Central Bureau for Astronomical Telegrams

Central Bureau for Astronomical Telegrams -- Image credits

IAUC 6258: 2EG J0432+2910; 94P

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 6257  SEARCH Read IAUC 6259

View IAUC 6258 in .dvi or .ps format.
IAUC number

                                                  Circular No. 6258
Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)

2EG J0432+2910
     S. C. Lundgren, R. S. Foster, and E. Waltman, Naval Research
Laboratory; D. J. Thompson, B. L. Dingus, and G. Madejski, Goddard
Space Flight Center; J. M. Cordes, Cornell University; and P. L.
Nolan, Stanford University, report:  "An outburst was detected
during Aug. 8-22 from the unidentified EGRET source 2EG J0432+2910,
now believed to be an active galactic nucleus (AGN).  Preliminary
analysis indicates the gamma-ray flux above 100 MeV during the
flare was enhanced by a factor of 5 over the average flux from this
source in 1991-1993 observations (1.4 x 10E-7 photon cmE-2 sE-1).
In the subsequent observation (Aug. 22-Sept. 6), the gamma-ray flux
returned to near its historic average.  The strongest flat spectrum
radio source in the 15' gamma-ray error box (11'.4 from the center),
87GB 0430+2859, was identified as a possible counterpart (Dingus et
al. 1996, Ap.J., submitted).  The 21-cm NRAO Very Large Array Sky
Survey has mapped this field and finds a source at R.A. =
4h33m37s.80, Decl. = +29o05'56".2 (equinox 2000.0), consistent with
an Effelsberg survey position (Neumann et al. 1994, A.Ap. Suppl.
106, 303).  Radio monitoring of this source with the Green Bank
Interferometer was initiated on Oct. 3.  The flux densities of 0.60
+/- 0.02 Jy at 2.25 GHz and 0.545 +/- 0.005 Jy at 8.3 GHz were 35
percent higher than Effelsberg survey flux-density measurements.
In 20 days, the 2.25 GHz flux dropped to 0.47 +/- 0.025 Jy with
smaller day-to-day variations, while the 8.3-GHz flux density
remained constant.  An optical counterpart near the limiting
magnitude of the Palomar Sky Survey has been identified within 2"
of the VLA position and within the astrometric uncertainty.  The
probability of chance superposition within 2" in this field is 1
percent.  A ROSAT HRI observation made on 1995 Mar. 2-4 reveals an
x-ray source within 5" of the VLA position, which is consistent
with the absolute pointing accuracy.  The combination of a gamma-
ray flare, radio variability in a candidate flat spectrum
counterpart, and possible optical and x-ray counterparts provides
strong evidence that the source is in the blazar class of radio-
loud AGN.  This source has the weakest radio flux density of any of
the blazars detected by EGRET.  Further observations are
recommended to determine the redshift, measure optical variability,
and monitor the high-frequency (> 10 GHz) radio flux associated
with the gamma-ray flare."

     CCD magnitudes:  Oct. 21.48 UT, 21.4 (J. V. Scotti, Kitt Peak,
0.91-m reflector); 26.33, 20.5 (W. Offutt, Cloudcroft, NM, 0.60-m

1995 November 7                (6258)            Daniel W. E. Green

Read IAUC 6257  SEARCH Read IAUC 6259

View IAUC 6258 in .dvi or .ps format.

Our Web policy. Index to the CBAT/MPC/ICQ pages.

Valid HTML 4.01!