Sky & Telescope - May 2021 - 17

G REGG DINDER M A N / S&T, SOURCE: WILLIA M H A NLON / UNIV. OF U TA H

Hotspot Connection
In the Northern Hemisphere, the smaller Telescope Array
project in western Utah is also undergoing an upgrade, quadrupling its current dimensions (some 750 square kilometers)
to a size comparable to Pierre Auger's. However, the Telescope

105

(1 particle/m2 per second)
1

Rate of incoming particles (m2 sr GeV sec)-1

phenomenon comparable to the sonic boom of a fighter jet
breaking the sound barrier.
Meanwhile, from four locations around the perimeter
of the observatory, a total of 27 wide-field telescopes with
3.6-meter segmented mirrors keep an eye on the sky above
the pampa, looking for the ultraviolet fluorescence caused
by the interaction of the air-shower particles with atmospheric nitrogen atoms. The Pierre Auger Observatory started
operating in early 2004 while still under construction and
was officially inaugurated in November 2008. " Our stations
have recorded many millions of signals to date, " says Castellina. " At energies above 3×1018 eV, where our detector is fully
efficient, the number of extensive air showers is on the order
of 15,000 per year. "
Using data from the surface detectors, scientists can
reconstruct the spatial orientation and the spread of the
air shower, as well as the number of secondary particles
that reach Earth's surface. From the UV observations of the
fluorescence detectors, they estimate the total energy of the
primary cosmic-ray particle, while the altitude at which the
fluorescence trail reaches its peak brightness indicates the
incoming particle's nature: Protons and electrons penetrate
to lower altitudes than heavier nuclei with the same energy.
Unfortunately, the fluorescence detectors can only operate
during cloudless and moonless nights - about 15% of the
time. That's where radio observations come in - they don't
care about weather or daylight. As Castellina explains, there
are two ways in which particle showers produce radio waves.
The more prominent source is electrons and positrons (antielectrons) produced by the decay of secondary cosmic-ray
particles: When they are deflected by Earth's magnetic field,
they emit radio pulses. But relativistic charged particles moving through the atmosphere also emit a cone of radio waves
known as Askaryan radiation, after the Soviet-Armenian
physicist who predicted the effect in 1962.
Test observations with the Auger Engineering Radio
Array (AERA) - a network of more than 150 simple dipole
radio antennas - have demonstrated that astronomers can
also use radio detections to estimate the energy of primary
cosmic rays. That's why engineers are now installing 1,660
radio antennas (one at every surface detector) as part of an
ongoing upgrade of the observatory, known as AugerPrime.
The upgrade also includes 1,660 flat particle detectors known
as scintillators, each with an active surface area of 3.2 by
1.2 meters, that will help characterize the secondary particles
in the air showers. These in turn provide more information
on the nature of the primaries. The AugerPrime deployment
has been delayed by the COVID-19 pandemic, but it should be
completed in 2022.

10-5

Knee
(1 particle/m2 per year)

10-10

10-15

10-20
Ankle
(1 particle/km2 per year)
10-25
(1 particle/km2 per century)
1010

1012

1014

1016

1018

1020

Energy (eV)
S COSMIC RAYS The flux of cosmic rays bombarding Earth as a function of their energy per particle. Scientists think those above the " knee "
come from within the Milky Way, while those of higher energies come
from outside our galaxy. Ultra-high-energy cosmic rays lie around the
" ankle " or beyond.

Array lacks Cherenkov water tanks; it just consists of hundreds of scintillators and three fluorescence detector stations.
" It's not easy to compare the results of the Pierre Auger
Observatory and the Telescope Array, " says theorist Anchordoqui. " They are different experiments with different
properties, and they use different analysis techniques. " Still,
scientists from both projects are working together to combine
the two data sets.
Interestingly, the Telescope Array has detected a 40°-wide
UHECR hotspot in the sky centered in Ursa Major, possibly
associated with the starburst galaxy M82. If confirmed, it
would support the possible link between UHECRs and nearby
starburst galaxies found by the Pierre Auger collaboration.
" Everything seems to be closing together, " Anchordoqui says,
" although it's still unclear what makes these handful of
starburst galaxies so special. There are many dozens of other
galaxies at similar distances that do not appear to contribute
as strongly to the observed UHECR flux. "
Central black holes can't be the answer, he adds, since
they are found in almost every galaxy. Anchordoqui's favorite explanation is galactic superwinds - powerful gaseous
outflows that result from huge numbers of supernova explosions. Indeed, M82 and NGC 253 show clear evidence of such
s k y a n d t e l e s c o p e . o r g * M AY 2 0 2 1

17


http://www.skyandtelescope.org

Sky & Telescope - May 2021

Table of Contents for the Digital Edition of Sky & Telescope - May 2021

Contents
Sky & Telescope - May 2021 - Cover1
Sky & Telescope - May 2021 - Cover2
Sky & Telescope - May 2021 - 1
Sky & Telescope - May 2021 - Contents
Sky & Telescope - May 2021 - 3
Sky & Telescope - May 2021 - 4
Sky & Telescope - May 2021 - 5
Sky & Telescope - May 2021 - 6
Sky & Telescope - May 2021 - 7
Sky & Telescope - May 2021 - 8
Sky & Telescope - May 2021 - 9
Sky & Telescope - May 2021 - 10
Sky & Telescope - May 2021 - 11
Sky & Telescope - May 2021 - 12
Sky & Telescope - May 2021 - 13
Sky & Telescope - May 2021 - 14
Sky & Telescope - May 2021 - 15
Sky & Telescope - May 2021 - 16
Sky & Telescope - May 2021 - 17
Sky & Telescope - May 2021 - 18
Sky & Telescope - May 2021 - 19
Sky & Telescope - May 2021 - 20
Sky & Telescope - May 2021 - 21
Sky & Telescope - May 2021 - 22
Sky & Telescope - May 2021 - 23
Sky & Telescope - May 2021 - 24
Sky & Telescope - May 2021 - 25
Sky & Telescope - May 2021 - 26
Sky & Telescope - May 2021 - 27
Sky & Telescope - May 2021 - 28
Sky & Telescope - May 2021 - 29
Sky & Telescope - May 2021 - 30
Sky & Telescope - May 2021 - 31
Sky & Telescope - May 2021 - 32
Sky & Telescope - May 2021 - 33
Sky & Telescope - May 2021 - 34
Sky & Telescope - May 2021 - 35
Sky & Telescope - May 2021 - 36
Sky & Telescope - May 2021 - 37
Sky & Telescope - May 2021 - 38
Sky & Telescope - May 2021 - 39
Sky & Telescope - May 2021 - 40
Sky & Telescope - May 2021 - 41
Sky & Telescope - May 2021 - 42
Sky & Telescope - May 2021 - 43
Sky & Telescope - May 2021 - 44
Sky & Telescope - May 2021 - 45
Sky & Telescope - May 2021 - 46
Sky & Telescope - May 2021 - 47
Sky & Telescope - May 2021 - 48
Sky & Telescope - May 2021 - 49
Sky & Telescope - May 2021 - 50
Sky & Telescope - May 2021 - 51
Sky & Telescope - May 2021 - 52
Sky & Telescope - May 2021 - 53
Sky & Telescope - May 2021 - 54
Sky & Telescope - May 2021 - 55
Sky & Telescope - May 2021 - 56
Sky & Telescope - May 2021 - 57
Sky & Telescope - May 2021 - 58
Sky & Telescope - May 2021 - 59
Sky & Telescope - May 2021 - 60
Sky & Telescope - May 2021 - 61
Sky & Telescope - May 2021 - 62
Sky & Telescope - May 2021 - 63
Sky & Telescope - May 2021 - 64
Sky & Telescope - May 2021 - 65
Sky & Telescope - May 2021 - 66
Sky & Telescope - May 2021 - 67
Sky & Telescope - May 2021 - 68
Sky & Telescope - May 2021 - 69
Sky & Telescope - May 2021 - 70
Sky & Telescope - May 2021 - 71
Sky & Telescope - May 2021 - 72
Sky & Telescope - May 2021 - 73
Sky & Telescope - May 2021 - 74
Sky & Telescope - May 2021 - 75
Sky & Telescope - May 2021 - 76
Sky & Telescope - May 2021 - 77
Sky & Telescope - May 2021 - 78
Sky & Telescope - May 2021 - 79
Sky & Telescope - May 2021 - 80
Sky & Telescope - May 2021 - 81
Sky & Telescope - May 2021 - 82
Sky & Telescope - May 2021 - 83
Sky & Telescope - May 2021 - 84
Sky & Telescope - May 2021 - Cover3
Sky & Telescope - May 2021 - Cover4
https://www.nxtbook.com/nxtbooks/aas/st_202405
https://www.nxtbook.com/nxtbooks/aas/st_202404_qr
https://www.nxtbook.com/nxtbooks/aas/st_202404
https://www.nxtbook.com/nxtbooks/aas/st_202403
https://www.nxtbook.com/nxtbooks/aas/st_202402
https://www.nxtbook.com/nxtbooks/aas/st_202401_aus
https://www.nxtbook.com/nxtbooks/aas/st_202401
https://www.nxtbook.com/nxtbooks/aas/st_202312_aus
https://www.nxtbook.com/nxtbooks/aas/st_202312
https://www.nxtbook.com/nxtbooks/aas/st_202311
https://www.nxtbook.com/nxtbooks/aas/st_202310
https://www.nxtbook.com/nxtbooks/aas/st_202309
https://www.nxtbook.com/nxtbooks/aas/st_202308
https://www.nxtbook.com/nxtbooks/aas/st_202307
https://www.nxtbook.com/nxtbooks/aas/st_202306
https://www.nxtbook.com/nxtbooks/aas/st_202305
https://www.nxtbook.com/nxtbooks/aas/st_202304
https://www.nxtbook.com/nxtbooks/aas/st_202304_qr
https://www.nxtbook.com/nxtbooks/aas/st_202303
https://www.nxtbook.com/nxtbooks/aas/st_202302
https://www.nxtbook.com/nxtbooks/aas/st_202301
https://www.nxtbook.com/nxtbooks/aas/st_202212
https://www.nxtbook.com/nxtbooks/aas/st_202211
https://www.nxtbook.com/nxtbooks/aas/st_202210
https://www.nxtbook.com/nxtbooks/aas/st_202209
https://www.nxtbook.com/nxtbooks/aas/st_202208
https://www.nxtbook.com/nxtbooks/aas/st_202207
https://www.nxtbook.com/nxtbooks/aas/st_202206
https://www.nxtbook.com/nxtbooks/aas/st_202205
https://www.nxtbook.com/nxtbooks/aas/st_202204
https://www.nxtbook.com/nxtbooks/aas/st_202203
https://www.nxtbook.com/nxtbooks/aas/st_202202
https://www.nxtbook.com/nxtbooks/aas/st_202201
https://www.nxtbook.com/nxtbooks/aas/st_202112
https://www.nxtbook.com/nxtbooks/aas/st_202111
https://www.nxtbook.com/nxtbooks/aas/st_202110
https://www.nxtbook.com/nxtbooks/aas/st_202109
https://www.nxtbook.com/nxtbooks/aas/st_202108
https://www.nxtbook.com/nxtbooks/aas/st_202107
https://www.nxtbook.com/nxtbooks/aas/st_202106
https://www.nxtbook.com/nxtbooks/aas/st_202105
https://www.nxtbook.com/nxtbooks/aas/st_202104
https://www.nxtbook.com/nxtbooks/aas/st_202103
https://www.nxtbook.com/nxtbooks/aas/st_202102
https://www.nxtbook.com/nxtbooks/aas/st_202101
https://www.nxtbook.com/nxtbooks/aas/skywatch_2021
https://www.nxtbook.com/nxtbooks/aas/st_202012
https://www.nxtbook.com/nxtbooks/aas/st_202011
https://www.nxtbook.com/nxtbooks/aas/st_202010
https://www.nxtbook.com/nxtbooks/aas/st_202009
https://www.nxtbook.com/nxtbooks/aas/st_202008
https://www.nxtbook.com/nxtbooks/aas/st_202007
https://www.nxtbook.com/nxtbooks/aas/st_202006
https://www.nxtbook.com/nxtbooks/aas/st_202005
https://www.nxtbook.com/nxtbooks/aas/st_202004
https://www.nxtbook.com/nxtbooks/aas/st_202003
https://www.nxtbook.com/nxtbooks/aas/st_202002
https://www.nxtbook.com/nxtbooks/aas/st_202001
https://www.nxtbook.com/nxtbooks/aas/st_201912
https://www.nxtbook.com/nxtbooks/aas/st_201911
https://www.nxtbook.com/nxtbooks/aas/st_201910
https://www.nxtbook.com/nxtbooks/aas/st_201909
https://www.nxtbook.com/nxtbooks/aas/st_201908
https://www.nxtbook.com/nxtbooks/aas/st_201907
https://www.nxtbook.com/nxtbooks/aas/st_201906
https://www.nxtbook.com/nxtbooks/aas/st_201905
https://www.nxtbook.com/nxtbooks/aas/st_201904
https://www.nxtbook.com/nxtbooks/aas/st_201903
https://www.nxtbook.com/nxtbooks/aas/st_201902
https://www.nxtbook.com/nxtbooks/aas/st_201901
https://www.nxtbook.com/nxtbooks/aas/st_201812
https://www.nxtbook.com/nxtbooks/aas/st_201811
https://www.nxtbook.com/nxtbooks/aas/st_201810
https://www.nxtbook.com/nxtbooks/aas/st_201809
https://www.nxtbook.com/nxtbooks/aas/st_201808
https://www.nxtbook.com/nxtbooks/aas/st_201807
https://www.nxtbook.com/nxtbooks/aas/st_201806
https://www.nxtbook.com/nxtbooks/aas/st_201805
https://www.nxtbook.com/nxtbooks/aas/st_201804
https://www.nxtbook.com/nxtbooks/aas/st_201803
https://www.nxtbook.com/nxtbooks/aas/st_201802
https://www.nxtbook.com/nxtbooks/aas/st_201801
https://www.nxtbook.com/nxtbooks/aas/st_201712
https://www.nxtbook.com/nxtbooks/aas/st_201711
https://www.nxtbook.com/nxtbooks/aas/st_201710
https://www.nxtbook.com/nxtbooks/aas/st_201709
https://www.nxtbook.com/nxtbooks/aas/st_201708
https://www.nxtbook.com/nxtbooks/aas/st_201707
https://www.nxtbook.com/nxtbooks/aas/st_201706
https://www.nxtbook.com/nxtbooks/aas/st_201705
https://www.nxtbook.com/nxtbooks/aas/st_201704
https://www.nxtbook.com/nxtbooks/aas/st_201703
https://www.nxtbook.com/nxtbooks/aas/st_201702
https://www.nxtbook.com/nxtbooks/aas/st_201701
https://www.nxtbook.com/nxtbooks/aas/st_201612
https://www.nxtbook.com/nxtbooks/aas/st_201611
https://www.nxtbook.com/nxtbooks/aas/st_201610
https://www.nxtbook.com/nxtbooks/aas/st_201609
https://www.nxtbook.com/nxtbooks/aas/st_201608
https://www.nxtbook.com/nxtbooks/aas/st_201607
https://www.nxtbook.com/nxtbooks/aas/st_201606
https://www.nxtbook.com/nxtbooks/aas/st_201605
https://www.nxtbook.com/nxtbooks/aas/st_201604
https://www.nxtbook.com/nxtbooks/aas/st_201603
https://www.nxtbook.com/nxtbooks/aas/st_201602
https://www.nxtbook.com/nxtbooks/aas/st_201601
https://www.nxtbook.com/nxtbooks/aas/st_201512
https://www.nxtbook.com/nxtbooks/aas/st_201511
https://www.nxtbook.com/nxtbooks/aas/st_201510
https://www.nxtbook.com/nxtbooks/aas/st_201509
https://www.nxtbook.com/nxtbooks/aas/st_201508
https://www.nxtbook.com/nxtbooks/aas/st_201507
https://www.nxtbook.com/nxtbooks/aas/st_201506
https://www.nxtbook.com/nxtbooks/aas/st_201505
https://www.nxtbook.com/nxtbooks/aas/st_201504
https://www.nxtbook.com/nxtbooks/aas/st_201503
https://www.nxtbook.com/nxtbooks/aas/st_201502
https://www.nxtbook.com/nxtbooks/aas/st_201501
https://www.nxtbook.com/nxtbooks/aas/st_201412
https://www.nxtbook.com/nxtbooks/aas/st_201411
https://www.nxtbook.com/nxtbooks/aas/st_201410
https://www.nxtbook.com/nxtbooks/aas/st_201409
https://www.nxtbook.com/nxtbooks/aas/st_201408
https://www.nxtbook.com/nxtbooks/aas/st_201407
https://www.nxtbook.com/nxtbooks/aas/st_201406
https://www.nxtbook.com/nxtbooks/aas/st_mars
https://www.nxtbook.com/nxtbooks/aas/st_201405
https://www.nxtbook.com/nxtbooks/aas/st_201404
https://www.nxtbook.com/nxtbooks/aas/st_201403
https://www.nxtbook.com/nxtbooks/aas/st_201402
https://www.nxtbook.com/nxtbooks/aas/st_201401
https://www.nxtbook.com/nxtbooks/aas/st_201312
https://www.nxtbook.com/nxtbooks/aas/st_201311
https://www.nxtbook.com/nxtbooks/aas/st_201310
https://www.nxtbook.com/nxtbooks/aas/st_201309
https://www.nxtbook.com/nxtbooks/aas/st_201308
https://www.nxtbook.com/nxtbooks/aas/st_201307
https://www.nxtbook.com/nxtbooks/aas/st_201306
https://www.nxtbook.com/nxtbooks/aas/st_201305
https://www.nxtbook.com/nxtbooks/aas/st_201304
https://www.nxtbook.com/nxtbooks/aas/st_201303
https://www.nxtbook.com/nxtbooks/aas/st_201302
https://www.nxtbook.com/nxtbooks/aas/st_201301
https://www.nxtbook.com/nxtbooks/aas/st_201212
https://www.nxtbook.com/nxtbooks/aas/st_201211
https://www.nxtbook.com/nxtbooks/aas/st_201210
https://www.nxtbook.com/nxtbooks/aas/st_201209
https://www.nxtbook.com/nxtbooks/aas/st_201208
https://www.nxtbook.com/nxtbooks/aas/st_201207
https://www.nxtbook.com/nxtbooks/aas/st_201206
https://www.nxtbook.com/nxtbooks/aas/st_201205
https://www.nxtbook.com/nxtbooks/aas/st_201204
https://www.nxtbook.com/nxtbooks/aas/st_201203
https://www.nxtbook.com/nxtbooks/aas/st_201202
https://www.nxtbook.com/nxtbooks/aas/st_201201
https://www.nxtbook.com/nxtbooks/aas/st_201112
https://www.nxtbook.com/nxtbooks/aas/st_201111
https://www.nxtbook.com/nxtbooks/aas/st_201110
https://www.nxtbook.com/nxtbooks/aas/st_201109
https://www.nxtbook.com/nxtbooks/aas/st_201108
https://www.nxtbook.com/nxtbooks/aas/st_201107
https://www.nxtbook.com/nxtbooks/aas/st_201106
https://www.nxtbook.com/nxtbooks/aas/st_201105
https://www.nxtbook.com/nxtbooks/aas/st_201104
https://www.nxtbook.com/nxtbooks/aas/st_201103
https://www.nxtbook.com/nxtbooks/aas/st_201102
https://www.nxtbook.com/nxtbooks/aas/st_201101
https://www.nxtbook.com/nxtbooks/aas/st_201012
https://www.nxtbook.com/nxtbooks/aas/st_201011
https://www.nxtbook.com/nxtbooks/aas/st_201010
https://www.nxtbook.com/nxtbooks/aas/st_201009
https://www.nxtbook.com/nxtbooks/aas/st_201008
https://www.nxtbook.com/nxtbooks/aas/st_201007
https://www.nxtbook.com/nxtbooks/aas/st_201006
https://www.nxtbook.com/nxtbooks/aas/st_201005
https://www.nxtbook.com/nxtbooks/aas/st_201004
https://www.nxtbook.com/nxtbooks/aas/st_201003
https://www.nxtbook.com/nxtbooks/aas/st_201002
https://www.nxtbook.com/nxtbooks/aas/st_201001
https://www.nxtbookmedia.com