Renewed radio activity from H1743-322 observed with the ATCA
ATel #1766; S. Corbel (Univ. Paris Diderot & CEA Saclay), T. Tzioumis (ATNF), M. Coriat (Univ. Paris Diderot & CEA Saclay), C. Brocksopp (MSSL) & R. Fender (Univ. Southampton)
on 7 Oct 2008; 12:45 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: S. CORBEL (firstname.lastname@example.org)
Subjects: Radio, X-ray, Gamma Ray, Request for Observations, Binary, Black Hole, Transient
Following the reactivation of H1743-322 (also known as IGR J17464-3213) as observed by
INTEGRAL (Atel #1745 and #1739), we have conducted radio observations with the Australia
Telescope Compact Array on 2008 October, 5 . A radio source is detected at a position consistent
with the location of H1743-322 with preliminary flux densities of 2.30 +/- 0.10 mJy at 4.8 GHz
and 1.80 +/- 0.15 mJy at 8.6 GHz, giving a spectral index of -0.42 +/- 0.16.
The radio spectral index during this ATCA observation seems to favour optically thin synchrotron emission
from H1743-322, which is surprising for a source that was still -- until recently -- in the hard state (Atel #1745 ).
However, we note that now in the RXTE/ASM weather map (http://heasarc.gsfc.nasa.gov/cgi-bin/xte_weather/xte_lc?source=H1743-322),
H1743-322 is detected at a level of ~5 c/s, while it seems to have reached a plateau in hard X-rays as observed
with Swift/BAT (http://heasarc.gsfc.nasa.gov/docs/swift/results/transients/weak/IGRJ17464-3213 ).
This seems to suggest that that H1743-322 may be undergoing a state transition from the hard state to a softer state.
The detected radio emission would likely arises from the compact jets (possibly in the "unstable phase" observed
during the brightest part of the initial hard state, see Fender et al. 2004, MNRAS 355, 1105). If this interpretation is
correct, a major relativistic ejection event would then be expected in the coming days. Further observations are
strongly encouraged to cover this transient episode.