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Sky Model for DC2: Celestial Sources in the Milky Way S. W. Digel Stanford Linear Accelerator Center

Sky Model for DC2: Celestial Sources in the Milky Way S. W. Digel Stanford Linear Accelerator Center. S. Ciprini. APOD (Flammarion/Nemiroff/Bonnell) http://antwrp.gsfc.nasa.gov/apod/ap000101.html. Credits.

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Sky Model for DC2: Celestial Sources in the Milky Way S. W. Digel Stanford Linear Accelerator Center

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  1. Sky Model for DC2: Celestial Sources in the Milky Way S. W. Digel Stanford Linear Accelerator Center S. Ciprini APOD (Flammarion/Nemiroff/Bonnell) http://antwrp.gsfc.nasa.gov/apod/ap000101.html

  2. Credits • Diego Torres & Olaf Reimer on high-latitude molecular clouds, SNRs, XRBs, OB associations • Omar Tibolla on specific models of HESS SNR • Max Razzano & Alice Harding on detailed definitions of pulsars • Larry Wai & Ping Wang on specific dark matter sources • Igor Moskalenko & Andy Strong on GALPROP model calculations for diffuse emission of the Milky Way • Jim Chiangfor implementing many of the celestialSources sources that are used in the model, and for generally being a voice of reason Errors of commission or omission are mine

  3. Gamma-ray sources in the DC2 Milky Way # g-rays (A+B)* • With the exception of Pulsars, which were based on a population model and a lot of research and fiddling, we included only likely examples each source class • Typically associated with an already-known source (sorry Olaf & Patrizia) without attempting a pop. synthesis • ‘Other 3EG’ means that we included all non-spurious sources from the 3rd EGRET catalog (Hartman et al. 1999) even if we did not have a specific counterpart in mind *Out of 3,340,146

  4. The rest of the presentation • Follows is a review of the source components • The authoritative reference is the source model itself and the online ‘Explanatory Supplement’…

  5. Diffuse emission of the Milky Way • The model is based on what we used for Checkout 3 (surprise), which is derived from the model of Strong, Moskalenko, & Reimer (2004) • Basically, it has the same CR distribution but updated gas maps • For DC2 the intent was to have the diffuse emission model for data generation to be detectably different from the analysis model but not so different to significantly affect results for point sources

  6. Diffuse emission of MW (cont) • The p0 component was scaled up by 11% in intensity and the IC intensity was decreased by 32% to compensate in overall intensity (>160 MeV) • For future reference • The model had no dark gas and did not include the anisotropic radiation field and anisotropic IC scattering that is now being implemented in GALPROP (Porter & Moskalenko)

  7. Diffuse emission (2) • All-sky average spectra, by component p0after & before scaling IC before & after scaling Bremsstrahlung not scaled

  8. High latitude clouds • These are an overlay, probably insignificant, in the DC2 sky model, and not in the diffuse emission model • These are 40 faint, small molecular clouds that will not be resolved by the LAT. Intensity and flux distribution consistent with Torres et al. (2005)

  9. Pulsars • Work of Max Razzano and Alice Harding • Several classes – RL/RQ, msec, EGRET coinc., EGRET • Radio loud pulsars have been assigned to positions of known radio pulsars • Spectra are all exponentially cut off power laws: • Light curves are factored separately

  10. Pulsars (cont) • For future reference • Max Razzano is working on making PulsarSpectrum able to simulate phase-dependent spectra • The light curves (in TimeProfile files) for many pulsars may need finer binning, especially for longer simulations, and smoothing for ‘copying’ EGRET light curves

  11. Plerions • Pulsar-powered nebulae - In the DC2 sky we have poor man’s plerions – pointsources placed on top of some DC2 pulsars • In some cases the spectra are from published sources • Crab plerion (de Jager et al. 1993, ApJ, 457, 253 – IC spectrum in eqn. 3 ignoring the low-E component) • GeV J1809-2327 (Braje et al., 2002, ApJ, 565, L91); NB – this is probably a variable EGRET source • GeV J1825m1310 (Roberts et al. astro-ph/0409104, Lamb & Macomb 1997, ApJ, 488, 872)

  12. Plerions (cont) • In others they are adjusted to make the overall flux the same as that of the presumably coincident 3EG source

  13. Supernova Remnants • The interesting ones are the work of Omar Tibolla • He will describe simulations of several HESS SNR (J1634-472, J1713-381, J1813-178, J1834-087, plus RX J1713-3946 and RX J0852-4622), including spectral extrapolation down to the energy range of the LAT • Some other SNRs were added not particularly systematically, guided by long-evident correlations of 3EG sources with SNR • Cas A is simulated as 2 point sources, one representing putative central (pulsar?) source, one representing the interaction of shock accelerated CRs in the shell with dense ISM – Allen et al. ICRC paper [ref] • IC 443 (3EG J0617+2238) – source is coincident with the plerion of Fig. 11 of Torres et al. (2003, Phys Rep., 382, 303) • Monoceros (3EG J0634+0521) – source is coincident with SAX J0635+0533 in Fig. 12 of Torres et al. op cit • W28 (3EG J1800-2338)

  14. SNR (cont)

  15. X-ray Binaries • “Big tent” philosophy: Microquasars or microquasar candidates • Some periodic, some episodic in DC2 • Details are in XML file, of course (source_xrb_v0.xml) • LS I + 61 303 • Period (26.4960 d) and phase reference according to Gregory (2002, ApJ, 575, 427) • Flux and spectral index are for 3EG J0241+6103 • Modulation assumed to be like LS 5039 • LS 5039 • Period (3.91 d) and modulation as in Boettcher & Dermer (2005, ApJ, 634, L81), flux a guess

  16. XRB (cont) • A0 5353+26 • Period (111 d) from Maisack et al. (1993, A&AS, 120, 179) • Flux and variability (40%) and spectral index (2.6) as suggested by D. Torres • GRS 1915+106 • Defined to have 2 outbursts, not periodic. Outbursts according to Atoyan & Aharonian (astro-ph/9706061); see XML file for detailed spectral profile • First flare is 8 days into DC2, 2nd is 106 s later and 10x brighter; each flare falls by factor of 20 in flux after 1 d. • Cen X-3 • Vestrand et al. (1997, ApJ, 483, L49) found this source in outburst for ~2 weeks in EGRET data, with no evidence for modulation at the 2.09 d period of the orbit. • So in DC2, it is a SimpleTransient source with flux and spectrum as found by Vestrand et al., flare for 10 d starting 17.2 d into DC2

  17. XRB (cont)

  18. OB Associations • OB/WR associations suggested as DC2 gamma-ray sources by D. Torres, along with their fluxes and spectral indicies (2.1-2.2) • WR 140, WR 146, WR 147, Cyg OB2 • Coordinates are from Simbad, except for Cyg OB2 (Plueschke et al. 2001) • Yes, these are all in Cygnus – maybe northo-centric bias

  19. Dark matter • From Larry Wai & Ping Wang • Galactic halo (line + continuum) plus satellite (continuum only) • Continuum (Pythia) – p0g-rays from B-B final state • Line from 1% branching fraction to g-g

  20. Dark matter (cont) • NFW profile for GC source • Taylor & Babul satellite (l,b = 80.5°, 49.5°) ~1.5° FWHM *2 MeV wide Continuum flux: 1 × 10-6 cm-2 s-1 (>1 MeV) Oops, but try to detect the shift Line (100 GeV*) flux: 1 × 10-8 cm-2 s-1 Fornengo et al. (2004, PhRvD, 70, 3529); Eke et al. (2001, ApJ, 554, 114) (Same spectral shape as above) Continuum flux: 3.26 × 10-8 cm-2 s-1 (>1 MeV) No line simulated ~1.1° FWHM 2004 MNRAS, 348, 811; 2005 MNRAS, 364, 515)

  21. Dark Matter (cont) • For future reference • Remember, the 55 days of DC2 is a much shorter interval than we’ll use in real life for searching for signatures of dark matter • GC source (line + continuum) is offset by (0.5°, 0.5°) from (0,0) • Continuum source ends at 65 GeV, 35 GeV below the line; this is certainly smeared out by instrumental response but still an artificial gap for the GC source

  22. Moon • A strong EGRET source (Thompson et al. 1997, JGR, 102, 14735) • The flux (from CR interactions on the surface) depends on the phase of the solar cycle • Near solar minimum (like early in the GLAST mission), flux will be greatest, ~6 x 10-7 cm-2 s-1 (>100 MeV) • Spectrum is fairly soft at high energies – photon spectral index estimated to be 1.5 below 200 MeV and 3.5 above • Roughly speaking this is about 60 LAT gamma rays per day • Of course, it is a moving source! • 27.322 day period • Moves 1 lunar diameter every ~hour RA from a gtobssim simulation Time

  23. Moon (cont) • We do not have a system for simulating moving sources • The moon source was defined as a composite of 1344 SpectralTransient sources (one per hour for 56 days – one extra day for good measure) • Each SpectralTransient is a broken power-law source on for 1 hour at the average position of the moon during that hour Dec

  24. Moon (cont) • For future reference • I entirely forgot about orbital parallax – the moon moves by ~±1° every orbit of GLAST around the earth just due to the changing position of the LAT • The moon does not turn on until 1000 s into DC2 • No, we are not simulating the obscuring effects of the moon • No, we don’t currently have a tool that can analyze a moving source, even with a known ephemeris • Monitoring the flux and spectrum of the moon would be at least a consistency check on our understanding of the variations of the cosmic-ray background with solar cycle

  25. Sun • The sun is not a gamma-ray source like the moon, but episodically produces flares with ~> GeV emission • Such as EGRET saw on June 11, 1991 (Kanbach et al. 1993, A&AS, 97, 349) • These are colossal, dead time-inducing events – EGRET was completely saturated until well into the flare • The solar flare in DC2 was an extrapolated, approximated version of the June 11, 1991 flare • Two e-folding time scales: 25 minutes and 255 minutes • Spectrum in Kanbach et al. is for a time effectively 144 minutes after the flare • Approximated as broken power law with G1 = 1.43, G2 = 2.5, and Ebreak = 150 MeV • Defined as a SpectralTransient source, with the position of the sun at the start of the flare and an entry for every 3 minutes for 15 hours

  26. Sun (cont) • In order to not extrapolate beyond all reason, and to try to finesse the deadtime and what-about-the-GBM questions, the flare time was carefully chosen: January 26, 2008, ~04:53 UT • Flare starts just after the LAT enters the SAA for a particularly long passage; 30 minutes later the LAT turns on, followed by a long time (albeit during a rocking slew) when the sun is visible • Slewing modulates the rates on top of the time evolution of the spectrum Integrated flux >10 MeV LAT leaves SAA Early figure – showing slewing and eclipse

  27. Sun (cont) • For future reference • The Gleam jobs during which the flare was extremely bright sometimes generated anomalously low rates of gamma rays from the source – introducing 150 s wide ‘steps’ into the light curve – re-running these odd jobs, sometimes more than once, worked • I don’t really know for how long after a large flare starts deadtime will be a problem owing to associated X-rays triggering the ACD

  28. Other 3EG • Non-spurious 3EG sources that were not otherwise assigned (or close to) sources in the DC2 sky model to help make the sky look ‘right’ • Their approx. average fluxes were used (typically smaller than Hartman et al. 1999) and all are steady power-law point sources

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