1. GAMMA-RAY BURSTS EFFECTS ON THE LOWER IONOSPHERE
Edith L. Macotela
Ionospheric physics project, April

2. PRELIMINARY CONCEPTS Gamma-ray bursts
A GRB is a fleeting blast of high-energy light, often lasting a minute or less, occurring somewhere in the sky every couple of days
The energy realized is up to 1010 times bigger than the most intense registered solar flare

4. GRBs come from all directions on the sky and are not simply confined to the plane of the Milky Way
GRBs realize with different energies

5. Types of GRBs
Short duration bursts are those that last less then 2 seconds
Associated with the merger of two neutron stars into a new black hole or a neutron star with a black hole to form a larger black hole.
Long-duration bursts last anywhere from 2 seconds to a few hundreds of seconds (several minutes),
associated with the deaths of massive stars in supernovas; though not every supernova produces a gamma-ray burst.

6. New discoveries
The duration distribution of GRBs recorded by BATSE (black) and Swift-BAT (red). Pronounced differences can be observed at the short end, where BATSE records many more short bursts due to its harder response. There is also an apparent preference for Swift to record somewhat longer durations than BATSE. The population of ultra-long bursts are visible at the right hand side around 104s.
A.J. Levan, J. of High Energy Astrophysics, 2015

7. Ly-β, star lights, meteorites
Lower ionosphere
Ly-α (λ: 1216 Å)
NO+ ← NO
F-region
Photons
E-region
90 – 140 km
D-region
Ly-β, star lights, meteorites km

8. STUDY THE LOWER IONOSPHERE: the VLF technique
VLF signal temporal variation 𝒇=𝟐𝟒 𝒌𝑯𝒛 (N-S)
Day (D-region): h~72.5 km
Night (E-region): h~87 km
Day (D-region): h~72.5 km
VLF waves propagating between the transmitter and the receiver inside the Earth-ionosphere waveguide
Night (E-region): h~87 km

9. Ionospheric disturbances
VLF amplitude
VLF amplitude
X-ray
X-ray
Day
Night
Night
Day
Night
Night
Quiet day
Perturbed day

10. STUDIES OF GRBs ON THE LOWER IONOSPHERE
So far, detection of ionization excesses on the lower ionosphere has been reported for only six events of this kind.
The single GRB on 1 August 1983, GRB830801, was detected using several VLF propagation paths [Fishman and Inan, 1988]
Another burst occurred on August 27th, 1998, SGR was also detected by using VLF networks in the US [Inan et al., 1999] and in Japan [Tanaka et al., 2008]. In this particular case, the VLF observations allowed constraining the low-energy photon spectrum in the absence of available X-ray data below 20 keV [Inan et al., 1999; Tanaka et al., 2008].

11. SGR
Disturbance of the lower ionosphere by gamma-rays from a magnetar. (a) The VLF great-circle paths from the NPM transmitter to Stanford University receivers in Boston, Palmer, and the HAIL network. The part of the globe illuminated by the γ–ray flare is indicated by shading. (b) The amplitude of the 21.4 kHz NPM signal as observed in Trinidad, Colorado, over a 10 hour period. (c) Expanded record of the γ–ray flare event which occurs at ~3:22 am PDT. (d) The intensity of the gamma ray burst as observed on the Ulysses satellite (from [Inan et al., 1999]).

12. The third event occurred on 29 March 2003, GRB030329, the authors observed a transient decrease in the strength of the radio noise coming from extraterrestrial sources (cosmic noise) at 38 MHz [Maeda et al., 2005].
The fourth event was, again, an isolated outburst from SGR occurred on December 27th, It was the largest burst ever observed, and it saturated most of the gamma-ray sensors in space [Hurley et al., 2005; Palmer et al., 2005].
The fifth event occurred on 22 January 2009 when SGR J released hundreds of bursts between 00:00 and 09:00 UT [Mereghetti et al., 2009]. Because the realize of many bursts Raulin et al. [2014] used this event to addres the nighttime sensitivity of the VLF response to a series of X-ray bursts emitted by SGR J using VLF data with a time resolution of 20 ms. They reported that the sensitivity depends on the illumination conditions.

13. SGR J
VLF propagation paths (white) and the part of the Earth affected by the SGR-J (south of the thick black line).
(source: Raulin et al., 2014)
The X-ray fluence F25 as a function of time for the 55 bursts observed and producing (green diamonds) or not producing (red diamonds) a significant ionospheric disturbance using (a) NPM-EACF and (b) NPM-ROI propagation paths. For each path, the illumination factor is shown by the black curve.
(source: Raulin et al., 2014)

14. The last event used to study anomalies in the VLF signal associated with a GRB was GRB090424, which occurred on 24 April 2009 [Chakrabarti et al., 2010].
Aside of the isolated studies on one GRB, Nina et al. [2015] study the possibility of detection of GRBs using a statistical analysis of perturbations of six VLF radio signals emitted by transmitters located worldwide. They consider a sample of 54 short-lasting GRBs (shorter than 1 min) detected by the Swift satellite during the period 2009–2012.
Histograms of number of peaks for signals emitted by DHO. The vertical lines denote the time of the GRB recorded at satellite. The black points indicate the statistically significant increase.

15. Current status
Mainly all the studies have been concentrated in the detectability of the GRB.
One of them indicate possible secondary processes that affect ionization in the low ionosphere.
Another study reported the nighttime ionospheric sensitivity using the X- ray emissions of a SGR.
Also, one study suggested that not only the huge events can produce ionospheric disturbances, but also the events of moderate energy.
Thus, from the previous study it is clear that detailed analysis of GRB influence on the ionosphere is needed

16. DATABASES GRBs database
IBAS - INTEGRAL:
Konus-Wind, on board Wind spacecraft:
NASA's Swift satellite: bin/sdc/ql?show-old=true
Fermi Gamma-ray Space Telescope:
Other sources are:

17. https://light2015blog.org/2015/10/21/gamma-ray-bursts-natures-brightest-flash-bulbs/

18. VLF database Data is available on
SID:
AWESOME:
A list with most of VLF laboratories to request data is:

19. CONCLUSION
Gamma-ray bursts are known as the most energetic phenomena in the universe.
There are some studies about the detectability of GRB on the lower ionosphere and the disturbances produced in the VLF signal.
It is clear that detailed analysis of GRB influence on the ionosphere is needed.

20. THANKS FOR YOUR ATTENTION

21. References
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Budden, K., The propagation of radio waves: the theory o radio waves of low power in the ionosphere and magnetosphere. Cambridge University Press, 1985.
Bracewell, R. N., and T. W. Straker, The study of solar flares by means of very long radio waves, Mon. Not. R. Astron. Soc., 109, 28–45, 1949.
Bracewell, R., Theory of formation of an ionospheric layer below E layer based on eclipse and solar flare effects at 16 kc/sec, J. Atmos. Terr. Phys., 2, 4, 226–235, 1952.
Correia, E., P. Kaufmann, JP. Raulin, et al., Analysis of daytime ionosphere behavior between 2004 and 2008 in Antarctica, J. Atmos. Solar Terr. Phys., 73, , 2011.
Cummer, S. A., Lightning and ionospheric remote sensing using VLF/ELF radio atmospherics, PhD Thesis, Stanford Univ., Stanford, Calif, 1997.