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INTEGRAL cataclysmic and symbiotic stars

R. Hudec, V. Šimon F. Munz, J. Štrobl, P.
Kubánek, P. Sobotka, R. Urban
Astronomical Institute, Academy of Sciences 251
65 Ondrejov, Czech Republic ISDC, Versoix,
Switzerland IBWS, Oct 25-28, 2006
v
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Non-magnetic cataclysmic variable (CV)

• Accretion disk thermal
• radiation (UV, optical, IR)

Donor, lobe-filling star
Bright spot (stream impact onto disk)

• Opt. thick, geom. thin boundary
• layer (therm. rad. - soft X-rays)
• (high m)

.
Mass stream
Non-mag. white dwarf

• Opt. thin, geom. thick boundary
• layer (bremsstrahlung hard
• X-rays) (low m)

Accretion disk
.
Dominant source of luminosity
accretion process
Intermediate polar (IP) mildly magnetized
white dwarf

• Impact region near the
• magnetic pole of the WD
• (bremsstrahlung hard
• X-rays)

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Magnetic CVs (polars)
ST LMi orbital modulation in hard Xrays
(1.9-8.5 keV) (EXOSAT)
Mason (1985)
hard X-ray sources

• cyclotron emission from
• accretion column (mainly
• optical and UV)
• bremsstrahlung from
• shocks above impact
• region on the WD (X-rays)

IBIS
AM Her orbial modulation top soft X-rays
(40-120 A) bottom- hard X-rays (1.9-8.5 keV)
(EXOSAT)
AM Her (kTbrem31 keV) (Rothschild et al. 1981)
Heise et al. (1985)
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Production of gamma-rays in CVs can reach
even TeV energies   Acceleration of particles by
the rotating magnetic field of the WD in
intermediate polars in the propeller regime AE
Aqr detected by ground-based Cherenkov
telescopes in the TeV passband (e.g. Meintjes et
al. 1992) _______________________________________
__________________ TeV emission from the polar
AM Her detected by ground-based Cherenkov
telescopes (Bhat et al. 1991) Domain of hard
X-rays/soft gamma rays was little exploited
before INTEGRAL ______________________________
___________________________
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Total exposure times of IBIS

INTEGRAL suitable for (a)
detection of the populations of CVs and
symbiotics with the hardest X-ray
spectra (b) simultaneous observations in
the optical and hard X-ray regions (c)
long-term observations with OMC
including a search for rapid variations in
observing series during science window
(OMC observations also for systems
bellow the detection limit in hard X-rays)
IBIS all obs.
Known CVs Catalog and Atlas of Cataclysmic
Variables (Downes et al. 2001)
Total exposure times of IBIS
IBIS Core Program
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• The summary of CV observations/detections by
  INTEGRAL during the first 3 years of INTEGRAL
• In total, 19 CVs detected (surprise, more than
  expected, almost 10 of INTEGRAL detections)
• 15 seen by IBIS (Barlow et al., 2006)
  correlation of IBIS data and Downes CV catalogue
• 4 are CV candidates revealed by optical
  spectroscopy of IGR sources (Masetti et al.,
  2006) new CVs, not in Downes catalogue
• Mainly magnetic systems
• 11 confirmed or propably IPs, 3 polars, 1 dwarf
  nova, 4 probable magnetic CVs

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Barlow et al., MNRAS 2006. The results of
cross-correlation with Downes CV catalogue
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Periods Vast majority Porb gt 3 h, ie. above the
period gap (only one lt 3 h) 5 long period systems
with Porb gt 7 h Variation No significant
modulation has been found in the 20-30 keV light
curves. The majority of the CVs displays
persistent soft gamma ray fluxes with exception
of V1223 Sgr and SS Cyg Spectrum Similar in most
cases, power law or thermal bremsstrahlung model
, Compare well with previous high energy
spectral fits (de Martino et al. 2004, Suleimanov
et al. 2005, Barlow et al. 2006) Mean G2.8,
kT20 keV
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Some statistics Intermediate polars only 2 of
the catalogued CVs,but dominate the group of CVs
seen by IBIS More such detections and new
identifications can be hence expected Many CVs
covered by CP remain unobservable by IBIS, but
new have been discovered IBIS tends to detect IPs
and asynchronous polars in hard X-rays, these
objects seem to be more luminous (up to the
factor of 10) than single synchronous polars
Detection of CVs by IBIS (non-flarig state)
typically requires 150-250 ksec or more, but some
remained invisible even after 500 ksec
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V1223 Sgr
Intermediate polar Most significantly detected
CV in the IBIS survey, with a significance of 38
sigma in the 20-40 keV final mosaic Accretion
via disk Bright X-ray source (4U
184931) Orbital period Porb 3.37 h (Osborne
et al. 1985, Jablonski and Steiner
1987) Rotational period of the white dwarf Prot
746 sec (Osborne et al. 1985) Beat period
(combined effect of Porb and Prot) Pbeat
794.3 sec (Steiner et al. 1981) Prominent
long-term brightness variations - outburst with
a duration of 6 hr and amplitude gt1 mag (van
Amerongen van Paradijs 1989) - episodes of deep
low state (decrease by several mgnitudes)
(Garnavich and Szkody 1988)
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• Indications for flaring activity
• Seen by IBIS (flare lasting for 3.5 hrs
• during revolution 61 (MJD 52743), peak flux
• 3 times of average (Barlow et al., 2006)
• Seen by INTEGRAL OMC in optical one year later
  (MJD53110, 53116) lasting for 15 min and 2.5
  hrs (Simon et al., 2005)
• Seen in optical by groud-based instrument
  (duration 6-24 hrs), Amerrongen van Paradijs
  (1989)
• Confirms the importance of OMC instrument onboard
  INTEGRAL even with V lim mag 15, it can provide
  valuable optical simultaneous data to gamma-ray
  observations

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• Similar flares known also for another IPs in
  optical, but not in soft gamma
• Example TV Col (Hudec et al., 2005), where 12
  optical flares have been observed so far, five
  of them on archival plates from the Bamberg
  Observatory. TV Col is an intermediate polar (IP)
  and the optical counterpart of the X-ray source
  2A0526-328 (Cooke et al. 1978, Charles et al.
  1979). This is the first cataclysmic variable
  (CV) discovered through its X-ray emission.
• Physics of the outbursts in IPs
• Disk instability or
• An increase in mass transfer from the secondary

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15 25 keV
25 40 keV
V1223 Sgr
Field of the intermediate polar V1223 Sgr.
Co-added frames from IBIS. Start exp. JD
2452730.17 Integration time 66 700 sec Size
of the field 9.1ox7.1o. North is up, East to
the left.
40 60 keV
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Relation between far X-ray flux and optical
magnitude Relating processes in different
regions Disk (optical) Impact region near
magnetic pole of white dwarf (X-ray)
V1223 Sgr
Time evolution of the V band magnitude and X-ray
flux in the 15 60 keV passband
IBIS spectrum in the 15 60 keV region Spectral
profile remains largely unchanged during
shallow low state ( 400 days)
Relation between the V band magnitude and X-ray
flux in the 15 60 keV passband
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V1223 Sgr
Fluctuations of brightness for JD lt 2 452
250 Short low state (LS) in JD 2 451 650

Long LS after JD 2 452 250
INTEGRAL observations in lower than average
level of brightness long-lasting and rather
shallow low state
Peak of high state
Shallow low state
Means for each science window
Relation between mass transfer rate and V band
magnitude, assuming the system parameters
according to Model A of Beuermann et al.
(2004) Disk may become thermally unstable in
shallow low state this is not
observed (irradiation of the disk by the X-rays
can occur)
Statistical distribution of the optical
brightness
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Search for rotational and beat modulation in OMC
data during shallow low state
V1223 Sgr
All OMC data
Smoothed beat modulation in folded OMC data (100
sec exp. only) (ephemeris of Jablonski and
Steiner (1987) Pbeat 794.3 sec)
Prot
Pbeat
Beat modulation still dominates over the
rotational modulation (streamdisk overflow
still operates in the shallow low
state) Streamdisk overflow persists when mass
transfer rate decreases 3 times
OMC data between JD 2 453 000 and JD 2 453 100
Prot
Pbeat
Time (days)
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V1223 Sgr
Orbital modulation V gamma
OMC data (100 sec exp. only) Ephemeris of
Jablonski and Steiner (1987) Porb 3.37 hr The
profile and phasing of the optical modulation
appears to be quite similar to that observed by
Jablonski and Steiner (1987) in the high
state Smooth curve moving averages Observations
of all three time intervals follow the
modulation and possess the same mean level of
brightness Scatter rotational modulation of
the WD contributes
Optical
15-40 keV
NH0 atoms/cm2
Flat modulation in hard X-rays Possible dip at
phase 0.9 may be caused by a very dense
material pushed away from the orbital plane by
the stream impact Observable emission region
does not vary through the orbital cycle
NH5x1023 atoms/cm2
NH1024 atoms/cm2
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Desynchronized polar (e.g. Patterson et al.
1995). Orbital period (3.37 hr) and the
rotational period of the WD differ by 0.3 percent
V 1432 Aql
Flux (15 40 keV) (8.8 /- 0.9) x 10-4
photon/cm2/s L (15 40 keV) 1.4 x 1032 erg/s
Averaged OMC light curve
Field of V1432 Aql. Co-added fully coded images
from IBIS JD 2 452 756. Integration time
37 160 sec. Size of the field 9ox7o. North is
up, East to the left.
15 40 keV
40 80 keV
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V2400 Oph
Diskless intermediate polar Orbital period Porb
3.4 hr Rotational period of the WD Prot 927
sec Beat period Pbeat 1003 sec (Buckley et al.
1997)
15 40 keV
IBIS image of the field of the intermediate polar
V2400 Oph and the symbiotic (neutron star) system
V2116 Oph. Co-added fully coded images from
IBIS JD 2452733 JD 2452920 JD
2453054. Integration time 53 760 sec. Size of
field 9.1ox7.1o. North is up, East to the left.
Averaged OMC light curve
Flux (15 40 keV) (9.37 /- 1.14) x 10-4
photon/cm2/s
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outburst
GK Per
IBIS range
quiescence
(Ishida et al. 1992)
Intermediate polar, very long Porb1.99 days
(Crampton et al. 1986) Spin period of the white
dwarf Pspin351 sec (Watson et al.
1985) Exploded as a classical nova in
1901 Fluctuations by 1 mag after return to
quiescence, later they developed into infrequent
dwarf nova-type outbursts (Sabbadin Bianchini
1983, Hudec 1981) X-ray (2.5 11 keV) spin
modulation 351 s (EXOSAT) during optical
outburst (Watson et al. 1985)
X-ray start can precede the optical start by up
to 40 days (Binachini Sabbadin 1985) Models
up to 80 120 days (Kim et al. 1992)
Relation between profile of optical and X-ray
outburst
(Simon 2004)
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GK Per
INTEGRAL
Interval between outbursts D t 973 days IBIS
obs. start at 42 percent of this interval
(measured since the previous outburst).
Ishidas et al. reference spectrum D t 983
days (start at 29 percent of this interval).
Amount of matter arriving to the WD and the
parameters of the X-ray emitting region on the
WD remained almost the same during these phases
of the quiescent intervals.
Flux (15 40 keV) (2.7 /- 1.2) x 10-4
photon/cm2/s L (15 40 keV) 4.6 x 1032 erg/s
IBIS
Quiescent X-ray spectrum Parameters from Ishida
et al. (1992) (kT 32 keV, NH 1022 cm-2,
norm. factor 0.0039/-0.0002 photon/cm2/s1/keV)
IBIS (2540 keV) image of GK Per (Integr. time
79 980 sec Co-added images 19 March 2003, 27
29 July 2003. Size of field 4.1ox3.0o. North is
up, East to the left.
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Examples of OMC light curves
Nova-like CV INTEGRAL OMC two intervals
covered Rapid variations (flickering)
superimposed on the long-term changes (a)
Outburst (duration lt14 days) (b) Short episode of
a low state
IX Vel
Superposition of both events the time scales of
the decaying and rising branches of both events
appear to be comparable
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• RS Oph Examples of OMC
  light curves
• relatively bright symbiotic system
• orbital period Porb460 days
• inclination angle 30o 40o
• giant component underfilling its lobe
  (Dobrzycka Kenyon 1994)
• white dwarf (WD) recurrent nova (five
  observed explosions) (e.g. Warner 1995)
• Quiescent brightness fluctuations (months and
  years) 11 12 mag(V), sometimes
• 10 mag(V) (e.g. Dobrzycka Kenyon 1994,
  Oppenheimer and Mattei 1996)
• Rapid optical variations time scale of tens
  of minutes, similar to those often seen in
• short-period CVs (e.g. Walker 1977,
  Dobrzycka et al. 1996)

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Mag. scale
Intens. scale
1
7
1
7
3
9
3
9
5
10
5
10
Weighted wavelet Z-transform WWZ indicates
whether or not there is a periodic fluctuation
at a given time at a given frequency (method of
Foster 1996).
RS Oph
6
6
V band OMC light curves Strong flickering
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Symbiotic stars as Hard-X-ray emitters RT Cru
and CD -57 3057 identified with IGR sources
(Masetti et al., 2005) Novae, some of which
occur in symbiotic stars, play an important role
in the chemical evolution of the Galaxy and the
symbiotic stars themselves. A common feature of
symbiotic recurrent novae (RNe) is rapid optical
flickering. At least one symbiotic RN (T CrB) has
also produced very hard X-ray emission. RT Cru
produces optical flickering, has an optical
spectrum like that of T CrB, and has recently
been discovered by Integral to produce X-ray
emission out to 60 keV. X-ray observations of
RT Cru from the Chandra and Swift satellites
clearly shows both thermal and non-thermal X-ray
emission. Absorption of soft X-rays that is
variable on a time scale of months suggests
occultation by the red giant. There are two
possible models for RT Cru a jet-producing
system viewed nearly edge on, or a magnetic white
dwarf viewed pole on.
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RT Cru optical monitoring
More detailed and more precise observations by
southern FRAM and WATCHER robotic telescopes
(Kubanek et al.) is in progress This one and the
newly detected symbiotics with INTEGRAL - CD-57
3057 (Masetti et al., 2005) are optically very
bright stars
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The End