A PUBL I CAT I ON OF T H E U N IV E R S IT Y O F V E R MO N T DEPARTMENT OF PHYSICS SUM M ER 2013
@UVMPhysics
Staff Notes
Faculty Notes
James (Tom) Warnock, our
lab coordinator, retired after 18
years of service. Tom started his
career as a high school teacher,
taught for a number of years, then
came to UVM for his Masters
degree. He stayed ever since.
Tom is remembered by many of our graduate
student alumni as the “point man” who introduced
them to the intricacies, pitfalls but also joy of
teaching in our department. Over the years, he
was instrumental in developing new experiments,
modernizing the equipment and teaching methods
in our labs and seeing that all labs ran smoothly.
Tom cared deeply about our students; he estimates
that about 5,000 undergraduates have been
“coordinated” by him, and he was passionate about
his teaching. He never hesitated to fill in at the last
moment for absent lab or recitation instructors. We
wish him many happy seasons of sugaring on his
farm in the Northeast Kingdom.
Professor Adrian Del Maestro
presented new research results at
the International Symposium on
Quantum Fluids and Solids held
in Matsue, Japan this summer.
The work, a collaborative effort
involving an experimental team
of investigators from McGill University with
the theoretical efforts of Professor Del Maestro,
concerns the anisotropic superfluid density and
the breakdown of the two-fluid model in lowdimensional helium.
Succeeding Tom, Dr. Luke
Donforth joined the physics staff
in June. Dr. Donforth graduated
from UC Davis in 2001 with a
thesis on superfluid Helium under
Professor Rena Zieve. He went on
to earn a Ph.D. in physics from
Cornell University in 2009 doing carbon nanotube
transistor work under Professor Paul McEuen.
In addition to his research, he’s accumulated
laboratory and teaching experience at a variety
of levels, from pre-school through university,
having worked at museums like the Connecticut
Science Center and schools like Vermont Commons
and Champlain College. He’s a member of the
American Association of Physics Teachers and the
Nanoscale Informal Science Education Network.
He also volunteers at ECHO Lake and Aquarium
Science Center. Luke is an avid contra dancer and
professional contra dance caller, helping to run a
monthly dance in Burlington. He’s excited to be
contributing to the physics department at UVM and
seeing how long he can keep up biking to work.
In memoriam
Dr. Robert W. Detenbeck, Emeritus Professor of
Physics, died on Aug. 8, 2013, in the Arbors, in
Shelburne. He received his B.S. degree in physics
at the University of Rochester and his Ph.D. in
physics at Princeton University. His research field
was originally experimental nuclear physics done
at University of Maryland for eight years. Later
at the University of Vermont, his research was
primarily in optical physics until his retirement
in 1995. But his real love was teaching students,
and for this he was recognized with an award
for his teaching at Maryland and the George V.
Kidder Outstanding Faculty Award in 1995 from
UVM. He was very active in the American Association of Physics Teachers, receiving their award
for distinguished service in 1968. He leaves a
lasting legacy of the many students he has influenced and mentored over his career.
Recent Grants
Professor Madalina Furis, “MRI: Development of a
Free Space Optical Spectroscopy System for Chemistry, Materials Science and Biophysics Research and
Education in the 25-T Split Coil Helix,” NSF, $146,907
over two years.
Professor Randall Headrick, “Real-Time Studies of
Solution-Processed Organic Semiconductor Thin
Films,” NSF, $371,921 over three years.
PAGE 2 PHYSI CS@UVM Awards and Honors
Two departmental awards were presented to physics undergraduates at the College of Arts and Sciences’
Honors ceremony held in Ira Allen Chapel on May 17, 2013. Thomas J. Howard was the recipient of the Albert D.
Crowell Award for experimental physics. Richard W. Kenyon received the David W. Juenker Prize for outstanding
scholarship in physics. Richard was also selected as a co-recipient of the award for outstanding senior in
mathematics.
Richard W. Kenyon (left) and Thomas J. Howard with
Professor Clougherty at CAS Honors Day in Ira Allen Chapel.
(Photo courtesy of Sally McCay.)
Lane Manning named GTF of Year
Lane Manning, a Ph.D. candidate in Materials Science, was named Graduate Teaching Fellow of the Year in
the Department of Physics. Lane received a certificate of achievement and a membership to the American
Association of Physics Teachers at the physics department awards reception on May 1, 2013.
Professor Del
Maestro with
Lane Manning,
Physics Graduate
Teaching Fellow
of the Year
at the physics
reception on May
1, 2013.
PHYSI CS@U VM PAGE 3
Undergraduate Honors Theses
Adam Z. Doherty, “Quantum Sticking of Atomic Hydrogen on Suspended Graphene.”
Adviser: Dennis P. Clougherty, Ph.D.
Darcy E. Glenn, “Working with a Thermosyphon: The Atmosphere That Hangs on a
Wall.” Adviser: Christopher Danforth, Ph.D
Phi Beta Kappa
Senior Physics majors Richard W. Kenyon and Erik Horak were inducted as new members into Phi Beta Kappa
honor society in a ceremony held in Royall Tyler Theatre on May 18, 2013. Phi Beta Kappa is the oldest honor
society in the country, and among the most prestigious. From the society’s website: “The ideal Phi Beta Kappan
has demonstrated intellectual integrity, tolerance for other views, and a broad range of academic interests. Each
year, about one college senior in a hundred, nationwide, is invited to join Phi Beta Kappa.” The Alpha Chapter
of Vermont was chartered in 1848. In 1875, it became the first chapter in the nation to admit women to its
membership.
2012 Sigma Pi Sigma Inductees
Five undergraduates were inducted in the UVM chapter of Sigma Pi Sigma in May 2013: Daniel G. Allman;
Matthew T. DiMario; Matthew T. Feeley; Joshuah T. Heath; and Cole Van Seters. Founded in 1921, Sigma Pi
Sigma is the national physics honor society. Sigma Pi Sigma honors outstanding scholarship and service in
physics, encouraging and stimulating members in their scientific pursuits.
Nota Bene
We would enjoy hearing from all UVM physics alums and
friends. Send your email to physics@uvm.edu.
PAGE 4 P HYSI CS@UVM
Path Integral Monte Carlo Study of
Proximity Effects in Confined Helium-4
By Adrian G Del Maestro
UVM Materials Science PhD student Max Graves was selected as one of five finalists in the
physical science, mathematics and engineering category at the President’s Student Poster
Competition on Wednesday October 3rd.
Max’s poster, entitled “Path Integral Monte Carlo Study of Proximity Effects in Confined
Helium-4” displays his recent numerical work on how the thermodynamic properties of
Helium-4 atoms confined to localized regions of space are affected by coupling to neighboring
regions at low temperatures. This study was motivated by recent experiments performed by the
Gasparini group at SUNY Buffalo that showed that Helium-4 under these conditions exhibits an
enhanced superfluid response as well as an excess specific heat. Max and Prof. Del Maestro believe that these strange phenomena are due to the intrinsic
indistinguishability of the bosonic Helium-4 atoms, and they plan to test their hypothesis by
studying both quantum and classical atoms. For the classical distinguishable atoms, they
conjecture that this exotic behavior should be absent, and that the phenomena is a macroscopic
manifestion of quantum mechanics.
Max Graves at the President’s Student Poster
Competition held at the UVM Davis Center.
PHYSI CS@U VM PAGE 5
Student Research
Dan Orfeo, an undergraduate physics major, was awarded a UVM Undergraduate
Research Summer Internship. Dan's summer project titled “Investigating the Partially
Filled, Rotating-Subbeam-Carousel Model for Radio Pulsar B0751+32” will be supervised by Professor Joanna Rankin. Dan will present his research results at UVM’s
Student Research Conference in April 2014.
Joshuah Heath ’15 presents a poster of his research as part of UVM Student Research
Day at the Davis Center on April 23, 2013. His project titled “Computational Study
of Ferromagnetic Phase Transitions in the Ising and XY Models via the Monte Carlo
Method” was supervised by Professor Del Maestro.
Physics major Joshuah Heath at the UVM Davis Center.
Outreach
Professor Madalina Furis participated in the “Scientist in Residence” Program at the Jericho
Elementary High School. She gave a presentation about what it means to be a physicist that
included physics demonstrations to nine different classes ranging from 1st to 4th grade.
PAGE 6 PHYSI CS@UVM 2013 Graduates
Bachelor of Science degree recipients
Brad M. Diamond
Michael R. Durant
Adam Z. Doherty
Darcy E. Glenn
Eric H. Horak*
Thomas J. Howard#
Richard W. Kenyon#
Evan W. Laird
Cody J. Lamarche
*Magna Cum Laude
#Cum Laude
Cody Lamarche, Brad Diamond, Darcy Glenn, Richard Kenyon, Michael Durant, Erik Horak, Adam
Doherty and Thomas Howard (left to right) with Professor Clougherty at UVM Commencement 2013
Congratulations graduates!
PHYSI CS@U VM PAGE 7
NanoDays 2013
The UVM chapters of the Society of Physics Students and Sigma Pi Sigma organized a series of events for NanoDays
2013, an annual national celebration of nanoscale science, technology and engineering that includes hands-on activities,
demonstrations and lectures for the general public. The ECHO Science Center hosted the event. This is the seventh
year of the UVM Physics-ECHO partnership. (Photos are courtesy of Dr. Furis.)
Physics major Darcy Glenn points out aspects of
3D imaging during NanoDays 2013.
Making polymers with Materials Science graduate
student Sanghita Sengupta at NanoDays 2013.
Ph.D. candidate Owen Myers (right) at UVMECHO Nanodays.
UVM graduate student Max Graves explains
magnetic storage at ECHO Science Center
during NanoDays 2013.
Fun with nanogold.
David Hammond (right) led the team of UVM
physics students in NanoDays 2013. David
Hammond, Peter Harnish, Cole Van Seters,
Joshuah Heath, Jeffrey Ulbrandt, Erik Horak,
Darcy Glenn, TJ Howard, Max Graves, Sanghita
Sengupta and Owen Myers (right to left).
PAGE 8 PHYSI CS@UVM NSF Summer Program on Complex Materials
Funded by the National Science Foundation, the UVM summer program on complex materials brings talented
undergraduates from universities across the country to Burlington to work on research projects with UVM faculty
in the materials science program. UVM has the only NSF Research Experience for Undergraduates (REU) site in
Vermont. The nine-week program culminates with oral presentations of summer research results by the student
participants. (Photos are courtesy of Dr. Furis.)
Ashleigh Bristol (left), an undergraduate from University of
Mississippi, working UVM graduate student Tianxin Miao
in the laboratory of Professor Rachael Oldinski, a faculty
member of the complex materials REU.
Colin Campbell, a 2013 REU program participant from
Georgia Tech, worked with Professor Del Maestro on
theoretical studies of superfluid Helium in nanocavities.
Professor Matt Liptak (right) with Jill Chipman (center),
an undergraduate at Hamilton College, and UVM graduate
student Cheryl Lockhart. Jill’s project was titled “CD
Investigation of Axial Ligand Effects on IsdG Secondary
Structure.”
2013 program participants with Professor Medsker, REU
program coordinator. Front row: Catherine Groschner,
Jill Hamilton, Ashleigh Bristol, and Sabrina Rosa (left
to right). Back row: Nicholas Gould, Colin Campbell,
Dr. Medsker, Noah Kohlhorst, Alexander Sylvester, and
Chan Tran (left to right).
We thank the faculty members of the complex materials program for supervising the research of the REU participants
this summer: Professors Adrian Del Maestro, Madalina Furis, Randall Headrick, Valeri Kotov, Matthew Liptak, Larry
Medsker, Rachael Oldinski, Frederic Sansoz, Rory Waterman and Adam Whalley.
Here’s a complete list of the REU students with their summer project titles: Ashleigh Bristol (Characterization of
RGD Surface Conjugation of AA-g-PEG Microcarriers), Colin Campbell (Macroscopic Superfluid Properties of Liquid
Helium), Jill Chipman (CD Investigation of Axial Ligand Effects on IsdG Secondary Structure), Nicholas Gould (Excitonic Properties of Tetraphenylporphyrin (TPP) Thin Films), Kate Groschner (The Role of Pressure, Atmosphere, and
Power on the Formation of WSi2 and Si Nanoclusters), Noah Kohlhorst (Production & Characterization of Organic Molecular Crystals Behaving as Electric Semiconductors), Sabrina Rosa (Synthesis of the First As-C Polymer), Alexander
Sylvester (Attraction Between Graphene Layers) and Chan Tran (Simulation Study on the Properties of Nanowires).
PHYSI CS@U VM PAGE 9
A Sound Way to Stop Stowaways
By Joshua E. Brown
Eighty percent of world trade is carried by
ships. A big cargo ship docks in the United
States about every six minutes. It unloads
goods that can come from any port on the
planet.
Unfortunately, these ships also often unload
invasive species — unwanted hitchhikers, like
zebra mussel larvae and purple loosestrife
seeds — travelling in the ship’s ballast water.
This, too, can come from any port on the
planet.
In the U.S., dumped ballast water may be
the leading source of invasive species found
in freshwater and marine ecosystems, according the Environmental Protection
Agency. From the Caspian Sea to Lake
Champlain, communities have suffered profound damage — like collapsed fisheries and
clogged pipes — due to invaders that arrived
in ballast water.
Efforts to remove species from ballast water
have proven very difficult, often toxic, and
expensive.
But Junru Wu, a physicist at the University
of Vermont, has invented a promising new
approach: blast them to death with sound.
He and Meiyin Wu (no relation), an ecologist
at Montclair State University in New Jersey,
have been collaborating for nearly a decade
to create a device — they call it BallastSolution. The machine will treat ballast water,
as ships take it in and dump it out, with a
lethal dose of ultrasound. (Lethal, that is, to
wee beasties; it’s harmless to people.)
In recent tests, “we thought we’d be happy if
we could kill close to ninety percent” of the
small clams, water fleas, and e. coli bacteria
sent into the machine, said Junru Wu, “but
the results were over ninety-nine percent.”
Stricter rules
Ballast water is essential to cargo ships (as
well as cruise-liners and sailboats) allowing
them to stay at the proper depth, steer correctly, and not tip over. But as ships take
on and unload cargo, they also pump and
dump enormous quantities of water. Globally,
twelve billion tons of the stuff is dumped
each year — with some ten thousand species
being carried across the oceans each day in
the ballast water of cargo ships, according to
expert testimony before the U.S. Senate.
“These species introductions are one of the
leading causes of losing biodiversity around
the globe,” says Meiyin Wu, “so we’re trying
to plug the hole.”
“The results are fantastic,” says Junru Wu,
“much better than expected.”
So are new tougher global regulations of
ballast water. The U.S. Coast Guard rolled
out rules in March requiring ocean-going
ships to have an onboard ballast treatment
system and limiting how many organisms
they can release in coastal waters. And the
U.N.’s International Maritime Organization
will require all ships to have a treatment
system by the end of 2016.
More demand than supply
“There will be a lot of market demand for
ballast treatment systems,” says Meiyin Wu.
“There are millions of ships out there that
will have to comply with these new regulations.”
Bubble solution
The scientists anticipate that their machine,
once commercialized, could be mounted inside the engine room of ships and available
for use whenever needed, either in dock or
as ships change their ballast at sea.
The device relies on what physicists call
“cavitation,” the formation and implosion
of tiny bubbles within the organisms. These
bubbles in liquid, created by mechanical
waves from the ultrasound, “basically rip
them apart,” says Junru Wu.
The ultrasound has advantages over other
treatments, like ultraviolet light that has
a hard time penetrating murky water, or
chemical treatments, like chlorine, which
have environmental problems. “Our goal is
to produce a system that doesn’t produce
secondary pollution,” says Meiyin Wu.
The patented BallastSolution device, funded
by a $673,000 grant from the U.S. Department of the Interior, is made from twenty
ultrasound transducers, arranged in a
spiral, that protrude into a pipe about ten
inches wide on the interior. As the ballast
water pumps through, the transducers oscillate at frequencies above the range of human hearing.
This fall, the BallastSolution machine will
be shipped to Wisconsin for a next round of
testing by an independent laboratory under
guidelines approved by the International
Maritime Organization and the U.S. Coast
Guard. If it passes these tests, it can be
submitted to the IMO for approval and international use.
Current treatment technologies can cost millions of dollars to install on a medium-sized
ship, Meiyin Wu says — which is why there
is a global hunt to find new systems that
work and are affordable.
“There are a lot of people and companies
working on ballast treatments,” she says.
“But there is simply no way that that the
supply will be enough for the demand by
2016.”
Three companies have shown interest in licensing the BallastSolutions technology, Meiyin Wu says. “We’re hoping it will be ready
before 2016,” she says, noting that the cost
of a commercial version of their machine is
very hard to predict at this early stage -- and
will depend on the size of the ship and the
complexity of retrofitting it.
“We’re researchers. We’re not in the place
or business to commercialize this,” she says.
Which is why she and Junru Wu are looking
for investors. And considering new research
applications for ultrasound.
“We’re looking at ways it could be used to
treat invasive jellyfish,” she says, “or clean
swimming pools.”
In goes a load of potential bad guys at one
end -- and out comes nearly sterile water at
the other.
At least that’s what the first tests have
shown. The machine, built at UVM by
Junru Wu and post-doctoral researcher Di
Chen, was delivered to Meiyin Wu at the
beginning of 2012 for testing in her laboratory in New Jersey.
Quake, zebra mussel. Junru Wu, professor
of physics has invented a machine to kill
invasive species lurking in the bottom of
boats. (photo: courtesy Professor Wu)
PAGE 1 0 PHYSI CS@UVM Chameleon Star Baffles Astronomers
By Joshua Brown
Few astronomical objects are as baffling as pulsars, and despite nearly fifty years of study,
they continue to defy theorists’ best efforts.
A pulsar with glowing cones of radiation stemming from its
magnetic poles. New observations reported in Science re-open
an old debate about how these spinning stars work. (Image:
European Space Agency/ATG medialab)
Pulsars — tiny spinning stars, heavier than the sun and
smaller than a city — have puzzled scientists since they were
discovered in 1967.
Now, new observations by an international team, including
University of Vermont astrophysicist Joanna Rankin, make
these bizarre stars even more puzzling.
The scientists identified a pulsar that is able to dramatically
change the way in which it shines. In just a few seconds,
the star can quiet its radio waves while at the same time it
makes its X-ray emissions much brighter.
The research “challenges all proposed pulsar emission
theories,” the team writes in the Jan. 25 edition of the
journal Science and reopens a decades-old debate about how
these stars work.
Unexpected X-rays
Like the universe’s most powerful lighthouses, pulsars shine
beams of radio waves and other radiation for trillions of
miles. As these highly magnetized neutron stars rapidly
rotate, a pair of beams sweeps by, appearing as flashes or
pulses in telescopes on Earth.
Using a satellite X-ray telescope, coordinated with two radio
telescopes on the ground, the team observed a pulsar that
was previously known to flip on and off every few hours
between strong (or “bright”) radio emissions and weak (or
“quiet”) radio emissions.
Monitoring simultaneously in X-rays and radio waves, the
team revealed that this pulsar exhibits the same behaviour,
but in reverse, when observed at X-ray wavelengths.
This is the first time that a switching X-ray emission has
been detected from a pulsar.
University of Vermont astrophysicist Joanna Rankin.
Flipping between these two extreme states — one dominated
by X-ray pulses, the other by a highly organized pattern of
radio pulses — “was very surprising,” says Rankin.
“As well as brightening in the X-rays we discovered that the
X-ray emission also shows pulses, something not seen when
the radio emission is bright,” said Rankin, who spearheaded
the radio observations. “This was completely unexpected.”
No current model of pulsars is able to explain this switching
behavior. All theories to date suggest that X-ray emissions
would follow radio emissions. Instead, the new observations
show the opposite. “The basic physics of a pulsar have never
been solved,” Rankin says.
Looking for the switch
The research was conceived by a small team then working
at the University of Amsterdam, including UVM’s Rankin,
who has studied this pulsar, known as PSR B0943+10,
for more than a decade; Wim Hermsen from SRON, the
Netherlands Institute for Space Research in Utrecht, and
the lead author on the new paper; Ben Stappers from the
University of Manchester, UK; and Geoff Wright from
Sussex University, UK.
These researchers were joined by colleagues from institutions
around the world to conduct simultaneous observations with
the European Space Agency’s X-ray satellite, XMM-Newton,
and two radio telescopes, the Giant Meter Wave Telescope
(GMRT) in India and the Low Frequency Array (LOFAR)
in the Netherlands, to reveal this pulsar’s so-far unique
behavior.
“There is a general agreement about the origin of the radio
emission from pulsars: it is caused by highly energetic
electrons, positrons and ions moving along the field lines of
the pulsar’s magnetic field,” explains Wim Hermsen.
PHYSI CS@U VM PAGE 11
Chameleon Star Baffles Astronomers, continued
“How exactly the particles are stripped off the neutron star’s
surface and accelerated to such high energy, however, is still
largely unclear,” he adds.
By studying the emission from the pulsar at different
wavelengths, the team’s study had been designed to discover
which of various possible physical processes take place in the
vicinity of the magnetic poles of pulsars.
Instead of narrowing down the possible mechanisms suggested
by theory, however, the results of the team’s observing
campaign challenge all existing models for pulsar emission. Few
astronomical objects are as baffling as pulsars, and despite nearly
fifty years of study, they continue to defy theorists’ best efforts.
Of the more than 2,000 pulsars discovered to date, a number of
them have erratic behavior, with emissions that can become weak
or disappear in a matter of seconds but then suddenly return
minutes or hours later.
B0943+10 is one of these erratic stars. Discovered at Pushchino
Radio Astronomical Observatory near Moscow, “this star has two
very different personalities,” that were uncovered by Svetlana
Suleymanova in the 1980s, says Rankin.
“But we’re still in the dark about what causes this, and other
pulsars, to switch modes,” Rankin says. “We just don’t know.”
“But the fact that the pulsar keeps memory of its previous state
and goes back to it,” says Hermsen, “suggests that it must be
something fundamental.”
Recent studies indicate that the switch between “radio-bright”
and “radio-quiet” states is correlated to the pulsar’s dynamics.
As pulsars rotate, their spinning period slows down gradually,
and in some cases the slow-down process has been observed to
accelerate and slow down again, in conjunction with the pulsar
switching between bright and quiet states.
This correlation between a pulsar’s rotation and its emission has
led astronomers to wonder about a connection between the star’s
surface and the much-larger surrounding magnetosphere, which
may extend up for 30,000 miles.
These new observations “strongly suggest that a temporary
‘hotspot’ appears close to the pulsar’s magnetic pole which
switches on and off with the change of state,” says Geoff Wright,
one of the team’s astronomers from the University of Sussex.
But the new results also suggest that something in the whole
magnetosphere is changing suddenly and not just at the poles or
other hotspots. “Something is happening globally,” Rankin says,
across the whole star.
In order for the radio emission to vary so radically on the short
timescales observed, the pulsar’s global environment must
undergo a very rapid – and reversible – transformation.
“If that is true, it means the entire magnetosphere is alive and
connected in very important ways,” Rankin says, allowing a
change in the pulsar’s basic mode of shining in about one second,
less time than it takes it to spin once on its axis.
“Since the switch between a pulsar’s bright and quiet states links
phenomena that occur on local and global scales, a thorough
understanding of this process could clarify several aspects of
pulsar physics,” says Hermsen. “Unfortunately, we have not yet
been able to explain it.”
No model works
The team planned to search for the same pattern in X-rays
that has been observed in radio waves – to investigate what
causes this switching behavior. They chose as their subject
PSR B0943+10, a pulsar that is well known for its switching
behavior at radio wavelengths and for its X-ray emission, which
is brighter than might be expected for its age.
“Young pulsars shine brightly in X-rays because the surface
of the neutron star is still very hot. But PSR B0943+10 is
five million years old, which is relatively old for a pulsar: the
neutron star’s surface has cooled down by then,” explains
Hermsen.
Astronomers know of only a handful of old pulsars that shine
in X-rays and believe that this emission comes from the
magnetic poles – the sites on the neutron star’s surface where
the acceleration of charged particles is triggered. “We think
that, from the polar caps, accelerated particles either move
outwards to the magnetosphere, where they produce radio
emission, or inwards, bombarding the polar caps and creating
X-ray-emitting hot-spots,” Hermsen adds.
There are two main models that describe these processes,
depending on whether the electric and magnetic fields at play
allow charged particles to escape freely from the neutron star’s
surface. In both cases, it has been argued that the emission of
X-rays follows that of radio waves.
Monitoring the pulsar in X-rays and radio waves at the same
time, the astronomers hoped to be able to discern between the
two models.
“The X-ray emission of pulsar PSR B0943+10 beautifully
mirrors the switches that are seen at radio wavelengths but,
to our surprise, the correlation between these two emissions
appears to be inverse: when the source is at its brightest in
radio waves, it reaches its faintest in X-rays, and vice versa,”
says Hermsen.
The new data also show that the source pulsates in X-rays
only during the X-ray-bright phase – which corresponds to
the quiet state at radio wavelengths. During this phase, the
X-ray emission appears to be the sum of two components:
a pulsating component consisting of thermal X-rays, which
is seen to switch off during the X-ray-quiet phase, and a
persistent one consisting of non-thermal X-rays.
Neither of the leading models for pulsar emission predicts such
behavior.
In the second half of 2013, the team plans to repeat the same
study for another pulsar, PSR B1822-09, which exhibits similar
radio emission properties but with a different geometry.
In the meantime, these observations will keep theoretical
astrophysicists busy investigating possible physical mechanisms
that could cause the sudden and drastic changes to the
pulsar’s entire magnetosphere and result in such a curious flip
in how they shine.
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