Out of the darkness: the infrared afterglow of the INTEGRAL burst GRB 040422 observed with the VLT - PowerPoint PPT Presentation

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Out of the darkness: the infrared afterglow of the INTEGRAL burst GRB 040422 observed with the VLT

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Title: Out of the darkness: the infrared afterglow of the INTEGRAL burst GRB 040422 observed with the VLT


1
Out of the darkness the infrared afterglow of
the INTEGRAL burst GRB 040422 observed with the
VLT
  • P. Filliatre
  • filliatr_at_cea.fr
  • Astroparticule et Cosmologie
  • CEA/Service dAstrophysique

Based on Filliatre, DAvanzo, Covino et al., to
appear in AA
2
The dark burst problem
  • No optical afterglow detected for a fraction of
    GRBs 10 (Lamb et al. 2004) - 60 (Lazzati et
    al. 2002)
  • Popular physical explanations
  • High z burst Lyman ? cut (Lamb 2000)
  • Population of intrinsically faint afterglows
    (e.g. Fynbo et al. 2001)
  • Dust-enshrouded afterglows (e.g. Reichart Price
    2002)
  • ? An issue for cosmology and understanding of the
    GRB environments
  • Or maybe the search is not efficient (not quick
    enough, no infrared)

The afterglow of GRB 040422 was detected thanks
to a quick observation in the NIR with VLT
3
Summary of the observations
  • T0 GRB 040422 detected by INTEGRAL
  • l 3337, b 259, error 2.5 (IBAS)
  • ? Strong Milky Way absorption
  • T1.90 h (!) VLT ISAAC/FORS 2
  • Ks (2.2 ?m 150 s)
  • R (0.7 ?m 120 s), I (0.9 ?m 120 s)
  • T 13.04 d VLT ISAAC
  • Ks (150 s) reference frames
  • T 64.82 d VLT ISAAC
  • Ks (1800 s) deep observation

4
INTEGRAL results (I)
SPI (20 - 200 keV) Duration 4 sec. Peak flux
2.8 ph cm-2 s-1
5
INTEGRAL results (II)
  • IBIS/ISGRI (15 - 200 kev)
  • Power law (N(E) ? E? )
  • ? -2.2 ? 0.4, ? 86.4/36
  • Broken power law (Band model)
  • Ep 41 ? 3 keV, ? -1.26 ? 0.03,
  • ? -4 (fixed), ? 39.9/35

Similar spectral properties to GRB 030131 Nothing
really special
6
Detection of the afterglow with ISAAC
  • Semi-automatic selection
  • Criteria
  • stellar-like
  • variation gt 2 mag
  • not blended
  • Detected only in Ks
  • Huge Galactic absorption
  • AR 4.4
  • AI 3.8
  • AK 0.5

7
Detection of the host galaxy
T 1.90 h
2
T 13.04 d
T 64.82 d
8
The lightcurve
Ks 18.00.1
Ks gt 20.2
Ks 20.30.2 (host)
I gt 23.4
R gt 24.2
9
Comparisons with other afterglows
  • The game
  • Correct for Galactic absorption
  • Extrapolate to T1.90 with F ? t-?
  • Extrapolate to K with F ? ?--?
  • Assumptions
  • Power law is valid
  • Intrinsic absorption small enough

10
Comparisons with other afterglows
Lowest delay Nearly the faintest
11
An almost dark burst
  • Shows that 8-m telescopes can lower the
    proportion of dark burst with
  • Quick follow-up (less than 2 hours, but 5min ?
    Ks14.6)
  • Multiband including NIR
  • Why GRB 040422 is faint ?
  • Remote ?
  • ? Unlikely, because the host is rather bright
  • A normal afterglow enshrouded by dust ?
  • ? Maybe
  • Belongs to a class of intrinsically faint
    afterglows ?
  • ? Maybe
  • These observations are all we have

12
How to gather more data ?
  • Need to have very quickly a 1 position
  • Use it to quickly have a large band spectrum with
    an high efficiency
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