Detection of ultra-long gamma-ray bursts with the ECLAIRs telescope aboard the SVOM mission Dagoneau, Nicolas ([email protected]) - Schanne, Stéphane - Gros, Aleksandra - Cordier, Bertrand 1

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1. French Alternative Energies and Atomic Energy Commission (CEA), Saclay, France

MT-252 E1.17-0046-18

Gamma-ray bursts

The SVOM Mission

Burst: fast and transient increase in the flux of a celestial body.

SVOM (Space-based multi band astronomical Variable Objects Monitor) is a Chinese-French space mission dedicated to the study of Gamma-Ray Bursts (GRBs) in the next decade [1].

Gamma-ray burst: 1. birth of a stellar black hole: • coalescence of compact objects (neutron stars): short burst ( 2s) 2. emission of ultra-relativistic jets: • internal shocks: prompt γ emission • external shocks with ISM: afterglow (X radio)

Goal: build a homogeneous sample of GRBs with a good timing and spectral coverage and redshift measurement, including X-ray rich, high-redshift, off-axis jet GRBs.

ECLAIRs coded mask telescope • Energy-band: 4-120keV

fireball model (illustration: NASA)

• Field of view: 2sr • Coded mask: Ti-Ta-Ti

ECLAIRs allows long stable pointings in same portions of sky, up to 1 day. Below: histogram of pointing durations over one year simulation.

• On axis sensitivity in 1s: 780mCrab • Localization error: < 12arcmin • Detection: ∼ 70GRB/year

Ultra-long gamma-ray bursts Some bursts have ultra-long durations (>1000s) and could represent a new class of bursts [2] [3].

Long time imaging / Ultra-long GRBs simulations Long time imaging requires good background cleaning: • CXB: Cosmic background

X-ray

• X sources in 4-120keV • Earth in field of view > 30% of time [2]

Origins: require a central engine powered during an ultra-long time (core collapse of a blue supergiant, magnetar birth, white dwarf 9 TDE [4], [5], [6]), BH of mass < 10 M at z > 6 [7]. Characteristics: long emission after the burst, fast variations in X-ray plateau (flares or dips).

Opposite: onboard image cleaning process

Raw shadowgram (counts in 20s):

Model shadowgram (counts in

Model subtracted shadowgram

Deconvolution of cleaned

•

Earth modulated CXB

20s):

(counts in 20s):

shadowgram  sky (SNR in 20s):

•

GRB contribution ?

•

•

Known sources, depending on

pointing (yes in this case)

Quadratic CXB: m = 𝑎𝑥 2 +

•

𝑏𝑦 2 + 𝑐𝑥 + 𝑑𝑦 + 𝑒𝑥𝑦 + 𝑓

•

Known sources models (1

Reduced non uniformity due

Reduced sources contribution

 source-illumination models are

param. per source), 5 sources

(non subtracted ones remain

known

max TBC

but are fainter)

•

𝑆𝑁𝑅 =

•

Part is occulted by Earth

•

Part is too close to known

to Earth modulated CXB

•

counts variance

•

sources

Fitting to raw shadowgram

Simulation of ultra-long GRBs from: • Ultra-long GRBs database from Swift/BAT tables (∼ 20 events): spectral analysis on BAT band only during a short time, BAT lightcurve is not always > 1000s • Long GRBs from [8] moved at different redshift (complete spectral analysis with Fermi and Wind/Konus)

More about SVOM E1.17-0036-18 Wed., July 18, 2018, 10:15-10:30 E1.17-0037-18 Wed., July 18, 2018, 10:30-10:45 E1.15-0015-18 Thurs., July 19, 2018, 11:30-12:00 www.svom.fr/en - twitter.com/svom_mission

Above: T90-fluence plan with ECLAIRs detection limit and Swift GRBs. Ultra-long GRBs to be placed in this plot. ECLAIRs could also detect other ultra-long events: TDE, SN shock breakout. Work in progress: simulations will allow to evaluate precisely the sensitivity of ECLAIRs to the ultra-long bursts and to decide if it is relevant to set up a particular strategy for their automatic detection onboard...

References [1]

J. Wei, et al., 2016.

[5]

Jochen Greiner, et al. 2015.

[2]

A. J. Levan, et al. 2013.

[6]

Kunihito Ioka, et al. 2016.

[3]

M. Boër, et al. 2015.

[7]

Tatsuya Matsumoto, et al. 2015.

[4]

B. Gendre, et al. 2013.

[8] V Heussaff. PhD Thesis, 2015.

ECLAIRs program is a cooperation between CNES, CEA and CNRS, with CNES acting as prime contractor. This work is supported by the CEA and by the "IDI 2017" project of the French "Investissements d’Avenir" program, financed by IDEX Paris-Saclay, ANR-11-IDEX-0003-02.