INTEGRAL Y6+ The New Soft Gamma-Ray Sky New Observational Results with Integral: GRB Pietro...

INTEGRAL Y6+ The New Soft Gamma-Ray Sky

New Observational Results with Integral: GRB

Pietro Ubertini, Neutron Stars & Gamma Ray BurstsAlexandia, April 1 2009,

P. Ubertini, A. Corsi, S. Foley, A. Bazzano, et al., on behalf of the IBIS Survey Team

INTEGRAL Instruments

IBIS mask

Optical Monitor

IBIS Detectors

JEM-X

JEM-X Masks

SPI

GRB within the instruments FoV:17keV-10 MeV GRB out of the FoV through IBIS and SPI shields:E>~200 keV

Real time data transmission

INTEGRAL GRBsINTEGRAL 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 – z = 0.1055GRB050223 – z = 0.584GRB050502a – z = 3.79GRB050525a – z = 0.606


Spatial Distribution of INTEGRAL GRBsSpatial Distribution of INTEGRAL GRBs

INTEGRAL exposure map inGalactic coordinates from Oct2002 to July 2007

Distribution of INTEGRAL GRBs in Galactic coordinates,dominated by the exposure


GRB 021125: GRB 021125: 11stst GRB GRB observed by INTEGRAL 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!.

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

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.

Pietro Ubertini, Neutron Stars & Gamma Ray BurstsAlexandria, Egypt, April 1 2009,


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

GRB 021219: 11st st Gamma-Ray Burst localized in real time with IBAS

GRB 030131: GRB 030131: 11stst detailed time-resolved spectroscopy detailed time-resolved spectroscopy of a faint of a faint GRBGRB

Gotz et al. 2003

IBIS/ISGRI light curvea) 15–50 keVb) 50–300 keVc) 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 BATSE in brighter GRBs GRBs (e.g. Preece et al. 1998) or (e.g. Preece et al. 1998) or by by BeppoSAX GRBs (e.g. BeppoSAX GRBs (e.g. Frontera et al. 2000; 2003). Frontera et al. 2000; 2003). The The fluence (7exp-6 erg cmfluence (7exp-6 erg cm-2-2) was a ) was a factor of 10 smaller than BATSE factor of 10 smaller than BATSE bright bursts, indicating that bright bursts, indicating that such spectral behavior applied such spectral behavior applied also to faint also to faint GRBs.


GRB 030227 a): 1GRB 030227 a): 1stst quick localization by quick localization by Integral…Integral…

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 about 8 hr 8 hr later by XMM-Newton (was later by XMM-Newton (was a record at that time!). a record at that time!).

Absorbed power-law fit to the afterglow spectrum: tentative evidence for a Fe emission line (see e.g. Piro (see e.g. Piro 2002), 2002), at 1.67 keV. The implied z∼3 was consistent with the z derived from the absorption.

Mereghetti et al. 2003

But the existence of Fe lines in GRBs remains an open issue:But the existence of Fe lines in GRBs remains an open issue:

EPIC PN best-fit spectra of GRB 030227 afterglow

GRB 030227 b):…and evidence for an IC GRB 030227 b):…and evidence for an IC componentcomponent

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).

IC component

Synchrotron component

Castro-Tirado et al. 2003


GRB 030406 a): an extremely hard burstGRB 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 Compton mode of IBISmode of IBIS, provided the burst is strong and spectrally hard, as in this case.Marcinkowski et al.2003


GRB 030406 b): an extremely hard burstGRB 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).Pietro Ubertini, Neutron Stars & Gamma Ray Bursts

Alexandria, Egypt, April 1 2009,

GRB 031203: GRB 031203: unusually low luminosityunusually low luminosity, nearby burst, 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)x10(4±1)x104949 erg at erg at z=0.1z=0.1.

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 sub-energetic in the -ray band-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 Searches for associated GW signals were perform by LIGO in coincidence with this GRB this GRB (Abott et al., 2005)(Abott et al., 2005)

Sazanov et al., Soderberg et Sazanov et al., Soderberg et al., 2003, worth 2 Nature al., 2003, worth 2 Nature paperspapers


Observed with IBIS+JEM-X: light curve and spectrum are consistent with other XRFs; Chandra data taken in two epochs (5 and 10 days (5 and 10 days after the burst) confirm the presence of the afterglow. 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 0.3<z<0.7 (D'Avanzo et al. 2004).

Taking into account z: it matches the Epeak-Eiso correlation; is more an ; is more an X-ray rich GRB rather X-ray rich GRB rather than an XRFthan an XRF (as instead are 060218 and 020903).

GRB 040812: a GRB 040812: a (false XRF) (false XRF) and X-ray rich GRB observed by Integral and X-ray rich GRB observed by Integral

GRB 041219a a): intense and ultra-long burst enable GRB 041219a a): intense and ultra-long burst enable polarisation studiesstudies

- 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.

McBreen et al. 2006



GRB 041219a b): polarization studies GRB 041219a b): polarization studies

Azimuthal distributions of the flux in the different time intervals. Chance

prob. of a non-polarized signal reported in each panel.

Light curve of GRB 041219A. The analyzed intervals, are shown with

dashed lines. P8 is omitted for clarity.

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 200–800 keV energy band.

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).

Gotz et al. 2009

GRB 041219a (II): polarization studies 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/BATSE TINTEGRAL/BATSE T90(%of 90(%of γγ ph) ph) DistributionDistribution

3 short

INTEGRAL GRBs global propertiesINTEGRAL GRBs global properties

INTEGRALdetectsProportionallyless short bursts than BATSE

INTEGRAL/Swift Photon Index DistributionINTEGRAL/Swift Photon Index Distributionapparently no big differenceapparently no big difference


INTEGRAL/Swift Peak Flux DistributionINTEGRAL/Swift Peak Flux Distribution

INTEGRALdetectsproportionallymore faintGRBs than Swift: why?: why?


Spectral LagsSpectral 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


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

Cumulative logN-log P distribution of the 55 GRBs detected by IBIS (20–200 keV) IBIS (20–200 keV) withwith the small subset of 12 long-lag GRBs12 long-lag GRBs shown separately. The distribution is biased by the lower sensitivity of IBIS at large off-axis angles, but they looks different.

New Observational Results with Integral

INTEGRAL GRB Distribution in INTEGRAL GRB Distribution in supergalactic Coordinatessupergalactic Coordinates

• INTEGRAL exposure map and GRB distribution in SupergalacticCoordinates• Supergalactic plane – plane containing local superclusters of galaxies, web of filaments and sheets rather than anisolated 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


Foley et al. 2008 A&A

Long-Lag GRBs: distance Scale & Rate of Low-Luminosity Long-Lag GRBs: distance Scale & Rate of Low-Luminosity GRBsGRBs

• A number of low-luminosity GRBs at low redshift detectede.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?


Distribution of Swift GRBs in Distribution of Swift GRBs in Supergalactic CoordinatesSupergalactic Coordinates

• No obvious concentration of long-lag GRBs with SG plane• Quadrupole Moment = 0.090 ± 0.072

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.

There is no obvious anisotropy for long-lag Swift GRBs with respect with the supergalactic plane, why?...

IBIS vs BAT sensitivity to weak GRBs 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 INTEGRAL GRB Summary 11

• INTEGRAL has detected 62 GRB 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-luminositylow-luminosity population distinct from the high-luminosityhigh-luminosity one

• 12/30 GRBs for which a 12/30 GRBs for which a spectral lag was measured spectral lag was measured have long have long lags (lags ( > 0.75 s) > 0.75 s). .

•In comparison, the 149 Swift GRBs with a measured lag, 12% have long lags, compared with 40% of the 40% of the INTEGRAL 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).


INTEGRAL GRB Summary 2INTEGRAL GRB Summary 2

Some of these bursts could be produced by the collapse of a Some of these bursts could be produced by the collapse of a massive star without a supernova. Alternatively, they could massive star without a supernova. Alternatively, they could result from aresult from adifferent progenitor, such as the merger of two white dwarfs different progenitor, such as the merger of two white dwarfs or a white dwarf with a neutron star or black hole, possibly in or a white dwarf with a neutron star or black hole, possibly in the clusterthe clusterenvironment without a host galaxy.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 dominates the local GRB population.


Thanks!


Lag-Luminosity Relation

Long-lag GRBs when a distanceof 250 Mpc is adopted

INTEGRAL GRBs with zshown in open circles

Other low-luminosity GRBs that do not fit on the relation

IBIS vs BAT sensitivity to weak GRBs 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!

Pietro Ubertini, Neutron Stars & Gamma Ray BurstsAlexandria, Egypt, April 1

2009,

INTEGRAL Y6+ The New Soft Gamma-Ray Sky New Observational Results with Integral: GRB Pietro...

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