SWIFT/BAT detection of SWIFT J1009.3-4250: a probable Compton-Thick object
ATel #864; M. Ajello, J. Greiner, A. Küpcü Yoldas, (all MPE Garching), J. Tueller (GSFC), S. Barthelmy (GSFC), C. Markwardt (GSFC/UMD), J. A. Kennea (PSU), A. Falcone (PSU), O. Godet (U. Leceister), D. Grupe (PSU), R. Mushotsky(GSFC), T. Belloni (INAF-OAB), K. Mukai (GSFC), S. T. Holland, N. Gehrels (GSFC)
on 25 Jul 2006; 12:00 UT
Credential Certification: J. Greiner (jcg@mpe.mpg.de)
Subjects: Optical, X-ray, Gamma Ray, AGN
We report the discovery of SWIFT J1009.3-4250, a new hard X-ray source.
The source was detected in the ongoing SWIFT Burst Alert Telescope (BAT)
survey; as in ATEL #697, BAT data from May-Nov 2005 have been used.
The BAT position is (ra,dec)=(152.401,-42.798) and the source significance
is 5.1 sigma.
SWIFT J1009.3-4250 was observed three times during followup observations
with the X-ray Telescope (XRT) on board SWIFT.
The first observation was on 2006-06-15 for a total of 1.8 ks, the second
one on 2006-07-11 for a total of 3.8 ks and the third one on 2006-07-13
for a total of 1.9 ks.
During all observations, we found a faint X-ray source within 3 arcmin (90%)
of the BAT position whose coordinates are RA(2000)= 10 09 48.3,
Dec(2000) = -42 48 44 with a position error of 5".
The position of this source coincides with ESO 263-13, a face-on spiral galaxy
at redshift z=0.03355, classified as Seyfert 2 (Fairall, A. P. 1983, MNRAS 203, 47).
Optical spectroscopy from the 6dF survey shows very strong narrow [OIII] lines
(widths of 500 km/s) and narrow Halpha, Hbeta lines (widths of 573, 536 km/s).
The extinction based on the Halpha/Hbeta ratio is A_V=1.55 which translates into
N_H=1.0E21 H-atom/cm2 (using the formula in Predehl, et al. 1995, A&A 293, 889).
The line ratios Log(NII/Halpha)=0.1 and Log(OIII/Hbeta)=1.1 place this object
at the top right corner of the figure 1 of Veilleux et al. (1987, ApJ 63, 295)
among Sy2 and NLRG objects.
A joint fit to XRT and BAT data with an absorbed power law model does not yield
acceptable results even accounting for variability between BAT and XRT data
(reduced chi-squared > 1.8).
Using a reflection model (pexrav in Xspec11), we get a good fit to
XRT and BAT data (reduced chi-squared of 0.94 with no variability required)
and the spectrum is required to be completely reflected. The power law index
is 1.97 (+/-0.09) and the unabsorbed flux in the 15-150 keV band is 2.8E-11 erg/s/cm2.
The unabsorbed source luminosity, in the same band, is 7.3E43 erg/s
(assuming H0=70.0, Lambda0= 0.730). The lower limit on the absorbing
column density is 1024 H-atom/cm2, suggesting that SWIFT J1009.3-4250 could be
a Compton-Thick source.
