9 research outputs found
Discovery of the X-ray Counterpart to the Rotating Radio Transient J1819--1458
We present the discovery of the first X-ray counterpart to a Rotating RAdio Transient (RRAT) source. RRAT J1819--1458 is a relatively highly magnetized (B G) member of a new class of unusual pulsar-like objects discovered by their bursting activity at radio wavelengths. The position of RRAT J1819--1458 was serendipitously observed by the {\sl Chandra} ACIS-I camera in 2005 May. At that position we have discovered a pointlike source, CXOU J181934.1--145804, with a soft spectrum well fit by an absorbed blackbody with cm and temperature keV, having an unabsorbed flux of ergs cm s between 0.5 and 8 keV. No optical or infrared (IR) counterparts are visible within of our X-ray position. The positional coincidence, spectral properties, and lack of an optical/IR counterpart make it highly likely that CXOU J181934.1--145804 is a neutron star and is the same object as RRAT J1819--1458. The source showed no variability on any timescale from the pulse period of 4.26~s up to the five-day window covered by the observations, although our limits (especially for pulsations) are not particularly constraining. The X-ray properties of CXOU J181934.1--145804, while not yet measured to high precision, are similar to those of comparably-aged radio pulsars and are consistent with thermal emission from a cooling neutron star
Chandra Smells a RRAT: X-ray Detection of a Rotating Radio Transient
"Rotating RAdio Transients" (RRATs) are a newly discovered astronomical
phenomenon, characterised by occasional brief radio bursts, with average
intervals between bursts ranging from minutes to hours. The burst spacings
allow identification of periodicities, which fall in the range 0.4 to 7
seconds. The RRATs thus seem to be rotating neutron stars, albeit with
properties very different from the rest of the population. We here present the
serendipitous detection with the Chandra X-ray Observatory of a bright
point-like X-ray source coincident with one of the RRATs. We discuss the
temporal and spectral properties of this X-ray emission, consider counterparts
in other wavebands, and interpret these results in the context of possible
explanations for the RRAT population.Comment: 5 pages, 2 b/w figures, 1 color figure. To appear in the proceedings
of "Isolated Neutron Stars", Astrophysics & Space Science, in pres
Buildout and integration of an automated high-throughput CLIA laboratory for SARS-CoV-2 testing on a large urban campus
In 2019, the first cases of SARS-CoV-2 were detected in Wuhan, China, and by early 2020 the first cases were identified in the United States. SARS-CoV-2 infections increased in the US causing many states to implement stay-at-home orders and additional safety precautions to mitigate potential outbreaks. As policies changed throughout the pandemic and restrictions lifted, there was an increase in demand for COVID-19 testing which was costly, difficult to obtain, or had long turn-around times. Some academic institutions, including Boston University (BU), created an on-campus COVID-19 screening protocol as part of a plan for the safe return of students, faculty, and staff to campus with the option for in-person classes. At BU, we put together an automated high-throughput clinical testing laboratory with the capacity to run 45,000 individual tests weekly by Fall of 2020, with a purpose-built clinical testing laboratory, a multiplexed reverse transcription PCR (RT-qPCR) test, robotic instrumentation, and trained staff. There were many challenges including supply chain issues for personal protective equipment and testing materials in addition to equipment that were in high demand. The BU Clinical Testing Laboratory (CTL) was operational at the start of Fall 2020 and performed over 1 million SARS-CoV-2 PCR tests during the 2020-2021 academic year.Boston UniversityPublished versio
The Polarized Cosmic Hand: IXPE Observations of PSR B1509-58/MSH 15-52
We describe IXPE polarization observations of the Pulsar Wind Nebula (PWN)
MSH15-52, the `Cosmic Hand'. We find X-ray polarization across the PWN, with B
field vectors generally aligned with filamentary X-ray structures. High
significance polarization is seen in arcs surrounding the pulsar and toward the
end of the `jet', with polarization degree PD>70%, thus approaching the maximum
allowed synchrotron value. In contrast, the base of the jet has lower
polarization, indicating a complex magnetic field at significant angle to the
jet axis. We also detect significant polarization from PSR B1509-58 itself.
Although only the central pulse-phase bin of the pulse has high individual
significance, flanking bins provide lower significance detections and, in
conjunction with the X-ray image and radio polarization, can be used to
constrain rotating vector model solutions for the pulsar geometry.Comment: To appear in the Astrophysical Journa
Accreting Pulsars: Mixing-up Accretion Phases in Transitional Systems
In the last 20 years our understanding of the millisecond pulsar (MSP)
population changed dramatically. Thanks to RXTE, we discovered that neutron
stars in LMXBs spins at 200-750 Hz frequencies, and indirectly confirmed the
recycling scenario, according to which neutron stars are spun up to ms periods
during the LMXB-phase. In the meantime, the continuous discovery of
rotation-powered MSPs in binary systems in the radio and gamma-ray band (mainly
with the Fermi LAT) allowed us to classify these sources into two "spiders"
populations, depending on the mass of their companion stars: Black Widow, with
very low-mass companion stars, and Redbacks, with larger companions possibly
filling their Roche lobes but without accretion. It was soon regained that MSPs
in short orbital period LMXBs are the progenitors of the spider populations of
rotation-powered MSPs, although a direct link between accretion- and
rotation-powered MSPs was still missing. In 2013 XMM-Newton spotted the X-ray
outburst of a new accreting MSP (IGR J18245-2452) in a source that was
previously classified as a radio MSP. Follow up observations of the source when
it went back to X-ray quiescence showed that it was able to swing between
accretion- to rotation-powered pulsations in a relatively short timescale (few
days), promoting this source as the direct link between the LMXB and the radio
MSP phases. Following discoveries showed that there exists a bunch of sources,
which alternates X-ray activity phases, showing X-ray pulsations, to radio-loud
phases, showing radio pulsations, establishing a new class of MSPs: the
Transitional MSP. In this review we describe these exciting discoveries and the
properties of accreting and transitional MSPs, highlighting what we know and
what we have still to learn about in order to fully understand the (sometime
puzzling) behavior of these systems and their evolutive connection (abridged)
European Pulsar Timing Array Limits on Continuous Gravitational Waves from Individual Supermassive Black Hole Binaries
We have searched for continuous gravitational wave (CGW) signals produced by
individually resolvable, circular supermassive black hole binaries (SMBHBs) in
the latest EPTA dataset, which consists of ultra-precise timing data on 41
millisecond pulsars. We develop frequentist and Bayesian detection algorithms
to search both for monochromatic and frequency-evolving systems. None of the
adopted algorithms show evidence for the presence of such a CGW signal,
indicating that the data are best described by pulsar and radiometer noise
only. Depending on the adopted detection algorithm, the 95\% upper limit on the
sky-averaged strain amplitude lies in the range at . This limit varies
by a factor of five, depending on the assumed source position, and the most
constraining limit is achieved towards the positions of the most sensitive
pulsars in the timing array. The most robust upper limit -- obtained via a full
Bayesian analysis searching simultaneously over the signal and pulsar noise on
the subset of ours six best pulsars -- is . These limits, the
most stringent to date at , exclude the presence of
sub-centiparsec binaries with chirp mass M out to a
distance of about 25Mpc, and with M out to a
distance of about 1Gpc (). We show that state-of-the-art SMBHB
population models predict probability of detecting a CGW with the
current EPTA dataset, consistent with the reported non-detection. We stress,
however, that PTA limits on individual CGW have improved by almost an order of
magnitude in the last five years. The continuing advances in pulsar timing data
acquisition and analysis techniques will allow for strong astrophysical
constraints on the population of nearby SMBHBs in the coming years.Comment: 16 pages, 11 figures, accepted for publication in MNRA
European Pulsar Timing Array Limits On An Isotropic Stochastic Gravitational-Wave Background
24 pages, 5 tables, 17 figuresInternational audienceWe present new limits on an isotropic stochastic gravitational-wave background (GWB) using a six pulsar dataset spanning 18 yr of observations from the 2015 European Pulsar Timing Array data release. Performing a Bayesian analysis, we fit simultaneously for the intrinsic noise parameters for each pulsar, along with common correlated signals including clock, and Solar System ephemeris errors, obtaining a robust 95 upper limit on the dimensionless strain amplitude of the background of at a reference frequency of and a spectral index of , corresponding to a background from inspiralling super-massive black hole binaries, constraining the GW energy density to at 2.8 nHz. We also present limits on the correlated power spectrum at a series of discrete frequencies, and show that our sensitivity to a fiducial isotropic GWB is highest at a frequency of ~Hz. Finally we discuss the implications of our analysis for the astrophysics of supermassive black hole binaries, and present 95 upper limits on the string tension, , characterising a background produced by a cosmic string network for a set of possible scenarios, and for a stochastic relic GWB. For a Nambu-Goto field theory cosmic string network, we set a limit , identical to that set by the {\it Planck} Collaboration, when combining {\it Planck} and high- Cosmic Microwave Background data from other experiments. For a stochastic relic background we set a limit of , a factor of 9 improvement over the most stringent limits previously set by a pulsar timing array
The Polarized Cosmic Hand: IXPE Observations of PSR B1509-58/MSH 15-5<SUP>2</SUP>
International audienceWe describe IXPE polarization observations of the pulsar wind nebula (PWN) MSH 15-52, the "Cosmic Hand." We find X-ray polarization across the PWN, with B-field vectors generally aligned with filamentary X-ray structures. High-significance polarization is seen in arcs surrounding the pulsar and toward the end of the "jet," with polarization degree PD > 70%, thus approaching the maximum allowed synchrotron value. In contrast, the base of the jet has lower polarization, indicating a complex magnetic field at significant angle to the jet axis. We also detect significant polarization from PSR B1509-58 itself. Although only the central pulse phase bin of the pulse has high individual significance, flanking bins provide lower-significance detections and, in conjunction with the X-ray image and radio polarization, can be used to constrain rotating vector model solutions for the pulsar geometry