On estimate of first solar proton arrival

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On estimate of first solar proton arrival

• Alexei Struminsky1,2 and Ivan Zimovets1
• 1 Space Research Institute, Moscow, Russia
• 2 IZMIRAN, Troitsk, Moscow region, Russia

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Introduction

• Analyzing SEP events it is very important to
  estimate accurately the time of first
  relativistic proton arrival to the Earth.
  Arbitrary a GLE onset observed by the NM network
  is considered as this time moment. A typical time
  resolution of NMs with reasonable statistic
  accuracy is /- one minute.
• This accuracy seems reasonable for estimates of
  first solar proton release into the
  interplanetary space since free parameters of
  propagation models, a length of magnetic field
  line and mean free path, will give a similar
  error. Depending on solar wind velocity a length
  of magnetic field line may vary by several tens
  of and mean free path is within the Palmer
  range.
• However this definition of first solar proton
  arrival does not consider an initial background
  of NM and a rate of proton intensity increase.
  These factors may create a larger error, which
  will lead to incorrect estimate of proton release
  and, consequently, moment of their acceleration.
• Do we have any instrument with less background
  level and better statistics? Yes, this is the
  Anti-Coincidence System (ACS) of Spectrometer on
  INTEGRAL (SPI)

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ACS SPI

• The Anti-Coincidence System (ACS) of Spectrometer
  on INTEGRAL (SPI) is sensitive to primary and
  secondary gamma-rays and effectively response to
  solar energetic particles.
• The ACS SPI provides unprecedented statistics and
  time-resolution in comparison with NMs.
• Therefore the ACS SPI may response to solar
  protons sometimes earlier than do NMs, if a flux
  of primary gamma-rays is rather low.

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December 13, 2006
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December 13, 2006
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• Is ACS SPI sensitive to relativistic electrons?

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• No, its sensitive to relativistic protons, which
  intensity is lower than NM threshold!

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January 20, 2005
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October 28, 2003
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DISCUSSION

• The proton event of 2006 December 13 began at
  0239 UT (lt17 min) by ACS SPI, at 0250 UT (28
  min) by NMs and at 0254 UT (32 min) by MEPhI
  muon hodoscope data.
• Is this difference of the proton event onset
  caused by a level of background or determined by
  a threshold energy of the detectors?

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• The same situation was observed for relativistic
  electrons by STEREO. The onset of electrons with
  higher energy is delayed.
• This delay is a result of different background.

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CONCLUSIONS

• An onset of anisotropic GLE phase does not
  correspond always to arrival of first solar
  protons to the Earth. Determining a moment of
  first solar proton arrival one needs to consider
  a detector background and a rate of proton
  intensity increase. An error caused by these
  factors may be greater than a data time
  resolution.
• During the 2006 December 13 event, when the
  intensity of primary gamma-rays was rather low, a
  massive gamma-ray space born detector (ACS SPI)
  appeared to be a more effective instrument for
  observation of the proton event onset than the
  NM network. The proton event onset was observed
  by the ACS SPI about 11 min earlier than the GLE
  onset.
• For two other considered GLE events, when a level
  of primary gamma-rays was rather high, an arrival
  of first solar protons was observed by ACS SPI
  simultaneously with NMs (2005 January 20) and
  later (2003 October 2003).

We thank Alexander Lutovinov (Russian INTEGRAL
data center) for ACS SPI data and all our
colleagues submitted NM data to the IZMIRAN data
base. IZ thanks the Russian foundation for Basic
Research and the Leading Scientific School
Program for the financial support.