new insights in grb phenomenon with next generation...

Lorenzo Amati

Italian National Institute for Astrophysics (INAF), Bologna

with contributions by: M. Feroci, F. Frontera, C. Labanti, E. Del Monte, G. Stratta, B. Gendre, V. D’elia

New insights in GRB phenomenon with next generation instruments

Outline q  The proposed Italian payload for MIRAX

q  GRB science with LOFT

q  GRB observations with NuSTAR and ASTRO-H

A proposed Italian contribution to the Lattes/ MIRAX Scientific

Payload

The Italian MIRAX Collaboration as of May 2011

INAF IASF Roma

M. Feroci**, A. Argan, R. Campana**, I. Donnarumma, Y. Evangelista**, E. Del Monte**, S. Di Cosimo, G. Di Persio, F. Lazzarotto, M. Mastropietro, E. Morelli, F. Muleri, E. Costa, L. Pacciani**, M. Rapisarda, A. Rubini, P. Soffitta

I A S F Bologna

Lorenzo Amati, Claudio Labanti, Martino Marisaldi, Fabio Fuschino, Mauro Orlandini, Alessandro Traci

O A B , Merate

Gabriele Ghisellini, Giancarlo Ghirlanda

INFN S e z . Trieste

Andrea Vacchi, Gianluigi Zampa, Nicola Zampa, Alexander Rashevski, Valter Bonvicini

S e z . Bologna

Giuseppe Baldazzi

LNGS Francesco Vissani, Giulia Pagliaro University Ferrara Filippo Frontera*, **, Alessandro Drago**, Cristiano Guidorzi*, Ruben

Farinelli*, Lev Titarchuk Como Ruben Salvaterra* L’Aquila Francesco Villante** Pavia Piero Malcovati, Luca Picolli, Marco Grassi Pisa Ignazio Bombaci** S N S , Pisa

Mario Vietri*, E. Pian

ICRANET Pescara Remo Ruffini and his team

Our scientific motivation for GRB studies: broad band spectroscopy (down to 1 keV) of

the prompt emission •  Physics of the GRB continuum prompt emission:

–  Broad spectrum from 10 MeV down to 1 keV –  Transient spectral components (e.g. BB);

•  Establishing the GRB progenitors and their distance from the properties of circumburst environment: –  Column density NH and its time behaviour; –  Absorption edges;

•  X-Ray Flashes: origin, population size, link with GRB •  Increasing the detection rate of high-z GRB with low

energy threshold: SFR up to dark ages, pop III stars, etc

•  Physical origin of spectral-energy correlations and their exploitation for cosmology.

BeppoSAX (top: 2-28 keV, bottom: 40-700 keV)

q  Relevance of GRB prompt low energy (<15 keV) X-ray emission

Swift XRT (rare / unique case) + Swift/BAT + konus/WIND

Amati et al. 2001, Frontera et al. 2000, Ghirlanda et al. 2007

q  Importance of the low energy X-rays (specially time resolved) for testing GRB prompt emission physics

q  Tansient bump, consistent with a 2 keV blackbody, observed in the low energy band with BeppoSAX WFC

Frontera et al. 2001

GRB 990712

q  X-ray features: properties (density profile, composition) of circum-burst environment ( progenitors, X-ray redshift)

(Frontera et al., ApJ, 2004, Amati et al, Science, 2000)

q  X-Ray Flashes: origin, population size, link with GRB

(Amati 2008, Pelangeon et al. 2008

(Amati et al. 2004, Sakamoto et al. 2005

q Soft/long X-ray transients GRB 060218 and XRF 080109 associated

with SN 2006aj (at z = 0.038) and SN 2008D at z = 0.0064 Ø  Debate: very soft/weak XRF or SN shock break-out ? Ø  Peak energy limits and energetics consistent with a very-low energy

extension of the Ep,i-Eiso correlation holding for normal GRBs and XRFs: Evidence that these transients may be very soft and weak GRBs, thus confirming the existence of a population of sub-energetic GRB ?

Modjaz et al., ApJ, 2008 Amati et al., 2009

q  Increasing the detection rate of high-z GRB with low energy threshold: SFR up to dark ages, pop III stars, …

(Salvaterra et al. 2007) (Stanek et al. 2010)

Background and context •  2002-2004: we participated to the ESA phase A study of LOBSTER-ISS with

the goal of extending the energy band of the lobster-eye (MCP based) wide field telescope from 0.1 – 5 keV up to at last 1 MeV in order to allow deteciton and study of GRBs soft X-ray emission

•  2005: LOBSTER-ISS phase A study successfully concluded, mission approved to phase B, but ESA program suspended following shuttle Columbia accident

•  2006-2009: Within an ASI-INAF contract for AAE studies, science goals and instrument requirements defined for:

a) broad band spectroscopy (1 keV – 10 MeV) of the GRB prompt emission;

b) X- ray Sky Monitoring in 1 – 50 keV •  In parallel, R&D activities performed at INAF/IASF institutes in Rome and

Bologna (supported by ASI and PRIN INAF) and in collaboration with INFN (Trieste, Bologna, Rome)

•  June 2010: Invited to join by MIRAX PI, science case and a payload

proposal presented and discussed at INPE (Brazil) •  July 2010: Brazilian Space Agency (AEB) invites ASI to discuss the

possible Italian contribution to MIRAX, based also on AEB-ASI cooperation agreements.

•  April 2011: ASI solicited INAF to perform an evaluation (currently in

progress) of the scientific merit of our proposed payload for MIRAX

The Lattes satellite Ø  Near equatorial orbit, 600 km, 4 yr life time, 6launch end of 2016 Ø Two scientific payloads

•  MIRAX for X-ray astrophysics; •  EQUARS for terrestrial

atmosphere studies Ø  Available resources for MIRAX:

•  1 m x 1 m x 1 m Payload Bay devoted to MIRAX.

•  Mass: ∼125 Kg, Power: 90 W •  Telemetry: X-band

Ø  Attitude:

•  Continuous scan of the sky at the speed of 4º/minute. •  This can allow MIRAX to scan almost the full sky each orbit and

EQUARS to continuously observe the Earth.

The proposed Italian payload for MIRAX

Proposed instrumentation: •  X-ray Monitor (XRM):

1-50 keV, 6 units, Imaging, Silicon Drift Detectors with Coded Mask

•  Soft Gamma-ray Spectrometer (SGS):

15 keV – 10 MeV NaI(Tl)/CsI(Na) phoswich detector, 8 units

Science Drivers: 1.  Wide-band spectroscopy of the prompt emission of GRBs down to 1 keV (and up to a few MeVs) 2. All-sky monitoring of Galactic and Extragalactic X-ray sources in 1-50 keV with a few arcmin location accuracy and high sensitivity (a few mCrab)

The X-Ray Monitor q  Use of Silicon Drift Detectors (SDC) heritage of the LHC/Alice experiment at CERN with excellent performances (energy resolution 200-300 eV, low energy threshold < 2 keV, time res. < 10µs) can be used to build large area detectors) q  The SDC detector has asymmetric position resolution: ≤100µm in one direction and ∼2-3 mm in the orthogonal direction.

⇒  Asymmetric 2D coded mask ⇒  2 orthogonal units always looking at the same FoV to guarantee arcmin prompt localization of Gamma Ray Bursts

Parameter Expected Value Energy Range ∼1-50 keV Energy Resolution From 250 to 500 eV FWHM Time Resolution ∼10 µs

Effective Area ∼550 cm2 in FCFoV (spectroscopy) Angular Resolution 5 arcminutes Point Source Location Accuracy <1 arcminute Field of View ∼2.5 steradians FCFoV

∼3.5 steradians PCFoV Sensitivity (5-σ, 1 detector, imaging, for spectroscopy 1.4 better)

700 mCrab or ∼2 ph/cm2/s in 1s, FCFOV 90 mCrab or ∼0.3 ph/cm2/s in 60s, FCFOV <26 mCrab/orbit in >Half Sky <10 mCrab/elapsed day over All Sky ∼ 3 mCrab/50 ks

Source Transit Time in FoV 700 s /orbit Telemetry (orbit average) 3800 kbits/s

X-ray Monitor parameters

The Soft Gamma-Ray Spectrometer: phoswich configuration

good NaI(Tl) events

good CsI(Na) events good mixed events particle events (to be identified and rejected)

Fast decay

Slow decay

X ray bkg out of FOV

Soft Gamma-ray Spectrometer parameters

Parameter Expected Value

Energy Range 20 – 10000 keV

Energy Resolution 15% @ 60 keV , 8% #662 keV

Time Resolution ~ 1 µs

Effective Area (on axis) ∼1000 cm2 up to 300 keV, ~ 700 cm2 up to 1000 keV

Field of View 2.5-3.5 steradians Sensitivity (5-σ) ~ 1 Crab in 1s

Telemetry (orbit average) 40 kbits/s

All Sky Monitor

High Energy Spectrometer

“Flying” direction

Possible Italian MIRAX Payload configuration Proposal

X-ray Fully Coded Field of View High Sensitivity

Gamma-ray Spectroscopy

q  X-ray Sky Coverage every orbit (90 minutes)

q  Eff. Area and GRB sensitivity of MIRAX w/r to present / next future GRB detectors

Swift/BAT Fermi/GBM

MIRAX

q  The k-edge from GRB990705 as would be detected by XRM+SGS

BeppoSAX WFC+ GRBM MIRAX ASM+SGS,

BeppoSAX WFC (10 keV eff. Area 140 cm2, en. res. > 1 keV)

MIRAX (10 keV eff.Area 500 cm2, en. Res. 250 eV)

q  Low energy efficiency of MIRAX vs.BeppoSAX WFC

q  MIRAX Simulation of the energy spectrum observed from GRB990705 with BSAX/WFC

Spectrum ASM+SGS, fit with an absorbed Band law

Sensitivity vs. GRB total fluence

Assumption: the same spectral shape and K-edge optical depth (1.5) of GRB 990705

q  Improvement in detection of high-z GRBs w/r to present and next future experiments

Main features of the MIRAX proposed payload compared with those of past and present GRB experiments

Mission Experiment Energy band (keV)

Field of view (sr)

G R B L o c a t i o n accuracy

M a x . eff. area (cm2)

E n e r g y r e s o l u t i o n (keV)

#GRB / year

N o m i n a l operation / launch

CGRO BATSE 25 - 2000 9 > 3° 2000 15@100 keV 300 1991 - 2000 BeppoSAX WFC 2 – 28 0.26 3’– 5’ 180 1.5@6 keV 15 1996 - 2002

GRBM 40 - 700 6 > 10° 700 20@100 keV 200 HETE-2 WXM 2 - 25 0.8 - 70 1.8@6 keV 15 2000 - 2006

FREGATE 7 - 400 1.74 - 40 15@100 keV 70 Swift BAT 15 - 150 1.4 3’ 2600 3@60 keV 120 2004 - WIND Konus 15 - 10000 4π - 250 15@100 keV 250 Fermi GBM 8 - 30000 9 > 3° 300 15@100 keV 250 2008 - INTEGRAL ISGRI 20 - 200 0.1 1.5 1300 3@60keV 10 2003 - MAXI (1) GSC 2 - 30 1.5ox160o 0.1o 5350 [email protected] keV 5 2009-

SSC 0.5 - 12 1.5ox90o 0.1o 200 [email protected] keV 2 MIRAX XRM 1 - 50 3.5 1’ 550 0.2@3 keV 200 2017 -

SGS 20 - 5000 3.5 - 1100 10@100 keV 200

Conclusions

MIRAX is a unique opportunity for the Italian high-energy astrophysics community (INAF, INFN, Univ.), allowing:

•  To achieve primary scientific goals on GRBs and galactic

sources and provide a fundamental service to the world-wide community (prompt emission of GRBs from 10 MeV down to 1 keV, X-Ray all-sky monitoring in 2-50 keV with unprecedented FOV and sensitivity).

•  To have a scientific outcome for R&D activities supported by

INAF, INFN, ASI and Universities (Ferrara, Pavia, …) •  To exploit a unique launch opportunity in a short time scale

(end of 2016) with bus, platform and sub-systems provided by Brazil.

Freely available at: http://prometeo.sif.it/papers/?pid=ncc9894

GRB Science with LOFT

The LOFT Coordination Group

34

Marco Feroci (INAF/IASF-Rome, Italy) Luigi Stella (INAF/OAR-Rome, Italy) Michiel van der Klis (Univ. Amsterdam, the Netherlands) Didier Barret (IRAP, Toulouse, France) Carl Budtz-Jorgensen (DTU, Copenhagen, Denmark) Thierry Courvousier (ISDC, Switzerland) Jan-Willem den Herder (SRON, the Netherlands) Margarita Hernanz (IEEC-CSIC, Spain) Renè Hudec (CTU, Czech Republic) Andrea Santangelo (Univ. Tuebingen, Germany) Dave Walton (MSSL, United Kingdom) Andrzej Zdziarski (N. Copernicus Astronomical Center, Poland)

on behalf of more than 150 scientists from the following countries and institutions:

Brazil, Canada, Czech Republic, Denmark, France, Germany, Greece, Ireland, Israel, Italy, Japan, the Netherlands, Poland, Spain, Switzerland, Turkey, United Kingdom, USA

INAF (IASF-Rome, IASF-Bologna, IASF-Milan, IASF-Palermo, HeadQuarters Rome, OA Rome, OA Padua, OA Palermo, OA

Cagliari); INFN (Trieste, Bologna, Milan, Rome); ASDC Frascati; CBK Poland; CfA Cambridge; MPE Garching; IEEC-CSIC Barcelona; INPE S.J. dos Campos; ISAS/JAXA, Nakagawa; ISDC Geneve; ISSI Bern; MIT Cambridge; MSSL London; NASA/

MSFC, Huntsville, NRL Washington; N. Copernicus Warsaw; Polytechnic Milan; Prague Astronomical Institute; DTU Copenhagen; SRC Leicester; University of: Alberta, Amsterdam, Arizona, Bologna, Cagliari, Calgary, Cornell, Crete, Durham, Ferrara, Galway, Geneve, Groningen, Jerusalem, John Hopkins, Maryland, Opava, Padua, Palermo, Pavia, Prague Technical,

Sabanci, Stony Brook, Southampton, Thessaloniki, Tuebingen.

LOFT: Large Observatory For x-ray Timing

A mission proposal selected by ESA as a candidate CV M3 mission devoted to X-ray timing and designed to investigate the space-time around collapsed objects

35

Neutron Star Structure and Equation of State of ultradense

matter: - neutron star mass and radius measurements - neutron star crust properties

Strong gravity and the mass and spin of black holes - QPOs in the time domain - Relativistic precession - Fe line reverberation studies in bright AGNs

The LOFT Science Drivers

LOFT: Mission Profile

q  Large Area Detector (LAD) and Wide FIeld Monitor (WFM)

q  Based on Silicon Drift Detectors (SDC) heritage of the LHC/Alice experiment at CERN with excellent performances (energy resolution 200-300 eV, low energy threshold < 2 keV, time res. < 10µs) can be used to build large area detectors)

36

LAD

WFM

Solar Array

Bus

LOFT capabilities q LOFT is specifically designed to exploit the diagnostics of very rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter.

q LOFT will investigate variability from submillisecond QPO’s to years long transient outbursts.

q The LOFT LAD has an effective area ~20 times larger than its largest predecessor (the Proportional Counter Array onboard RossiXTE) and a much improved energy resolution.

q The LOFT WFM will discover and localise X-ray transients and impulsive events and monitor spectral state changes, triggering follow-up observations and providing important science in its own.

LOFT in one plot

39

Strong gravity: The high frequency QPOs in the BHC XTE J1550-564

ν1=188 Hz, ν2=268 Hz, frac rms ν1= 2.8%, frac rms ν2=6.2% (Miller et al.

2001), flux = 1 Crab, RXTE Exposure 54 ks,

significance 3-4σ.

LOFT simulation: Texp=1 ks

Strong gravity: study of the QPO evolution with flux and fractional rms

Epicyclic Resonance Model (Abramowicz & Kluzinak 2001)

Relativistic Precession Model (Stella et al 1999)

Once the ambiguity of the interpretation of the QPO phenomena is resolved, the frequency of the QPOs will provide access to general relativistic effects (e.g, Lense-Thirring or strong-field periastron precession) and to the mass and spin of the black hole.

Strong gravity: Fe line reverberation studies in bright AGNs

LOFT simulation of a steady and variable Fe line.

F=3mCrab, a=0.99, rin=1rg, rout=100rg, q=45°, e~r-3, rsp=10rg, Torb=4 ks Texp=16 ks ◊ mapping 4 phases (1000 s each) in four cycles

M=3-4 x 106 Msun a=0.93-0.99 R=0.98(0.02)

MCG-6-30-15

rout

rin

rsp

Equation of state of NS: Pulse Shape Modelling and Fitting

LOFT simulation: SAX J1808.4-3658 Simulation of the (401 Hz) pulse profile measurement On coherent pulsations and/or burst oscillations: 5% uncertainty (90% confidence level) on mass and radius

R=11,12,13 km

M=1.3,1.4,1.5 Msun

X-ray oscillations are produced by hot spots rotating at the neutron star surface. Modeling of the pulses (shape, energy dependence) taking into account Doppler boosting, time dilation, gravitational light bending and frame dragging will constrain the M/R of the NS. Poutanen and Gierlinski 2003

LOFT Constraints to NS EOS from M-R measurements

Swift J1749.4-2807 (508 Hz) SAX J1808.4-3658 (401 Hz) 4U 1636-53 (582 Hz)

from Demorest et al. 2010

What can do LOFT for GRBs ?

q  LOFT, possibly in combination with other GRB experiments flying at the same epoch, can give us useful clues to some of the still open issues through:

1) Measurements of the prompt emission down to ~1 keV with the WFM

2) Measurements of the early afterglow with the LAD

(1) GRB X-ray prompt emission with LOFT/WFM

•  Physics of the GRB continuum prompt emission: –  Broad spectrum from 10 MeV down to 1 keV –  Transient spectral components (e.g. BB);

•  Establishing the GRB progenitors and their distance from the properties of circumburst environment: –  Column density NH and its time behaviour; –  Absorption edges;

•  X-Ray Flashes: origin, population size, link with GRB •  Increasing the detection rate of high-z GRB with low

energy threshold: SFR up to dark ages, pop III stars, etc

•  Physical origin of spectral-energy correlations and their exploitation for cosmology.

q  Eff. Area and GRB sensitivity of the LOFT/WFM w/r to present / next future GRB detectors

Swift/BAT Fermi/GBM

LOFT/WFM

q  Expected spectrum with LOFT/WFM assuming the K-edge observed from GRB990705 with BeppoSAX/WFC

BeppoSAX WFC+ GRBM LOFT/WFM

BeppoSAX WFC (max eff. Area 140 cm2, en. res. > 1 keV)

LOFT/WFM (max eff. Area 320 cm2, en. Res. 250 eV

Spectrum of XRM + high energy detector, fit with an absorbed Band law

Sensitivity vs. GRB total fluence

Assumption: the same spectral shape and K-edge optical depth (1.5) of GRB 990705

q  Combining LOFT/WFM spectrum with that of an higher energy GRB spectrometer (e.g., based on NaI or CsI)

q  Improvement in detection of high-z GRBs w/r to present and next future experiments

Loft/wfm (2–50 keV)

q  Preliminary expected rates

Ø  ~60 GRB/year in FCFOV, 50% of which with fluence high enough to perform sensitive spectroscopy and moderate timing (100 ms)

Ø  ~150 GRB/year in PCFOV, 20% of which with fluence high enough to perform sensitive spectroscopy and moderate timing (100 ms)

Ø  ~ 30 XRFs/year

Ø  ~ 2 GRBs/year at z > 7

Ø  for ~90% of detected GRBs/XRFs can provide a few arcmin location

(2) GRB X-ray early afterglow with LOFT/LAD

BeppoSAX era (1997-2002)

prompt

afterglow

Swift era q  Swift: transition from prompt to afterglow (>2005)

q The complex Early X-ray Afterglow phenomenology

Ø  new features seen by Swift in X-ray early afterglow light curves (initial very steep decay, early breaks, flares) mostly unpredicted and unexplained

Ø  initial steep decay: continuation of prompt emission, mini break due to patchy shell, IC up-scatter of the reverse shock sinchrotron emission ?

Ø  flat decay: probably “refreshed shocks” (due either to long duration ejection or short ejection but with wide range of G) ?

Ø  flares: could be due to: refreshed shocks, IC from reverse shock, external density bumps, continued central engine activity, late internal shocks…

q Sensitivity of the LOFT/LAD to GRB X-ray emission as a function of observation time

Ø  strongly dependent on the time required to slew to the GRB position Ø  by assuming the orbit duration as the minimum time required (~5500 s) -> only

very few or no detection of flares Ø  may provide sensitive measurements (at least for brightest GRBs) around the end

of the “plateau” phase (e.g., Ta, La), very important to test models for the physics, jet structure, central engine

Swift/XRT

LOFT/LAD Swift/XRT

LOFT/LAD

Ø  emission lines in afterglow spectrum detected by BeppoSAX and Chandra for a few events, but not by Swift

Ø  Swift detects intrinsic NH for many GRB afterglows, often inconsistent with NH from optical (Lyα)

Ø  exploit large area and good spectral resolution of the LAD to solve the line issue and characterize with accuracy NH variation ?

q  Absorption column and emission lines

The LOFT Wide Field Monitor and the MIRAX X-Ray Monitor are based on the same experimental design and have similar performances (but the MIRAX/XRM has a significantly larger FCFOV and slightly higher sensitivity). However: Ø  MIRAX would operate in 2017-2019/20, while LOFT would be launched not before 2020-2022

Ø  the LOFT WFM is co-aligned with the LAD and will have a not uniform sky coverage (dependent on the LOFT/LAD observing strategy), while the MIRAX XRM will observe the entire sky every 90’ Ø  the MIRAX ASM will operate in sinergy with the SGS; LOFT does not include a high energy GRB detector.

q  Scientific profile

MIRAX vs. LOFT

q  Tecnological profile

Ø The All Sky Monitor (XRM) of MIRAX is based on large area Silicon Drift Detectors developed by INAF-INFN collaboration which are at the basis also of the LOFT instrumentation (both LAD and WFM).

Ø The R&D activity on the detectors and front-end electronics of MIRAX and LOFT is completely synergic.

2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022

MIRAX Fase A Launch & Operation

LOFT Assessment Fase 0/A

Definition Fase A/B1

Implementation Fase B2/C/D

Launch

q  Temporal profile

Conclusions q  Loft can do significant GRB science by: ü  exploiting the broad FOV, low energy threshod, excellent energy resolution and good effective area / sensitivity of the WFM to investigate the physics of prompt emission, absorption features by circum-burst material, the population of XRFs and high-z GRBs

ü  complementing simultaneous observations by GRB experiments flying on other satellites (e.g., Swift + Fermi, Swift + KW)

ü  investigating the transition from plateau phase to the “normal decay” and emission lines with the LAD

q  GRB trigger logic and GRB operation modes of the WFM may be optimized; WFM energy resolution and eff. down to 1-2 keV is essential; fast TOO observations with LAD of bright/interesting GRB could be foreseen

Unveiling GRB hard X-ray afterglow emission with NuSTAR and ASTRO-H

Ø  ms time variability + huge energy + detection of GeV photons -> plasma occurring ultra-relativistic (Γ > 100) expansion (fireball or firejet) Ø  non thermal spectra -> shocks synchrotron emission (SSM) Ø  fireball internal shocks -> prompt emission Ø  fireball external shock with ISM -> afterglow emission

Standard scenarios for GRB phisics

q  most time averaged spectra of GRBs are well fit by synchrotron shock models q  at early times, some spectra inconsistent with optically thin synchrotron: possible contribution of IC component and/or thermal emission from the fireball photosphere q  thermal models challenged by X-ray spectra

Amati et al. 2001, Frontera et al. 2000, Frontera et al. 2001, Ghirlanda et al. 2007

… but prompt and afterglow emission mechanisms still to be settled !

q  Fermi: significant evidence (at least for the brightest GRBs) of a delayed onset of GeV emission with respect to soft gamma rays, GeV excess (additional spectral component),…

q  again, challenging for models: hadronic scenarios, Pynting flux dominated fireball, afterglow rise

Ghisellini et al. 2010 Fermi collaboration; Abdo et al. 2009, 2010

q  new features seen by Swift in X-ray early afterglow light curves (initial very steep

decay, early breaks, flares) mostly unpredicted and unexplained q  initial steep decay: continuation of prompt emission, mini break due to patchy

shell, IC up-scatter of the reverse shock sinchrotron emission ? q  flat decay: probably “refreshed shocks” (due either to long duration ejection or

short ejection but with wide range of G) ? q  flares: could be due to: refreshed shocks, IC from reverse shock, external density

bumps, continued central engine activity, late internal shocks…

Late afterglow emission: less complex …

q  Power-law decay q ~power-law spectra q ~power-law decay

SAX

Swift

SAX

Sari et al. (1998, 1999)

The multi-wavelength afterglow emission is modeled as due to synchrotron.

F(t,ν) ∝ t-α ν-β

with α and β depending on p, where

N(E) ∝ E-p

is the electron energy distribution.

…but standard model not always works !

q  SED of GRB 970508: fit with standard synchrotron shock model in slow cooling regime is OK

q  SED of GRB 000926: excess of X-ray emission with respect to synchrotron prediction: IC component ?

Galama et al. (1997) Harison et al. (2001)

The puzzling case of GRB990123 q  Only one case of afterglow emission clear detection at energies > 10 keV: the

bright GRB 990123 by BeppoSAX/PDS

q  The 15-60 keV flux is inconsistent with the lower energy spectrum and synchrotron emission models predictions

Maiorano et al. (2005)

The puzzling case of GRB990123 q  the fit with a synchrotron + IC component is more satisfactory, but still

problems with the “closure relationships” between spectral and decay indices

q  alternative explanations include peculiar circum-burst properties and/or peculiar shock physics

q  this shows the relevance of sensitive measurements of GRB hard X-ray afterglow emission

Corsi et al. (2005)

GRB afterglow emission with coming hard X-ray telescopes q  Unprecedented sensitivity 15-60 keV: several hundreds times better than

BeppoSAX/PDS

q  Critical issue: time needed to be on-target for a TOO observation

q  Simbol-X (study), NuSTAR (2012), ASTRO-H (2014)

Pareschi & Ferrando (2006) Harrison et al. (2010)

q  Performed simulations based on observed distributions of flux and spectral indices, on the spectrum of GRB 990123 and by using available response and backgound files

q  time required for starting TOO observation is critical and may range from a few hours up to 24-48 hours after the GRB

q  by assuming the average photon index of 2.2 (~Crab-like) and the average temporal decay index (1.3), the average 15-60 keV flux for a 100 ks observation of an afterglow of medium intensity observed after 12 hr from the GRB is ~25 µCrab

De Pasquale et al. (2006)

GRB afterglow emission with coming hard X-ray telescopes

Afterglow hard X-ray emission with NuSTAR and ASTRO-H

NuSTAR (2012)

ASTRO-H (2014)


ASTRO-H


ASTRO-H

likely possible to start TOO observations a few hours after GRB

q  Simulation of spectrum of a medium intensity afterglow with no IC component observed with a 100 ks TOO starting 8 hours after the GRB (assumed decay index 1.3, the average flux is 50 µCrab)

q  clear detection (about 18 σ) and well determined spectral shape in 10-60 keV


NuSTAR ASTRO-H

q  Simulation of GRB 990123 (including IC component) with a 100 ks TOO starting 8 hours after the GRB

q  the IC excess in 20-60 keV is clearly visible in the residuals

q  low energy (0.3 – 10 keV) spectrum (ASTRO-H SXT+HXI), Chandra/XMM + NuSTAR) improves significance

BeppoSAX at 6-10 hr


NuSTAR ASTRO-H

q  Simulation of GRB 990123 (including IC component) with a 100 ks TOO starting 8 hours after the GRB

q  the IC excess in 20-60 keV is clearly visible in the residuals

q  low energy (0.3 – 10 keV) spectrum (ASTRO-H SXT+HXI), Chandra/XMM + NuSTAR) improves significance

BeppoSAX at 6-10 hr


NuSTAR (Γ fix) ASTRO-H

Who will provide GRB detection and localization ?

q GRB detection and localization to a few arcmin is necessary; q  information on afterglow brightness and decay slope is also important to

decide to perform a TOO; these can be inferred from prompt emission intensity and early optical afterglow intensity and decay slope

q  who will provide these measurements in the 2012 – 2020 time frame ? Ø  Present/near future experiments: several tens of GRB/year by Swift (up to

2014?), SVOM/ECLAIRS (> 2014); a few GRB/year by Fermi (up to 2014 ?),IPN, MAXI; UFFO pathfinder ?

Ø  Proposed: LOBSTER, MIRAX, JANUS, UFFO-100,…

Conclusions q  despite the enormous observational progress occurred in the last 10 years, the

physics at the basis of GRB prompt and afterglow emission is still far to be fully inderstood

q  the case of GRB 990123 shows that measurements of the nearly unexplored

GRB hard (> 15 keV) X-ray afterglow would add a further important piece of information for the models

q  simulations based on the observed distributions of X-ray afterglow fluxes and

spectral and decay indices show that next generation hard X-ray focusing telescopes (NuSTAR, ASTRO-H, …), thanks to their unprecedented sensitivity in the 15-80 keV energy band, will provide sensitive spectral measurements of GRB hard X-ray afterglow, allowing to discriminate different emission components for a significant fraction of the events

q  the needed GRB detection and few arcmin localizations, together with other

information crucial to decide a TOO observation, will be provided by space missions likely flying in the >2012 time frame (Swift, SVOM; LOBSTER, JANUS, MIRAX, UFFO, … ?)

Back-up slides

q  In the > 2014 time frame a significant step forward expected from SVOM: Ø  spectral study of prompt emission in 5-5000 keV -> accurate estimates of Ep and reduction of systematics (through optimal continuum shape determination and measurement of the spectral evolution down to X-rays)

Ø  fast and accurate localization of optical counterpart and prompt dissemination to optical telescopes -> increase in number of z estimates and reduction of selection effects

Ø  optimized for detection of XRFs, short GRB, sub-energetic GRB, high-z GRB

Ø  substantial increase of the number of GRB with known z and Ep -> test of correlations and calibration for their cosmological use

Opportunity reasons

•  Exploitation of the successful experience acquired with BeppoSAX, AGILE and recent R&D activity supported by ASI.

•  International collaboration with one of the most advanced countries among the rapidly growing economies (driver for Italian industry opportunities).

•  Low cost opportunity for the National high energy Scientific Community bridging to 2020 missions.

•  Science return to the wider Italian community through monitoring of most classes of sources.

•  Opportunity for Italian geophysical Community (EQUARS).

q  GRB trigger sensitivity: MIRAX vs. SVOM

new insights in grb phenomenon with next generation...

Documents