1. GLAST LAT Project GLAST-for-lunch, 4 November 2004 1 Gamma-ray Astronomy: Talking the Talk S. W. Digel SLAC Gamma-ray Large Area Space Telescope

2. GLAST LAT Project GLAST-for-lunch, 4 November 2004 2 Outline Coordinate systems –Celestial, Galactic, ecliptic Units –Flux, intensity, time, distance The sky –Solar neighborhood, Milky Way, local group, etc. –What you see vs. what we care about Naming sources Overview of gamma-ray sources

3. GLAST LAT Project GLAST-for-lunch, 4 November 2004 3 Coordinate systems Celestial coordinates – natural for astronomy from the ground Right ascension (time) + declination –Denoted RA, Dec or  –RA in hours, Dec in degrees –Telephone number in catalogs N.B.: Epoch must always be specified –Precession period ~26,000 yr [~20 arc sec/yr] Vernal equinox (i.e., start of spring) is RA = 0 hours With the RA & Dec you can tell right away whether a given direction on the sky will rise, how high it will reach, and what time of year it will be up at night R. Pogge * Polaris

4. GLAST LAT Project GLAST-for-lunch, 4 November 2004 4 Coord. systems (2): Galactic coordinates Galactic coordinates – natural for astronomy if you don’t use a telescope Even for extragalactic observations, the coordinate system is relevant (for foreground emission/obscuration) The plane of the Milky Way traces the Galactic Equator –(0,0) is direction to the Galactic center –(180,0) is the anticenter M109 (AURA/NOAO/NSF), SBc Powell 8.5 kpc Sun

5. GLAST LAT Project GLAST-for-lunch, 4 November 2004 5 Galactic coordinates (cont) Galactic longitude is the angle along the Galactic Equator, latitude is angle above or below plane Denoted l, b [I don’t know why] Range in degrees is l = 0-360° (or -180° to +180°) and b = -90° to +90° In older (~30 yrs) literature you will notice l II and b II listed. This was to distinguish between ‘new’ (i.e., correct) and old Galactic coordinates (before radio astronomy cleared up the question of where the Galactic center actually is) Epoch does not need to be specified –Orbit period ~250 Myr [5 mas/yr]

6. GLAST LAT Project GLAST-for-lunch, 4 November 2004 6 Coord systems (3): Ecliptic coordinates Plane of the solar system, illustrated by dust in the plane of the solar system, which is bright at 12  m Denoted  IRAS

7. GLAST LAT Project GLAST-for-lunch, 4 November 2004 7 Units Fluxes are in photons cm -2 s -1. If an energy range is not specified, you can probably assume >100 MeV –Sometimes ‘photons’ is not explicitly written –If you want to convert this to ergs cm -2, then you need to know the spectrum* –Implicitly this is an instantaneous quantity, i.e., applies to a specific time Intensities (relevant for extended sources) have units of photons cm -2 s -1 sr -1 For GRBs, flux determinations are problematic because the emission is so impulsive. Instead what is quoted are fluences, ergs cm -2. You can ask what’s a magnitude? What is a Jansky? EGRET sources ~5 magnitudes, LAT ~ 8 magnitudes * I don’t know why astronomy is stuck in cgi units

8. GLAST LAT Project GLAST-for-lunch, 4 November 2004 8 Units (2): Dates and distances JD is Julian Date – number of days since noon on January 1, 4713 BC MJD – Modified Julian Date = JD – 2,400,000.5 (i.e., number of days since midnight on November 17, 1858 –Today is MJD ~ 53,314 (Truncated Julian Date TJD = MJD – 40,000) Distance - Parsec (pc) is the distance at which a star would have an annual parallax of 1” (~3.26 light years)

9. GLAST LAT Project GLAST-for-lunch, 4 November 2004 9 Local Group Milky Way and M31 are the dominant galaxies in the local group Many others are irregular or dwarf spheroidal Additional members are still being discovered "Teacher's Guide to the Universe by Lindsay M. Clark, MAP Education/Outreach Coordinator", www.astro.princeton.edu/ ~clark/

10. GLAST LAT Project GLAST-for-lunch, 4 November 2004 10 Local clusters of galaxies R. Powell

11. GLAST LAT Project GLAST-for-lunch, 4 November 2004 11 Way beyond the local cluster Way, way beyond: Romani et al. (astro-ph/0406252) blazar at redshift z = 5.47

12. GLAST LAT Project GLAST-for-lunch, 4 November 2004 12 The sky we see Aitoff (equal area, allsky) projection

13. GLAST LAT Project GLAST-for-lunch, 4 November 2004 13 The sky we see (2) Stars, dust, Galactic equator, local galaxies Do we care about stars? Basically no –Stars are not gamma-ray sources [OB associations notwithstanding, ref. D. Smith’s talk] –They are good gamma-ray absorbers, but their filling factor is small Same for most galaxies, too

14. GLAST LAT Project GLAST-for-lunch, 4 November 2004 14 EGRET all-sky map ~1.4 M , ~60% interstellar emission from the MW ~10% are cataloged (3EG) point sources 3EG catalog (Hartman et al. 1999) EGRET (>100 MeV)

15. GLAST LAT Project GLAST-for-lunch, 4 November 2004 15 Gamma-ray sky Milky Way is bright with diffuse emission Indications are that the Galactic sources that we care about (i.e., can detect) are relatively nearby on the scale of the Milky Way –Concentration toward the equator is evident –Typical luminosity ~ (1–15) × 10 35 erg s -1 (isotropic) for an EGRET Galactic point source (characteristic distance 1–6 kpc), Mukherjee et al. (1995) –The bright pulsars are within a few 100 pc, i.e., not detectable by the LAT if they were as distant as the G.C. Some extragalactic sources have large fluxes –They are quite variable – see later GRBs are briefly more intense than the entire rest of the sky EGRET also saw a solar flare, and the moon Thompson et al.

16. GLAST LAT Project GLAST-for-lunch, 4 November 2004 16 Astronomical catalogs The idea is to label sources so you can refer to them No uniform standards, although standards are being imposed Historically, naming was just sequential, e.g., HD12345, W49 Now the convention is to use the ‘telephone number’, with appropriate level of precision, along with a designator for the origin; catalogs that undergo revisions also have a version number; the J indicates the epoch – hence, 3EG J1835+5918 One exception is transient sources –E.g., GRBs, for which the name is the date (not Y2K compliant) of the burst, e.g., GRB030328 –SNR, which are numbered by the year of discovery, with a letter (or letters) to indicate sequence, e.g., SNR 1998bw Henry Draper Gart Westerhout

17. GLAST LAT Project GLAST-for-lunch, 4 November 2004 17 Naming sources (2) One-of-a-kind sources can get unique names For extended sources, they can be descriptive, or too cute –Becklin-Neugebauer Object –Baade’s Window, Lockman’s Hole –Rabbit, Mouse, and the Galactic Center Snake

18. GLAST LAT Project GLAST-for-lunch, 4 November 2004 18 Identified Gamma-Ray Sources Pulsars (7-10 known from EGRET) –Rotating magnetized neutron stars –They do this: Blazars (~70+ known as  -ray sources) –Active galaxies (accreting masive black holes with jets toward Earth) –They do this: Geminga Sreekumar PKS 1622-297 Mattox et al. (1997) 237 ms

19. GLAST LAT Project GLAST-for-lunch, 4 November 2004 19 Some plausible (or not impossible) new source classes Millisecond pulsars, binary pulsars (microquasars), pulsar wind nebulae (plerions) Supernova remnants, SNOBs, OB/Wolf-Rayet star associations Galaxy clusters Starburst (ultraluminous infrared) galaxies

20. GLAST LAT Project GLAST-for-lunch, 4 November 2004 20 A little jargon can go a long way The conventions and nomenclature shouldn’t be a hurdle Gamma-ray astronomy is not stellar astrophysics Summary EGRET Phases 1-5 LAT Sim. 1-yr

21. GLAST LAT Project GLAST-for-lunch, 4 November 2004 21 Backup slides follow

22. GLAST LAT Project GLAST-for-lunch, 4 November 2004 22 Spectrum Astro GLAST Large Area Telescope (LAT) e+e+ e–e– Calorimeter Tracker ACD 1.8 m 3000 kg Within its first few weeks, the LAT will double the number of celestial gamma rays ever detected 5-year design life, goal of 10 years Years Ang. Res. (100 MeV) Ang. Res. (10 GeV) Eng. Rng. (GeV) A eff Ω (cm 2 sr) #  rays EGRET 1991 – 00 5.8°0.5° 0.03 – 10 7501.4 × 10 6 AGILE 2005 – 4.7°0.2° 0.03 – 50 1,5004 × 10 6 /yr AMS 2005+? –– 0.1° 0.3 – 300 1,6007 × 10 5 /yr GLAST LAT 2007 – 3.5°0.1° 0.02 – 300 25,0001 × 10 8 /yr

23. GLAST LAT Project GLAST-for-lunch, 4 November 2004 23 Galactic  -rays in perspective Diffuse luminosity is miniscule relative to optical and IR (and small relative to blazars) –Particle acceleration and  -ray production mechanisms don’t have to be very efficient Diffuse luminosity >> total luminosity of Galactic point-sources –Typical luminosity ~ (1–15) × 10 35 erg s -1 (isotropic) for an EGRET Galactic point source (characteristic distance 1–6 kpc), Mukherjee et al. (1995) BandLuminosity (10 38 erg s -1, aka 2.5 × 10 4 L ☼ ) Radio3 IR 3 × 10 3 Optical 3 × 10 5 ! X-ray10-100 >100 MeV 40 Zombeck, M. V. 1990, Handbook of Astronomy and Astrophysics, Second Edition (Cambridge, UK: Cambridge University Press).

24. GLAST LAT Project GLAST-for-lunch, 4 November 2004 24 History of  -ray astronomy of the Milky Way 1948-1952, relevant cosmic production mechanisms of  -rays understood (Feenberg & Primakoff, Hutchinson, Hayakawa) 1951, 21-cm line of H I (Ewen & Purcell, Muller & Oort) 1949-1960s, upper limits on cosmic fluxes from balloon, suborbital, and satellite experiments 1960s-1970s, theoretical development from advances in particle physics (Stecker, Ginsburg,...) 1967-1968, OSO-3 detection of Milky Way as an extended  -ray source - Kraushaar et al. (1972) 1975-1982, COS-B maps of the plane, study of CRs and ISM 1991-2000, EGRET all-sky maps, same plus resolution of spurious sources, better statistics

25. GLAST LAT Project GLAST-for-lunch, 4 November 2004 25 Brief History of Detectors 1967-1968, OSO-3 detected Milky Way as an extended  - ray source, 621  -rays 1972-1973, SAS-2, ~8,000 celestial  -rays 1975-1982, COS-B, orbit resulted in a large and variable background of charged particles, ~200,000  -rays. 1991-2000, EGRET, large effective area, good PSF, long mission life, excellent background rejection, and >1.4 × 10 6  -rays SAS-2 COS-B EGRET OSO-3 SAS-2 COS-B EGRET

26. GLAST LAT Project GLAST-for-lunch, 4 November 2004 26 Future Missions AGILE (Astro-rivelatore Gamma a Immagini LEggero) –ASI small mission, late 2005 launch, good PSF, large FOV, short deadtime, very limited energy resolution AMS (Alpha Magnetic Spectrometer) –International, cosmic-ray experiment for ISS, will have sensitivity to >1 GeV gamma rays, scheduled for 16 th shuttle launch once launches resume GLAST…