Central Bureau for Astronomical Telegrams
IAUC 6445: 1995N; RX J0720.4-3125
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Circular No. 6445
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
SUPERNOVA 1995N IN MCG -2-38-017
W. H. G. Lewin, Massachusetts Institute of Technology; and
H.-U. Zimmermann and B. Aschenbach, Max-Planck-Institut fur
Extraterrestrische Physik, report: "On July 23, the ROSAT
satellite's HRI detector was pointed toward SN 1995N for a total
exposure of 1331 s. About 3" off the optical position (IAUC 6170,
6386), which is well within the ROSAT error box, a pointlike x-ray
source was detected with very high significance. During the ROSAT
All-Sky Survey in 1990/1991, no x-ray source of similar strength
was observed at that position; we therefore identify this x-ray
source with SN 1995N. The observed rate was 0.0075 +/- 0.0025
count/s. Assuming a galactic hydrogen column density of NH = 0.8 x
10E21 cmE-2, a thermal spectrum with kT about 1 keV, and the
distance to the host galaxy as 24 Mpc, the observed countrate
corresponds to an (unabsorbed) x-ray luminosity of 2-3 x 10E40
erg/s in the ROSAT band (0.1-2.4 keV)."
RX J0720.4-3125
F. Haberl and W. Pietsch, Max-Planck-Institut fur
Extraterrestrische Physik, Garching; C. Motch, Observatoire de
Strasbourg; and D. A. H. Buckley, South African Astronomical
Observatory (SAAO), Cape Town, communicate: "We have discovered
what appears to be an isolated, x-ray-pulsating neutron star that
is accreting matter from the interstellar medium. The object was
found in the ROSAT All-Sky Survey as a soft x-ray source with 1.6
counts/s. A ROSAT observation using the Position Sensitive
Proportional Counter in 1993 revealed a blackbody-like x-ray
spectrum with kT = 75-83 eV, attenuated by little absorption with
a hydrogen column density of 1.3 x 10E20 cmE-2. The best
determined position of R.A. = 7h20m25s.04, Decl. = -31o25'48".4
(equinox 2000.0; uncertainty +/- 2" using a nearby optically
identified source as reference) was derived from an observation
with the ROSAT High Resolution Imager on 1996 May 7. In all
pointed ROSAT observations, a periodic modulation of the x-ray flux
is detected with a period of 8.38 s. No long-term variations of
more than +/- 10 percent on time scales of years between the ROSAT
observations are seen in the source intensity, and archival
Einstein IPC and EXOSAT LE detections are consistent with this.
CCD images obtained at the SAAO failed to detect an optical
counterpart to a limiting magnitude of V about 21.2. We encourage
multi-wavelength observations to confirm this candidate."
(C) Copyright 1996 CBAT
1996 August 6 (6445) Daniel W. E. Green
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