First Year Fermi Gamma ray Space Telescope Observations of Centaurus A

Transcription

1 First Year Fermi Gamma ray Space Telescope Observations of Centaurus A C.C. Teddy Cheung (NASA GSFC) Yasushi Fukazawa (Hiroshima Univ) on behalf of the Fermi LAT collaboration The Many Faces of Centaurus A Sydney, 30 June

2 Fermi LAT Collaboration France Italy Japan CNRS/IN2P3, CEA/Saclay INFN, ASI, INAF Hiroshima University ISAS/JAXA RIKEN Tokyo Institute of Technology Sweden Royal Institute of Technology (KTH) Stockholm University PI: Peter Michelson (Stanford) ~390 Scientific Members (including 96 Affiliated Scientists, plus 68 Postdocs and 105 Students) Cooperation between NASA and DOE, with key international contributions from France, Italy, Japan and Sweden. Managed at SLAC. United States Stanford University (SLAC and HEPL/Physics) University of California, Santa Cruz Santa Cruz Institute for Particle Physics Goddard Space Flight Center Naval Research Laboratory Sonoma State University The Ohio State University University of Washington 2

3 3

4 Launch: June 11,

5 Year 1 Science Operations Overview August 12, 2009 LAT, GBM turnspacecraft on turn-on checkout check out week LAUNCH June 11, 2008 week Start Year 1 Science Ops Start Year 2 Science Ops first light whole sky Observatory week renaming pointed + sky survey tuning week sky survey + ~weekly GRB repoints + extraordinary TOOs month 12 months L+60 days initial tuning/calibrations 2nd Symposium in-depth instrument studies 1st LAT Catalog Release Flaring and Monitored Source Info GBM and LAT GRB Alerts GI Cycle 1 Funds Release continuous release of new photon data GI Cycle 2 LAT Year 1 photon Proposals data release PLUS LAT 6-month Diffuse Model high-confidence source release, GSSC science tools advance release 5

6 EGRET Observations of Cen A Only clearly associated EGRET radio galaxy (two other possible associations: with 3C111 and NGC6251) Year and sub-year timescales: limited to 2.1σ 3.9σ detections Cumulative 6.2σ detection from (50 MeV to 2 GeV) Average F(>100 MeV) = 1.36 (+/0.25) E-7 ph/cm2/s and Γ=2.58 +/0.26 3EG catalog: Hartman et al. (1999) see also Sreekumar et al. (1999) 6

7 Cen A: Expectations for GLAST (Fermi) Poor EGRET localization r(95%)=0.53 degrees 50%, 68%, 95%, 99% contours Hartman et al. (1999) 7

8 Cen A: Expectations for GLAST (Fermi) Poor EGRET localization r(95%)=0.53 degrees GLAST Brochure (ca. 2000) 50%, 68%, 95%, 99% contours Hartman et al. (1999) 8

9 Basic Questions and Goals for LAT Establish Cen A as a MeV-GeV emitter Cen A was associated with 3EG J which had a poor localization: r(95%)=0.53 deg (Hartman+ 1999; Sreekumar+ 1999) In the Revised EGRET catalog (Casandijian & Grenier 2009), Cen A is outside of the localization of EGR J Localize the MeV-GeV emission; determine spectrum, variability Many possible production sites: pc-scale core, jet, kpcscale jet, lobes, and (10 deg scale) giant lobes Is Cen A an unique γ-ray source? Extragalactic γ-ray sky dominated by blazars; Cen A was the only confident EGRET radio galaxy association Are other radio galaxies (i.e., misaligned jets) γ-ray emitters? 9

10 Additional Motivation Giant Lobes Glowing in γ-rays? Hardcastle, Feain talks Hardcastle, Cheung, Feain, Stawarz 2009 γ-ray signature of UHECRs? Clay, Ostapchenko, Hardcastle talks Haslam image with directions of Auger UHECR events indicated (r=3.2d) (from Moskalenko et al. 2009) 10

11 Outline 1: Introducing the Fermi LAT Basic capabilities of the Large Area Telescope (LAT) Sky survey (3-month) results Fermi LAT radio galaxies (e.g., Perseus A = NGC 1275) 11

12 Outline 1: Introducing the Fermi LAT Basic capabilities of the Large Area Telescope (LAT) Sky survey (3-month) results Fermi LAT radio galaxies (e.g., Perseus A = NGC 1275) 2. LAT Results on Cen A Cen A detected as bright source in 3-months (Steinle s talk) Preliminary results from 10-month data (Aug 4 May 31): localization, spectrum, variability Work on giant lobes in progress and will not be announced here 12

13 Fermi Key Features Large Area Two instruments on board: Telescope (LAT) LAT: high energy (20 MeV 300 GeV) GBM: low energy (8 kev 30 MeV) Huge field of view Spacecraft Partner: General Dynamics GLAST Burst Monitor (GBM) - LAT: 20% of the sky at any instant; in default sky survey mode, expose all parts of sky for ~30 minutes every 3 hours (2 orbits). Huge energy range - including largely unexplored band 10 GeV GeV. - angular resolution <1 deg at 1 GeV 13

14 Overview of LAT: How it works Precision Si strip Tracker (TKR) Measure the photon direction; gamma ID. Hodoscopic CsI Calorimeter (CAL) Measure the photon energy; image the shower. Segmented Anticoincidence Detector (ACD) Reject background of charged cosmic rays; segmentation removes self veto effects at high energy. ACD Electronics System Includes [surrounds flexible, robust hardware trigger 4x4 array of TKR towers] and software filters. γ e+ Tracker e Calorimeter Atwood et al, ApJ 2009, 697, 1071 Systems work together to identify and measure the flux of cosmic gamma rays with energy 20 MeV >300 GeV. 14

15 LAT All Sky Sensitivity (Atwood et al. 2009, ApJ, 697, 1071) In 1 day, ability to detect (at 5σ ) the weakest EGRET sources. In 2 weeks, detect # of photons that EGRET detected in entire mission. 15

16 Fermi LAT First Light 4 days of all sky exposure Equivalent to 1 year of Compton EGRET observations 16

17 Fermi LAT First Light 4 days of all sky exposure Equivalent to 1 year of Compton EGRET observations 17

18 3 Month All sky Survey Maps entire sky every 2 orbits (~3 hrs) Movie of 1 day exposures for first 3 months 18

19 3 Month All sky Survey Maps entire sky every 2 orbits (~3 hrs) Movie of 1 day exposures for first 3 months 19

20 3 Month All sky Survey Maps entire sky every 2 orbits (~3 hrs) Movie of 1 day exposures for first 3 months 20

21 LAT Data Products During the first year, we release: ATELs for flaring sources: >1-2 e-6 ph/cm2/s, i.e., 7x EGRET flux Cen A 1-day bins Lightcurves for 23+ sources Bright source list (N=205) Data release ~Aug 12, week bins First year catalog ~Oct

22 LAT High Confidence Bright Source List (N=205) Based on 3 months sky survey (Abdo et al. 2009, ApJS, 183, 46) 206 sources 205 sources with significance > 10σ (EGRET found fewer than 30). Typical 95% CL error radius is <10 arcmin. 1/3 show variability. (Contact authors: J. Ballet, S. Digel, I. Grenier, D. Thompson) 22

23 Radio Galaxies in LAT Bright Source List Cen A NGC1275 (Perseus) 2 radio galaxies: Confirmed EGRET detection of Cen A and new LAT detection of NGC

24 Fermi LAT Detection of Perseus A Abdo et al ApJ, 699, 31 (contact author: Jun Kataoka) NGC 1275 = Perseus A = 3C84, D~75 Mpc 35σ in 3-months, r(95%)=5.1 arcmin No previous detection with EGRET First new LAT radio galaxy 3 month all-sky map Cen A NGC1275 (Perseus A) 24

25 Diffuse or Compact? θ 68 = 0.6o EGeV (Atwood et al. 09) Counts distrib. of NGC1275 & src_a consistent with point source. 25

26 Short term Variability Search for temporal variation of γ -ray flux and spectrum Average LAT spectrum: Γ = 2.17 ±

27 Long Term Radio γ COS-B Variability EGRET Historical γ -ray activity compared w/ long-term radio light curve. Note, radio light curve is in a rising state during Fermi observations. 27

28 Flaring Radio (VLBI) Core 3C84 (15 GHz) MOJAVE Difference (Aug 08 Sep 07) 15 GHz VLBA observations taken simultaneously w/ Fermi show a significant brightening of the core (flare starting!). 28

29 Long Term γ ray Variability & Radio Correlation? LAT flux 6x brighter than EGRET limit Year timescale variability r~0.3 pc Radio light curve rising during the Fermi observations with pc-scale outburst seen in MOJAVE maps 1 mas = 0.35 pc 29

30 Centaurus A: LAT Results Well-localized LAT source, r(95%)=0.071 deg in 10months r(95%)=0.30 deg in 3-month LAT (0FGL J ) r(95%)=0.53 deg for 3EG J The γ-ray variability: versus EGRET (decade timescale) within LAT observations (10-months) relationship to other wavelengths (hard X-rays) 30

31 LAT Detection of Cen A and Localization preliminary Increased significance in 10month (32σ) over LAT 3-month (12σ) Confirmed the 3EG source; EGR source displaced from Cen A LAT localization: r(95%)=0.071 deg; vast improvement over 3EG r(95%)=0.53 deg. EGRET (Hartman et al. 1999); EGR (Casandijian & Grenier 2009) 31

32 LAT Detection of Cen A and Localization preliminary Error circle includes pc-scale core, jet, and the kpc-scale jet Other sources like kpc-scale lobes may contribute but not dominant γ-ray source Excludes 10 deg scale giant lobes (results TBD) 32

33 10 month Spectrum & Long term Variability preliminary Consistent with initial 3-month data, where LAT F(>100 MeV) flux ~1.6x larger than EGRET one* However, some possible contamination of LAT spectrum from extended emission - LAT 10-month (red) - 3EG (50 MeV 2 GeV) - TeV data from HESS (Aharonian et al. 2009) *We stated ~2x larger (>100 MeV) flux in submitted version of LBAS paper (Abdo et al. arxiv: v1) 33

34 Cen A: LAT vs. BAT Lightcurves LAT ~1-month binned: χ2/dof = preliminary Brightest AGN in hard X-rays: during LAT observations, dramatic variability seen with BAT Hard X-rays dominated by disk emission so correlation with LAT emission not necessarily expected 34

35 Cen A in Gamma ray Context Cen A Per A Per A has average γ-ray spectrum while Cen A has very steep spectrum Are typical γ-ray radio galaxies more like Cen A or Per A? Per A γ-ray luminosity ~400x that of Cen A (20x more distant) FSRQs (filled circles) BL Lacs (open circles) LBAS sample paper : Abdo et al. arxiv: v1 35

36 Summary of LAT Results Well-associated LAT source, r(95%)=0.071 deg Encloses the pc-scale core, jet, and kpc-scale jet. Kpc-scale lobes may contribute but certainly not dominant Excludes giant (100 s kpc-scale) lobes. (results TBD) The γ-ray variability: versus EGRET (decade timescale) within ~2x within LAT observations (10-months) no large flares relationship to other wavelengths (hard X-rays) Not well-established. Other monitoring data desirable. Possible origin(s) of γ-ray emissions: Outlined in HESS paper (Aharonian et al. 2009) and defer to Aharonian s talk. Possible signature of UHECR accelerator (Clay, Ostapchenko) 36

37 2009 Fermi Symposium Capitol Hill, Washington DC, Nov 2-5 (early reg. Oct 1); please join us! 37

38 Cen A in Gamma ray Context Per A has average g-ray spectrum while Cen A has very steep spectrum Are typical g-ray radio galaxies more like Cen A or Per A? Cen A Abdo et al. arxiv: v1 38

39 Spectral Energy Distribution Abdo et al. (2009) Ghisellini et al. (2005) 39