The current status of the Fermi/Gamma ray Burst Monitor (GBM) and the Magnetar Key Project C. Kouveliotou (NASA/MSFC) on behalf of the GBM and the Magnetar teams
The Fermi Observatory Launched 2008 June 11 Large AreaTelescope (LAT) 20 MeV ->300 GeV Gamma-ray Burst Monitor (GBM) NaI and BGO Detectors 8 keV - 40 MeV KEY FEATURES Spacecra' Partner: • Large field of view General Dynamics LAT: 20% of the sky at any instant; in sky survey mode, expose all parts of sky for ~30 minutes every 3 hours. GBM: whole unocculted sky at any time. • Over 7 decades energy range largely unexplored band 10 GeV - 100 GeV
GBM • 4 x 3 NaI Detectors with different orientations. • 2 x 1 BGO Detector either side of spacecraft. • View entire sky while maximizing sensitivity to events seen in common with the LAT The Large Area Telescope (LAT) GBM BGO detector. 200 keV -- 40 MeV 126 cm 2 , 12.7 cm Spectroscopy Bridges gap between NaI and LAT. GBM NaI detector. 8 keV -- 1000 keV 126 cm 2 , 1.27 cm Triggering, localization, spectroscopy.
• GBM Triggered sources – Gamma-ray bursts (GRBs) – Soft gamma repeaters (SGRs) aka magnetars – Terrestrial gamma flashes (TGFs) – Short transients detected by on-board trigger algorithm – Solar Flares • Non-triggered sources – Pulsed sources detected by power spectral analysis and/or epoch folding – Longer-term transients and persistent sources detected by Earth occultation
Paciesas et al. 2010 Trigger Summary (July 12, 2008 - – Locations • RA, Dec July 11, 2009) – Durations Gamma-Ray Bursts 258 • (t 50 , t 90 ) in 50–300 keV Soft Gamma Repeaters 168 – Peak flux (ph/cm 2 -s) Terrestrial Gamma • 64 ms, 256 ms, 1024 ms 12 • 50–300 keV, 10–1000 keV Flashes – Fluence (erg/cm 2 ) Solar Flares 1 • 50– 300 keV, 10–1000 keV Particles (local or distant) 17 – Light curves Commanded tests 62 Will be accessible on-line through FSSC Others (sources, accidentals, 35 unclassifiable) Total 553 Current total number of GRBs detected: 448
Goldstein et al. 2010, Preece et al. 2010 1. The “Peak Flux and Fluence” Spectral Catalog: Two Spectra from all but the weakest GRBs: 2.048 s Peak Flux Spectrum > 3.5 sigma integrated Fluence Spectrum Approximately 200 bursts per year (BATSE Heritage: Mallozzi et al. 1995; Goldstein et al. 2010) 2. The “Time-Resolved” Spectral Catalog for Bright Bursts: At least two spectra for each burst, fit as a time sequence: > 15 sigma integration for each spectrum Approximately 50 bursts per year (BATSE Heritage: Preece et al. 2000; Kaneko et al. 2006) Four Spectral Models Fit to each spectrum: – Power Law: A & α – Exponentially-attenuated Power Law (“Comptonized”): A, α & E peak – Band function: A, α , β & E peak – Smoothly-Broken Power Law: A, α , β , Δ & E break Will be accessible on-line through FSSC
Band (Cstat: 699/607 dof) Cutoff PL + PL (Cstat: 689/606 dof) 10000 10000 α β 1000 1000 PL 100 100 Cutoff PL 10 E peak 10 6 6 0 0 ‐6 ‐6 10 100 1000 10000 10 100 1000 10000 Energy (keV) Energy (keV) Cutoff PL+PL prefered over the Band function => Additional component ? Guiriec et al. 2010
Guiriec et al. 2010 100 8 to 200 keV 1600 80 1200 60 800 40 400 20 0 0 9 1600 1 to 38 MeV 8 7 1200 6 5 800 4 3 400 2 1 0 0 0 0.05 0.1 0.15 0.2 Time since GBM trigger in seconds
Fermi/GBM Accreting Pulsars GBM Key Project PI: M. Finger Persistent Sources Her X-1 1.24 1.70 Eclipsing LMXB Cen X-3 4.80 2.09 Eclipsing Disk-fed HMXB 4U 1626-67* 7.63 0.023 Super-Compact LMXB OAO 1657-415 37.1 10.4 Eclipsing Wind-fed HMXB GX 1+4 158 1161 Symbiotic Binary (red giant+ns) Vela X-1 283 8.96 Eclipsing Wind-fed HMXB 4U 1538-52 525 3.73 Eclipsing Wind-fed HMXB GX 301-2 686 41.5 Wind-fed HMXB Transient Sources V 0332+53 4.37 34.2 Be/X-ray Binary 2S 1417-624 17.5 42.1 Likely Be/X-ray Binary Swift J0513.4-6547 27.3 ? Likely Be/X-ray Binary in LMC EXO 2030+375 41.3 46.0 Be/X-ray Binary Cep X-4 66.3 ? Be/X-ray Binary GRO J1008-57 93.7 248 Be/X-ray Binary A 0535+26 103 111 Be/X-ray Binary MXB 0656-072 160 ? Be/X-ray Binary LS V +44 17 205 ? Persistent Be/X-ray Binary? GX 304-1 275 132 Be/X-ray Binary A 1118-615 407 ? Be/X-ray Binary *Camero-Arranz et al. 2009
Times of Transient Outbursts October 2008 http://gammaray.msfc.nasa.gov/gbm/science/pulsars/
Fishman et al. 2010 • Twelve TGFs in year 1 – Rate is higher now by ~8X, due to inclusion of BGO detectors in trigger algorithm – Over 50 to date • Duration < ~1 ms, maximum energy > ~40 MeV – High instantaneous rates imply significant deadtime & pulse pile-up • Associated with thunderstorms: – “Runaway electron” process produces gamma-rays – Sometimes GBM detects electrons & positrons directly WWLLN sferics Briggs et al 2010 others Connaughton et al. 2010
Two Well-separated, Double-Pulse TGFs seen with GBM, All Detectors – Time Profiles Narrowest Pulse seen with GBM, ~0.08 ms Weakest Pulse Fishman et al. 2010, TGF Catalog
• Using the EOT we are currently monitoring 70 sources, including the Sun. • To date, we detect 8 of these sources above 100 keV: 1E 1740-29, Cen A, Crab, Cyg X-1, GRS 1915+105, Swift J1753.5-0127, XTE J1752-223, and GX339-4 (Case et al. 2010). • Preliminary detections for 55 sources below 100 keV (either > 10 sigma long-term average or activity coincident with other observatories) including Mrk 421 (Wilson-Hodge et al. 2010). • This is our “bright source” catalog and consists primarily of X- ray binaries, the Crab, and a few AGN (currently active transients and sources added by request). http://gammaray.msfc.nasa.gov/gbm/science/occultation/
PI: Chryssa Kouveliotou SGR Source Active Period Triggers Comments J0501+4516 08/22/08-09/03 26 New source at Perseus /08 arm 1806-20 11/29/08 1 Old source - reactivation J1550-5418 10/03/08-10/20 7 Known source – first time /08 117 exhibiting burst active 01/22/09-02/24 14 episodes /09 03/22/09-04/17 /09 J0418+5729 06/05/09 2 New source at Perseus arm SGR 1833-0832 discovered 10/03/19 with Swift and RXTE – no GBM detection http://gammaray.nsstc.nasa.gov/gbm/science/magnetars
Magnetars are magnetically powered neutron stars ~17 are discovered to date – three in 2008-2010 – Only 2 extragalactic sources Discovered in X/ γ -rays; radio, optical and IR observations: Short, soft repeated bursts . P = [2-11] s, P ~[10 -11 - 10 -13 ]s/s . τ spindown (P/2 P) = 2-220 k yrs . B~[1-10]x10 14 G (mean surface dipole field: 3.2x10 19 √ PP ) Bright sources, L~10 33–36 erg/s , >> rotational E-loss No evidence for binarity so far (fallback disks?) SNe associations?
Neutron star populations which may comprise Magnetars: Soft Gamma Repeaters (SGRs) Anomalous X-ray Pulsars (AXPs) Dim Isolated Neutron Stars (DINs) Compact Central X-ray Objects (CCOs) Rotation Powered PSRs?! PSR J1846 − 0258
PSR J1846 − 0258 SGR 0418+5729 SGR 1833-0832
2008-2010: Good years for Magnetars! Fermi IPN Swift RXTE
SGR 0501+4516 Swift triggered on 4 bursts on 22 August 2008 RXTE ToO program triggered ~4 hours after the first Swift trigger for 600 s P = 5.7620 s was reported ~ 9 hours after the first Swift trigger! . P = 7.4980x10 -12 and B = 2.1 x 10 14 G CXO HRC location: RA = 05h 01m 06.756s DEC = +45d 16m 33.92s (0.1” error) IR Counterpart with UKIRT, K~18.6 (Tanvir & Varricatt 2008) GBM triggered on 26 events from the source – total of 56 events in ~ 3.5 days
BURSTS Suzaku data for 080826_136: Integrated spectrum best fit by 2 BB: kT1 = 3.3 keV, kT2 = 15.1 keV Enoto et al. 2009
GBM data for 080826_136 (common with Suzaku): Integrated spectrum can be fitted with two BB or one BB + PL kT 1 = 8 keV, kT 2 = 18 keV or kT = 11 keV, γ = -2.4 Watts et al. 2010 Lin Lin et al. 2010
PRE in thermonuclear bursts • Luminosity reaches Eddington limit, triggering Photospheric Radius Expansion (PRE). • Expanding layers cool, leading to a multi-peaked light curve. • Standard candle to measure a neutron star distance or mass/radius and hence equation of state. Watts et al 2010
PRE in thermonuclear bursts >10 keV 5-10 keV Counts/s 2-5 keV Time
PRE in magnetar bursts • Identifying PRE during a magnetar burst would give us the magnetic Eddington limit. If the magnetic field is known (e.g. from timing) this would again constrain distance/equation of state. Miller 1995 • PRE can only occur under certain burst emission scenarios. A PRE burst will therefore also constrain the burst trigger mechanism, a major unknown.
The first magnetar candidate PRE burst Other candidate PRE bursts being investigated! Watts et al. 2010 • Distance and field strength known. • Predicted critical flux matches that recorded by GBM! • Emission becomes softer during the dip in the lightcurve.
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