2

= ermi

Gamma-ray Space Telescope

Fermi GBM Counterparts to LIGO/Virgo Gravitational-VVave Candidates

Valerie Connaughton

Universities Space Research Association Huntsville, AL

for the GBM team and the GBM-LIGO/Virgo electromagnetic follow-up group: Lindy Blackburn, Michael S. Briggs, Eric Burns, Jordan Camp, Nelson Christensen, Valerie Connaughton, Tito del Canto, Adam Goldstein, Peter Jenke, Tyson Littenberg, Judith Racusin, Peter Shawhan, Leo Singer, Colleen Wilson-Hodge, Binbin Zhang

Thursday, January 7, 16

Mergers of binary neutron star systems produce both short Gamma-Ray Bursts

(GRBs) and gravitational radiation.

Gamma ray radiation is seen in a jet as a short GRB detected by GBM if the jet is pointed at us. GBM can see very far.

Jet-ISM Shock (Afterglow) Optecal (hours—days motte (weeks~y cars : Ejecta-ISM Shock sf Radio (years)

Kilonova wT Optical (t ~ | Gay)

Gravitational radiation is emitted isotropically and nas seen by LIGO/Virgo LIGO (|

~ te * vw OlO3e 4 a \ Ps q ~ = }

can’t see very far (70 Mpc in ~~ - ~ Ol, ~200 Mpc at design).

| Merger Ejecta

Figure 1 of Meztger & Berger 2012

V. Connaughton 227th AAS meeting Thursday, January 7, 16

Kissimmee, FL January 2016

Joint GBM LIGO/Virgo events happen when the jet is pointed towards us and the merger happens nearby i.e., quite rarely ~|-- handful joint detections per year (model- dependent). It is very important to maximize the probability of joint GBM LIGO/Virgo detections and enable supporting observations that will provide the distance scale and energetics of the explosion.

Owing to all-sky coverage, Fermi GBM detects and localizes more short GRBs than other GRB detectors.

Fermi GBM short GRBs as of 151030 GBM: 40 short GRBs per year,

90 coarse localization (tens square degrees)

-90 Dec Swift BAT: 9 short GRBs per year, arcminutes y. 291 Short GRBs localization facilitating - 27 also triggered Swift-BAT follow-ups. V. Connaughton 22/thAAS meeting Kissimmee, FL January 2016

Thursday, January 7, 16

Weak short GRBs are not necessarily more distant than bright short GRBs and may lie within the detection horizon of LIGO/Virgo.

LIGO/Virgo detection horizon for on-axis events with favorable sky

position

10° = 10° o VU Cc Vv LL

10°

0.0 0.5 1.0 | e. 2.0 2.5 3.0 Redshift

> GBM and Swift detect the same population of short GRBs (Burns et al. in press)

» Extrapolating from sGRBs with known redshift gives <0.5 - 5 per year sGRB for GBM within LIGC Virgo horizon (nearby z uncertain).

» This number is doubled with unseeded search for GRBs that do not trigger on-board.

V. Connaughton 22/7th AAS meeting Kissimmee, FL January 2016 4 Thursday, January 7, 16

Even a large banana and a large orange can help: using joint GBM-LIGO/Virgo detections and GBM non-detection to guide follow-up observers

Typical GBM GRB localization region Typical LIGO localization region from for weak GRB http://www.ligo.org/scientists/first2years/: changes in 2016 with addition of Virgo

18 +/- 5 nearby galaxies (N. Gehrels et al. 2015, arXiv:1508.03608)

Typical reduction of 80% in sky region:

4 nearby galaxies: easier to follow up with XRI or optical telescopes.

» Using the non-detection of a GRB (triggered or untriggered) by GBM or Swift: limiting the sky region to that not viewed by either instrument reduces LIGO sky region by about 50%, assuming on-axis GVV candidate with sGRB above detection threshold.

» Taken from E. Burns at Swift meeting (and in prep)

http://www.clemson.edu/ces/physics-astro/conferences/Swift2015 V. Connaughton 227th AAS meeting Kissimmee, FL January 2016 Thursday, January 7, 16

GBM can contribute in many ways to the breakthrough observations of gravitational wave radiation

» A detection by GBM of a short GRB in coincidence with LIGO/Virgo strengthens the significance of the GW detection

» Sub-threshold searches of GBM data for short GRBs may yield twice as many short GRBs within the LIGO/Virgo horizon

Searches for LIGO/Virgo sub-threshold searches in the GBM data can find candidates that would otherwise go undetected, increasing LIGO sensitivity by 15-20% (Blackburn

et al. 2015)

> Observing GBM localization regions of |Os sq degs has been successful (S. Kulkarni’s talk on ZIF)!

> GBM localization regions can greatly reduce (by 80%) the region of sky to be observed at lower energies

The non-detection of GBM short GRBs can similarly limit the follow-up region for on- axis merger afterglows.

Next Huntsville GRB workshop: 24 - 28 October 2016, in Huntsville AL. Organizers: VC, Neil Gehrels, Adam Goldstein. Details soon!

V. Connaughton 227th AAS meeting Kissimmee, FL January 2016 Thursday, January 7, 16