1. M.L. Cherry Louisiana State University for the GBM Earth Occultation team Earth Occultation Monitoring of the Hard X-ray/Low Energy Gamma Ray Sky with GBM Louisiana State University NASA Marshall Space Flight Center National Space and Technology Center Univ. of Alabama in Huntsville Universities Space Research Association Intl. School of Particle Astrophysics, Erice, July 6, 2012

2. C.A. Wilson-Hodge (NASA/MSFC), W.H. Baumgartner (NASA/CRESST), E. Beklen (METU/SDU), P.N Bhat, M.S. Briggs (UAH), A. Camero-Arranz (NSSTC), G.L. Case (LSU), V. Chaplin, V. Connaughton (UAH), M.H. Finger (USRA), N. Gehrels (NASA/GSFC), J. Greiner (MPE), K. Jahoda (NASA/GSFC), P. Jenke (NPP/NASA/MSFC), R.M. Kippen (LANL), C. Kouveliotou (NASA/MSFC), H. A. Krimm (CRESST/NASA/GSFC/USRA), E. Kuulkers (ESA/ESAC), C.A. Meegan (USRA), L. Natalucci (INAF-IASF), W.S. Paciesas (USRA), R. Preece (UAH), J.C. Rodi (LSU), N. Shaposhnikov, G.K. Skinner (UMD/CRESST/NASA/GSFC), D. Swartz (USRA), A. von Kienlin, R.Diehl, X. Zhang (MPE) Collaborators MAXI data from http://maxi.riken.jp

3. Why hard X–rays? Spectrum of the galactic black hole source Cygnus X-1 showing its high and low states (McConnell et al., 2000).

4. Swift all-sky map of high energy X-ray sources. The Swift survey, extending up to ~195 keV, is thought to be a complete survey of AGNs out to 100 Megaparsecs (http://heasarc.gsfc.nasa.gov/docs/swift/results/bs22mon).

5. SNR RX J1713 – Multiwavelength observations shed light on hadron vs electron acceleration

6. INTEGRAL view of the Galactic Center region at 511 keV (Revnivtsev et al., 2004). Reflected emission from the molecular hydrogen cloud Sgr B2 located 350 light years from the central black hole source Sgr A* provides a recent time history of the transient activity in the Galactic Center.

7. 44 Ti (t = 86 years) is an excellent probe of nucleosynthesis in young galactic supernova remnants  lines at 68, 78, 1157 keV. Upper series of images shows the signal from the young remnant Cas A measured by INTEGRAL in six energy bands: 63-65, 65-70, 70-74, 74-76, 76-80, 80-86 keV. The 65-70 and 76-80 keV bands clearly show 44 Ti emission. Spectrum at the bottom shows a power law spectrum with two separated lines at 67.9 and 78.4 keV at 3s above the continuum (Renaud et al., 2006).

8. Hard X-ray sky is transient: GRO J1655-40 – BATSE light curve

9. GRO J0422+32 Ling & Wheaton (2003)

10. Characteristics of the ideal hard X-ray telescope: Wide field of view to detect transient events Energy coverage up to ~ 1-2 MeV Good energy resolution for lines 10 Minute-of-arc-scale angular resolution CASTER and EXIST were coded aperture telescopes (CZT and LaBr 3 respectively) proposed for Black Hole Finder Probe that satisfied these requirements. ACT – proposed Compton telescope designed to detect nuclear lines HARMENI – Proposed wide-field balloon-borne rotating modulation telescope

11. No current detector satisfies all these requirements GBM (Gamma ray Burst Monitor) on Fermi provides best available wide-field sensitivity 8 keV – 1 MeV with 0.5 o angular resolution

12. GBM Earth Occultation Highlights (8 keV – 1 MeV) Earth occultation approach 3-year catalog High energy (> 100 keV) sources Crab variability Cyg X-1 All-sky imaging Variable sources A 0535+26

13. GBM Bismuth Germanate (BGO) Detector GBM Sodium Iodide (NaI) Detector LAT Launched June 11, 2008 550 km orbit 25.6 deg inclination GBM 12 NaI detectors 8keV - 1 MeV 12.7 cm x 1.27 cm 2 BGO detectors 150 keV - 40 MeV 12.7 cm x 12.7 cm Fermi GBM

14. GBM Earth Occultation Technique (EOT) Current catalog includes 213 sources, primarily recently active X-ray binaries, the Crab, 68 AGN, SGRs, and the Sun Fluxes for cataloged sources measured by fitting the change in count rate due to Earth occultation Source model: assumed spectrum combined with atmospheric transmission model convolved with changing detector response 8 energy bands in NaI detectors 6 persistent and 2 transient sources detected above 100 keV (Case et al. 2011, ApJ) Over 85% of sky viewed every orbit Entire sky viewed every ~26 days Sensitivity exceeds CGRO/BATSE below 25 keV and above ~1 MeV No solar constraints

15. All-sky survey Other surveys: RXTE/ASM (1995 – 2012), 2 - 10 keV MAXI/GSC, 1.5 - 20 keV INTEGRAL/IBIS, 17 - 60 keV Swift/BAT, 14 – 195 keV CGRO/BATSE (1991 – 2000), 20 - 1800 keV GBM EOT survey covers 8 – 1000 keV Greater sensitivity than BATSE 1 MeV Full sky coverage every 26 days

16. The Satellites Good overlap with GBM in time and energy RXTE 1995 - 2012 PCA 2 - 60 keV INTEGRAL 2002 - present JEM-X 3 - 35 keV IBIS/ISGRI 15keV-10MeV Swift 2004 - present BAT 15 - 200 keV GBM 2008 - present 8 keV - 40 MeV MAXI 2009 - present 0.5 - 30 keV Gamma Ray Burst Monitor (GBM) Fermi Rossi X-ray Timing Explorer (RXTE) Swift INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL)

17. Three year catalog 104 sources detected, 8 – 1000 keV 41 low-mass X-ray binary/neutron star systems 33 high-mass X-ray binary/neutron star systems 12 black hole binaries 12 active galaxies Crab Nebula Sun 4 other sources 12 sources detected, 100 – 300 keV Crab Cen A, 3C 273 9 black-hole candidates, X-ray binaries 2 sources detected, 300 – 500 keV Crab Cyg X-1 Up-to-date light curves can be found at: http://heastro.phys.lsu.edu/gbm/ To be published, Wilson-Hodge (2012)

18. High energy sources 12 sources detected, 100 – 300 keV 8 sources detected in first 2 yrs of mission (Case et al., 2011): ◦ Cen A ◦ Crab ◦ Cyg X-1 ◦ SWIFT J1753.5-0127 ◦ 1E 1740-29 ◦ GRS 1915+105 ◦ Plus two transient sources (GX 339-4, XTE J1752-223) 4 additional 100 – 300 keV sources after 3 yrs: ◦ 1E 445.1-6141 ◦ 1A 1742-294 ◦ GS 1826-238 ◦ 3C 273

19. The Crab is NOT a Standard Candle!

21. Crab time variability 7% decline observed by GBM in 15 – 50 keV during first 2 years of mission Decline in Crab flux: 5.4 ± 0.4% 12-50 keV 6.6 ± 1.0% 50-100 keV 12 ± 2% 100-300 keV 39 ± 12% 300-500 keV Wilson-Hodge et al. (2011)

22. Swift BAT Survey: 14-100 keV Crab Light Curves BAT team 65-month Survey to May 2010 Transient monitor May- Dec 2010 Points shown are ~50 day averages Constructed from single pointing light curves Restricted partial coding fractions to >85% Included systematic error of 0.75% of the rate 14-50 keV Flux decline of 6.2±0.5% observed during MJD 54690-55340 2005 2011

23. INTEGRAL IBIS and JEM-X Crab Light Curves Publicly available Crab observations Produced using OSA 9.0 Offset <10° (ISGRI); < 3°(JEM-X) Corrections based upon constant Crab are omitted. ~8% decline is seen in the 20-50 and 50- 100 keV bands (MJD 54690-55340) Possible upturn after 55340 JEM X 3-10 keV JEM X 10-25 keV 2002 2010 IBIS 20-50 keV IBIS 50-100 keV IBIS 100-300 keV

24. RXTE PCA Crab Light Curve Extracted light curves using standard 2 data Observations shorter than 300 s were excluded Background subtracted and deadtime corrected Corrected for known time dependence of response Selected layers 2+3 Variations of 5.1  0.2% (2-15 keV) and 6.8  0.3% (15-50 keV) visible from MJD 54690-55435 in all 3 PCUs Flattening/increase since summer 2010 2-15 keV 15-50 keV GB M 1999 2011

25. RXTE Crab Pulsed Flux Event mode data (250μs, 129 channel) 3.2-35 keV, all PCU2 layers Pulsed flux shows steady decrease at 0.2% per year – consistent with pulsar spin down. The larger ~5% per year variation is not seen in pulsed emission Likely has nebular origin Pulsed Flux Total Flux Wilson-Hodge et al. 2011, ApJ, 727, L40

26. Light curves for each instrument are normalized to its average rate from MJD 54690 - 54790. RXTE/PCU2 - Black BAT - Red IBIS/ISGRI - Green JEM X2 - orange SPI - Light blue GBM - Blue squares Instruments on four separate spacecraft show ~7% decline in Crab (nebula + pulsar) flux from summer 2008 to summer 2010. The Crab Nebula 1999-2011 19992011

27. RXTE PCA Spectra Colors denote “rising”, “declining” and “flat” intervals. Photon index softens from 2.15 to 2.17 during 2008-2010 flux decline Individual observations fitted, results averaged PCU2 layer 2&3 data Absorbed Power-law N h fixed 0.97  10 22 cm -2

28. Comparing “rising”, “declining”, and “flat” intervals Photon index softened from 2.14 to 2.17 Softening occurring in declining phases Hardening during initial rise. Similar results in PCU 3 & 4

29. Evidence for Softening in Swift/BAT Color scheme matches RXTE softening during 2008-2010 decline Earlier intervals consistent with constant hardness Hardness ratios 14- 50 keV/50-100 keV BAT 58-month survey data 50-day averages

30. 54690-54763 55297-55343 Spectral Softening in GBM GBM 8-1000 keV Earth occultation measurements Beginning and end of decline interval Spectral index increases from 2.11 to 2.17

31. Recent Data 2008-2012 <15 keV 15-50 keV

32. 20-year Crab Nebula Light Curve 15-50 keV 50-100 keV

33. Crab -- Summary & Conclusions The Crab Nebula was surprisingly variable from 2001-2010, with less variability before 2001 and since mid-2010. We presented evidence for spectral softening from RXTE, Swift/BAT, and Fermi GBM during the mid-2008-2010 flux decline. We will miss RXTE, but will continue our monitoring program using Fermi/GBM, MAXI, and Swift/BAT.

34. Cyg X-1 state transitions (Case et al., 2012)

35. GBM-MAXI anticorrelations GBM MAXI

36. Why hard X–rays? Spectrum of the galactic black hole source Cygnus X-1 showing its high and low states (McConnell et al., 2000).

37. BATSE observations of state transitions: GRO J0422+32 Ling & Wheaton (2003)

38. GRO J1655-40 Case et al. (2008) During “mini-flare”, power law steepens as flux increases.

39. GX 339-4 Ling et al. (2008, in preparation)

40. GX 339-4 Ling et al. (2008)

41. All-sky imaging intended to complete the all-sky catalog and reduce systematic errors – Differential filtering

42. Occultation imaging (Rodi et al., 2011) Image using EOT by dividing sky into 0.25 o bins, assigning virtual source to each, performing occultation analysis for each, cross correlating with Swift, RXTE, INTEGRAL.

43. Imaging analysis also applied to BATSE 10-year catalog 55 new sources found 26 identified with sources in other surveys 29 so far unidentified Next: redo spectral analysis with expanded catalog. Do new sources affect BATSE systematics?

44. Transient Search Method Sliding average for each of the 8 energy bands using 5, 9, and 19 day binning Join continuous bins > 2.5σ Keep continuous time periods > 5σ Select the most significant period when overlapping occurs with different sliding avg binning

45. Transient search Updated light curves at http://heastro.phys.lsu.edu/gbm/. High energy (> 100 keV) emission seen from GX 339-4 and XTE J1752-223 (right) BHC Discovered by RXTE on Oct 29, 2009 (Markwardt et al. 2009)

46. GX 339-4 LMXB/BHB P orb =1.7 day (Hynes et al. 2003)

47. A0535+262 HMXB/NS P orb =110.0 days (Coe et al. 2006)

48. GX 304-1 HMXB/NS P=132.5 day (Priedhorsky & Terrell 1983)

49. GRO J1008-57 HMXB/NS P orb =247.8 day (Coe et al 2007)

50. GK Per CV P orb =1.99 days (Crampton, Cowley, & Fisher 1986)

51. Correlated X-ray/optical observations of outbursts in Be/XRB A 0535+26 Camero-Arranz et al., 2012

52. A 0535+26 -- X-ray binary pulsar Optical companion – O9.7 IIIe star with a disk that interacts with neutron star X-ray flares associated with large speed-ups in spin frequency Correlation of pulsed flux with spin-up rate  indication of accretion disk around neutron star Correlated Ha and pulse profile measurements allow detailed comparison with disk model geometries

53. Summary 3-year catalog -- Wilson-Hodge et al., 2012 High energy (> 100 keV) sources – Case et al., 2011 Crab variability – Wilson-Hodge et al., 2011 Cyg X-1 – Case et al., 2012 All-sky imaging – Rodi et al., 2011 Variable sources – Rodi et al., 2012 A 0535+26 – Camero-Arranz et al., 2012 Up-to-date light curves can be found at: http://heastro.phys.lsu.edu/gbm/