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IAUC 6900: 1998bv; XTE J1806-246

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                                                 Circular No. 6900
Central Bureau for Astronomical Telegrams
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SUPERNOVA 1998bv IN HS 1035+4758
     A. Yu. Kniazev and N. Arkhyz, Special Astrophysical
Observatory (SAO), Russian Academy of Sciences; D. Engels,
Hamburger Sternwarte; S. A. Pustilnik and A. V. Ugryumov, SAO; and
J. Masegosa, Institute de Astrofizica de Andalucia, Granada, report
their discovery of a supernova located 3".1 west and 3".7 south of
the emission-line galaxy HS 1035+4758 (R.A. = 10h38m25s.71, Decl. =
+47o42'36".5, equinox 2000.0; redshift z = 0.0050), which is a
typical blue compact dwarf galaxy (size about 20") with strong H II
emission in its central part.  Spectra of the new star (which is
certainly absent on the Digital Sky Survey), obtained on Apr. 6.914
(range 370-610 nm) and 19.774 UT (range 370-740 nm) with resolution
about 0.4 nm, are characteristic to the spectra of type-IIP
supernovae in their transition phase, about 1 to 2 months after
peak brightness.  They show broad emission lines of H-alpha and
H-beta with redshift close to that of host halaxy, and P-Cyg
absorption in Balmer series up to H_7.  Two broad absorptions of
multiplets Fe II (42) 454.9-455.5-nm and Fe II (37) 516.9-nm are
well seen, blueshifted in relative systemic velocity by about 4000
km/s.  The FWZI of H-alpha is 13 500 km/s, and its centroid is
shifted blueward about 120 km/s (Apr. 19) relative systemic
velocity of the galaxy.  Broad emission H-beta is blueshifted by
about 200 km/s on Apr. 6, but redshifted by 300 km/s on Apr. 19.
Broad and strong Balmer absorption lines have central velocities
blueshifted relative to those of broad emission lines by about
5500 km/s; they show a systematic trend of FWHM from 4500 km/s in
H-alpha to 1900 km/s in H-delta.  The magnitude of SN 1998bv,
estimated from the calibrated spectrum of Apr. 6, is B about 17.1;
on Apr. 24, a CCD image yielded B = 17.4, B-V = +0.85.

XTE J1806-246
     R. M. Hjellming, National Radio Astronomy Observatory (NRAO);
A. J. Mioduszewski, Joint Institute for VLBI in Europe and NRAO;
and M. P. Rupen, NRAO, report:  "On May 10.49 UT, a radio source
was observed with the Very Large Array in the field of the x-ray
transient XTE J1806-246 at R.A. = 18h06m50s.72 +/- 0s.04, Decl. =
-24o35'28".6 +/- 0".8 (equinox 2000.0).  This radio source is well
within the error region for the RXTE PCA position reported on IAUC
6891.  On May 10.49 the radio source had flux densities of 0.8 +/-
0.3 and 0.8 +/- 0.2 mJy at 1.43 and 4.86 GHz, respectively.  It was
not present on May 3 and 6, with upper limits of 0.3 mJy at the
same frequencies.  This variability makes the source a candidate
for the radio counterpart of XTE J1806-246."

                      (C) Copyright 1998 CBAT
1998 May 11                    (6900)            Daniel W. E. Green

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