gamma-ray bursts: what do we need in the 2020s? · the proton density in gamma ray burst ﬁreballs...

Gamma-Ray Bursts: what do we need in the 2020s?

Valerie ConnaughtonUSRA

Working group for GRB roadmap: Nicola Omodei, Bing Zhang, VC. Others?

1

Wednesday, July 15, 15

HEAD meeting on experiments for the 2020s - GammaSIG session

What motivates gamma-ray observations of GRBs?

‣ Understanding the physics of GRBs and jetted relativistic outflows

‣ GRBs as a tool for cosmology

‣ GRBs as beacons for multi-messenger astronomy

2Wednesday, July 15, 15


GRB physics (1) Spectral energy distributions of GRBs probe the physics of jetted relativistic outflows

‣ Current: Fermi provides 8 decades of energy. Very active area of research - science moving beyond empirical functions to physical modeling of jet content, radiation mechanism.

‣ Future needs: Broad energy range in peak(10s - 1000s keV) and higher energies. Localization good enough for follow-ups; probe of MeV - 100 MeV region that is ill-observed.

3

GRB 090902BEpeak

α β

Extra power law at low and high energies.

GRB 090902BAbdo et al. 2009

High-energy emission is extended in time - relation to afterglow?

Photospheric interpretationRyde et al. 2009



GRB Physics (2) Polarization of GRB prompt emission - new territory to distinguish between models based on inferences about magnetic fields

‣ Current: Some tantalizing results from IKAROS, INTEGRAL, RHESSI but no conclusive measurements.

‣ Needs: Large area for gamma-ray polarimetry of dozens -100 GRBs, broad gamma-ray energy coverage to reduce MDP. Crude localization.

4

Expected polarization fraction for different models as a function of GRB EPeak

Toma et al. 2009

Synchrotron - ordered B

Compton Drag

Synchrotron - random B



Cosmology (1) can GRBs probe the time of the earliest stars and the epoch of reionization?

5

‣ Current: Swift rapid XRT response enables optical follow-up to reveal many z. Results imply source number or luminosity evolution.

‣ Future needs: Rapid location good enough for spectroscopy of distant GRBs; GRB detector sensitive enough for weak, distant GRB; on-board IR capability for distant z?

Salvaterra et al. 2012



Cosmology (2) Can GRBs be used like SN 1a in the distant universe?

6

‣ Current: Golden age. Fermi reveals observer-frame energetics. Follow-up to Swift reveals z.

‣ Future needs: If relations are calibrated, gamma-ray observations suffice; rapid X-ray response and/or sensitive long-term X-ray response to uncover full range of jet breaks.

Inferred jet break timesGoldstein et al. submitted

Relations (Liang, Amati, Ghirlanda, Yonetoku) Physics and cosmology from (same authors, Levinson & Eichler, Guiriec, Goldstein)



Cosmology (3): The GRB - Core collapse supernova connection. Nearby long GRBs tend to have associated 1bc SN detections

7

‣ Current: Swift rapid XRT response enables optical follow-up to reveal z and allow optical tracking of lightcurve to uncover SN.

‣ Future needs: Wide field-of-view GRB detector as these local events are not common. Localization good enough for follow-up.

GRB 130702A - iPTF 13bxlSinger et al. 2014

GRB 130702A - SN 2013dxd’Elia et al. 2015



Multi-messenger (1) GRB fireballs should have protons that produce a detectable neutrino flux for bright GRBs providing Γ < 400 - 500

8

‣ Current: IceCube limits to neutrino fluxes from bright GRBs.

‣ Future needs: A more sensitive IceCube! Bright GRBs - broad sky coverage. Broad energy range covering peak of SED for meaningful predictions.

5

300 350 400 450 500 550 600 650 7005

10

20 region (this result)

3 years IC86

FIG. 4. Constraints on fireball parameters. The shaded re-gion, based on the result of the model-dependent analysis,shows the values of GRB energy in protons and the averagefireball bulk Lorentz factor for modeled fireballs6,9 allowed bythis result at the 90% confidence level. The dotted line in-dicates the values of the parameters to which the completedIceCube detector is expected to be sensitive after 3 years ofdata. The standard values considered9 are shown as dashed-dotted lines and are excluded by this analysis. Note that thequantities shown here are model-dependent.

boost factor �. Increasing � increases the proton en-ergy threshold for pion production in the observer frame,thereby reducing the neutrino flux due to the lower pro-ton density at higher energies. Astrophysical lower limitson � are established by pair production arguments9, butthe upper limit is less clear. Although it is possible that� may take values of up to 1000 in some unusual bursts,the average value is likely lower (usually assumed to bearound 3006,9) and the non-thermal gamma-ray spectrafrom the bursts set a weak constraint that � . 200021.For all considered models, with uniform fixed proton con-tent, very high average values of � are required to becompatible with our limits (Figs. 3, 4).

In the case of models where cosmic rays escape fromthe GRB fireball as neutrons8,10, the neutrons and neu-trinos are created in the same p� interactions, directlyrelating the cosmic ray and neutrino fluxes and remov-ing many uncertainties in the flux calculation. In thesemodels, � also sets the threshold energy for productionof cosmic rays. The requirement that the extragalacticcosmic rays be produced in GRBs therefore does set astrong upper limit on �: increasing it beyond ⇠ 3000causes the proton flux from GRBs to disagree with themeasured cosmic ray flux above 4⇥1018 eV, where extra-galactic cosmic rays are believed to be dominant. Limitson � in neutron-origin models from this analysis (& 2000,Fig. 3) are very close to this point, and as a result allsuch models in which GRBs are responsible for the entireextragalactic cosmic-ray flux are now largely ruled out.

Although the precise constraints are model dependent,

the general conclusion is the same for all the versions offireball phenomenology we have considered here: eitherthe proton density in gamma ray burst fireballs is sub-stantially below the level required to explain the highestenergy cosmic rays or the physics in gamma ray burstshocks is significantly di↵erent from that included in cur-rent models. In either case, our current theories of cos-mic ray and neutrino production in gamma ray burstswill have to be revisited.

1Waxman, E. Cosmological gamma-ray bursts and the highestenergy cosmic rays. Phys. Rev. Lett. 75, 386–389 (1995).

2Vietri, M. The Acceleration of Ultra–High-Energy Cosmic Raysin Gamma-Ray Bursts. Astrophysical Journal 453, 883–889(1995). arXiv:astro-ph/9506081.

3Milgrom, M. & Usov, V. Possible Association of Ultra–High-Energy Cosmic-Ray Events with Strong Gamma-Ray Bursts.Astrophysical Journal Letters 449, L37 (1995). arXiv:astro-ph/9505009.

4Waxman, E. & Bahcall, J. High energy neutrinos from cosmolog-ical gamma-ray burst fireballs. Phys. Rev. Lett. 78, 2292–2295(1997).

5Avrorin, A. V. et al. Search for neutrinos from gamma-ray burstswith the Baikal neutrino telescope NT200. Astronomy Letters37, 692–698 (2011).

6Abbasi, R. et al. Search for Muon Neutrinos from Gamma-rayBursts with the IceCube Neutrino Telescope. Astrophysical Jour-nal 710, 346–359 (2010).

7Abbasi, R. et al. Limits on Neutrino Emission from Gamma-RayBursts with the 40 String IceCube Detector. Phys. Rev. Lett.106, 141101 (2011). 1101.1448.

8Rachen, J. P. & Meszaros, P. Cosmic rays and neutrinosfrom gamma-ray bursts. In C. A. Meegan, R. D. Preece, &T. M. Koshut (ed.) Gamma-Ray Bursts, 4th Hunstville Sym-posium, vol. 428 of American Institute of Physics ConferenceSeries, 776–780 (1998). arXiv:astro-ph/9811266.

9Guetta, D., Hooper, D., Alvarez-Muniz, J., Halzen, F. &Reuveni, E. Neutrinos from individual gamma-ray bursts in theBATSE catalog. Astroparticle Physics 20, 429–455 (2004).

10Ahlers, M., Gonzalez-Garcia, M. C. & Halzen, F. GRBs on pro-bation: Testing the UHE CR paradigm with IceCube. Astropar-ticle Physics 35, 87–94 (2011). 1103.3421.

11Becker, J. K. High-energy neutrinos in the context of multi-messenger astrophysics. Physics Reports 458, 173–246 (2008).0710.1557.

12Abbasi, R. et al. The IceCube data acquisition system: Sig-nal capture, digitization, and timestamping. Nuclear Instru-ments and Methods in Physics Research A 601, 294–316 (2009).0810.4930.

13Ahrens, J. et al. Muon track reconstruction and data selectiontechniques in AMANDA. Nucl. Instrum. and Meth. A 524, 169–194 (2004).

14GRB Coordinates Network. http://gcn.gsfc.nasa.gov.15Becker, J. K., Stamatikos, M., Halzen, F. & Rhode, W. Coinci-dent GRB neutrino flux predictions: Implications for experimen-tal UHE neutrino physics. Astroparticle Physics 25, 118–128(2006). arXiv:astro-ph/0511785.

16Waxman, E. Astrophysical sources of high energy neutrinos.Nucl. Phys. B Proc. Suppl. 118, 353–362 (2003).

17Feldman, G. J. & Cousins, R. D. Unified approach to the classicalstatistical analysis of small signals. Physical Review D 57, 3873–3889 (1998).

18Guetta, D., Spada, M. & Waxman, E. On the Neutrino Fluxfrom Gamma-Ray Bursts. Astrophysical Journal 559, 101–109(2001).

19Baerwald, P., Hummer, S. & Winter, W. Systematics in Ag-gregated Neutrino Fluxes and Flavor Ratios from Gamma-RayBursts. Astroparticle Physics 35, 508 – 529 (2012). 1107.5583.

Abbasi et al. 2012Constraints from 196 GRBs



Multi-messenger (2): if short GRBs are compact object binary mergers, they offer a clear e/m counterpart to gravitational waves detectable by LIGO/Virgo

9

‣ Current: GBM sees 45 short GRBs per year. aLIGO/Virgo coming online. Sub-threshold searches in both directions (GW and GRB) important. Handful per year within aLIGO horizon (Kalogera, this morning)

‣ Future needs: Capability to detect many short GRBs - broad sky coverage, energy coverage in 100s - 100s keV, sensitivity to impulsive events, location good enough for RAPID follow-up - not so important when aLIGO at full sensitivity.

Aasi et al. 2013(submitted andarXiv:1304.0670)



Other: Fundamental Physics - Lorentz Invariance, the unknown....

10

‣ Current: Fermi offers broad energy range for LIV studies. Bright GRBs easy to locate well enough for follow-up to determine z.

‣ Current: High-energy emission from GRBs provides a probe of Extragalactic Background Light to more distant z than blazars.

‣ Future needs: Unclear how to improve LIV or EBL - very high energy detections would help both. Expect the unknown.

‣ Role of short-lived millisecond magnetars in GRB production



Other: An all-sky monitor of transient or variable high-energy emission provides value to other space missions

11

‣ Current: Fermi GBM and Swift BAT offer all/broad-sky monitoring of hard X-ray sky.

‣ Future needs: Maintain this capability to support e.g., Athena. Lower energy threshold than needed for GRB triggering is desirable for galactic transients.

The transient sky to GAIA

Figure credit: A. Smith, H. Campbell (IoA, Cambridge)



Summary of bucket list. Some of this can be done elsewhere. What is most important?

‣ All/Broad sky coverage

‣ Broad energy coverage for GRBs 10 keV - 1 GeV

‣ Highest energies - on-ground with HAWC/CTA

‣ Lower threshold desirable for non-GRB transients

‣ Localization capability for follow-up observations - how good?

‣ ZTF/DES/LSST can help - ok for physics, multi-messenger

‣ On-board afterglow and redshift determination

‣ short GRBs need rapid follow-up

‣ high-z needs IR spectroscopy (on-board? JWST/TMT/GMT?)

‣ Sensitive instrument - weak GRBs needed for high-z universe 10^-9 erg/cm^2 fluence (between 50 - 300 keV)?

‣ Large collection area needed for 100s keV - MeV polarization.



The three main paths to cover GRB science needs in the 2020s

‣ A probe-class mission that does it all: sky monitor, spectral coverage, localization, afterglow and redshift determination. Can polarization be accommodated too? More of a flagship.

‣ A secondary transient-detecting instrument on-board a probe doing something else e.g. a polarization or pair telescope.

‣ A stand-alone transient monitor or fleet of monitors concentrating on GRB physics but enabling follow-ups on-ground or on another satellite.



‣ Time to start our roadmap. Do we need a mailing list? A schedule? Coordination with other science groups?


gamma-ray bursts: what do we need in the 2020s? · the proton density in gamma ray burst ﬁreballs...

Documents