Central Bureau for Astronomical Telegrams
IAUC 2731: X-RAY FLARE FROM YZ CMi; IAUC 2730; LUNAR Occn OF THE CRAB NEBULA IN LOW ENERGY X-RAYS; LUNAR Occns OF X-RAY SOURCES; BINARY PULSAR
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 2732
Circular No. 2731
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Cable Address: SATELLITES, NEWYORK
Western Union: RAPID SATELLITE CAMBMASS
X-RAY FLARE FROM YZ CANIS MINORIS
J. Heise, A. C. Brinkman, J. Schrijver, R. Mewe, E.
Groneschild and A. Den Boggende, Space Research Laboratory,
Utrecht; J. Grindlay, H. Schnopper, E. Schreier and H. Gursky,
Center for Astrophysics, Harvard and Smithsonian Observatories; and
D. Parsignault, American Science and Engineering, report: "On Oct.
19d20h05m06s UT an x-ray burst from the direction of the flare star
YZ CMi was detected in the soft (below 0.28 keV) and medium energy
(0.6 to 8 keV) detectors of the Utrecht instrument on board ANS,
the Astronomical Netherlands Satellite. The total duration of the
soft burst was 6 min with a rise time of 28 seconds, whereas the
duration in the medium energy range was approximately 1.5 min. The
count rates at the flare peak were factors of 3.5 and 3 above
background for the soft detector and medium energy detector,
respectively. The total flux from YZ CMi suggests an energy release of
1.0 +/- 0.1 x 10**32 erg in the low energy range and 2.8 +/- 0.4 x 10**32
erg in the medium energy range; and peak luminosities of 6 +/- 1 x
10**29 erg/s and 3.9 +/- 0.8 x 10**30 erg/s, respectively. No increase
in the count rate was found in the Cambridge detector (2 to 20 keV)
on board ANS, although it has comparable sensitivity, and a significant
flux was observed in the Utrecht detector above 3.5 keV. It
is probable that the satellite pointing was such that the source
was in the 35' field of the Utrecht detector but not in the 13'
field of the Cambridge hard x-ray experiment. Failure to detect an
increase in the Cambridge detector excludes the possibility that
this was a particle event. The measurement was obtained during a
period of low and constant background above the earth's equator. A
total of 22 000 seconds of observations composed of 10-15 min
pointings on YZ CMi have been examined. Optical and radio coverage
was available during some of the ANS observations though unfortunately
not, to our knowledge, during the period of the x-ray burst.
"A similar observing program to search for x-ray flares will
be conducted on UV Cet during 1975 Jan. 3-9. Interested observers
may obtain the times of ANS observations by contacting either Dr.
J. Heise (Space Research Laboratory, Utrecht, The Netherlands) or
Dr. J. Grindlay (Smithsonian Astrophysical Observatory, Cambridge,
MA 02138, U.S.A.)."
IAUC 2730
The number, which was 2730, was inadvertently omitted from the
last Circular, issued on Friday, Dec. 13.
LUNAR OCCULTATION OF THE CRAB NEBULA IN LOW ENERGY X-RAYS
R. S. Wolff, H. Kestenbaum, W. Ku and R. Novick, Columbia
Astrophysics Laboratory, write: "Preliminary results of a low-energy
(1.5 to 20 keV) rocket observation of the lunar occultation of the
Crab Nebula on Nov. 3 (at emersion, with the lunar limb at p.a.
255o) show that 80 percent of the flux between the western limb of
the Nebula and the pulsar is contained within an angular range of
36". There is evidence for a possible small energy dependence in
the x-ray distribution. When combined with the observations on
Aug. 13, the results show an elongation of the x-ray emission along
the direction of the maqnetlc field of the Nebula. There is a
sudden jump in the counting rate when the pulsar appears and x-ray
pulses are clearly detected. Examination of the data at pulse
phases when the pulse profile indicates no pulsed emission suggests
the presence of a compact continuously emitting x-ray source at or
near the pulsar. Observers planning measurement of future occultations
are encouraged to contact either Dr. R. Wolff (212-280-3263)
or Dr. H. Kestenbaum (212-280-2819) of the Columbia Astrophysics
Laboratory (538 West 120th Street, New York, NY 10027, U.S.A.) for
further details."
LUNAR OCCULTATIONS OF X-RAY SOURCES
Mr. L. V. Morrison writes: "The table below gives the first
and last dates on which lunar occultations of x-ray sources will
occur during the next few years. The letters following the dates
give the poles from which the first and last occultations will be
visible. Further details may be obtained by writing to me at the
address: H.M. Nautical Almanac Office, Royal Greenwich Observatory.
Herstmonceux Castle, Hailsham, East Sussex BN27 1RP. England."
Source First Last
3U 0531+21 = Crab (current) N 1975 Aug. 31 S
3U 1758-20 = GX9+1 (current) S 1976 Aug. 6 N
3U 0254+13 = Abell 401 1977 July 10 N (beyond 1978) S
3U 1811-17 = GX13+0 1977 Aug. 24 S (beyond 1978) N
3U 1611-15 = Sco X-1 1978 Mar. 1 S (beyond 1978) N
3U 1728-16 = GX8+9 1978 Mar. 3 S (beyond 1978) N
BINARY PULSAR
B. Jones, D. Graham and R. Wielebinski, Max Planck Institut
fur Radioastronomie, Bonn, report: "We have detected the binary
pulsar at 1420 MHz using the 100-m telescope. The average flux
density is 0.2 mJy, and the pulse width is less than 2 ms. The
variation in period agrees with the binary system elements."
1974 December 18 (2731) Brian G. Marsden
Read IAUC 2732
Our Web policy. Index to the CBAT/MPC/ICQ pages.
