Transcript INTEGRAL AO-1: preliminary results

INTEGRAL Y6+
The New Soft Gamma-Ray Sky
New Observational Results
with Integral: GRB
P. Ubertini, A. Corsi, S. Foley, A.
Bazzano, et al., on behalf of the
IBIS Survey Team
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandia, April 1 2009, Page 1
Real time data
transmission
INTEGRAL Instruments
JEM-X Masks
IBIS mask
GRB within the
instruments FoV:
17keV-10 MeV
GRB out of the
FoV through IBIS
and SPI shields:
E>~200 keV
Optical Monitor
SPI
IBIS Detectors
JEM-X
INTEGRAL GRBs
• INTEGRAL has detected 62 GRBs since launch in
October 2002 up to January 2009 ~1/month
• 1st INTEGRAL catalogue of 46 GRBs published
(Foley et al. A&A, 2008)
• 4 INTEGRAL GRBs have confirmed redshifts:
GRB031203
GRB050223
GRB050502a
GRB050525a
–
–
–
–
z
z
z
z
=
=
=
=
0.1055
0.584
3.79
0.606
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandia, April 1 2009, Page 3
Spatial Distribution of INTEGRAL GRBs
INTEGRAL exposure map in
Galactic coordinates from Oct
2002 to July 2007
Distribution of INTEGRAL
GRBs in Galactic coordinates,
dominated by the exposure
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandia, April 1 2009, Page 4
GRB 021125: 1st GRB observed by INTEGRAL
On Nov. 25th, 2002, the
satellite was set up for a
special observation with the
PICsIT layer in a non–standard
photon–by–photon
mode,
reduced number of channels,
and most of the satellite
telemetry allocation: we new
IBIS was able to see GRBs!.
SPI light-curve (in Crab units) obtained
from the detector count rates in the
energy range 0.02–8 MeV; time starts
from 17:58:00 UT.
During this test, at 17:58:30
UTC GRB occurred in the
partially coded field of view of
IBIS (about 7.3 deg off–axis),
and lasted about 24 s.
Malaguti et al. 2003
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandria, Egypt, April 1 2009,
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GRB 021219: 1st Gamma-Ray Burst localized in real time with IBAS
One month larer, on December 19,
2002, during the Performance and
Verification Phase GRB has been
detected and localized in real time
with the INTEGRAL Burst Alert
System (IBAS).
-IBIS/ISGRI light curve of 021219
in the 15–500 keV band (upper
panel),
-SPI light curve of GRB 021219
(middle)
-A clear hard-to-soft spectral
evolution with time was observed
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
GRB 030131: 1st detailed time-resolved spectroscopy of a faint GRB
IBIS/ISGRI light curve
a) 15–50 keV
b) 50–300 keV
c) 15–500 keV.
The 6 data gaps are caused by
satellite telemetry saturation. 4 peaks
can be identified at 15, 40, 55, 85 s.
d) Spectral variation of the GRB with
time.
Spectroscopy: consistent with the
hard-to-soft evolution observed by
BATSE in brighter GRBs (e.g. Preece
et al. 1998) or by BeppoSAX GRBs
(e.g. Frontera et al. 2000; 2003).
The fluence (7exp-6 erg cm-2) was a
factor of 10 smaller than BATSE
bright bursts, indicating that such
spectral behavior applied also to faint
GRBs.
Gotz et al. 2003
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GRB 030227
a): 1st quick localization by Integral…
Mereghetti et al. 2003
Quick localization by INTEGRAL
Burst Alert System: discovery
of X-ray and optical afterglow.
The GRB lasted about 20 s, and
the
X-ray
afterglow
was
detected about 8 hr later by
XMM-Newton (was a record at
that time!).
Absorbed power-law fit to the
afterglow spectrum: tentative
evidence for a Fe emission line
EPIC PN best-fit spectra of GRB
(see e.g. Piro 2002), at 1.67
030227 afterglow
keV. The implied z∼3 was
consistent with the z derived
from the absorption.
But the existence of Fe lines in GRBs remains an open issue:
GRB 030227
b):…and evidence for an IC component
Synchrotron component
IC component
Castro-Tirado et al.
2003
The NIR/optical (solid line) and X-ray (dotted line) afterglow spectrum at
0.87 days since trigger. The NIR/optical spectral index is consistent with the
X-ray one, but they dot match each other’s extrapolations, similarly to e.g.
GRB 000926 (Harrison et al. 2001), GRB 010222 (in’t Zand et al. 2001), GRB
990123 (Corsi et al. 2005), GRB 070125 (Chandra et al. 2008).
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandria, Egypt, April 1 2009,
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GRB 030406
a): an extremely hard burst
INTEGRAL detects GRBs in
two different ways
from 17 kev up to 10 MeV:
- a small number of events fall in
the FoV of IBIS and SPI;
- a significantly larger number
occurs outside of the FoV but can
be monitored by the SPI-ACS. For
some of these bursts it is also
possible to perform a more
detailed localization analysis using
the Compton mode of IBIS,
provided the burst is strong and
spectrally hard, as in this case.
Marcinkowski et al.2003
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Alexandria, Egypt, April 1 2009,
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GRB 030406
b): an extremely hard burst
Combined ISGRI and Compton mode data. Broken power law model in each
case: precursor (left), peak part (center) and tail (right). The peak spectrum
is very hard: low energy νFν spectrum below 400 keV rises with index ≈+3.5
and above this energy is still positive ≈+0.3, so Epeak>1.1 MeV.
Clear contradiction with the synchrotron model of GRBs which predicts that
there is a strict upper limit on the low energy spectral index of −2/3
(Preece et al. 1998). The low energy spectral slope is consistent within the
error bars with the jitter synchrotron model of GRBs (Medvedev 2000).
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GRB 031203: unusually low luminosity, nearby burst
On 2003 December 3 at 22:01:28
UTC, IBIS detected a pulse of 40 s
duration, with a simple profile. The
spectrum was also typical, with a
single
power
law
model
that
constrained Epeak>190 keV.
The burst fluence in the 20–200 keV
band implied an isotropic energy of
(4±1)x1049 erg at z=0.1.
Sazanov et al., Soderberg et al.,
2003, worth 2 Nature papers
Is sub-energetic as GRB 980425, associated with the nearby (z=0.0085) SN 1998bw,
that had Eiso<1048 erg and violates the Eiso–Epeak relation, that would predict Epeak<10
keV, as GRB 980425.
The 2 nearest long GRBs are clearly sub-energetic in the -ray band, and their
proximity (and hence implied abundance) makes it of great interest to understand their
origin and relation to the more distant cosmological GRBs.
Searches for associated GW signals were perform by LIGO in coincidence with this GRB
(Abott et al., 2005)
GRB 040812: a (false XRF) and X-ray rich GRB observed by Integral
Observed with IBIS+JEM-X: light curve and spectrum are consistent with
other XRFs; Chandra data taken in two epochs (5 and 10 days after the
burst) confirm the presence of the afterglow. The 1” X-ray afterglow
localization enabled to discover the host galaxy of this XRF at 0.3<z<0.7
(D'Avanzo et al. 2004).
Taking into account z: it
matches the Epeak-Eiso
correlation; is more an Xray rich GRB rather than
an XRF (as instead are
060218 and 020903).
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GRB 041219a a): intense and ultra-long burst enable polarisation studies
McBreen
et al.
2006
- Brightest burst localized by
INTEGRAL. Peak flux: 1.84
×10−5 ergs cm−2s−1 (20 keV–
8MeV, 1 s integration);
- T90 duration of ∼186 s (∼20
keV–8MeV).
- The intense burst occurred
about ∼250 s after the
precursor and the long delay
enabled
optical
and
near
infrared telescopes to observe
the prompt emission.
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Alexandria, Egypt, April 1 2009,
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GRB 041219a
b): polarization studies
Measuring the polarization of the prompt GRB can significantly improve our understanding
of both the emission mechanisms as well as the underlying engine driving the explosion.
The technique was to use the IBIS telescope on board the INTEGRAL to measure the
polarization of the prompt gamma-ray emission of the long and bright GRB 041219A in
the 200–800 keV energy band.
Gotz et al. 2009
No polarization signal found integrating
over the whole first peak, and the
upper limit is 4%. On the other hand, a
modulated signal is seen in the second
peak corresponding to 43 ± 25%.
Integrating over smaller portions of the
GRB, give highly polarized signals,
especially in P8, P9 and P30 (Gotz et
al. 2009, but see also McGlynn et al.
2007, Kalemci et al. 2007).
Light curve of GRB 041219A. The
analyzed intervals, are shown with dashed
lines. P8 is omitted for clarity.
Azimuthal distributions of the flux in the
different time intervals. Chance prob. of a
non-polarized signal reported in each panel.
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandria, Egypt, April 1 2009,
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GRB 041219a (II): polarization studies
Measuring the polarization of the
prompt GRB emission can significantly
improve our understanding of both
the GRB emission mechanisms as well
as the underlying engine driving the
explosion.
SPI has the capability to detect the
signature of polarised emission from
a bright γ–ray source. Polarisation
can be measured using multiple
events
scattered
into
adjacent
detectors because the Compton
scatter angle depends on the
polarisation of the incoming photon.
GRB 041219a (McGlynn et al. 2007): degree of linear polarisation in the brightest
pulse of duration 66 s: 63+31−30% at an angle of 70+14−11 deg (100–350 keV). In the
brightest 12 s of the GRB: 96+39−40% at an angle of 60+12−14 deg (100–350 keV).
A systematic effect that could mimic the weak polarisation signal could not be
definitively excluded. However, this case demonstrated the effectiveness of using
SPI as a polarimeter in intense GRBs.
McGlynn et al. 2007, Kalemci et al. 2007
INTEGRAL GRBs global properties
INTEGRAL/BATSE T90(%of γ ph) Distribution
INTEGRAL
detects
Proportionally
less short
bursts than
BATSE
3 short
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
INTEGRAL/Swift Photon Index Distribution
apparently no big difference
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandia, April 1 2009, Page 18
INTEGRAL/Swift Peak Flux Distribution
INTEGRAL
detects
proportionally
more faint
GRBs than
Swift: why?
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandia, April 1 2009, Page 19
Spectral Lags
Many GRBs show time delay between the arrival time of
high and low energy photons  more energetic photons
tend to arrive earlier
•
• Cross-correlation analysis of light-curves in different
energy bands is used to determine this time lag ()
• Anticorrelation observed between lag and luminosity in
long-duration GRBs: Lpeak ~ 1.3x1053 (/0.01)-1.14 erg sec-1
(Norris et al. 2000)
 Can in principle use spectral lag as a GRB distance
indicator
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
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INTEGRAL Spectral Lag Distribution
• Lags determined for 30 GRBs in the sample between
the 25-50keV and 50-300keV energy bands
• No negative lags observed (i.e. low energy photons
leading high energy photons)
• the are 12 Long-lag GRBs with τ > 0.75 seconds
 = 0.75s
τ = 0.75 s
New Observational Results with Integral
Cumulative logN-log P distribution of the 55 GRBs detected
by IBIS (20–200 keV) with the small subset of 12 long-lag
GRBs shown separately.
The distribution is biased by the lower sensitivity of IBIS
at large off-axis angles, but they looks different.
INTEGRAL GRB Distribution in
supergalactic Coordinates
Foley et al. 2008 A&A
INTEGRAL exposure map and GRB distribution in Supergalactic
Coordinates
• Supergalactic plane – plane containing local superclusters of
galaxies, web of filaments and sheets rather than an
isolated pancake structure, superclusters evident out to ~400 Mpc
•10/12 Long-lag GRBs within ± 30o of Supergalactic plane
• Quadrupole Moment = -0.225 ± 0.090 for long-lag GRBs
•
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
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Long-Lag GRBs: distance Scale & Rate of Low-Luminosity GRBs
• A number of low-luminosity GRBs at low redshift detected
e.g. GRB980425 (36 Mpc, =2.8s) and GRB060218 (145 Mpc, =66s)
• Weak BATSE bursts are correlated with galaxies out to ~150 Mpc
(Chapman et al. 2007)
• 8 Long-lag GRBs in the partially coded field of view of IBIS (0.1sr)
• Assume 2 are at high redshift
• Adopt a distance of 250 Mpc for the remainder
• All-sky rate ~2500 Gpc-3 yr-1 for these GRB with a large
uncertainty due to distance3 factor
• This exceeds the upper limit of 300 Gpc-3 yr-1 of Type 1b/c SNe
which produce GRBs, assuming that all low-luminosity GRBs produce a
SN (However not all GRBs produce SNe, e.g. low-luminosity
GRB060505)
- Galaxy clusters may play a role – new progenitor?
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandia, April 1 2009, Page 24
Distribution of Swift GRBs in
Supergalactic Coordinates
The distribution of Swift GRBs in supergalactic coordinates. Short-lag
GRBs are shown as dark green diamonds and the 17 long-lag GRBs are
identified by purple circles.
• No obvious concentration of long-lag GRBs with SG plane
There
is no obvious
anisotropy
long-lag Swift GRBs with respect
• Quadrupole
Moment
= 0.090for
± 0.072
with the supergalactic plane, why?...
IBIS vs BAT sensitivity to weak GRBs
The answer could be that Integral has a factor of 2-4 better
sensitivity to weak GRBs and an efficiency extending up to several
MeV.
The detection sensitivity of a number of γ-ray missions, shown as the
peak flux threshold (1–1000 keV) to a GRB with a given Epeak.
INTEGRAL GRB Summary 1
• INTEGRAL has detected 62 GRB up to January 2009 and provides
localisations for ~ 1 GRB / month
• detects proportionally more faint GRBs than Swift and appears to
probe a low-luminosity population distinct from the high-luminosity one
• 12/30 GRBs for which a spectral lag was measured have long lags ( >
0.75 s).
•In comparison, the 149 Swift GRBs with a measured lag, 12% have
long lags, compared with 40% of the INTEGRAL sample, the median
peak flux of the 17 Swift long-lag GRBs is 1.71 ph cm-2 s-1 a factor
of 3 times higher than for INTEGRAL long-lag bursts
• Long-lag GRBs have low peak fluxes, long slow pulses faint optical and
X-ray afterglows and appear to be associated with the Supergalactic
plane, and appear to be distinct from high-luminosity population (Foley
et al., 2008).
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Alexandia, April 1 2009, Page 27
INTEGRAL GRB Summary 2
Some of these bursts could be produced by the collapse of a massive
star without a supernova. Alternatively, they could result from a
different progenitor, such as the merger of two white dwarfs or a
white dwarf with a neutron star or black hole, possibly in the cluster
environment without a host galaxy.
& no narrow gamma-ray lines (SPI)
Nor broad (IBIS)!
Finally, INTEGRAL detects a large proportion of faint, long-lag GRBs
that are inferred to be local. The sensitivity of IBIS is such that it
can detect very faint GRBs, allowing INTEGRAL to probe the
population of low-luminosity GRBs with long lags. This population
appears to be distinct from that of high-luminosity GRBs and
Pietro
Ubertini, Neutron Stars & Gamma Ray Bursts
dominates the local GRB
population.
Alexandia, April 1 2009, Page 28
Thanks!
Pietro Ubertini, Neutron Stars & Gamma Ray Bursts
Lag-Luminosity Relation
INTEGRAL GRBs with z
shown in open circles
Other low-luminosity GRBs
that do not fit on the relation
Long-lag GRBs when a distance
of 250 Mpc is adopted
IBIS vs BAT sensitivity to weak GRBs
EXIST will provide a larger area and better on-axis sensitivity with a
SeXI X-Ray follow-up capability
Thanks!