Central Bureau for Astronomical Telegrams
IAUC 4110: MXB 1730-335; 4U 1957+11
The following International Astronomical Union Circular may be linked-to from your own Web pages, but must not otherwise be redistributed (see these notes on the conditions under which circulars are made available on our WWW site).
Read IAUC 4111
Circular No. 4110
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-495-7244/7440/7444
MXB 1730-335
L. Stella, A. N. Parmar and N. E. White, EXOSAT Observatory;
W. H. G. Lewin, Massachusetts Institute of Technology; and J. van
Paradijs, University of Amsterdam, report: "The rapid burster MXB
1730-335 produced 40 type-II, flat-topped bursts during a 16-hr
EXOSAT observation (medium energy; 1-15 keV) on Aug. 28. The burst
intervals varied from ~ 8 min to ~ 1 hr. The brightest bursts
lasted ~ 2 min and had a peak flux of ~ 0.7 Crab (1-10 keV); 13
other bursts were observed that lasted 4-11 min with peak fluxes
of 0.2-0.5 Crab. Substantial persistent emission was detected
between bursts at a level of 0.06 Crab; this persistent emission
pinched off just before and after each burst. This burst behavior
is similar to that observed with Hakucho by Tawara et al. (1982,
Nature 299, 38), who also reported 2-Hz oscillations during two of
63 flat-topped bursts. During the EXOSAT observation quasiperiodic
oscillations (QPO) were observed in six of the 24 brightest (and
shortest) and in all but one of the longer (and fainter) bursts
between frequencies of 2 and 5 Hz. The QPO frequency was
anticorrelated with the peak burst flux, with a power-law slope of -0.9
+/- 0.1. The FWHM was ~ 10 percent of the QPO frequency for the
brightest bursts and ~ 20-30 percent for the longer bursts. When
the QPO were detected, the rms pulsation amplitude was high, up to
11 percent during the longer bursts and ~ 4 percent during the
brightest bursts. Quasiperiodic oscillations (5-20 percent rms
amplitude) were also observed occasionally in the persistent emission
between some of the brighter bursts. In these cases the QPO
frequency changed in an S-shaped pattern from ~ 3 Hz shortly after
a burst to a maximum frequency of ~ 4 Hz and then to ~ 2 Hz in 5-
15 min. During some of the flat-topped bursts the rms amplitude of
the low-frequency noise (in the 0.06-2-Hz range) was ~ four times
smaller than the corresponding QPO rms amplitude."
4U 1957+11
J. R. Thorstensen, Dartmouth College, writes: "I have discovered
a periodic photometric modulation of ~ 0.25 mag full amplitude
in 4U 1957+11. The period is either 0.389 or 0.280 days;
these are daily cycle-count aliases. There were 288 measurements
taken during 11 nights spanning Sept. 2-13 with the McGraw-Hill
Observatory direct CCD in the V band."
1985 September 23 (4110) Brian G. Marsden
Read IAUC 4111
Our Web policy. Index to the CBAT/MPC/ICQ pages.
