M.L. CherryLouisiana 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 UniversityNASA Marshall Space Flight Center

National Space and Technology CenterUniv. of Alabama in Huntsville

Universities Space Research Association

Intl. School of Particle Astrophysics, Erice, July 6, 2012

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

Why hard X–rays?

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

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).

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

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.

44Ti ( = 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 44Ti emission.

Spectrum at the bottom shows a power law spectrum with two separated lines at 67.9 and 78.4 keV at 3 above the continuum (Renaud et al., 2006).

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

GRO J0422+32

Ling & Wheaton (2003)

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 LaBr3 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

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 0.5o angular resolution

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

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

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

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 <25 keV and >1 MeV

Full sky coverage every 26 days

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)

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)

High energy sources12 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

The Crab is NOT a Standard Candle!

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)

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

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

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 5.10.2% (2-15

keV) and 6.80.3% (15-50 keV) visible from MJD 54690-55435 in all 3 PCUs

• Flattening/increase since summer 2010

2-15 keV

15-50 keV

GBMGBM

1999 2011

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

• 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

1999 2011

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

• Nh fixed 0.971022 cm-2

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

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

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

Recent Data 2008-2012

<15 keV

15-50 keV

20-year Crab Nebula Light Curve

15-50 keV

50-100 keV

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.

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

GBM-MAXI anticorrelations

GBM

MAXI

Why hard X–rays?

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

BATSE observations of state transitions: GRO J0422+32

Ling & Wheaton (2003)

GRO J1655-40

Case et al. (2008)

During “mini-flare”, power law steepens as flux increases.

GX 339-4

Ling et al. (2008, in preparation)

GX 339-4

Ling et al. (2008)

All-sky imaging intended to complete the all-sky catalog and reduce systematic errors –

Differential filtering

Occultation imaging (Rodi et al., 2011)

Image using EOT by dividing sky into 0.25o bins, assigning virtual source to each, performing occultation analysis for each, cross correlating with Swift, RXTE, INTEGRAL.

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?

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

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)

GX 339-4

• LMXB/BHB

• Porb=1.7 day (Hynes et al. 2003)

A0535+262

• HMXB/NS

• Porb=110.0 days (Coe et al. 2006)

GX 304-1

• HMXB/NS• P=132.5 day

(Priedhorsky & Terrell 1983)

GRO J1008-57

• HMXB/NS

• Porb=247.8 day (Coe et al 2007)

GK Per• CV

• Porb=1.99 days (Crampton, Cowley, & Fisher 1986)

Correlated X-ray/optical observations of outbursts in Be/XRB A 0535+26

Camero-Arranz et al., 2012

• 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 H and pulse profile measurements

allow detailed comparison with disk model geometries

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/