Refusing to Go Quietly: Gamma-Ray Bursts and Their Progenitors Andy Fruchter STScI Hubble Science Briefing 5 Dec. 2013

What Are We Doing Here? An introduction to Gamma-Ray Bursts (GRBs) Massive stars and the long bursts Short bursts and merging neutron star binaries A new view on the universe 2

The Vela Satellites: Protecting the Free World from Illicit GRBs Designed to detect nuclear tests (in violation of the test ban treaty), the Vela satellites discovered GRBs 3

Compton Gamma-Ray Observatory 4

All Shapes and Sizes 5

BATSE Band Energies: 1: keV 2: keV 3: keV 4: keV Two Classes of GRBs Kouveliotou et al

BATSE Band Energies: 1: keV 2: keV 3: keV 4: keV Two Classes of GRBs Kouveliotou et al

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The Milky Way According to COBE 9

So... GRBs must be very close -- the Solar System GRBs must be very far (distant galaxies) 10

But... If they are far out in the solar sytem, they must be produced by colliding balls of ice. Throwing snowballs may be more dangerous than we realized! If they are very far, their energies may be stupendous....something like the rest mass of the sun being turned into gamma-rays! 11

Where Do GRBS Come From?

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GRB One of the brightest GRBs observed At its brightest, it was visible through a pair of binoculars But the light from the burst travelled over 12 billion light years before hitting the binoculars! Estimated energy in gamma rays of the burst = rest mass of the sun! 14

GRB Fruchter et al Now You See It The transient has faded by a factor of two million since peak in this first HST image 15

GRB Now You Don’t Fruchter et al

A Side View of a GRB Doomed Star Black Hole Regions of γ-ray formation GRB Hitting Interstellar Medium 300,000 light seconds Internal Shocks? Photosphere? 17

GRBs Go Bump in the Night 18 Expected from GRB Alone Expected from SN Alone

The Star Underneath Interestingly, the spectra of the supernovae underneath Long GRBs are missing both Hydrogen and Helium. 19

GRB Hosts Box Width 3.”75 Fruchter et al

GOODS cc SNe Hosts Box Width 7.”5 Fruchter et al

Long GRBs Are Not Just Like Other Supernovae They like to be on the very brightest parts of their host galaxy (much more so than regular supernovae) They like their hosts small -- probably to avoid “metals” 22

Artist’s Conception of GRB Environment 23

Long GRBs like this Not this You Are Here 24

Just When You Thought You Were Safe

A Short-Burst Host Mosaic Images on the left were taken in the blue, on the right in the infrared Short Bursts like all types of galaxies -- small to large, young to old. 26

So What Causes Short Bursts? Deep searches show no sign of supernovae, and Short GRBs do not greatly favor star-forming hosts, so massive stars are probably out. Neutron star binaries can merge anywhere between 10 million years and a Hubble time, and are found in all types of galaxies. But is there an observation that would be a “smoking gun”? 27

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Environment of GRB B 30

SGRB B in Black and White µ m = visible light 1.6 µ m = infrared light

What Have We Found?

If Confirmed Will conclusively show that short bursts come from merging neutron stars Will explain much, and perhaps vast majority, of heavy elements 33

Merging Neutron Stars Make Waves 34

A Future Astronomical Observatory Advanced LIGO will be able to detect gravitational waves that stretch the length of the arms by a fraction of the size of a proton 35

Listening to Neutron Star Mergers Figure: Caltech/Cornell/Cita Collaboration Audio: Ben Farr, Northwestern U. 36

The Nearest(?) SGRB GRB a 1.5 Billion light years away 37

We Might Not Need a GRB A kilonova could act as a marker Large new surveys instruments, such as LSST, could locate kilonovae These may be our best way to find the first gravitational wave sources 38

The Lesson When there are two competing theories in science, often one is right and the other is wrong. But in more interesting cases, they are both right. Welcome to the progenitors of GRBs! 39