Pharos:distant beacons as cosmological probes

Fabrizio Fiore, Fabrizio Nicastro INAF-OAR, Martin Elvis SAO

The “Pharos” of Alexandria, oneof the Seven Wonders of the ancient world, was the tallestbuilding on Earth (120m). Its mysterious mirror, which reflection could be seen more than 55 km off-shore fascinated scientists forcenturies.

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The fate of baryons

Lyclouds

WH

HG green ~10

red ~104

The warm intergalactic mediumThe warm intergalactic medium

Cen et al. 2005

Hellsten et al. 1998 ApJ, 509, 56

OVIII

OVII

IGM density

IGM temperature

IGM metallicity

The warm intergalactic mediumDave’ et al 2000

Cen et al. 2005

Cen et al. 2005

Cen et al. 2005

Cen et al. 2005

•HRC/LETG 63 ksec on 21mCrab source

•R=400

•~700 counts/resolution element.

•PKS2155-304 z=0.116 blazar & Cal. target.

•Strong detection of OVII ,

•NeIX K

•Weaker detection of OVIII K

•EW 10-20 mA

•FUSE detection of OVI 2s->2p

•All lines at z~0, -135 km s-1 from FUSE

Detection of the Local Warm IGMby Chandra: PKS2155 line of sight

OVII

NeIX OVIII

Nicastro et al. 2002 ApJ

Detection of Warm IGM

by Chandra: Mark421 line of sight The highest S/N grating The highest S/N grating spectrum ever!spectrum ever!

40-60mCrab source yielded2500 counts per resolution el.at 0.6 keV!

Fluence of 10Fluence of 10-4-4 erg cm erg cm22!!

First detection of warm First detection of warm IGM at z>0IGM at z>0

OVII(z=0.011) EW=0.05eVOVII(z=0.027) EW=0.03eV 10101515 cm cm-2-2 NVII(z=0.027) EW=0.05eV Nicastro et al. 2005

Cen et al. 2005

Ωb(NOVII>7x1014 cm-2)• Mkn 421 (2 Filaments.): z=0.03

• Combined Mkn421+1ES1028+511 (3 Filaments):

Consistent with missing =2.5 0.4

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(Nicastro et al., 2005, Nature, 433, 495; Steenbrugge et al., 2006, in prep.)

Physics and Astrophysics of the Warm IGM

• How many lines? The baryon density at low redshift

• How is the Warm IGM heated? shocks? -> R>=6000

• What is the history of the heating? mirrors decline of Lyman forest? -> z=1- 2 X-ray forest

• Did chemical enrichment trace heating? tracks star formation rates? -> R>=6000

• Does the `X-ray forest’ redshift structure match

CDM predictions? trace later formation of large scale structures

-> z=0.1-1 X-ray forest

Reducing Uncertainties•GOALGOAL: Reduce : Reduce bb and d and dNN/dz uncertainties /dz uncertainties down to down to fewfew % from current (+140,-70) % % from current (+140,-70) %

Needs 100 to Needs 100 to 1000 1000

Detections!Detections!

•Resolve Warm IGM line widths:

50 km s-1, R = 6000

•Span 0<z<2 for OVII, OVIII:

(OVIII K18.97A; OVIII Ka = 22.09A)

i.e. 18 - 66A, 0.19 keV 0.7 keV minimum

• Extra line diagnostics:

NeIX (13.69A) : 0.31 - 0.92 keV

CVI (33.73A) : 0.13 - 0.38 keV

weak lines need high resolving power

Warm IGM Spectroscopy Goals

FWHM= 20 km s-1

Chandra LETG OVII

FUSE OVI

goal

FWHM= 660 km s-1

51014 cm-2

The minimum detectable EW scales with the square root of E. Since the rest frame EW scales with (1+z)EWobs and since for gratings E scales with E-1, the minimum detectable rest frame EW is nearly constant with z. • Similar column densities can be probed with gratings in the z range 0-2

Physics and Astrophysics of the Warm IGM

• How many lines? The baryon density at low redshift

• How is the Warm IGM heated? shocks? -> R>=6000

• What is the history of the heating? mirrors decline of Lyman forest? -> z=1- 2 X-ray forest

• Did chemical enrichment trace heating? tracks star formation rates? -> R>=6000

• Does the `X-ray forest’ redshift structure match

CDM predictions? trace later formation of large scale structures

-> z=0.1-1 X-ray forest

How was the Warm IGM heated?Thermal broadening of O linesis ~50 km/s at T=4106 K

Fang et al 2002

Hydrodynamic simulations show that reasonable warm intergalactic gas turbulence may be of ~100 km s-1 up t0 200 km/s (implying a resolution of 1500-3000 to resolve these lines and measure the Doppler term b.

If the temperature of the gas can be constrained through OVI, OVII and OVIII line ratios the measure of b can provide information on the heating history of the gas. For example, if the gas were shock heated one would expect that the gas temperature is proportional to the square of the gas sound speed, which in turn should be proportional to the gas turbulence.

By measuring b and T it would be possible to check this idea and to provide tests and constraints to hydrodynamic models.

Constellation-X SWG Sept 2002

Gamma-ray Bursts

BATSE all sky GRB map (http://f64nsstc.nasa.gov/batse/grb/skymap)

• GRBs come from distant (z>1) explosions

• Brighter than Crab Nebula for a few minutes

•brightest GRB fluence

= 10-5 erg cm-2 (1min-12hr)

= 10 Msec (4months) observing brightest z~2 quasar, flux: 10-12 erg cm-2 s-1

GRBs are best `lighthouses’ to study intervening matter

Stupor CoeliStupor Coeli

Greatest Lighthouses of the Universe

BeppoSAX GRBM+WFC Frontera et al. 2000 Fiore et al. 2000

Assuming F(2-10)@30sec/Fpeak(50-300)=0.01 and a power law decay with =-1.3

GRBs are the best path Fiore et al 2000 ApJL, astro-ph/0303444

• Most GRB have X-ray afterglows, a few can be very bright (fluence> 1x10-5 erg s-1 )

•brightest z~0.5-1 quasars (0.5 mCrab) take 2 weeks to gather same fluence

•1-2 GRB/yr at fluence>1x10-5 erg/cm2

= 1 Msec obs of a half mCrab AGN

•40 GRB/yr at fluence>1x10-6 erg/cm2

=100 ksec of a half mCrab AGN

resolve lines, detect faint lines

• 100 GRB/yr at fluence>1x10-7 erg/cm2

detect X-ray forest

But … Swift will tell….!

44 GRB localized by Swift BAT

8 GRB localized by BSAX WFC,Extrapolated from 30sec to 100 sec, 2.4 hrassuming =-1.3

100 sec

2.4 hr

Primary Targets: GRB Afterglows; Secondary Targets: QSOs, Blazars

Pharos Concept

• Goal: R=6000 (50 km s-1) soft (<1 keV) X-ray spectroscopy• Cosmological driver: measure baryon density at low z• Physics driver: resolve thermal widths of X-ray lines• Astronomy driver: resolve internal galaxy motions

Gamma-ray Burst (GRB) afterglows may produce many more X-ray photons than any other high redshift source (i.e. quasars).

Requires acquisition within 10 minutes of GRB

1 minute goal, as Swift

Constellation-X SWG Sept 2002

Pharos: Rapid X-Ray-rich GRB Trigger & Location

0.1-1 keV (5-10” mirror): short focal length

reduces moment of inertia, I=mR2

(factor 25 for 2 m vs. 10 m)

• Problem: require <1armin location + acquisition in 0.5-1 minutes and require quasi-4coverage: conflicting goals

• Solution: trigger in the 5-30 keV with 2 1-D Coded Masks

TriggerTrigger

5-30 keV ‘light’

ASM Coded Mask 1’ localization in

0.5-1 s

Rapid rough slewRapid rough slew to 1’ location

Fine slewFine slew to <1 arcmin position

X-ray spectrometer starts to take data R>5000 @ 0.5 keV:

Out-of-plane Reflection Gratings

GRB trigger must be on-board & autonomous: 5-30 keV triggers X-ray rich

t=0 st=1-15 s

t=30 s

SuperAGILE in short

1-D Coded Masks

Collimator

Si μ-strip Detectors

Energy Range 15-40 keV

Energy Resolution

7-8 keV FWHM

Geometric Area 1360 cm2

Max Effective Area

280 cm2

Field of View (ZR) 2 x (68° x 107°)

Angular Resolution

6 arcmin (on-axis)

Source Location Accuracy

2-3 arcmin

for bright sources

Point Source Sensitivity

10 mCrab

(50 ks, on axis)

Timing Accuracy 5 μs

Imposed by AgileCosta, Feroci & the Super-Agile Coll.

16 46x46 deg2 “SA”s cover Half Sky

•Current Size and Thickness Imposed by Agile

Presence of Agile anticoincidence limits current sensitivity by 1.5-2

•Only 5.5 kg (can be improved): Integral/IBIS=700 kg; Swift/BAT>100 kg; ISS/MAXI=490 kg

•Current Energy Range: 15-40 keV-Low Energy Threshold halved just doubling the points of read-outs 7-40 keV for free!!-High Energy Threshold increases with thickness

•650 μm Si-thickness + FOV=46x46 deg2 Sensitivity: 1 mCrab in 50 ks (5-10 keV) at 5σ

CHEAP!: 1 M$ to redo itLIGHT!: Total weight ~ 80 kg

X-ray Mirror Area

Baseline mirrorMinimum mirror1200 cm-2 2000 cm-2 60kg (incl. 40%support) 200 kg (incl. 40% support)

•Low energy band allows wide grazing angles (up to 3-4 degrees) and

short focal length: 2-2.5 meters – larger Aeff

•Use Ni coating for E<0.9 keV higher reflectivity than Au

Pharos goal

Citterio & Pareschi

X-ray Gratings

• R=6000 is technically achievable

XMM RGS gratings behind Chandra mirror -> R=5000

(subject to improved facet alignment)• Out-of-plane reflection gratings

give higher dispersion (Cash 1991)• Need 5” FWHM mirror assembly.

Control of grating scattering crucial.

(else wings fill in absorption lines)

5” resolution R=5400!!!

MIT gratings+ HRC efficiency ~25-30%

Calorimeter +Filter efficiency~50%

Figure of Merit: Comparison with other Missions

• No other mission matches R = 6000 in X-rays

WHIM and high z galaxy dynamics unavailable.

• Other missions can still detect WHIM systems in GRBs

Compare a figure of merit:

FoM = Aeff (cm2) x peak x R (0.5 keV) x GFFoM = Aeff (cm2) x peak x R (0.5 keV) x GF

XMM 1RGS # 2100

Chandra LETG # 5000

Chandra HETG # 9000

Swift 1000

Con-X 1 unit # * 123,000

Con-X 4 units # * 500,000

Minimal Pharos 600,000

Baseline Pharos 2,500,000

* assumes R=1000

# for a 4-8hr response time

x 24 for 10 min response

FoM

GF= Gain in Fluence = 1 Pharos,Swift t=10mGF=0.04 Chandra, XMM, Con-X t=4-8hr

Pharos Summary

• GRB afterglows combine 4 themes of

early 21st Century astrophysics: – The most energetic events in the Universe 19971997– The fate of the baryons & large scale structure 19991999– Galaxies in the age of star formation 19971997– The recombination epoch 20002000

• R=6000 X-ray spectroscopy opens up all of these new physics and astrophysics

• A small, short, soft X-ray telescope is enough• Rapid GRB trigger & autonomous slewing essential

Gamma ray bursts: one of the great wonders of the Universe• GRBs combine 4 themes of

early 21st Century astrophysics: – Among the most energetic events in the Universe

1997 11997 1stst GRB redshift (thank to BeppoSAX) GRB redshift (thank to BeppoSAX)– Galaxies in the age of star formation

metal abundances, dynamics, gas ionization, dust– The recombination epoch

2000-200? Gunn-Peterson trough at z~6-?2000-200? Gunn-Peterson trough at z~6-?– The fate of the baryons & large scale structure

1999 Warm IGM simulations1999 Warm IGM simulations

2001 12001 1stst Warm IGM detection (thank to Chandra) Warm IGM detection (thank to Chandra)

Minutes after the GRB event their afterglows are the brightest sources in the sky at cosmological redshift.

Afterglows can be used to probe the high redshift Universe through the study of the intervening matter along the line of sight. Two possible applications:

Galaxies in the age of star-formationthrough high resolution spectroscopy of UV lines

The warm intergalactic mediumthrough high resolution X-ray spectroscopy of highly ionized C,O,Ne lines

GRB01022210 Crab!

Crab

1mCrab i.e. a bright AGN

Galaxies in the Age of Star Formation

Mann et al. 2002 MNRAS, 332, 549

• Star formation in the Universe peaked at z~2

• Studies of z=>1-2 galaxies are biased against dusty environments.

• GRB hosts are normal galaxies

• GRB afterglows will reveal host

Galaxy dynamics, abundances, & dust content at z>1

redshift, (1+z)

sta

r fo

rmat

ion

rate

GRB Hosts

peak of star formation

GRBs also probe normal high z galaxies

X-ray high resolution spectroscopyOptical-near infrared high resolution spectroscopy

GOALS

1- The GRB environment: size and density of the region surrounding a GRB can be constrained by monitoring the absorption line equivalent widths (Perna & Loeb 1998). This can be used to discriminate among competing GRB progenitor scenarios.

2- Metal column densities, gas ionization and kinematics These studies have so far relied upon either Lyman Break Galaxies or Damped Lyman Alpha systems. However, it is not clear if these systems are truly representative of the whole high-z galaxy population.

GRB afterglows can provide new, independent tools to study high z galaxies.

Results from low resolution spectroscopy

Savaglio, Fall & Fiore 2002DLAs

High dust depletion

High dust content

Denser clouds

DATA

UVES spectra 3800-9400 A, slit 1”, resolution=42,000

GRB020813: z=1.245 - Exposure of 5000 sec. 24 hours after the GRB; R=20.4, B=20.8

GRB021004: z=2.328- Exposure of 7200 sec. 12 hours after the GRB; R=18.6, B=19

GRB021004

FORS1 R~1000 CIV CIV z=2.296 z=2.328

UVES R=40000

z=2.296 z=2.328

GRB021004 AlIII1854

AlII1670

SiIV1402

SiIV1393

CIV1550

CIV1548

z=2.321 z=2.328

GRB021004 z=2.321 z=2.328

MgII2803

FeII1608

FeII2344

FeII2374

FeII2382

Constellation-X SWG Sept 2002

GRB021004

AlIII1670

SiIV1393

SiIV1402

CIV1548

CIV1550

z=2.296 z=2.298

Constellation-X SWG Sept 2002

GRB021004 z=2.296 z=2.298

MgII2796

MgII2803

FeII1608

FeII2344

FeII2374

FeII2382

Relative abundances in GRB021004

Constellation-X SWG Sept 2002

Comparison with CLOUDY models:

Ionization parameter assuming solar abundances

GRB020813 z=1.2545

MgII2796

MgII2803

FeII2344

FeII2374

FeII2382

FeII2600

Summary

High resolution UVES observations can provide reliable ion column densities.

The GRB021004 higher z systems have much fainter low ionization lines (FeII, MgII) than the GRB020813 systems (and most other GRBs), and strong high ionization lines.

The photoionization results of CLOUDY yield ionization parameters constrained in a relatively small range with no clear trend with the system velocity. This can be interpreted as density fluctuations on top of a regular R-2 wind density profile.

…but this is only the begining!

With Swift we will have many more prompt triggers, say 20/yr during the Paranal night

and we will use the VLT in Rapid Response Mode (10-20 minutes to go on the GRB!)

so .. stay tuned for many more results on GRB host galaxies!

Beacons of the Recombination Era

HST Deep Field (http://www.stsci.edu/ftp/science/hdf/hdf/html)

• Gunn-Peterson trough found in z=6.28 quasar: Epoch of reionization Becker et al., Djorgovski et al.

• Primordial star formation (PopIII) may create 100-1000s Msol `stars’ Madau, Norman et al.

• Quickly produce hypernovae GRBs?

• 10% of GRBs may be at z>6

Bromm & Loeb

First metal production, snapshot of IGM

GRBs may be the only bright z>6 sources

• No quasars at z>>6?

• GRBs a unique probe of recombination epoch?

In the meantime…Swift is due to launch on Sept 2004!!!

Swift will trigger medium resolution R=400@1keV observations with Chandra and XMM-Newton, R=1000@6keV observations with AstroE2

A few events/yr with Fluence10-6 erg cm2

A dozen events/yr with Fluence310-7 erg cm2

Warm IGM:Statistics of OVII lines: first reliable measure of B at low z

Host galaxy ISM:Observations with the calorimeters of AstroE2 will measure: metal column densities, gas ionization parameter, gas dynamics

Rapid GRB Trigger & Location

short focal length reduces moment of inertia, I=mR2

(factor 25 for 2 meters vs. 10 meters)

• Problem: require <1armin location + acquisition in 1-10 minutes and require quasi-4coverage: conflicting goalsconflicting goals

• Solution: divide GRB trigger from location (as on BeppoSAX)

TriggerTrigger

faceted CsI solid 1o in seconds

Rapid rough slewRapid rough slew to 1o location

LocationLocation small X-ray coded mask eg XMM pn chip with 10ox10o fov to obtain arcmin location in a few seconds

Fine slewFine slew to <1 arcmin position

X-ray spectrometer starts to take data

GRB trigger must be on-board & autonomous

~20cm dia

x ~50cm lengtht=0s t=3s t=30s

t=60s

t=40s

Con-X Pros & Cons

• Pros:– Real project: 2010 launchNext new MIDEX launch 200X

– Includes 1-10 keV

+10 -100 keV spectra

• Cons:– 1min vs 12 hr slews– R=6000 vs R~400 or R~2000

– Add GRB trigger/locator

`Christmas tree’ effect