Docstoc

Poster VLF GRBs

Document Sample
Poster VLF GRBs Powered By Docstoc
					Alternative Detections of
   Gamma Ray Bursts


  René Hudec2 and Rudolf Slosiar1
   1 Slovak Union of Amateur Astronomers, Bojnice,
                   Slovak Republic
  2 Astronomical Institute, Academy of Sciences of the
  Czech Republic, CZ-251 65 Ondrejov, Czech Republic
                                  Image credit: NASA
Alternative GRB Detections

•By Ionospheric Response
•By Bright Prompt Optical Emission
•By Promt X-ray Emission
Indirect detection of GRBs
 by ionospheric response
                Introduction
• We report on the independent and indirect
  detection of GRBs by their ionospheric response
  (SID – Sudden Ionospheric Disturbance)
  observed at VLF (Very Low Frequency).
• Although few such detections have been already
  reported in the past, the capability of such
  alternative and indirect investigations of GRBs
  still remains to be investigated in more details.
  We present and discuss the examples of further
  such VLF/SID detections.
 Previous VLF detections of GRBs
• SGR1806: Detection of a Sudden
  Ionospheric Disturbance. Campbell et al.,
  GCN 2932, 2003.
• GRB030329 observed as a Sudden
  Ionospheric Disturbance (SID) P.W.
  Schnoor GCN 2176, 2003.
      Physics behind ionospheric
              detection I
• The solar particle stream, solar wind, shapes and
  controls the Earths‚ magnetic envelope - the
  magnetosphere- and increases heat in the aurora zones.
  But not all ionospheric variability is caused by solar or
  geomagnetic disturbances. The ionosphere is not a
  constant 'mirror in the sky'. The E layer (100-200 km
  above ground) and the F1 layer (170-200 km) usually
  behave in regular, solar-controlled way, but the F2 layer
  (250-350 km) does not.
• It is the F2 layer, which has the greatest density of free
  electrons, and is potentially the most effective reflector of
  radio waves. (Rishbeth, Nature Vol. 418, 4 July 2002)
       Physics behind ionospheric
               detection II
• The ionossperic D layer plays in the GRB detections an
  important role, as the detection of X-ray and gamma-ray
  triggers is based on the measuremeńt (monitoring) of
  reflected radio waves from this layer. The ionospheric D
  layer is not transparent for radio VLF waves (frequencies
  3kHz to 30 kHz) and behaves like a mirror.
• If the transmitter is at large distance (800 to 2000 km)
  then the radio waves are guided like in a waveguide
  consisting of the D layer and the earth surface.
• Any change in the quality of this waveguide results then
  in the signal change in the SID monitor. The change can
  be positive but in some cases such as the sudden phase
  anomaly also negative.
     Typical ionospheric behaviour




This picture shows the typical behaviour of the ionosphere during one day.
Note the different behavior at night with absence of the D layer.
   The plot from the SID monitor
during the period of enhanced solar
               activity       Demonstration of the
                             possibility and
                             sensitivity of the
                             method. Four Solar
                             Flares (SF) are visible
               Dec 6, 2006   with intensities M6, C6,
                             C2, C4, exactly
                             corresponding to the
                             measurements by the
                             GOES satellite. The
                             peak related to the SF
                             C4 occurs around
                             15:03UT, which is
                             nearly the detection
                             time of GRB060124A, on
                             Jan 24, 2006, confirming
                             that even at the time of
                             the decay of the D
                             ionospheric layer
                             reliable measurements
                             are feasible.
    SGR1806-20: A sharp spike, then re-
normalization of the ionosphere (Howe, 2004)
      The SID receiver and cross loop
                 antenna
2-channel receiver used to eliminate false
triggers




 Instrumentation used for the
 indirect detection of GRB 060124A.
 The antenna size is 75 x 75 cm         Inexpensive instrumentation suitable
                                        for easy duplication for other sites
The detection of GRB 060124A
                GRB_TIME: 15:54:51.82 UT




                 SID trigger detection 15:56:31 +/- 5sec




Swift BAT LCT
The detection of GRB 060124A
   For comparison: SID from
C2-class solar flare erupted from
          sunspot 958
           GRB080319D – possible
                detection
GRB_TIME: 17:05:09.34 UT
SID signal: 17:05:41 +/- 5sec   Swift BAT LCT
             GRB080320A – possible
                  detection      Swift BAT LCT


GRB_TIME: 04:37:38.46 UT
SID signal: 04:38:59 +/- 5sec.




   Emitter Tavolara (Sardinia)       Emitter Sainte
                                     Asise (France)
            Speculations
• In the both recent cases of possible
  detection     of    GRB080319D        and
  GRB080320A, some structure appeared
  afterwards, resembling a propagation
  ionospheric wave
• Further observations are necessary to
  confirm this hypothesis
GRB Induced Propagating
  Ionospheric Waves




                 Speed: 300 to 1200m/s
Possible GRB080319D Induced
Propagating Ionospheric Waves
      For illustration: Recent Earthquake
     May 29, 2008, at 15:46 UT (during yesterday talk of
                                    Claudio)

                         Ionospheric waves can be triggered both from
                         outside (space radiation) but also from inside (e.g.
                         earthquakes)
Distance Bojnice-
Island (epicentre)
2680 km

SID disturbance
detected with delay of
74 min

Hence mean speed of
propagation of the
ionospheric wave
was 603 m/s

(In Vulcano, the wave
arrived during talk of
Anatoly)
                        Discussion
The conditions to detect GRB with SID monitor in VLF

•   The presence of the D layer of the ionosphere
•   The suitable combination of the GRB position (RA, DEC) and time and hence
    direction and angle of the incoming gamma-ray radiation in relation to the D
    layer and observing site.
•   The fluence and duration of the GRB.

The detection statistics

•   The recent detection rate of GRBs is about 130 in a year.
•   For one observing station, the number of GRBs occuring during the presence
    of a D layer and in the field of view is about 20
•   This is ideal number, the real one is less than 10 due to occassional non-
    availability of transmitters and other technical and observational issues.
             Discussion II
• If the ionospheric detection of GRBs will
  be definitely confirmed, a dedicated
  experiment could be considered, namely a
  dedicated emitter
 GRB Detection by Bright OT
         Emission
• A small fraction of GRBs is accompanied
  by bright optical prompt emission (OT)
• This emission can be as bright as mag 6,
  and perhaps even brighter
• Such triggers can be detected in optical
  light, independently on gamma-ray
  detection
                                   GRB080319B
                                   For ~ 1 minute
                                   Brighter in
                                   optical light
                                   than mag 6



Naked eye visibility at z ~ 0.75




                 Indication exists that
                 some OT may be as
                 bright as mag 4 at
                 early times
                                                Prompt optical
                                                emission of
                                                GRB060117
                                                Peak 11.5 mag 2 min after
Images by WF lens 70 mm aperture at the Czech   GRB, decline 1.4 mag in
FRAM RT in Argentina (related to Auger).        2 min
Methods to detect bright OTs
         of GRBs
• Wide-field monitoring systems, CCD
  (preferably All-Sky)
• Wide-field monitoring systems, photographic
  (secondary use of meteor patrol)
• Archival Astronomical Plates
• Always sophisticated s/w needed to find and
  to verify the triggers
• Problem: (1) large background (2) typically,
  we have to look for 1 new object among 10
  000 - 100 000 stars: job for informatics
  students
                        CONCAM All
                        Sky Optical
                        Monitoring

                        Lim mag 4….5
                        i.e. not enough for
                        most scientific goals
                        Price 10x more than
                        the alternative system
                        shown before




Vulcano Workshop 2008                    27
                        Peleng 8 mm fish-
                        eye lens (1:3,5-1:16)
                        that provides a 24
                        mm circular 180°
                        field of view, and

                        a CANON EOS
                        350D digital CCD

                        camera

   Digital CCD
   all-sky
   monitoring
   lim mag ~11
   Karlovy Vary
   Observatory,
   CZ



Vulcano Workshop 2008                   28
All Sky CCD Camera, Sonneberg Observatory, 7K x 4K CCD and f/3.5 FE lens.
10/11/2004              Sterrewacht min integration
                  Lim mag 10 in 1 Leiden Lunch Talk time.              29
CCD Sky Patrol
Test Images
Sonneberg lim
mag 14 - 15




                 Vulcano Workshop 2008   30
                        How the
                        OTs of
                        GRBs
                        should
                        look like?
                        Example of fast
                        OT found -
                        duration less
                        than 5 minutes
                        … and that’s
                        expected

                        Results promising-
                        only 1 OT per plate
                        found (typically)
Vulcano Workshop 2008                         31
                                        Another short OT
         OT                             example, mag < 10


                                          Optical Transient
                                          Analyses - OT in
                                      Triangulum, Sonneberg
                                      Astrograph Plate, 6 mag
                                           above plate limit
                                       real object of unknown
                                          The searches for
                                         analogous OTs are
Comparison plate: no OT               difficult since the plates
                                        contains typically 100
                                        000 – 1 000 000 star
                                                images
              Vulcano Workshop 2008                        32
Problem: backround triggers
simulating OTs




The OTs of (unknown) astrophysical origin have been confirmed also
by CCD observations (Brno 60 cm CCD telescope, Filip Hroch)
Stars elongated, OT image not elongated – short OT
 April 27-May 1, 2005    38. Variable Stars Conference         33
                                  ValMez 2006
GRB Detections By Prompt X-
       ray emission
• So far most GRB are detected by their
  gamma-ray emission
• Most of the GRBs exhibit also X-ray emission
• Hence the GRBs can be detected also in X-
  rays (as independent detections)
• This goal requires sensitive all-sky
  monitoring
• Obvious solution is offered by X-ray All-Sky
  Monitors with Lobster Eye Optics
                                               LE lens
                                               arrangement
                                               according to
                                               Angel




                                               X-ray All
The front wiew of the mini - lobster module,
Schmidt arrangement, based on 100 micron
                                               Sky Monitor
thick plates spaced by 300 microns, 23 x 23    with LE
mm each                                        modules
The X-ray measurement at 8 keV in
comparison with mathematical simulation



     measured                   model
                 Conclusions
• The independent and indirect detection of GRBs by their
  ionospheric response (SID – Sudden Ionospheric
  Disturbance) observed at VLF (Very Low Frequency) is
  feasible.

• We present and discuss examples of such VLF/SID
  detections of three GRB.

• The capability of such alternative and indirect
  investigations of GRBs, as well as the possible
  contribution to analyses of GRBs still remains to be
  investigated in more details.

• The GRBs can be also (independently) detected in
  optical light and in X-rays, based on suitable optical and
  X-ray all-sky monitors
The End
GRB080319D – possible
     detection
GRB080319D – possible
     detection

				
DOCUMENT INFO