Central Bureau for Astronomical Telegrams
IAUC 6998: 1998dq; XTE J1710-281 = 1RXS J171012.3-280754
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Circular No. 6998
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1998dq IN NGC 6754
Brett White, Linden, New South Wales, has reported -- directly
and via R. Evans (Hazelbrook, N.S.W.) and B. Schmidt (Mount Stromlo
and Siding Spring Observatories) -- his visual discovery with a
0.41-m reflector on Aug. 23.4 UT of an apparent supernova located
about 18" west of the nucleus of NGC 6754; the visual magnitude of
the new star was reported by Evans as being 14.3. An image
obtained by T. Dobosz (Nepean Astronomy Centre) on Aug. 24 yielded
an offset of 20" west. Schmidt reports that BVRI CCD images
obtained on the MSSSO 0.76-m telescope by B. Crook on Aug. 23.6
show a new blue object at R.A. = 19h11m23s.78, Decl. = -50o38'25".5
(equinox 2000.0), which is 18".7 west and 5" north of the galaxy
nucleus. SN 1998dq is located about 5" from SN 1998X, is clearly a
new object, and is extremely blue (B-V about 0). SN 1998dq is also
seen on CCD images taken on Aug. 24.6 by A. Gutierrez with the
Mount Stromlo 0.76-m telescope. Comparison with the discovery
images of SN 1998X (cf. IAUC 6847) shows that SN 1998dq is not
present on Mar. 13.9 to a limiting magnitude of R = 18.
XTE J1710-281 = 1RXS J171012.3-280754
C. B. Markwardt, National Research Council and Goddard Space
Flight Center (GSFC); F. E. Marshall and J. Swank, GSFC; and T.
Takeshima, Universities Space Research Association and GSFC,
report: "A transient x-ray source was serendipitously detected with
the RXTE PCA in two slews, first on July 22.0 UT at a level of 24
counts/s, and on Aug. 12.7 at a level of 64 counts/s (per five
PCUs). In subsequent PCA scans on Aug. 19.3, the source had
decreased to 23 counts/s (5 x 10E-11 erg sE-1 cmE-2 over 2-10 keV).
The best-fit position is R.A. = 17h10m12s, Decl. = -28o07'.1
(equinox 2000.0), with a position uncertainty of +/- 2' in R.A. and
+/- 4' in Decl. (90-percent confidence), and it is consistent with
the location of the unidentified source 1RXS J171012.3-280754 of
the ROSAT All-Sky Survey Bright Source Catalogue. The spectrum on
Aug. 19.3 is consistent with either thermal bremsstrahlung (kT = 14
+/- 3 keV) or a power law (photon index 1.8 +/- 0.1), with
interstellar absorption < 2 x 10E22 cmE-2. No spectral lines are
apparent. No short-timescale variability was observed, although
the 400-s pointed observation only provided a 3-sigma upper limit
of 14 percent for the best case of coherent oscillations. Further
observations at other wavelengths are desirable."
(C) Copyright 1998 CBAT
1998 August 26 (6998) Daniel W. E. Green
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