HETE (High Energy Transient Explorer) and GRBs

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HETE (High Energy Transient Explorer) and GRBs

• HETE first launch (failed) Nov. 4, 1996.
• HETE second launch (HETE-2) Oct .9, 2000.

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HETEs energy range

• Blue HETE
• Red Swift

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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
• unlikely that HETE-2 or Swift will see another
  such event.
• First localization by HETE released after 73
  minutes (HETE can do much better), first optical
  detection after 37 more (Peterson Price).

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GRB030329 Implications

• HETE-2localized burst GRB030329/SN 2003dh
  confirms the GRB SN connection.
• 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,
• Quotation from S. Colgate, 1959, to the Russian
  delegation of the conference in Geneva for the
  cessation of nuclear testing in space SNe or
  something like them might trigger our treaty
  detectors in orbit, causing us to lob nuclear
  weapons at each other.

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HETE-2 Observations of GRB021211
Crew et al. (2003) first HETE localization after
33 sec., OT reported by Fox Price (GCN 1731)
after 5317.
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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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Are GRB021211 and GRB030329 unusual events?

• They fit the Epeak-Erad Amati relationship, also
  if corrected by the jet opening angle (graph from
  Ghirlanda, Ghisellini Lazzati 2004), but
  030329 has lower Epeak,Erad
• They are both XRR, but with a different duration
  T90 2.41s for 021211 and 22.86s for 030329
• CONCLUSION we CANNOT TELL from the GRB if it is
  coincident or not with a SN.

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Why did it take so long to find the GRB-SN
connection?

• Even when GRBs where still not well and promptly
  localized, we might have found the SN-GRB
  connection as an excess of coincidences within
  fixed time intervals why did not we find them?
• We do not detect all SNe and all GRBs.
• GRBs are highly directional, thus we detect only
  a small fraction of them.
• We detect SNe at most at redshift 1, while for a
  large fraction of GRBs the detected redshift is
  larger
• SN1998bw z0.0085 SN2003dh z0.1685,
  GRB021211 z 1.006, GRB031203 z 0.1055

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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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Long and short GRBs
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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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FREGATE and WXM

• The YB counter of the WXM is not working since
  2003 January 11

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SXC

• Built by MIT/CSR
• Dimensions 10 cm x 10 cm x 17.5 cm
• Effective area 7.4 sqcm per unit
• Two CCDs per SXC 2048 x 4096 15 micron pixels
• Energy range 0.5 to 14 keV
• Spectral resolution 46 eV _at_ 525 eV, 129 eV _at_ 5.9
  keV
• Detector quantum efficiency 93 _at_ 5 keV, gt20
  (0.5-14 keV)
• Timing resolution 1.2 s
• Field of View 0.91 sr
• Focal plane scale 33 per CCD pixel
• Burst sensitivity (4 sigma) 700mcrab t(-1/2)
• Localization precision 15 (5 sigma burst) to 3
  (22 sigma burst)

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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 . First HETE error box
  after 88 minutes.
• X-Ray afterglow detected (Butler et al. 2002), no
  optical detection.
• Probably need even faster localizations.

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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.
• HETEs main task fast (even lt 1 minute) and
  precise (even lt3 arcmin) localization of GRBs
• is currently localizing 20 (?)GRBs yr-1, many
  more are detected, but not localized,
• has localized 55 GRBs so far, delays ranging
  from lt 1 minute for onboard error boxes to 2 3
  hours for refined ground locations,
• 8 of these localizations have led to the
  detection of X-ray afterglow, 18 to optical and
  5 to radio afterglows,
• 13 of these afterglows have led to redshift
  determinations.
• Including HETE events, 183 GRBs well localized
  since 1996, detected afterglows 54 X-rays, 51
  optical, 27 radio (BSAX 57, 30, 19, 12 in 6
  years).
• 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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HETE-2 International Science Team
(Mission Scientist)
IASF/CNR, Bologna Graziella Pizzichini, Ennio
Morelli, Fulvio Gianotti, Patrizia Ferrero
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HETE-2 is a very small spacecraft

• HETE-2 compared to some X and Gamma-Ray
  experiments.
• Weight lt 124 Kg.
• Height 89 cm.
• Width approx. 47 x 47 cm.

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HETE most data are public immediately

• Burst locations, light curves, spectral
  information and a possible estimate of z for all
  HETE GRBs are free and available as soon as
  possible via the public HETE web page. This fit
  (red line) of the GRB030329 HETE light curve was
  published on the preprint server astro-ph on
  April 6, 2003 (Dado, Dar De Rujula).
• Up to now there are 58 papers and preprints on
  this event, plus 187 GCN messages.

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• HETE GRB rates