Relevance of GMT for GRB studies

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					Relevance of GMT for GRB studies

Ram Sagar ARIES, NainiTal, India

• Introduction to Gamma-Ray Bursts (GRBs) Discovered in 1967 by the Vela satellites • Era of BATSE on CGRO – 1991 • Beppo-SAX and HETE-II-- Afterglow era Multi-wavelength observations - 1997 • Swift multi-wavelength era – 2005 • GRBs in GMT era – Near IR and High resolution spectroscopy

Introduction to Gamma Ray Bursts (GRBs):
 Discovered in 1967 by the Vela satellites but known to public in 1973

    

Short lived (10–3 – 10+3 sec) Extremely luminous gamma-ray sources (release ~ 10 50-52 ergs energy) Non – thermal spectra Short intense flashes of  rays at Cosmological distances – 0.008 < z < 6.3 Hardness ratio = F(50-100 Kev)/F(25-50 Kev)

Classification – Evidence for 2 GRB classes

Duration (T90)
Long (T90 > 2 sec) Short (T90 < 2 sec)

Bright (~6x10-6 erg ) Faint (~4x10-7 erg)

Soft (1.6) Hard (3.3)

The GRB light curves
990316 970508



 BATSE on CGRO – 1991; Statistical analyses started  Isotropic distribution  Cosmological distances

Bi-modal distribution of GRBs

 Long duration T90 > 2 sec; mean ~ 25 sec; and soft γ-ray spectrum  Short duration T90 < 2 sec mean ~ 0.3 sec; and Hard γ-ray spectrum

GMT observations may provide better classifications??

Bloom et al. 2005, Zhang Bing 2007

Possible progenitors

GRB Afterglow and Fireball model
The ejected matter finally hits thehole &to form is ejected an The star collapses to form a black other matter internal shocks Layers of ejecta collide with each ambient medium driving external shock into it

GRB Afterglow and Fireball model
Shocks interact with ISM, the electrons gyrate around the magnetic field and emits non-thermal synchrotron radiation ranging from X-ray, optical to radio known as Afterglows

Cartoon of fireball model

- ray band alone Short lived – seconds


GRBs vs Afterglows: 2 phases

multi-wavelength phenomena long lived – days to years depending upon the burst & band of observation


Lessons from multi-wavelength observations of ~300 afterglows

( ~250 in X-ray; 175 in optical and 50 in Radio)

Story of Smoking gun?? GMT ??
Probe constraints on the current theoretical models Surroundings :: distance :: energetics Light curve break :: collimation Supernova association :: progenitors

Sensitivity discovery space
8 m
GMT 1 < z < 5 galaxies IGM DE Baryon Tomo

First light
Spectroscop y

Angular resolution discovery space

8 m GMT

Afterglows of GRBs

Jet Signatures in Optical/X-ray

Temporal slope  & spectral slope , in the synchrotron afterglow model with no spectral breaks, are related as

F (t, )  t -  -
where  and  are functions of p, p is the power law exponent of the electron Lorentz factor

As a relativistic jet decelerates we see a larger fraction of the emitting surface / [( t/t see the(edges)of the jet. These leads to a f(t) = 21/s f0 until we j )1s + t/tj 2s]1/s + fg j panchromatic break slope of the the afterglow light curve.

Achromatic break in light curves

E = (1 - cosj) Eiso,

GRB 021211 afterglow, Optically dim burst
 Optically dim, ~3 mag fainter than GRB 990123  Detected ~90 sec after the burst  R band, single power law ~ 11 min to 35 days with decay index  ~ 1.1  Compared with GRB 000630 & GRB 020224 Similar GRBs have R ~ 23 mag, one day after the burst  It would have been classified as optically dark burst in absence of rapid follow-up  Observed at very early hours from India, courtesy Longitudinal advantages Possible explanations: Intrinsic faintness; High red shift and extinction

GRB 021211, Pandey et al., 2003

Advantage with GMT nearIR capabilities ??

Afterglow temporal breaks

GRB 010222, Sagar et al. (2001)

GRB 030226, Pandey et al., (2004)

GMT near-IR observations are possible for similar objects at high Z -> Relevance

Overlapped variability in the optical afterglow light curve

Deviation from simple power law Bumps & Wiggles in

the light curve

GRB 000301c (Sagar et al. 2000), GRB 021004 (Pandey et al. 2003)

Complex density structure around the burst (Wang & Loeb 2000), Refreshed shocks (Rees & Meszaros 1998), Patchy shell model (Kumar & Piran 2000), Microlensing (Garnavich et al. 2000)

GRB 030329/SN 2003dh (Resmi et al 2004)

Monitored from 3 hours to 33 days After the burst UBVI, earliest observations Peculiar afterglow light curves with overlapped variability and SN 2003dh contribution

Swift era – 2005 (launched in Nov 2004)
X-ray and optical behavior dissimilar Early steep decay: X-ray

Many afterglows exhibit jet breaks relatively early Afterglows with jet break beyond ~2 days are not rare GRB 000301C, GRB 011211 and GRB 021004

No supernova associated with two long duration GRBs: GRB 060505 & GRB 060614

Could GRB 060505 & GRB 060614 be short GRBs or at higher redshifts?

GRB 050724

The outflows of SHBs are collimated

SHB facts
Closer on average than long bursts <z>=0.3 Occur in both spiral & elliptical galaxies (cf SN Ia) GRB/host offsets do not trace the blue light of their host galaxies Release less energy Central engines are long-lived

Multi-λ observations and Energetics indicates
 Long duration GRBs are most probably produced from stellar-like systems Some clues: Association with star-forming regions in galaxies GRB 980425  SN 1998bw (Galama et al. 1998) GRB 030329  SN 2003dh (eg. Hjorth et al. 2003)

 At least, some GRBs are deaths of massive stars! -- especially from massive He stars (or WR stars)
Chandra observations indicates presence of Fe lines in GRB 991216; GRB 000926 and 3 others Large amount of dust extinction (Av ≥ 1 mag); high star formation rate in the star forming host galaxies  While Short duration GRBs are most likely formed with a merger of compact objects

GRBs as distance indicators alternative to SNe Ia;
can be discovered out to extremely high red-shift (Z~ 15-20)

Cosmic star formation theory (10% GRBs have Z > 6) so far only one GRB 050904 have Z = 6.3 First generation star Z~20; First generation quasar Z~7 and CMB Z~ 1100 Unveil the dark universe and the re-ionization history of the Universe

Star formation & galaxy assembly
• There are discrepancies at z=1 to z=3; IMF?? • The star-formation history beyond z~5 is even not understood

Star formation rate

Instantaneous SFR (M/yr/Mpc3)

0 1 2 3 4


Internal properties of high-z galaxies 1

40 x 40 IFU

• GMT will be able to probe chemistry and dynamics of high-z galaxies and study their assembly with ~100 pc resolution. • Use large single IFUs for detailed studies at moderate z z= • Star-formation @ image) with HST Use multiple 0.1 (H + continuum deployable IFUs to

Abundances Ages Masses

Star-formation @ z = 1.4 with GMT (1.6m image, 1 hour exposure)

Physics of galaxy formation
• GMT will be able to map the physical properties of galaxies over the redshift range (1<z<5)
– Star formation rate
– Metallicity maps – Extinction maps
z = 0.0

z = 2.5

– Dynamical masses
– Gas kinematics

z = 5.5


SFH of old galaxies at z>2
• NIR spectra; star-formation histories, ages, abundances • GMT+GLAO+NIRMOS; spectra to J=24.5 in 5 hrs; • With better NIR detectors  may be reach J=27!
GMT+GLAO+NIRMOS+OH-suppression+lownoise GMT+GLAO+NIRMOS (simulation by P.McCarthy)

Kreik et al. GNIRS

Ly- in high-z galaxies
• GLARE survey; 36hr exp with Gemini+GMOS
[Stanway, Glazebrook et al., 2006]

• Simulated observation of z=6 Ly galaxy; 30hr with GMT+GMACS [McCarthy
Ly flux (erg/cm2/s)

Ly flux > 5x10-18 erg/cm2/s

 To observe faint GRB afterglows in near-IR GRB Z Tb(days) H mag 990510 1 2 20 ? 10 11 24 VLT ~ 23 mag for 1 hour Exposure time

GRB jet configuration: absence of achromatic breaks

 Faint GRB afterglows so that dark GRBs can be studied.
 High resolution spectroscopic and near-IR imaging of the host galaxies -> learn more about the GRB classification scheme and unveil the dark universe and the re-ionization history of the Universe

GRBs as distance indicators alternative to SNe Ia;
can be discovered out to extremely high red-shift (Z~ 15-20)

Cosmic star formation theory (10% GRBs have Z > 6) so far only one GRB 050904 have Z = 6.3 First generation star Z~20; First generation quasar Z~7 and CMB Z~ 1100

Optical prompt emission in case of GRB 990123 (Galama et al. including ARIES GRB Team, 1999, Nature). The Gamma-ray light curve with the ROTSE optical observations (in Red-bands) are shown

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