101+384)
Miller (1975) reports the light curve of Mkn 421 in the B band from 1899 to
1975. The main features are: the presence of a luminosity maximum on January
19, 1934, when the source reached B=11.6; the high luminosity state shown in
1901, 1916, and 1936, with B<12.5; the fast brightness decline of 1.6 mag in 16
days observed in January 1942. The maximum magnitude variation over the
considered period was {DELTA}B=4.7. According to Xie et al. (1988), a
variability time scale of 2.5 hours can be inferred (on January 13, 1986 a 1.4
mag increase in the B band was registered in that time), from which the authors
estimate the mass of the Mkn 421 black hole to be about 1.810^7^ M_sun_. More
recently, another flare was announced by Hurst (1992), who observed a 0.9 mag
increase in the V band in about 40 days. Mkn 421 was the first BL Lac object to
be revealed in the {gamma} band; its {gamma} flux is however weak. It is also
the only AGN, besides Mkn 501, that was detected at TeV energies by the Whipple
Observatory High Resolution Atmospheric Cerenkov Camera (Kerrick et al. 1995).
In particular, a flare at TeV energies was registered in May 1994; in the same
period the ASCA satellite detected a high X-ray flux, while EGRET did not
observe a flux change and the International Ultraviolet Explorer (IUE)
satellite measured a normal ultraviolet (UV) flux. Another multifrequency
campaign was performed in April-May 1995 when observations by the Whipple and
ASCA observatories showed a high state in both the energy bands (Takahashi et
al. 1995; Buckley et al. 1995).
A photometric sequence was calibrated by Veron & Veron (1975) in the B band,
but all their stars (except Star 1) are too far from the source to be included
in our frames. Therefore, the data in Tables 17 and 18 and in Figs. 14 and 15
are expressed as magnitude differences with respect to the minimum value
The maximum magnitude variation that we detected is about 0.4 in both the R and
B bands, the steepest variation being 0.19 mag in 1 day (R band). The box in
Fig. 14 shows the EGRET pointing period.

14. 1996ApJS..103..109W
Re:[HB89] 1101+384
1101+384 (Mrk 421).--This famous BL Lac object lies within 3' of a very bright
star, requiring us to limit exposure times to 20 s only. Further, none of our
images were obtained in photometric conditions, so absolute quantities could
not be obtained. Ulrich (1989) gives several references for previous studies
of this object and its M_r_ = -22.7 elliptical host galaxy. The apparently
large core offset of the isophote just above sky level is spurious, owing to
the presence of this very bright star.

15. 1995ApJS..100...37G
Re:MRK 0421
This blazar (Angel & Stockman 1980; Maccagni et al. 1989; Burbidge &
Hewitt 1992) has been classified as an XBL object (Giommi et al. 1990;
Hewitt & Burbidge 1993). It was observed on many epochs with EXOSAT and
IUE between 1984 and 1985 (George, Warwick, & Bromage 1988a; Edelson et
al. 1992). X-ray spectra of this blazar were fitted using a power-law
plus absorption model, and the fitting parameters are listed in Table 3.
This model fitted all the spectra well, except for three spectra of this
source when it was in a brighter state (1984 days 337, 338, and 340).
Next, we have used other models, mentioned in Section 4.1, to fit the
three spectra. From F-test analysis we find that, among all these models,
the power-law plus absorption plus high-energy cutoff and the power-law
plus absorption plus absorption-edge models fit best with the three
spectra, and these two models are highly significant compared with the
simple power-law model ({DELTA}_x^2^_> 15, which is significant at better
than the 99.9% level. Results of the fit parameters are listed in Tables
4B and 4C, respectively. Values of N_H_ listed in Tables 3, 4B, and 4C
suggest that no intrinsic absorption is present in Mrk 421. It has
displayed rapid and correlated variability of the ME count rate with the
hardness ratio, which was also noted by Giommi et al. (1990). Derived
values of F and ME fluxes (Table 3) are also correlated (George et al.
1988a). Simultaneous observations of radio through X-rays were used to
construct the multifrequency spectrum of Mrk 421 (Makino et al. 1987),
and it can be fitted by a single parabolic curve (Fig. 4e). The presence
of the blue emission bump can also be seen in this figure.

16. 1993MNRAS.260...77P
Re:MRK 0421
RE 1104 + 381. Identified with the BL Lac object Mrk 421. The DC white
dwarf also in the EUV source error circle is probably too cool to be

17. 1973UGC...C...0000N
Re:UGC 06132
Paired with UGC 06140 at 3.2, 78

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