Gamma Ray Bursts
Maurizio Falanga The First Discoveries • Designed to detect nuclear test (in viola on of the Nuclear Test Ban Treaty, 1963) Vela 4 and 5 satellite pair were launched in 1963 and 1969. • The Gamma Ray Bursts (GRB) were discovered accidentally in 1967 by US military satellites in search of non authorized nuclear explosions. The discovery was announced by Klebesadel, Strong, and Olson (ApJ, 182, 85) in 1973. • The Vela 5 satellites detected a total of 73 gamma ray bursts similar to what they would expect3C273 from such explosions, but coming from space. • These bursts where short, from 0.01 to about 100 s, and had most of their energy carried by photons in the energy range between 150-750 keV . • They remained mysteries for more than 30 years. Follow-Up: Compton Gamma-Ray Observatory 1991-2000
BATSE was a high energy astrophysics experiment in orbit around Earth on NASA's Compton Gamma-Ray Observatory. With its 8 modules, it was able to see the whole sky, and detected about 1 GRB per day.
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D4.)(B.#(/".--8(&""'"'(B.#(#*,/+"($'"&2E+.2*&#$ Ø First observed in 1967 by U.S. Vela 3 Ø For decades, searches were made to and 4 satellites launched in iden fy counterparts in other spectral conjunc on with Nuclear Test Ban regimes without success Treaty Ø Breakthrough reached in 1997 with Ø Signature unlike a nuclear weapon, satellite BeppoSAX detected the burst but observa ons were classied GRB 970228 Ø Con nued observa ons of bursts Ø X-ray camera detected fading X-ray con nued, and solar and terrestrial emission and op cal observa ons origins ruled out found a fading op cal counterpart. Ø Observa ons declassied in 1973 Deep imaging revealed a faint host galaxy at this loca on. Dimness of Ø Controversy concerning loca ons of galaxy did not allow a redshi bursts: Milky Way or cosmological? measurement at the me. se led only a er launch in 1991 of the Compton Gamma Ray Observatory Ø A second GRB detected by BeppoSAX, containing the Burst and Transient GRB 970508, was iden ed in op cal Source Explorer (BATSE), which only 4 hours a er its discovery. showed isotropic, and therefore Redshi of z = 0.835 measured (D = 6 cosmological, distribu on billion lt. yr.) What was really needed was source iden fica ons BeppoSax 1996-2002 (Italian-Dutch X-ray astronomy mission)
Beppo-SAX made some further discoveries possible due to its good angular resolu on. While BATSE had about 4 degrees pixels, Beppo-SAX reached about 50" (i.e. 290 mes be er). It had on board, in addi on to a GRB monitor, various X-ray detectors (lower 3 months later, GRB 970508 was detected energy than gamma). by Beppo-SAX and ground-based spectrometers were able to mesure the op cal spectrum of the a erglow. This th On February 28 of 1997, Beppo-SAX saw allowed to measure the redshi of the a burst both with its Gamma Ray detector object: z~0.84. It was the confirma on and X-ray. It observed the burst during a that GRBs were cosmologicals. few days and saw an a erglow in X: the X- However, this discovery posed a new ray image became dimmer on mescales problem. If GRBs were so distant, then of days. they had to be incredibly powerful: about 1051 to 1054 ergs, the light of a billion galaxies! '.HH3D"G$!%'$@8S77P$:<0*234.).<$;0+-$Z/69$ •! /0)*+$$+3$>32">0F.$"$!%'*$"=<$\)*+$$#(>[T;"4.>.=L+-$23(=+.)H")+*$ <.+.2+.<$$ $T$$$dT)"&$@8S???$ T! MH[2">V$@8S77P$ T! %"<03V$@8SQSP$$ MH[2">V$!%'$@8S77P$ MH[2">$*H.2+)(#$3E$+-.$-3*+$L">"G&$3E$!%'$@8S77P$3B+"0=.<$"+$+-.$J.2U$7,.>.*23H.I$ k)3#0=.=+$.#0**03=$>0=.*$3E$3G&L.=$"=<$=.3=$").$0=<02"+.<$"=<$*-3;$+-"+$+-.$L">"G&$0*$ >32"+.<$ "+$ "$ ).<*-0c$ 3E$ F$ e$ SIA@QI$ '>33#K$ 1_3)L34*U0K$ "=<$ J(>U")=0$ :7SS?9K$ NHOK$ QQ^K$ A8PI$D..$">*3$!6X$7P@K$`"&$5K$?@@@I$ From the red shi , z, a distance can be inferred [ cz ≈ dH(t0) from the Hubble-law] – billions of light years. Far, far outside our galaxy. From the distance and brightness an energy can be inferred:
Ø 1050-54 erg in gamma rays alone
This is 13 mes as much energy as the sun will radiate in its ten billion year life me, but emi ed in gamma-rays in less than a minute. It is 2000 mes as much as a really bright supernova radiates in several months. Distances to GRBs !%'$<()"[3=$0*$(*(">>&$p("=[\.<$"*$"*$,@SK$+-.$<()"[3=$<()0=L$;-02-$ Qq$+3$@Qq$3E$+-.$+3+">$r(.=2.$0*$<.+.2+.<$B&$+-.$+)0LL.)0=L$<.+.2+3)I$
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Open/free communica on to all the worldwide astronomers
Automated system to rapidly distribute GRB posi ons to sites worldwide via web
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A black hole forms at the center of the GRB source. It is rapidly rota ng and almost certainly has a large magne c field. It creates a fireball of rela vis c electrons, positrons and photons which expands and collides with stellar material and creates gamma rays which emerge from the star in beams ahead of the blast wave.
This illustra on shows the most common type Addi onal emissions, or a erglow, are of gamma-ray burst, thought to occur when a created by collisions of the shock (and a massive star collapses, forms a black hole, and reverse shock) with intervening ma er. blasts par cle jets outward at nearly the We can see both the jet and the a erglow speed of light. Credit: NASA/GSFC if the beam is directed towards us. '."#0=L$3E$"$!%'$
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N$).>"[40*[2$_.+$-"*$"=$3H.=0=L$3)$B."#0=L$"=L>.$w$m?sxI$ Ø Flashes of gamma rays associated with energe c explosions in distant galaxies. GRBs occur in galaxies. Ø Isotropic distribu on shows they are at cosmological distances. Ø Observed frequency is about 1 per day; actual rate due to beaming is much greater. Ø Bursts last from milliseconds to tens of seconds and show great variety. Ejecta moves at rela vis c speed Ø Believed to be most luminous electromagne c events since the Big Bang. Ø Observed fluxes are hundreds of mes brighter than supernovae, although seem to be highly beamed, so that total luminosity is comparable to that of a supernova. Ø O en followed by an a erglow in longer wavelengths up to radio, in some cases resembling the light curve from a supernova. Ø Almost every long GRB has been associated with a galaxy with rapid star forma on, and some long GRBs are linked to supernovae. The evidence favors that the parent SN popula on of GRBs are hypernovae, or Type Ib/c SNe from massive progenitors characterized by high luminosity, high expansion veclocites and no H/ He in spectra. The brightest SNe are associated with rela vely faint GRBs.
Ø Short GRBs have no supernova link, and must be physically dis nct from long GRBs. The most prevalent sugges on is that short GRBs are formed in mergers of neutron stars or black holes and neutron stars. Observed for the first me in 2017. A erglows of minutes to hours in X-rays are consistent with fragments of dally-disrupted neutron star material (r-process radia on).
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Mul -messenger astronomy
Curiosi es Rates of Gamma Ray Bursters
More than 1 per day is observed, but due to beaming, the actual rate is perhaps 1 per minute in the universe.
Within our galaxy, the rate is es mated to lie between 1 per 100,000 and 1,000,000 years. Less than 10% of these would be beamed in our direc on.
It has been suggested that the Ordovician-Silurian ex nc on, 450 Myrs ago, was caused by a GRB. Evidence is the ex nc on of tribolites which were upper ocean dwellers. Other species living on land or in shallow seas were also par cularly hard hit. Species that were deep-water dwellers were rela vely unharmed.
The rate per volume of long GRBs is es mated to be between 100 and 1000 per Gpc3 per year, which is 1 to 10% of the rate of Type Ib/c supernovae. This difference is probably due to beaming, i.e., θ-1.
!"##"$%"&$'()*+.)*$"=<$+-.$/.)#0$ k")"<3G$ N=$"*+)3H-&*02">$.GH>"="[3=$E3)$+-.$~L)."+$*0>.=2.$$ New discoveries Fast radio burst The first FRB was discovered by Duncan Lorimer and his student David Narkevic in 2007 when they were looking through archival pulsar survey data (2001 data). Many FRBs have since been recorded, including several that have been detected to repeat in seemingly irregular ways. Nonetheless, one FRB, as of February 2020, has been detected to repeat in a regular way: par cularly, FRB 180916 seems to pulse every 16.35 days. Although the exact origin and cause is uncertain, most are extragalac c. The first Milky Way FRB was detected in April 2020.
The origin of the FRBs has yet to be iden fied; proposals for their origin range from a rapidly rota ng neutron star and a black hole, to extraterrestrial intelligence.