Olaf Reimer -...

RELEVANT GAMMA-RAY OBSERVATIONS FORDARK-MATTER INTERPRETATIONS

Olaf ReimerStanford University

(i) Gamma-ray emission from the GC (region)

[keV: INTEGRAL]

(MeV-GeV) COS-B -> EGRET

(GeV-TeV) CANGAROO, WHIPPLE -> H.E.S.S.

(ii) The galactic diffuse gamma-radiation

GeV-Excess (EGRET), TeV (Milagro, H.E.S.S., + u.l.s)

[Seth: How to … (construct a diffuse model),

Igor: interpretation by means of a CR propagation model]

(iii) The extragalactic gamma-ray background

detection as residual <-> upper limit interpretation

(EGRET instument team) <-> (Keshet et al. ’04)

[GALPROP, once again by Igor]

(iv) dwarf galaxies in local halo, Galaxies and Galaxy Clusters -> closest: H.E.S.S. confirmation of M87 from HEGRA (but FRI, jet)SLAC July‘05

DM Suspects in Gamma-Rays

The (in)famous „fountain of antimatter“

aka 511 keV pair annihilation from the Galactic Bulge/Center

SLAC July‘05


CGRO/OSSE (Kinzer et al. 2001)

Spectroscopy• centroid ~ 511 keV• Gaussian FWHM ~ 1.8-2.9 keV• positronium fraction 0.93 ± 0.04

Why am I mention this?Every second 1.3 _1043 positrons annihilatein the Galactic bulge!Quest: Where is the positronium coming from?… see below!

The (in)famous „fountain of antimatter“

aka 511 keV pair annihilation from the Galactic Bulge/Center

SLAC July‘05


CGRO/OSSE (Purcell et al. 1997)

Morphology & Flux• 3 components : - bulge - disk - PLE• Bulge morphology highly uncertain• Total flux : (1-3) x 10-3 ph cm-2 s-1

• Bulge / Disk flux ratio : 0.2 - 3.3

…is gone now ! -> INTEGRAL

INTEGRALs view on the 511 keV in the Galactic Center

SLAC July‘05


(Knödelseder et al. 2004)

Morphology: Bulge/Halo <-> Bulge/Halo + Disc

But dont forget the image reconstruction issues in acoded mask instrument!

SLAC July‘05

(Loujou 2004)

#10

#0

#25 #70 #100

flux log likelihood


Now leaving the 511 keV towards the continuum emission

A galactic center source ?

SLAC July‘05


IBIS 20-40 keV SPI 40-100 keV

(Durouchoux 2004)

(Durouchoux ’04)

SLAC July‘05


(Revnivtsev ’04)

intgccat (IBIS hard X-ray): binaries, binaries everywhere,IGR J17475-282217 UNIDENTIFIED -0.053 0.695

…but this is X-ray astronomy, thereforenow up to the high MeVs

150 MeV < E < 300 MeV

COS-B @ http://www.rssd.esa.int/, anno 2005“It has become evident that if the background is modelled moreprecisely a significant number of the sources of the 2CG cataloguedisappear and can be explained by the presence of known amounts ofgas. While the *** group goes as far as suggesting new sources (orunexplained excesses) the *** analysis does not throw up new sourcecandidates. It is hoped that the work on the definitive Cos-Bcatalogue can soon be concluded so that it may be of use inestablishing viewing programmes of future high energy astronomymissions like GRO and Sigma.”

SLAC July‘05


Approaching the data used in nowadays DM interpretations:

EGRET [30 MeV]- 100 MeV – 10 GeV [- 50 GeV]

The galactic center point-source:

keys to DM interpretation:

- gamma-ray excess location (offset to 0.0°, 0.0° or not)

- spectrum -> spectral break, cutoff, energetic extend

- discriminiation methods against galactic diffuse

- source variability

SLAC July‘05


SLAC July‘05


The data(1) Mayer-Hasselwander et al. 1998• EGRET P1 … P5, but an own, pre-3EG normalization• >25° off axis cut (against standard 40°)• Hunter et al. 1997 diffuse model, standard calibration• 0.1° binning (against standard 0.5°),• 4 energy intervals (but 100-300, 300-1000, >1000 for

variability)

results: E > 500 MeV l=0.0° b=0.0° +- 0.2°only weak evidence for variability, spectral break 1.3 -> 3.1

SLAC July‘05


The data(2) Hartman et al. 1999 (the 3EG catalog)• EGRET P1 … P4, matching normalization• >30° off axis cut (against standard 40°)• Hunter et al. 1997 diffuse model, standard calibration• 4 energy intervals, contour & position provided from E > 1 GeVresults:3EGJ1746-2851 (aka 2EGJ1746-2852 aka GEVJ1746-2854)

l=0.11° b=-0.04° +- 0.13° (trend towards offset)fluxes only -> separate variability studies,average spectrum only -> later in-depth studies

SLAC July‘05


The data(3) Hooper & Dingus (Phys Rev D 2004)• unbinned EGRET events E > 1 GeV only, P1…P4 data (?)

• Hunter et al. 1997 diffuse model (pre-binned -> individual p forunbinned events ?),

• new method applied to Crab, Vela, but never to a faint source nor inconfused region

results: l=0.19° b=-0.08° +- 0.13° (offset from 3EG confirmed)no flux, no spectrum determined

SLAC July‘05


The data(4) Pohl 2005

used the reprocessed EGRET P1..4 data (?), however 3EG source list,finalized normalization (?),

Hunter et al. 1997 model, but with individual corrections applied

(treatment of psf-exposure convolution in diffuse model)

repeats 3EG procedure by incl. two more individual vp‘s, but not the

3EG co-adds (P1, P2, P12, P34, etc.)

results:

confirms exactly 3EG location l=0.11° b=-0.04° and spectrum

(-> a matching source list and/or psf-convolution minor issue),

indicates a „problem“ with the E>100 MeV data, but not

apparent in the 100-300, 300-1000, >1000 data (??)

little evidence for variability (simplistic χ2/dof)

SLAC July‘05


Variability of the EGRET Galactic Center source

(i) McLaughlin et al. 1996 „V“ = 1.49 -> variable

(ii) Mayer-Hasselwander -> „only weak evidence“(method unspecified)

(iii) Torres et al. 2001 „I“ = 2.0 -> variable

(iv) Nolan et al. 2003 „V12“ = 2.35 -> fairly strong evidence forvariability

(v) Pohl 2005 -> χ2/dof ->„little evidence“

(vi) Wallace et al. 2000 -> Systematic search for short-timevariability „V“ = 2.1 -> variable on ~1 day timescale

-> check methodological details in the papers

SLAC July‘05


2nd gas refill

1st gas re

fill

3rd gas refill

4th par tial re

fill

5th par tial re

fill

sc B failure

last partial re

fill…always keep in mind:

SLAC July‘05


, log-normal distribution , likelihood function used to calculate τRayleighs

Variability of EGRET-sources1. McLaughlin et al. 1996 (ApJ 473, 763): all 2EG (+P3 online), vps Wallace et al. 2000 (ApJ 540, 184):short-term time variability, sub-vps

2. Nolan et al. 2003 <- Tompkins 1999 (PhD Thesis Stanford University)

3. Zhang, Zhang & Cheng 2000: 38 UNIDs at low Galactic latitudes, <> = 77 Torres et al. 2000, 2001: all 3EG sources, <> = 26.9 (Method: Romero, Combi & Colomb 1994)

psr

psr

... a measure of inconsistency of data with the assumption of constant source flux

... a fractional variability measure calculating the likelihood for obtaining any source flux

... a weighted fluctuation index with pulsars as "standard candle"

m± 50m

SLAC July‘05


VHE Source in Galactic Center (region)(i) pre-H.E.S.S. observations

Veritas (obviously: Whipple telescope, LZA)26 hours between ´95 and ´03

Kosack et al. 2004: 3.7 sigma,

Cangaroo, (HZA -> low thresh -> spectrum)67 hours in ´01 and ´02

Tsuchiya et al. 2004: -4.6 spec. index,connection to 3EGJ1746-2851

SLAC July‘05


VHE Source in Galactic Center (region)(ii) H.E.S.S. (t.b.c.)

2004 A&A: ~ 16 h of two telescope data (´03), 9.2 sigma, spectrum

SLAC July‘05


VHE Source in Galactic Center (region)(ii) H.E.S.S. (t.b.c.)

SLAC July‘05


VHE Source in Galactic Center (region)(ii) H.E.S.S. (t.b.c. ICRC’05)

2004: 35 h of four telescope data -> 34 sigma, ~1750 gamma-events-> spectral and temporal variability studies

SLAC July‘05


VHE Source in Galactic Center (region)(ii) H.E.S.S. (t.b.c. ICRC’05)

SLAC July‘05


VHE Source in Galactic Center (region)(iii) the apparent inconsistency between Cangaroo/HESS spectra

SLAC July‘05


VHE Source in Galactic Center (region)

SLAC July‘05



conventional interpretations: Sgr A East SNR (plausable: since H.E.S.S. sees many already)

-> signature: morphology match, spectra-> multifrequency modeling

central bh Sgr A* (low luminosity -> transparent for VHEs)-> (contemporaneous) flaring activity-> multifrequency modeling

CR interactions with concentrated molecular material-> guaranteed, but intensity unclear <- tracers

SLAC July‘05



DM interpretation(s):

location: offset to GC origin ? signs of activity/variability ?

features/cutoffs in spectrum ? halo ? halo shape ?

Horns 2004

SLAC July‘05


…towards diffuse VHE emission from the GC

beyond the GC point source:H.E.S.S. has documented that scans are possible andsuccessfully -> perfectly understood instrument required,clever observation strategy, cut and data quality management

sufficient more exposure in region-of-interest (achieved in 2004)

high-quality data (4 telescope stereo)

SLAC July‘05


…towards diffuse VHE emission from the GC

• point source removal G0.9+0.1, HESS J1745-290 (Sgr A[*/East])• investigate residual• gas dist. in GC region -> more meaningful tracer here: CS

-> ICRC’05 & full paper submitted (journal embargo policy)

SLAC July‘05


…towards diffuse VHE emission from the GCMilagro: -> GC out of reach!

EGRET diffuse GeV flux (in black)-> point source removed ??Milagro exposure (dash-dot)

H.E.S.S./Cangaroo: HZA -> low threshold, exposure -> variability LZA -> spectrum @ TeV

MAGIC/Veritas: LZA observations only, generally under unfavoured observation conditions

SLAC July‘05


EGRET measured diffuse gamma-rays

Hunter et al. 1997

Excess

6<b<10

2<b<6

-2<b<2

-6<b<-2

Data

Data

E2dN/dE

Eγ [MeV]

SLAC July‘05


EGRET measured diffuse gamma-rays

EGRET: Hunter et al. 1997• no IC at high latitude• dynamic balance of gas/gamma, no CR propagation

GeV excess can now be accounted* for:Strong, Moskalenko & Reimer 2000, … , 2004probing the valid parameter space in contemporaray multichannelCR propagation modelsKamae et al. 2004diffractive process and Feynman Scaling Violation in the pp interactionsusing phythia [All secondary particle fluxes will increase in the GeV-TeV range]

Porter & Strong 2005: new ISRFmyself: dpmjet3 simulations for γ-ray production in pp on ISM

->down to the Κ, Λ, Σ, Ξ

Any diffuse model is a prediction as f(time) !(remember that for LAT…)

SLAC July‘05


Extragalactic diffuse gamma-ray background

…is determined as a residual in diffuse gamma-ray investigation

upper & lower bounds on EDGB

average EDGB

Strong, Moskalenko & Reimer 2004

If one understands the dominant diffuse galacticgamma radiation, one may proceed to the EDGB.

But, please, not before you do so !

The "case for a low EDGB" (Keshet, Waxman & Loeb 2004):• (small) pole region := best choice

• choose your favorite tracer only,ignore all others

•dont care about spectrum



ps: Any measurement can be interpreted as an (less sensitive) u.l. …

radio continuum (408 MHz)

atomic hydrogen

radio continuum (2.5 GHz)

GalacticGalactic TracersTracers of ISM of ISM

molecular hydrogen

carbon monoxide

infrared

NIR


SLAC July‘05


Elsässer & Mannheim 2005

…but where is the contribution from unresolved blazars then ?


SLAC July‘05


Pluralitas non est ponenda sine necessitate("pluralities ought not be supposed without necessity")

William of Ockham (~ 1285-1349)-> Occam's Razor:

When multiple explanations are available for a phenomenon,the simplest is preferred.

Of two equivalent theories or explanations, all other thingsbeing equal, the simpler one is to be preferred.If we miss a unique observational DM signature, there will be always

conventional models around (since there are essentially all ingredientsfor successful multifreuqncy modelling aparent in the currentobservations).

That'sThat's all, all, folksfolks ! !

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