Central Bureau for Astronomical Telegrams
IAUC 6997: 1998dk; 1998dm; SAX J1748.9-2021, MX 1746-20,, NGC 6440
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Circular No. 6997
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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SUPERNOVA 1998dk IN UGC 139
A. V. Filippenko, University of California at Berkeley,
reports that inspection of an uncalibrated CCD spectrum of SN
1998dk (cf. IAUC 6991) obtained on Aug. 24 by C. De Breuck
(Lawrence Livermore National Laboratory) with the 3-m Shane
reflector at Lick Observatory reveals that the object is a type-Ia
supernova close to maximum brightness, with strong Si II lines.
SUPERNOVA 1998dm IN MCG -01-4-44
Filippenko also notes that inspection of an uncalibrated CCD
spectrum of SN 1998dm (cf. IAUC 6993), obtained as above by De
Breuck, reveals that this object is a type-Ia supernova prior to
maximum brightness. The spectrum is unusually red, and the Si II
line near 575 nm seems strong relative to Si II 615-nm, suggesting
that this is a subluminous type-Ia event.
SAX J1748.9-2021, MX 1746-20, AND NGC 6440
J. in 't Zand and J. Heise, Space Research Organization of the
Netherlands (SRON), Utrecht; A. Bazzano and P. Ubertini, Istituto
di Astrofisica Spaziale, CNR, Rome; M. J. S. Smith, BeppoSAX
Science Operation Center (BSOC), Rome, and SRON; J. M. Muller,
BeppoSAX Science Data Center, Rome, and SRON; and V. Torroni, BSOC,
communicate: "During an observation with the Wide Field Cameras on
BeppoSAX on Aug. 22.48-23.19 UT, an x-ray transient and burster was
detected at R.A. = 17h48m52s, Decl. = -20o21'.4 (equinox 2000.0;
99-percent confidence error radius 2'). We designate the source
SAX J1748.9-2021. The centroid is 0'.3 from the center of the
globular cluster NGC 6440, which makes an association very likely.
The average intensities are about 30 mCrab in 2-10 keV and about 45
mCrab in 10-25 keV. On an hourly basis, the source does not show
variability above an upper limit of 20 percent. One x-ray burst
was detected from the same transient, with a peak flux of about 0.7
Crab (2-25 keV), indicating that the transient is a low-mass x-ray
binary. This is the first time that an x-ray transient was seen
coincident with NGC 6440 since December 1971, when MX 1746-20 was
discovered (Markert et al. 1975, Nature 257, 32), which was active
for 1.5-3 months with a peak flux of about 150 mCrab and had a
large 90-percent confidence error box of about 6' by 30' (Forman et
al. 1976, Ap.J. 207, L25). Follow-up observations with the narrow-
field instruments on BeppoSAX and with RXTE have been scheduled."
(C) Copyright 1998 CBAT
1998 August 25 (6997) Daniel W. E. Green
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