Diapositiva 1

1
EDGE Science Breakdown for Transient Sources

L. Natalucci on behalf of the ESTREMO Transient
Working Group
image courtesy ESA
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
2
WFM Sensitivity
WFM / 5100cm2
ISGRI / 2600cm2
(very) worst case sensitivity (scaled from ISGRI
in-flight data)

• FOV ratio WFM / ISGRI 15-20
• the estimated background rate is 4000 c/s in
  the 10-200 keV band

(from IBIS observers manual, courtesy ESA and
IBIS team)
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
3
Science Breakdown/ Compact objects / Bursts

• Burst Spectroscopy / Detection of redshifted
  lines by NS atmosphere can be challenged on
  selected objects.
• Superbursters are appealing as they carry a
  fluence 1000 times that of normal X-ray
  bursts, and may flare for min to hours.

? 10 objects known so far. Mostly luminous
sources, accreting at 0.07-0.8LEdd.
NS LMXB with detected superbursts 4U 1254-690
(1) KS 1731-260 (1) 4U 1735-444 (1) Ser X-1
(1) GX172 (4 bursts) 4U 0614091 (1) 4U
1608-522 (1) 4U 1636-536 (3 bursts) GX
31 (1) 4U 1820-303 (1)
Depending on the coverage of the Galaxy by the
WFM, the expected rate of SB is 2-3 events/year
(courtesy J.in t Zand)
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
4
Science Breakdown/ Compact objects / Bursts

• Normal type I bursts, good candidates sources
  for multiple burst detection EXO 0748-676, KS
  1731-26, GS 1826-238.

EXO 0748-676 28 X-ray bursts accumulated by XMM
over 5x105s observation time.
(Cottam Paerels 2002)
GS 1826-238 clocked burster with recurrence
time of few hours (very tight anti-correlation
with accretion rate)
Easy to accumulate events but do not need
re-pointing
Strohmayer 2003
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
5
Science Breakdown/ Compact objects / Transients
3 IBIS Catalog 72 Galactic transients (28 HMXB
32 LMXB) 20 of them are new entries 13 new
sources 7 other known sources in outburst.
These sources were not present in the 2
Catalog How many transients/year do we expect to
be detected by the WFM? Probably 15-20/year

• SFXT (Supergiant Fast X-ray Transients)
  characterized by hour-long outbursts
• Mechanism unclear, probably related to clumpy
  accretion of matter (winds?) or alternatively,
  instabilities in close orbit systems

IGR J17544-2619
within this (very recent) class, 7 objects are
now identified and other 5 are candidates.
(Sguera et al. 2006)
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
6
Compilation by Sguera et al. 2006 most objects
show recurrent outburst events we may expect a
few events/year
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
7
Science Breakdown/ Compact objects / Magnetars

• AXP (Anomalous X-ray Pulsars) they emit well
  beyond 100 keV, and show bursting behaviour
  during outbursts. ? 9 objects known so far.
• Magnetars (but distinct properties from SGR),
  they show spinup glitches, bursts (few ms to
  1s), and long term variability

• Short outburst discovered fortuitously from 1E
  2259586.
• Lasting few hours, with luminous afterglow (1041
  erg/s)
• accompanied by emission of short bursts, pulse
  profile changes, dramatic hardening of the
  spectrum, period glitch
• (Kaspi 2006, and refs.therein)

1E 2259586
How many of these outbursts are hidden or simply
show up as glitches in regular monitoring?
(Kaspi 2006)
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
8
Science Breakdown/ Compact objects / BH science
BH spectroscopy short outbursts from BHs and
study of outflows, winds and possible disk-jet
interactions on short time scales

• Possible to establish trigger criteria for a few
  objects
• V4641SGR has dramatic flux changes (spectral
  data suggest the presence of huge variations in
  absorption column)
• XTE J0421560 CI Cam
• XTE J1650-500 (Tomsick et al-2003)
• Cyg X-1 giant outbursts (Golenetskii et al. 2003)

Study of spectra throughout a BH outburst may
useful to determine the jet production mechanism.
The matter is much challenging, but X-ray
spectroscopic capability along with simultaneous
broad band coverage can help to establish the
physical and geometric properties of the disk,
which is an important clue to understanding
Survey and monitoring (WFM standalone) science
source monitoring over years with intense
coverage and improved sensitivity respect to ASM
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
9
Science Breakdown/ Compact objects / NS accretion
disks
Unveiling properties of NS accretion disks
through reflection of superburst emission

• detected event from 4U 1820-30 (see Ballantyne
  Strohmayer)
• Fe K line and edge observed
• ? fit by disk reflection models

• X-ray line spectroscopy to determine the
  ionization of the reflecting material
• relativistic broadening of Fe emission lines (if
  detected) can provide information on the
  inclination angle and help constraining the mass
  of the NS

Spectral parameters evolution during 4U 1820-30
superburst (RXTE-PCA 3-40 keV)
Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma
10
Conclusions

• The WFM, basically designed on the science
  requirements for WHIM and GRB science, shows up
  as an outstanding opportunity to probe the
  compact objects science in a wide variety of
  phenomena
• In (tentative) priority order, one can identify
• X-ray burst spectroscopy (M-R relationship and
  NS EOS)
• Detection and spectroscopy of fast X-ray
  transients
• Spectroscopy and broad band monitoring of BH
  outbursts and state transitions (clue to
  understanding jet production mechanism and
  system-jet interactions).
• The rate of transient events available for study
  on the basis of the current INTEGRAL and RXTE
  coverage could be 30-50/year including
  superbursts, LMXB outbursts and Fast X-ray
  transient events
• 1 event/month (not a real challenge for
  observing program)

Lorenzo.Natalucci_at_iasf-roma.inaf.it
ISTITUTO NAZIONALE DI ASTROFISICA-IASF Roma