The Fermi Large Area Telescope Towards the (first) 10 years in orbit Luca Baldini Università di Pisa and INFN–Sezione di Pisa luca.baldini@pi.infn.it Pisa, September 25, 2014 Prelude: the Fermi Observatory Large Area Telescope (LAT) I Pair conversion telescope. I Energy range: 20 MeV–> 300 GeV I Large field of view (≈ 2.4 sr): 20% of the sky at any time, all parts of the sky for 30 minutes every 3 hours. I Long observation time: 5 years minimum lifetime, 10 years planned, 85% duty cycle. Gamma-ray Burst Monitor (GBM) I 12 NaI and 2 BGO detectors. I Energy range: 8 keV–40 MeV. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 2 / 19 Fermi status and timeline SR 2012 SR 2014 Prime phase 2008 2009 2010 2011 Extended phase 2012 2013 2014 2015 2016 2017 2018 Year 0 10000 20000 # orbits 30000 ×10 Distance traveled [km] ×10 # triggers ×10 # events downlinked ×10 # events @ FSSC ×10 # γ -ray candidates 6 0 500 1000 9 0 50 100 150 200 250 300 350 9 0 10 20 30 40 50 60 70 6 0 500 1000 1500 2000 6 0 0 0 50 25 10 100 50 20 75 150 0 10 5 0 12 15 30 200 5 17 40 250 0 20 300 5 25 50 60 70 80 22 0 5 27 # ATELs # GCNs Baseline: operate through FY 2018 (i.e., 10 years) TBR in 2016. Full SR reports @ http://science.nasa.gov/astrophysics/documents/ Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 3 / 19 The Fermi science menu in a nutshell A remarkably wide dynamic range SNR CRE EGB GRB 10-2 10-1 1 3 102 10 5 104 10 6 10 10 Energy [MeV] GRB extended GRB prompt TGF Solar flares Pulsar periods AGN flares Binary systems Pulsar substr. -5 -3 -4 10 10 10 -2 10 -1 10 1 10 2 10 3 10 5 4 10 10 6 10 8 107 10 Time [s] Sun GRB Moon AGN Earth limb Galactic TGF CRE 6 10 8 10 Luca Baldini (UNIPI and INFN–Pisa) 10 10 12 10 14 10 16 10 18 10 Pisa, September 25, 2014 20 10 1022 1024 26 10 Distance [m] 4 / 19 Dark matter constraints from dSph Ackermann et al., PRD 89, 42001 (2014) I Dwarf Spheroidal Galaxies among the cleanest targets for indirect DM searches: I I I largely DM-dominated objects; do not expect significant γ-ray emission through conventional channels. Stringent DM limits based on a combined analysis of 25 dSph. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 5 / 19 The Fermi bubbles Ackermann et al., ApJ 793, 64 (2014) I I First discovered by Su, Finkbeiner & Slatyer in 2010. First Fermi-LAT publication on the topic. I I I Hard spectrum with cutoff at ∼ 110 GeV. I I I I Based on 50 months of data. Modeling of the diffuse emission is the foremost challenge. No spectral variations in latitude stripes. No energy dependence of the overall morphology. Excess emission in the the South-East; no evidence for a jet. Leptonic and hadronic interpretation of gamma-ray data possible. I Assuming association with microwave haze prefers leptonic models. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 6 / 19 The IGRB and EGB (Re)Submitted to ApJ I Updated LAT measurement of IGRB spectrum. I I I I 50 months of data, dedicated event selection(s). Extended energy range: 200 MeV–100 GeV → 100 MeV–820 GeV. Roughly ∼ 1/2 of total EGB intensity above 100 GeV now resolved into individual sources. Significant high-energy cutoff feature around ∼ 250 GeV. I I Consistent with simple source populations attenuated by EBL. Reality might be more complex, with multiple populations contributing. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 7 / 19 The 3FGL Coming soon, and heading toward ∼ 3000 sources I 4 years of reprocessed LAT data above 100 MeV: I I I vs. 2 years of (un-reprocessed) data for the 2FGL. Front/Back handled separately (different isotropic and Earth limb). More data and improved performance (due to reprocessing): I Better localization on average (error radius ∼ 15% smaller outside the Galactic plane). I Improved interstellar model of Galactic diffuse (e.g., Fermi bubbles): I Association process improved. I I Lower overall detection threshold. Dedicated multiwavelength follow-up, new surveys. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 8 / 19 Prospects for the extended mission Beating the square root of time I Time-domain astronomy (GRB, AGN, Solar Flares, TGFs, novæ). I I I Steady sources. I I Large acceptance and FOV, all-sky coverage and long integration time are key. Fermi plays a prominent role, in synergy with other instruments and observatories. High-energy limiting sensitivity comes from photon counting statistics (rather than the background). Many specific LAT analyses rely on external inputs: I I I radio timing solutions for pulsar searches; targets for indirect DM searches (e.g., dwarf spheroidal galaxies); maps for modeling the gamma-ray diffuse emission (e.g., Planck). I Long-baseline measurements. I And Pass 8 (see next slides). Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 9 / 19 Pass 8 Cover image: a 540 GeV simulated gamma ray z x I Long-term effort aimed at a comprehensive revision of the entire LAT event-level analysis. I I I Simulation, reconstruction, background rejection, analysis methods. Goals: extending the energy reach, maximizing the S/N, reducing the systematic uncertainties. Basic analysis components ready, now entering science validation. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 10 / 19 na mi eli Pr 2 ry 1.5 P8_SOURCE prototype P7REP_SOURCE_V15 1 Ratio (P8/P7) 0.5 0 Energy [MeV] 10 1 103 102 104 105 Containment angle [°] 3 2.5 Ratio (P7/P8) Acceptance [m2 sr] IRFs: Future vs. present P7REP_SOURCE_V15 (on-axis 95%) P8_SOURCE prototype (on-axis 95%) P7REP_SOURCE_V15 (on-axis 68%) P8_SOURCE prototype (on-axis 68%) 10 1 10 2 1.5 1 0.5 Pr ry na mi eli -1 Energy [MeV] 102 103 Energy [MeV] I 104 105 Energy [MeV] Larger acceptance (effective area and field of view) at all energies. I Most notably below 100 MeV (×2 at 100 MeV and ×10 at 30 MeV) I Performing spectral analysis down to such low energies presents significant challenges (e.g., energy dispersion). I Pass 8 will double the number of photons detected by the LAT above 30 MeV. I Narrower PSF at moderate-to-high energies, with reduced tails. I I I For both archival data and future observations. Can improve PSF further by tightening event selections. Preliminary indications that an in-flight correction is not needed. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 11 / 19 Pass 8 at high energy Energy [GeV] New high-energy photons from GRBs GRBs (Pass 6 and Pass 8) GRBs (new in Pass 8) BLLacs FSRQs 102 Predicted optical depth (τ = 1) for various EBL models 10 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Redshift I ∼ 20% acceptance increase at high energy. I I I I And relatively (much) larger at large off-axis angles. Re-analysis of the prompt phase of GRBs with measured redshift in the first LAT GRB catalog. Really testing the new event reconstruction. 4 photons above 10 GeV (previously discarded) recovered in Pass 8. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 12 / 19 Pass 8 at low energy Crab (30-60 MeV) P8_SOURCE prototype nsource = 23480, H = 6097 ry na mi eli Pr Pulse phase P7REP_SOURCE_V15 nsource = 4049, H = 1489 Counts/bin 450 400 350 300 250 200 250 200 150 100 50 0 800 700 600 500 400 300 200 600 500 400 300 200 100 0 0 Pulse phase P7REP_SOURCE_V15 nsource = 8961, H = 6307 15 10 GRB100826A (30-60 MeV) Preliminary P8_TRANSIENT prototype nevts = 81 GRB100826A (60-100 MeV) Preliminary P8_TRANSIENT Time sinceprototype trigger nevts = 18 P7REP_TRANSIENT_V15 nevts = 16 5 phase P8_SOURCEPulse prototype nsource = 27941, H = 18444 Crab (60-100 MeV) ry na mi eli Pr Counts/bin Counts/bin Counts/bin Counts/bin Counts/bin Periodic and transient sources 0 5 4 3 [s] P7REP_TRANSIENT_V15 nevts = 9 2 1 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 -300 -200 -100 0 Pulse phase 100 200 I Substantially improved sensitivity for pulsar searches: I Substantially improved sensitivity for time-domain astronomy: I I 300 Time since trigger [s] blind and epoch-folding pulsar searches. transient searches (e.g., GRB). Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 13 / 19 More Pass 8 at low energy Counts/bin Solar flares 10 SFR2010-06-12 8 Preliminary P8_SFR prototype P7_REP_TRANSIENT_V15 6 4 2 0 -100 -80 -60 -40 -20 0 20 40 60 80 100 Time since flare (sec) I Dedicated event selection for Solar Flares: I I alleviate the effect of X-ray pile up in the impulsive phase; increase the number of flare for localization studies. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 14 / 19 Looking after Fermi Spaced-based gamma-ray astronomy I The Fermi LAT has its sweet spot between ∼ 1 and ∼ 10 GeV. I I The high-energy frontier: I I I several projects being actively developed: CALET, DAMPE, Gamma-400, HERD (in order of appearance); all of them are gamma-ray and cosmic-ray instruments. Here we should keep in mind our ground-based big cousins! I I Hard to do significantly better there without an instrument significantly bigger. Both the current generation of IACTs and the forthcoming CTA. The low-energy frontier: I several concepts, both in the Compton and in the pair-production regime: AdEPT, COMPAIR, GammaCube, GAMMA-LIGHT, HARPO, LArGO, PANGU (in alphabetical order). Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 15 / 19 Primary protons AMS01 (Aguilar et al. 2002) Pamela (Adriani et al. 2011) ATIC-2 (Panov et al. 2006) CREAM (Yoon et al. 2011) 104 103 102 Primary positrons Pamela (Adriani et al. 2008) 10 103 102 1 -2 10-1 10 10 10-2 10-3 10-4 10-5 1 particle/hour Gamma-ray all-sky intensity Fermi LAT (unpublished) 1 particle/day Gamma-ray extragalactic diffuse Fermi LAT (Abdo et al. 2010) 10-3 10-4 10-5 1 particle/month 1 10 102 103 Rigidity (GV) or Energy (GeV) 10-6 Statistics is the main limiting factor! Is high-energy gamma-ray astronomy really IACT playground? I I 104 10 1 10-1 I 105 -1 10-6 I Primary electrons AMS01 (Aguilar et al. 2002) Pamela (Adriani et al. 2011) Fermi LAT (Abdo et al. 2010) H.E.S.S. (Aharonian et al. 2008) Integral rate of particles crossing the LAT (Hz) Integral flux above a given energy (m -2 s-1 sr -1) High energy: acceptance Possibly not, e.g., wide FOV sky monitoring and diffuse emission. Most future instruments putting emphasis on the energy resolution, instead. I (And most of them smaller than the Fermi LAT.) Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 16 / 19 0 0. 25 50 0. LAT 0. 00 10 2. 00 1. Energy resolution [%] 0. 12 An example: Line-search sensitivity Gamma-400 (CC) 4. 00 CALET DAMPE Gamma-400 HERD 8. 00 1 1 102 10 Exposure factor [m2 sr year] I The basic figure of merit Q is ns Q=√ ∝ nb I s E . σE /E Better energy resolution is obviously beneficial. I But the sensitivity is really a trade-off between exposure and energy resolution. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 17 / 19 PSF 68% containmnent [°] Low energy: point-spread function 10 Fermi-LAT (back) Fermi-LAT (total) Fermi-LAT (front) Kinematic limit 1 10-1 10-2 10-1 1 10 102 Energy [GeV] I Can we get closer to the limit dictated by nuclear recoil? I I I I I Silicon only, no converters (GAMMA-LIGHT, COMPAIR). Go to gas/liquid (AdEPT, HARPO, LArGO). Measure single-track energies (PANGU). What about ∼ 1 m3 of scintillator (GammaCube)? At low energy statistics is not so much of an issue. I Trading acceptance for PSF can be advantageous. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 18 / 19 Conclusions I Fermi has been operating in space flawlessly for more than six years. I I I No sign of performance degradation. On track for the original goal of a ten year mission. More results to come in the next few years. I And more than one would expect just based on the deeper exposure. I Path forward for space-based gamma-ray astronomy not as clear as for the ground-based instruments. . . I . . . but definitely a lot of margin for improvements and many clever ideas around. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 19 / 19 Spare slides Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 Spare slides √ Faster than the t: steady sources —Low energy —High energy Bkg. dominated √ ∝ t Photon counting nearly ∝ t I Envelope of the minimum detectable power-law spectra over the full band, varying the spectral index. I I (i.e, not a differential sensitivity plot.) High-energy limiting sensitivity comes from photon counting statistics (rather than the background). I Increase nearly linear with time, rather than Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 √ t. Spare slides Something fading out. . . The 130 GeV line, see arXiv:1303.1798 Expected for signal (1–2σ) Data Expected for pure noise (1–2σ) Fix signal hypothesis I Weniger’s updated results are consistent with the results from the recent LAT line-search paper. I I Likely that the original putative line signal was a statistical fluctuation. More data and Pass 8 will hopefully give the final word. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 Spare slides And a continuing challenge DM from the Galactic center? arXiv:1402.6703 I I I “The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter” Example of a clever analysis of public LAT data performed outside the collaboration. The Inner Galaxy is notoriously a very complicated region. I I Modeling the diffuse emission is the foremost challenge. The LAT collaboration is targeting a presentation (and paper) for the Fermi Symposium in October. Luca Baldini (UNIPI and INFN–Pisa) Pisa, September 25, 2014 Spare slides 60 θ68 = 0.15° 10 40 20 0 1 -20 -40 -60 -80 PSF 68% containment [°] 80 Integral flux > 10 GeV within θ68 [m-2 year-1] Latitude [°] DGE: interplay between aeff and PSF 10 Tobs = 10 years PSF-limited E0 = 100 G eV 1 E0 = 10 GeV LAT 10-1 Statistics-limited 10-1 -150 -100 -50 0 50 100 150 Longitude [°] Luca Baldini (UNIPI and INFN–Pisa) 10-1 Pisa, September 25, 2014 1 10 Acceptance [m2 sr] Spare slides
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