SOFT GAMMA REPEATERS Kevin Hurley UC Berkeley Space Sciences Laboratory SOFT GAMMA REPEATERS AN OBSERVATIONAL REVIEW Kevin Hurley UC Berkeley Space Sciences.

SOFT GAMMA REPEATERS Kevin Hurley UC Berkeley Space Sciences Laboratory SOFT GAMMA REPEATERS AN OBSERVATIONAL REVIEW Kevin Hurley UC Berkeley Space Sciences Laboratory khurley@ssl.berkeley.edu

THE SOFT GAMMA REPEATERS ARE SPORADIC SOURCES OF BURSTS SGRs can remain dormant for many years; during these periods, no bursting behavior is observed They become active and emit bursts at apparently random times Two common types of bursts: –Short (100 ms, up to 10 41 erg s -1 ) –Giant flares (several hundred seconds, periodic emission, up to 10 46 erg s -1 )

BURSTING ACTIVITY OF 3 SGRs OVER 17 YEARS

SINGLE, ~100 ms LONG BURST (MOST COMMON)

TWO SGR GIANT FLARES 5.16 s period 7.56 s period SGR1900+14 AUGUST 27 1998 ULYSSES 25-150 keV E γ =4x10 44 erg SGR1806-20 DECEMBER 27, 2005 RHESSI 20-100 keV E γ =8x10 45 erg Three phases: 1) Fast rise (<1 ms) 2) Very intense initial spike, ~100 ms long 3) Periodic decay (~300 s)

GIANT SGR FLARES ARE SPECTACULAR! Occur perhaps every 30 years on a given SGR Second only to supernovae in intensity Intense (E γ ≳ 10 46 erg at the source, 1 erg/cm 2 at Earth) Very hard energy spectra (up to >10 MeV) Create transient radio nebulae Cause dramatic ionospheric disturbances Should be detectable in nearby galaxies

SHORT BURST ENERGY SPECTRA, 2-150 keV: SUM OF TWO BLACKBODIES, kT=3.4 and 9.3 keV (SGR1900+14, Feroci et al. 2004) BeppoSAX MECS kT=3.4 keV BeppoSAX PDS kT=9.3 keV R= 14 km at 10 kpc R=2 km at 10 kpc

GIANT FLARE ENERGY SPECTRUM: 175 keV BLACKBODY, THEN 10 keV BLACKBODY

THE SGRs ARE QUIESCENT X AND γ-RAY SOURCES Luminosities: 10 34 – 10 36 erg/s (>spin-down energy) This quiescent component varies slowly, and exhibits pulsations (~10-20% pulsed fraction)

QUIESCENT X-RAY SOURCE ASSOCIATED WITH SGR1806-20 ASCA, 2-10 keV INTEGRAL-IBIS, 18-60 keV 10 -11 erg cm -2 s -1 10 -10 erg cm -2 s -1

QUIESCENT X-RAY FLUX LEVEL IS RELATED TO THE BURSTING ACTIVITY Bursts and quiescent emission are probably both related to magnetic stresses on the surface of the neutron star GIANT FLARE SGR1806-20 Woods et al. 2006

P and P-dot FROM QUIESCENT SOFT X-RAYS (2-10 keV) SGR1900 (P=5.16 s, P=10 -10 s/s) SGR1806 (P=7.48 s, P~10 -10 s/s) Kouveliotou et al. 1998 Woods et al. 2000Woods et al. 1999 Hurley et al. 1999 8x10 -11 s/s 10 -10 s/s..

SPINDOWN IS IRREGULAR, SOMETIMES RELATED TO BURSTING ACTIVITY, SOMETIMES NOT RELATED (Woods et al. 2002, 2006) SGR1900+14 Woods et al. 2006 GIANT FLARE This argues against accretion as the cause of the bursts

BROADBAND QUIESCENT X-RAY SPECTRA Blackbody 20 keV Götz et al. 2006 SGRs AXPs

MAGNETARS COMPARED TO OTHER NS: P-P DIAGRAM SGRs, AXPs High B Radio Pulsars Radio Pulsars Millisecond Radio Pulsars V. Kaspi 2006.

ESSENTIAL SGR PROPERTIES *initially thought to be an AXP

HOSTS AND PROGENITORS One or two SGRs are probably in supernova remnants One SGR may have been ejected from its supernova remnant Two SGRs are probably in massive star clusters The SNR association implies a normal progenitor mass (~5-8 M  ) The massive cluster association implies a massive progenitor (~50M  )

THE SGR-SNR CONNECTION SGR0525-66 is almost certainly in the N49 SNR in the LMC 1E1547-5408 lies within the radio SNR G327.24-0.13 SGR0501-4516 may have been ejected from its supernova remnant

MASSIVE CLUSTER-SGR ASSOCIATIONS SGR1900+14 ~13 stars 1-10 Myr old (Vrba et al. 2000) SGR1806-20 ~12 stars 3-5 Myr old SGR progenitor mass ~48M  (Fuchs et al. 1999; Bibby et al. 2008)

COUNTERPARTS Two SGRs exhibited transient radio nebulae after giant flares One SGR has a persistent radio counterpart One SGR has a variable NIR counterpart

SGRs ARE TRANSIENT RADIO SOURCES AFTER GIANT FLARES: RADIO NEBULA CREATED BY GIANT FLARE FROM SGR1806-20 (Taylor et al. 2005) VLA THIS RADIO EMISSION COMES FROM AN EXPANDING CLOUD OF RELATIVISTIC ELECTRONS ACCELERATED IN THE MAGNETOSPHERE AND EXPELLED. BUT SGRs ARE NOT OBSERVABLE QUIESCENT RADIO SOURCES

SGR1806-20 IS INVISIBLE IN THE OPTICAL (n H ~6x10 22 cm -2 ), BUT IT IS JUST BARELY VISIBLE IN THE INFRARED m K’ =22 Kosugi et al. 2005 This is the only optical or IR counterpart to an SGR so far Israel et al. 2005 m Ks =20 10″ 1.5″

IR FLUX IS NOT AN EXTRAPOLATION OF HIGH ENERGY QUIESCENT FLUX But the IR flux varies with the quiescent flux and/or with bursting activity Israel et al. 2005 IR X-γ

ESSENTIAL SGR PROPERTIES

HOW MANY SGRs ARE THERE? 5 or 6 confirmed SGRs (depending on 1E1547) Three unconfirmed SGRs: 1801-23, 1808-20, GRB050925 Some short GRBs could be extragalactic giant magnetar flares Muno et al. (2008) estimated <540 in the galaxy, based on Chandra, XMM data

CONCLUSIONS There is good evidence that the known SGRs are magnetars There is growing evidence that the members of the magnetar family (AXPs and SGRs) are very similar to one another

SGRs AND AXPs OBSERVATIONAL PROPERTIES COMPARED SGRsAXPs Small BurstsFrequentRare Giant FlaresYesNo Quiescent X-raysYes, to >100 keV Radio emissionFollowing giant flares only 1-2 cases known, transient Periods5 – 8 s2 – 11 s Spindown.5 – 20 × 10 -11 s/s0.05 – 20 × 10 -11 s/s HostsMassive star clusters?SNRs?

In 1992, Duncan and Thompson, and Paczyński, independently proposed that neutron stars with large magnetic fields could explain SGR bursts and giant flares In 1995, Thompson and Duncan expanded their model to explain the AXPs Duncan and Thompson called these neutron stars magnetars Motivation: –High B  low opacity, so L>>L Eddington is allowed –High B  neutron star magnetosphere can contain the energy of the radiating electrons in a giant flare –High B causes rapid spindown of newly born pulsar – in the case of SGR0525, the age of the SNR is 10,000 y, and the period is 8 s –High B is a reservoir of energy to power the quiescent emission and the bursts

MAGNETARS Definition: a neutron star in which the magnetic field, rather than rotation, provides the main source of free energy; the decaying field powers electromagnetic radiation (R. Duncan & C. Thompson, 1992; C. Thompson & R. Duncan, 1995, 1996) Note that the definition does not specify the magnetic field strength To explain SGRs and AXPs, however, B must be greater than the quantum critical value 4.4 x 10 13 G, where the energy between electron Landau levels equals their rest mass Some AXPs and SGRs require B~10 15 Gauss, so these magnetars have the strongest cosmic magnetic fields that we know of in the universe

ORIGIN OF THE MAGNETIC FIELD Unknown, but there are two hypotheses: 1.Fossil field: massive (25 M  ) progenitor star’s field (10 4 G or more) is amplified during core collapse and frozen into highly conducting compact remnant (the neutron star). Initial period of neutron star is 4-10 ms, too slow for a dynamo to operate efficiently. 2.Dynamo amplification: field is generated by convective dynamo in the proto-neutron star. Initial period is 1-3 ms. These hypotheses are not mutually exclusive

MAKING A MAGNETAR WITH A DYNAMO (Duncan & Thompson 1992) A neutron star undergoes vigorous convection in the first ~30 s after its formation Coupled with rapid rotation (~1 ms period), this makes the neutron star a likely site for dynamo action If the rotation period is less than the convective overturn time, magnetic field amplification is possible In principle, B ~ 3 x 10 17 G can be generated (magnetic field energy should not exceed the binding energy of a neutron star, so B<5 x 10 18 G)

Differential rotation and magnetic braking quickly slow the period down to the 5-10 s range Magnetic diffusion and dissipation create hot spots on the neutron star surface, which cause the star to be a quiescent, periodic X-ray source The strong magnetic field stresses the iron surface of the star, to which it is anchored The surface undergoes localized cracking, shaking the field lines and creating Alfvèn waves, which accelerate electrons to ~100 keV; they radiate their energy in short (100 ms) bursts with energies 10 40 – 10 41 erg (magnitude 19.5 crustquake) There is enough energy to power bursting activity for 10 4 y

NEUTRON STAR B≈10 15 G Thompson & Duncan 1995

Localized cracking can’t relieve all the stress, which continues to build Over decades, the built-up stress ruptures the surface of the star profoundly – a magnitude 23.2 starquake Magnetic field lines annihilate, filling the magnetosphere with MeV electrons Initial spike in the giant flare is radiation from the entire magnetosphere (>10 14 G required to contain electrons) Periodic component comes from the surface of the neutron star

THE STATISTICS OF SHORT SGR BURSTS ARE CONSISTENT WITH THE MAGNETAR MODEL Burst durations Distribution of the time between bursts Number-Intensity relation for short bursts

STATISTICS: DISTRIBUTION OF SHORT BURST DURATIONS (Gogus et al. 2001) LOGNORMAL

STATISTICS: DISTRIBUTION OF THE TIME BETWEEN BURSTS RXTE SGR1900 Gogus et al. 1999 LOGNORMAL SGR1900+14 Gogus et al. 1999

STATISTICS: NUMBER-INTENSITY DISTRIBUTION Götz et al. 2006 POWER LAW

STATISTICS DISTRIBUTIONS OF SGR PROPERTIES Lognormal duration and waiting time distributions, and power law number-intensity distribution, are consistent with: Self-organized criticality (Gogus et al. 2000) –system (neutron star crust) evolves to a critical state due to a driving force (magnetic stress) –slight perturbation can cause a chain reaction of any size, leading to a short burst of arbitrary size (but not a giant flare) A set of independent relaxation systems (Palmer 1999) –Multiple, independent sites on the neutron star accumulate energy –Sudden releases of accumulated energy

OUTLINE History SGRs 1.Bursts –X-and γ-ray time histories, giant flares, QPO’s –X-ray afterglows –energy spectra, lines 2.Quiescent emission in X- and γ-rays AXPs Interpretation of the data Data at other wavelengths: radio, optical Non-electromagnetic emissions: gravitational radiation Magnetar locations: SNRs, massive clusters Magnetar census Terrestrial effects of giant flares Extragalactic magnetars The latest news (SGR0501, AXP 1E1547)

AXPs At least 4 AXPs have optical/IR counterparts All have an IR excess with respect to an extrapolation of their X- ray blackbody spectra One or two AXPs display transient, pulsed radio emission

Magnetars may be deformed during bursts and especially during giant flares QPOs may be evidence of this deformation It follows that they may be sources of gravitational radiation

LIGO LIMITS ON GRAVITATIONAL RADIATION Upper limit to GR from GRB070201, an SGR giant flare in M31 (Abbott et al. 2008) Search for GR from SGR0501 bursts is in progress

BUT SGR1900+14 IS NOT ASSOCIATED WITH THE SNR G42.8+0.6! If the SGR originated in the SNR, a proper motion of 110 mas/yr is implied DeLuca et al. (2008) have set an upper limit to the proper motion using 5 years of Chandra data: < 70 mas / yr SGR1900

AXPs 3 or 4 AXPs are at the geometrical centers of SNRs Implied proper motions are small, and these associations are considered to be likely 1 AXP is in the cluster Westerlund 1

GIANT FLARES TURN NIGHT INTO DAY! Inan et al. 1999 Level of the ionosphere as measured by propagation of VLF signal from Hawaii (21.4 kHz) descends to daytime value, due to ionization by 3-10 keV X-rays at 30-90 km Effect of the giant flare of 1998 August 27 from SGR1900+14

THE GIANT FLARE FROM SGR1806-20 The most intense solar or cosmic transient ever observed X- and gamma-ray energy released at the source: 3x10 46 erg Measured X- and gamma-ray flux at the top of the atmosphere: 1.4 erg/cm 2 This should be considered a lower limit to the energy released (saturation effects, limited energy ranges) It would require ~10 6 erg/cm 2 absorbed by the atmosphere (a giant flare at 15 pc) to cause an effect similar to “nuclear winter” (ozone depletion, destruction of the food chain) To cause damage to the biosphere, SGR1806-20 would have to be about 16000 times closer, at the distance of the nearest stars Probability: 10 -6

ARE SOME SHORT GRBs ACTUALLY MAGNETAR FLARES IN NEARBY GALAXIES? GIANT FLARE FROM SGR1806-20 RHESSI DATA Giant flare begins with ~0.2 s long, hard spectrum spike The spike is followed by a pulsating tail with ~1/1000 th of the energy Viewed from a large distance, only the initial spike would be visible It would resemble a short GRB It could be detected out to 100 Mpc Some short GRBs are almost certainly giant magnetar flares, but how many?

GRB051103 – A POSSIBLE EXTRAGALACTIC GIANT MAGNETAR FLARE FROM M81 (3.6 Mpc) IPN Error Ellipse M81 M82 Swift BAT 15-150 keV (Not imaged) E γ =7x10 46 erg Frederiks et al. 2007

GRB070201 – A POSSIBLE EXTRAGALACTIC MAGNETAR FLARE FROM M31 (780 kpc) IPN Error Box M31 E γ =1.5x10 45 erg LIGO measurements indicate that this could not have been a binary merger in M31 (Abbott et al. 2008) Mazets et al. 2008

5 GIANT FLARE ENERGIES Assumed distance, kpcE γ, erg SGR1900+14 August 27 1998 154x10 44 SGR0525-66 March 5 1979 557x10 44 SGR0044+42 (M31) February 1 2007 780 (M31)1.5x10 45 SGR1806-20 December 27 2004 8.78x10 45 SGR0952+69 (M81) November 3 2005 3600 (M81)7x10 46

INTEGRAL-IBIS IMAGE OF THE QUIESCENT EMISSION FROM SGR0501

JOINT FIT TO THE QUIESCENT SPECTRUM WITH XMM AND INTEGRAL DATA (2BB+PL) N. Rea et al., 2009

SGR 0501+4516 PL indices of the hard tails: 0.95 3.1±0.5 1.5-1.9 0.73±0.17 1.46± 0.21 0.94±0.16 Götz et al. 2006 Rea et al. 2009 Different spectral shapes below and above 10 keV ⇒ different emission mechanisms

AXP 1E1547-5408: THE INTEGRAL SPI-ACS BURST ZOO

1E1547 was initially classified as an AXP But the bursts from 1E1547 are SGR-like Two possibilities –1E1547 was incorrectly classified; it’s really an SGR –SGRs and AXPs are really the same type of object

Chandra-INTEGRAL Spectrum of 1E1547 (Courtesy G.L. Israel)

OPEN QUESTIONS What is the number-intensity relation for giant magnetar flares? What is the SGR birth rate and lifetime? What is the progenitor magnetic field? What kind of supernova produces an SGR? Why can’t we detect its remnant? How are AXPs different from SGRs? Are some high-B radio pulsars actually like magnetars? How is the high energy tail of the quiescent component generated?

BUT…WHAT IF THEY’RE NOT MAGNETARS? Fallback accretion disk Phase transitions in strange stars

AND LOCATION SGR0525-66 lies in the direction of the N49 SNR in the LMC This association has been controversial since March 6 1979 Important to resolve, because –it is the only unobscured SGR, and –if the SGR is in N49, it is the only SGR with an accurately known distance and age; HST measurements reveal no optical counterpart (Kaplan et al. 2001); accretion disk ruled out Chandra measurements indicate that the quiescent X-ray spectrum resembles that of an AXP, suggesting that the neutron star may be intermediate between and SGR and an AXP

SHOULD YOU BUY A MAGNETAR SHELTER? (WORST CASE CALCULATION) Say each giant flare releases 3x10 46 erg ~10 6 erg/cm 2 absorbed by the atmosphere (a giant flare at 15 pc) would cause an effect similar to “nuclear winter” (ozone depletion, destruction of the food chain) Assume magnetars are distributed uniformly throughout the disk of the galaxy (900 kpc 3 ), and that ~10 are active at any given time Probability ~ 10 -6

LOCATIONS OF THE FOUR KNOWN SGRS SGR 1806-20 SGR 1900+14 SGR0525-66 N49 LMC SGR1627-41  Magnetars are young objects

MAGNETAR LOCATIONS IN THE GALAXY s MM M M M M M M M M M M M M M M YOU ARE HERE

MMMMMMMMMMMMMMM MAGNETAR LOCATIONS IN THE GALAXY ⇒ MAGNETARS ARE YOUNG OBJECTS

SGR1806-20 DISTANCE ESTIMATES

DUST RING AROUND SGR1900+14 If the SGR is at the distance of the massive cluster, the August 27 1998 giant flare could have created a dust-free cavity The ring would be illuminated by the stars in the cluster Wachter et al. 2008 Spitzer observation

SGR1900+14 DISTANCE ESTIMATES

NUMBER-INTENSITY RELATION FOR 5 GIANT SGR FLARES* *not to be taken too seriously

HOW TO ANSWER THEM More detailed theory More sensitive instruments, longer observation times Another 30 years of data

THE GIANT FLARE FROM SGR1806-20 December 27 2004 21:30:26 UT SGR1806-20 was over longitude 146.2º W, latitude +20.4º (near Hawaii) Detected by at least 24 spacecraft (and probably numerous military spacecraft) – most of which had no X- or gamma-ray detectors! The most intense solar or cosmic transient ever observed Measured X- and gamma-ray flux at the top of the atmosphere: 1.4 erg/cm 2 X- and gamma-ray energy released at the source: 3x10 46 erg This should be considered a lower limit to the energy released (saturation effects, limited energy ranges)

A FEW NUMBERS FOR COMPARISON Peak luminosity: 2x10 47 erg/s –Peak luminosity of all the stars in the Galaxy: 8.7x10 43 Total energy released: 3x10 46 erg in ~ 1 second –=300,000 years of the sun’s energy output –=8x10 18 times the yearly world energy consumption –=8x10 19 times the energy in the world’s nuclear arsenal But the dose outside the Earth’s atmosphere, 0.14 rem, was roughly equivalent to a medical X-ray To cause damage to the biosphere, SGR1806-20 would have to be about 16000 times closer, at the distance of the nearest stars

GIANT SGR FLARES ARE SPECTACULAR! Occur perhaps every 30 years on a given SGR Intense (3x10 46 erg at the source, 1 erg/cm 2 at Earth), ~5 minute long bursts of X- and gamma-rays with very hard energy spectra (up to several MeV at least) Are modulated with the neutron star periodicity Create transient radio nebulae, dramatic ionospheric disturbances Display fast oscillations which provide a clue to the structure of the neutron star

LESS WELL KNOWN SGR PROPERTIES

THE GIANT FLARE FROM SGR1806-20 December 27 2004 21:30:26 UT SGR1806-20 was over longitude 146.2º W, latitude +20.4º (near Hawaii) Detected by at least 24 spacecraft (and probably numerous military spacecraft) – most of which had no X- or gamma-ray detectors! The most intense solar or cosmic transient ever observed Measured X- and gamma-ray flux at the top of the atmosphere: 1.4 erg/cm 2 X- and gamma-ray energy released at the source: 3x10 46 erg This should be considered a lower limit to the energy released (saturation effects, limited energy ranges)

A FEW NUMBERS FOR COMPARISON Peak luminosity: 2x10 47 erg/s –Peak luminosity of all the stars in the Galaxy: 8.7x10 43 Total energy released: 3x10 46 erg in ~ 1 second –=300,000 years of the sun’s energy output –=8x10 18 times the yearly world energy consumption –=8x10 19 times the energy in the world’s nuclear arsenal But the dose outside the Earth’s atmosphere, 0.14 rem, was roughly equivalent to a medical X-ray To cause damage to the biosphere, SGR1806-20 would have to be about 16000 times closer, at the distance of the nearest stars

IS SGR1900+14 ASSOCIATED WITH A HISTORICAL SUPERNOVA? (Wang, Li, and Zhao 2002) “During the 3rd month of the 3rd year of Jian-Ping in the period of the king of Han Ai (4 BC, April), a po star was seen near He-Gu” Similar description is found in Korean records “po” star had m~5 In this direction, m=5 corresponds to M=-21; possibly a hypernova

R. Mallozzi, 1998

On August 22, 2008, SGR0501+4516 awoke from a long sleep and became burst-active The first detection was by the Swift BAT This was the first new SGR to be confirmed in 10 years Many ToO observations were called (AGILE, Chandra, INTEGRAL, RXTE, Suzaku, Swift, XMM) We activated our INTEGRAL AO-6 ToO program on August 27, and observed the source for about 200 ksec We detected the quiescent emission, and four weak bursts

TIMELINES OF BURSTING ACTIVITY AND TOO OBSERVATIONS

August 27 2008 16:25 20-40 keV 40-100 keV 100-300 keV BURST #1 COUNTS/50 ms

20-40 keV 40-100 keV 100-300 keV August 27 2008 22:26 BURST #2 COUNTS/50 ms

BURST PARAMETERS Duration, ms Fluence, erg cm -2 Peak flux, erg cm -2 s -1 (50 ms) kT, keV (OTTB) August 27 16:251506.6x10 -9 4.8x10 -8 --- August 27 22:252004.8x10 -8 8.4x10 -8 --- August 28 03:322003x10 -8 1.4x10 -7 28 August 28 20:59502x10 -8 3x10 -7 33 These bursts are very weak; spectra are typical for SGR bursts

Spectrum of August 28 20:59 burst OTTB fit kT=33 keV

SUMMARY INTEGRAL-IBIS ToO observation of SGR0501+4516 was successful 4 weak bursts were detected. The spectra of two of them were typical of SGR bursts; the other two were too weak for analysis Quiescent emission was detected up to 100 keV; flux was 4x10 -11 erg cm -2 s -1, 18-100 keV, a typical number for SGRs XMM/INTEGRAL spectrum indicates a rising νF ν spectrum above 10 keV with a hard power law, which is fairly typical of magnetars

“STRANGE” BURSTS, 1000 TIMES LONGER (RARE) INTERMEDIATE DURATION BURSTS (RARE)

INTERMEDIATE BURST ENERGY SPECTRUM: SUM OF TWO BLACKBODIES, kT=4.3 and 9.8 keV (SGR1900+14, Olive et al. 2004) HETE WXM HETE FREGATE

NO GLITCH AT THE TIME OF THE SGR1806-20 GIANT FLARE

HOW MANY ARE THERE? When they burst normally in gamma-rays, they are bright enough to detect anywhere in the galaxy When they don’t, you can detect them as quiescent X-ray sources, but you have to know exactly where to look Long periods (decades) with no bursts  possible hidden galactic SGRs Muno et al. (2008) estimated <540 based on Chandra, XMM data

SOFT GAMMA REPEATERS Kevin Hurley UC Berkeley Space Sciences Laboratory SOFT GAMMA REPEATERS AN OBSERVATIONAL REVIEW Kevin Hurley UC Berkeley Space Sciences.

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