Swift X-ray observations confirm outburst of GX 339-4
ATel #5252; Devraj Pawar (R. J. College, U. Mumbai), Diego Altamirano (UvA), Gregory R. Sivakoff (U. Alberta), James Miller-Jones (ICRAR Curtin), Tomaso Belloni (INAF), Dipankar Maitra (Wheaton College, MA and U. Michigan, MI) Michelle Buxton (Yale Univ.), Jeroen Homan (MIT), Dave Russell (IAC, Tenerife), Fraser Lewis (Faulkes Telescope Project, Univ. of South Wales), John Tomsick (SSL/UCB), Mickael Coriat (University of Cape Town)
on 6 Aug 2013; 16:38 UT
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Credential Certification: Diego Altamirano (email@example.com)
Subjects: X-ray, Black Hole, Transient
On August 2, 2013, Buxton et al. (Atel #5244) reported optical and
near-infrared flaring of the canonical black hole X-ray binary (BHB) GX
339-4. An increase in the optical and infrared band usually indicates
the onset of an X-ray outburst in BHBs.
We requested X-ray observations of GX 339-4 with Swift/XRT and the
first observation was performed on August 6, 2013 (03:23:59 UTC, MJD =
56510.1417) in PC mode (ObsID: 00032490012, total of ~1.1 ks).
Inspection of the image clearly shows a bright source with coordinates
consistent with those of GX 339-4.
Following Evans et al. (2009, MNRAS, 397, 1177) we extracted an X-ray
spectrum and find GX 339-4 at a 0.5-10 keV count rate of 2.3 cts/sec.
The spectrum is well fit in the energy range 0.3 to 10 keV with an
absorbed power law with photon index of 1.37+/-0.20 (unabsorbed flux
of 1.58e-10 erg/cm2/s in 0.3 to 10 keV) for neutral Hydrogen column
density (4.6+/-0.9)e21/cm2 (using phabs and "wilm" abundances in
XSPEC). Assuming lower limit of the distance at 6 kpc (Hynes et
al. 2004 ApJ 609, 317) we estimate a 2-10 keV luminosity of at least ~6.8e35
Given that GX 339-4 is well above its quiescent flux level of ~5e-13
erg/cm2/s (ATel #3383
) our Swift observation confirms that GX 339-4 is
in outburst. Furthermore, the luminosity and X-ray spectrum are
consistent with GX 339-4 being in the low-hard state. At this time, we
can not yet predict whether GX 339-4 will undergo a full outburst with
state transitions (e.g., 2010-2011: ATel #2577
, ATel #3117
) or a
failed outburst (e.g., 2012: ATel #4247
GX 339-4 will be observed daily by Swift for ~1 ks observations at
least for the next 10 days. We strongly encourage observations at
other wavelengths to follow the rise of the outburst.
Coordinated announcements of multi-wavelength observations of this
outburst can be found at
Please contact firstname.lastname@example.org to include any observations you are
scheduled to perform.
We thank the Swift team for scheduling our observations.