The HETE2 Mission and GRBs

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The HETE-2 Mission and GRBs
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HETE-2 International Science Team
(Mission Scientist)
IASF/CNR, Bologna Graziella Pizzichini, Ennio
Morelli, Fulvio Gianotti, Patrizia Ferrero
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Why work on GRBs?The first GRBs detected by an
Italian instrument, the second error box not fron
IPN
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Why Optical Observations of GRB Afterglows?See
Pedersen et al., Nature, 1984 (It was an SGR in
N49, but no one knew that)
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HETE-2 RESULTS on GRBs

• HETE-2
• Instruments Fregate 6-400 keV, 3 sr WXM 2 25
  keV, 1.6 sr SXC 0.5 keV, o.91 sr.
• is currently localizing 25 GRBs yr-1, many
  more are detected, but not localized
• has localized 41 GRBs so far, delays ranging
  from lt 1 minute for onboard error boxes to 2 3
  hours for refined ground locations
• 14 of these localizations have led to the
  detection of X-ray, optical, or radio
  afterglows
• 11 of these afterglows have led to redshift
  determinations
• HETE is a small mission height 89 cm, width lt
  47 cm, weight lt124 Kg no pointing instruments
  for afterglow observations
• Implications of HETE-2 and follow-up observations
  for
• GRB-SN connection
• Short, hard GRBs
• Optically dark GRBs
• X-Ray Flashes (XRFs) and X-ray-rich GRBs
• Nature of GRB jets

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Which hardware did we contribute to HETE?

• In order to disseminate fast on-board burst
  alerts and locations, HETE needs to be constantly
  in contact with a chain of Secondary Ground
  Stations along its equatorial orbit. Our double
  SGS , funded by ASI and hosted by CRPSM, is
  located in the San Marco base in Malindi, Kenia.
  It was set up by Ennio Morelli and Fulvio
  Gianotti. We constantly monitor it.
• Funding only ASI, residual from 2002, 20000
  euro
• mesi-uomo 24 (11 9 2 2)

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HETEs future

• HETEs operations are approved by NASA until July
  2004.
• New senior review in 3 months shall decide on
  further extension
• HETE is complementary to Swift and INTEGRAL it
  observes a different part of the sky than both of
  them and it detects and localizes very well also
  XRFs, while Swift shall detect mostly
  classical, i.e. gt 30 keV GRBs.
• HETE points in the anti-sun direction, its
  GRB locations are well suited for optical
  observations.
• Note HETE was built for GRBs, but it detects
  also many x-ray flashes and SGR events. It has
  probably discovered a new SGR source.

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GRB030329 HETE Hits a Home Run(Don Lambs
quotation)
Vanderspek et al. (2003)
z 0.1675 ? probability of detecting a GRB this
close by is 1/3000 gt unlikely that HETE-2 or
Swift will see another such event
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GRB030329Spectrum of SN 2003dh
Stanek et al. (2003)
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GRB030329 Implications

• HETE-2localized burst GRB030329/SN 2003dh
  confirms the GRB SN connection
• Science Magazine lists this one and other HETE
  result as one of the top ten in 2003, actually
  the only one in Astrophysics, and explicitly
  mentions HETE results and HETEs key Team
  work
• Implications
• We must understand Type Ib/Ic core collapse SNe
  in order to understand GRBs and GRBs in order
  to fully understand Type Ib/Ic core collapse SNe
• GRBs are a vital laboratory for studying core
  collapse SNe
• GRBs occur out to high z , and are therefore a
  powerful probe of cosmology and the early
  universe
• Quotation from Palumbo, Pizzichini Vespignani,
  1974 If one assumes that the burst is of
  extragalactic origin, the energy output would
  call for a supernova explosion

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HETE-2 Observations of GRB 020531

Lamb et al. (2002)

• GRB 020531 is the first detection of a short,
  hard GRB that has allowed rapid (t 2-3
  hours) optical and X-ray follow-up observations
  none from BeppoSax in 6 years .
• X-Ray afterglow detected (Butler et al. 2002), no
  optical detection
• Probably need even faster localizations

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HETE-2 is Solving Mystery of Optically Dark GRBs

• Two explanations of optically dark GRBs have
  been widely discussed
• Optical afterglows are extinguished by dust in
  the host galaxy (see, e.g., Reichart and Price
  2001)
• GRBs lie at very high redshifts (Lamb and
  Reichart 2000)
• Rapid follow-up observations of HETE-2localized
  burst GRB030115 show that this burst is best case
  to date of extinction by dust
• Rapid follow-up observations of HETE-2localized
  burst GRB021211 show that this burst is
  optically dim without rapid follow-up would
  have been classified as optically dark

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HETE-2 Observations of GRB021211
Crew et al. (2003)
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GRB021211 Afterglow Light Curve Relative to
Those of Other GRBs
Fox et al. (2003)

• The optical afterglow of some bursts is much
  fainter ( 3 mag) than those previously
  observed without HETEs prompt localization,
  this GRB would very likely have been listed as
  dark, instead of dim. But it proves that at t
  lt 10 min even dim afterglows may be bright (m
  13). This is very promising for Swift.

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HETE-2 extends Amatis relationship to XRFs
and X-ray Rich GRBs same phenomenon?
Sakamoto et al. (2003)
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Conclusions

• HETE-2 has confirmed the GRB SN connection
• HETE-2 and Chandra follow-up observations of
  short, hard GRB 020531 show that its X-ray
  afterglow is gt 100 x fainter than is typical of
  long GRBs (Swift XRT observations likely crucial)
• HETE-2 is solving the mystery of optically dark
  GRBs
• HETE-2 and follow-up observations of GRB030115
  have provided the best example so far of a GRB
  which is optically dark because of extinction
  by dust (Swift XRT should detect all of these)
• HETE-2 and follow-up observations of GRB021211
  have shown that the afterglows of some GRBs can
  be much fainter than those observed previously
  (i.e., they are optically dim, rather than
  optically dark) yet these afterglows can be
  very bright at t lt 10 minutes after the burst
  (Swift UVOT should detect most of these)
• Other optically dark GRBs are expected to lie
  at very high redshifts (Lamb and Reichart 2000)
  we hope HETE-2 will soon detect some and Swift
  many!
• HETE-2 observations have provided strong new
  evidence that XRFs, X-ray-rich GRBs, and GRBs
  are the same phenomenon and that a unified
  (uniform) jet model can explain them all

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Observations of GRB afterglows from Loiano
GRB021004
TOO Observations of GRB optical afterglows made
at the 152 cm telescope of the Bologna
Observatory in Loiano, in collaboration with C.
Bartolini, A, Guarnieri and A. Piccioni of the
Department of Astronomy of the University of
Bologna, for a short time also with N. Masetti
(IASF/CNR, Bologna). We try as much as possible
to make multifilter observations, in order to
further confirm the findings of Simon, Hudec,
Pizzichini Masetti, 2001 on the colors of
afterglows. THE FUTURE we expect many more TOO
observations also from INTEGRAL and Swift GRBs.
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Observations of optical afterglows from Loiano
GRB030226
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Observations of optical afterglows from Loiano
GRB030328
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Observations of Optical Afterglows from Loiano
GRB030418