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| Miscellaneous :
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Gotz et al. 2006 ATel 813:
- 20-40 keV peak flux of 250 mCrab
- HD 74194 is a 7th Mag O star @1.7 kpc => Xray luminosity
1036erg/s
- Candidate Supegiant fast XRT
- peculiar GRB can't be completely ruled out
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Mereghetti et al. 2006 ATel 814:
- outburst lasting 2 hours in July 2003
- peak flux of 6 x 10-10 erg/s/cm2
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Masetti et al. 2006 ATel 815:
- Analysis of ESO archival spectra of HD 74194 => Hα emission with EW 1 Angstrom
- => HeI absorption at 6675 and 7065 A
- this indicates HD 74194 is the optical counterpart to IGR J08408-4503 which confirms the
supergiant FSXT nature
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Brandt et al. 2006 ATel 817:
- Refined position => strenghtens the association with HD 74194
- Alhtough several other candidates: finding chart available here
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Kennea & Campana 2006 ATel 818:
- Refined position => confirms the association with HD 74194
- Source at 3 kpc => L0.5-10 keV=2x1032 erg/s
- probable quiescent emission from X-ray source rather than emission from the star
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Barba, Gamen and Morrell 2006 ATel 819:
- HD 74194 is a O 8.5Ib (Walborn 1973)
- Change of Halpha line profile from double peak to P cygni
- SFXT Similar to IGR J17544-2619
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Gotz et al. 2007
ApJL:
- Analysis of 3 flares detected up to 2007 with Swift and INTEGRAL
- Spectra during flares is power law like with a high Ecut, and absorption
(NH=~1021 cm-2, Ecut~15 keV, Gamma~0)
- Orbital period of 1 year, spin period of hours and B~1013 G,
based on donor star parameters and wind accretion conditions.
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Leyder et al. 2007
A&A:
- INTEGRAL ISGRI/JEM-X spectra: broken power law
break energy of 14 keV or comptt
kTe=7 keV τ=4
- Swift => 2-10 keV flux of 3.4e-13 erg/cm2/s but
most of the detected counts have an energy smaller than 1.5 keV
- distance to the source of 2.7 kpc.
- orbital separation of > 1013 cm
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Mangano et al. 2008
ATel
1727:
- Triggered Swift/BAT on 2008-09-21 at 07:55:08 UT.
- Light curve is constant until T+730s.
- Spectrum (same time interval) well represented by a powerlaw
with an exponential cutoff, with Γ=1.3 ,Ecut=22.7 keV
- Simple power law gives Γ=2.87 =>acceptable fit too
- Swift/XRT light curve: bright flare with a flat top phase that lasts
about 1 ks => spectrum well fitted by an absorbed powerlaw with a Γ=0.85 and
NH=2.9 x1021 cm-2
- 5 ks later decay by a factor of 40 in count rate=> absorbed
powerlaw with Γ=0.8 and NH=3.7 x1021 cm-2
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Romano et al. 2008 MNRAS:
- Swift obs of 2 outbursts: no significant (>3sig) variations of the hardness
ratio in 2006, but source gets softer with increasing luminosity in 2008
- 2008 outburst <=> multiple flares each exceding 1e36erg/s
- Two outbursts show significantly different spectral parameters: value of the
cut-off energy during the 2006 outburst suggest B~1e12 G (lower than previously suggested)
- During the 2008 outburst definite evolution of the absorbing column
density along the outburst
- Inter-flare spectrum much harder than the quiescent spectrum
=> accretion of the inter-clump medium occurs => density contrast of at least
1e3 in the wind of the supergiant
- Clump-accretion: flare duration of 500s =>distance ~1e13 cm from companion, which
implies a period of 35 days.
- 2008 outburst does not occur in an integer multiple of the 35 days orbital cycle
- Disk equatorial wind model of Sidoli and collaborators (<=>"double periodicity" of
outbursts), with P=11 and 24 days all outburst can be accounted for.
- Results suggestive of an ehanced equatorial wind from
the supergiant, which is inclined wrt equatorial plane of the system
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Sidoli et al. 2009 MNRAS:
- spectra well fitted with models of cut off power law or
power law with black body emission with little absorption
- Seems to be clearly two population of photons, as
a fit with a bmc model need the addition of a black body to
account for soft X-ray emission at 0.3 keV.
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Bozzo et al. 2010
(A&A):
- XMM analysis during quiescence
- Quiescent emission composed
of multiple flares occuring after period of faint X-ray emission.
- Hardness ratio and the intensity are positively correlated
- Spectral analysis => soft component below 2 keV, in addition to
a standard (cutoff) power law with absorption
- Excess well represented by either a black body or thermal plasma model
- Thermal plasma could be the X-ray emission
due to shocks in the wind of the supergiant companion.
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Sidoli et al. 2010
(MNRAS):
- Suzaku observations during a long low intensity state
- 3 different periods:
low intensity stateis well represented
by a thermal emission probably arising from the companion
and a power law both undergoing Galactic absorption.
- 2 other states <=> flares, well represented by
locally absorbed powerlaw (in addition to the thermal plasma), with spectral consistent parameters
- At very low luminosity the source still accretes matter
- Calculations about clump mass and density are also presented
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Romano et al. 2014(A&A):
- Study of long term Swift/XRT monitoring
- Behaviour similar to other SFXTs with 67% inactivity duty cycle, and a dynamic range
of ~7400 during bursts
- Two distinct populations of flares, which seems to be a ubiquitous
property of extreme SFXTs
- No correlation between duty cycle and orbital period
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