First hard X-ray detection of the neutron star X-ray transient SAX J1806.5-2215 with INTEGRAL
ATel #3210; M. Del Santo (INAF/IASF-Roma, Italy), P. Romano (INAF/IASF-Palermo, Italy), L. Sidoli, S. Mereghetti (INAF/IASF-Milano, Italy), C. Ferrigno (ISDC, Switzerland), N. Degenaar, R. Wijnands (University of Amsterdam, The Netherlands), E. Kuulkers (ESA/ESAC, Spain), A. Nucita (University of Salento, Italy), V. Savchenko (ISDC, Switzerland)
on 7 Mar 2011; 21:13 UT
Credential Certification: Melania Del Santo (melania.delsanto@iasf-roma.inaf.it)
Subjects: X-ray, Binary, Neutron Star, Transient
In the framework of the INTEGRAL observations of the Galactic Inner Disc,
we obtained the first hard X-ray detection above 20 keV
of the source SAX J1806.5-2215 (in't Zand et al. 1998, NuPhS, 69, 228).
The currently on-going outburst (ATels #3202, #3193) of
this so-called "burst-only" source (Cornelisse et al. 2004, NuPhS, 132, 518)
has been detected by INTEGRAL on 2011 March 06 from 10:01 to 23:21.
The IBIS/ISGRI (25.5 ks exposure time) significance levels
are 15 sigma and 8 sigma in the 20-40 keV and 40-80 keV energy bands, respectively.
The corresponding fluxes are 21.2+/-1.4 mCrab and 23.6+/-3.0 mCrab, respectively.
The source is also detected by JEM-X.
The joint JEM-X1, JEM-X2 and IBIS/ISGRI spectrum can be well fitted (red. chi^2=0.9 (13 d.o.f.))
by a simple power-law with photon index 2.0 +/-0.3, consistent with the findings of
Degenaar et al. (ATel #3202).
The estimated fluxes are 3.8E-10 erg/cm^2/s in 2-10 keV and 3.2E-10 erg/cm^2/s in 20-80 keV.
For a distance of 8 kpc (the upper limit reported in Cornelisse et al. 2002, A&A 392, 931),
this translates into a 2-10 keV luminosity of ~3E36 erg s-1 which is roughly a factor of 1.5 higher than the last Swift/XRT pointing (ATel #3202).
We found no type-I X-ray bursts either in the IBIS/ISGRI, or in the JEM-X light curves.
Further INTEGRAL and Swift observations are planned.
We encourage further monitoring at all wavelengths of this source.
