73 research outputs found
Simultaneous Chandra and VLA Observations of the Transitional Millisecond Pulsar PSR J1023+0038: Anti-correlated X-Ray and Radio Variability
We present coordinated Chandra X-ray Observatory and Karl G. Jansky Very Large Array observations of the transitional millisecond pulsar PSR J1023+0038 in its low-luminosity accreting state. The unprecedented five hours of strictly simultaneous X-ray and radio continuum coverage for the first time unambiguously show a highly reproducible, anti-correlated variability pattern. The characteristic switches from the X-ray high mode into a low mode are always accompanied by a radio brightening with a duration that closely matches the X-ray low mode interval. This behavior cannot be explained by a canonical inflow/outflow accretion model where the radiated emission and the jet luminosity are powered by, and positively correlated with, the available accretion energy. We interpret this phenomenology as alternating episodes of low-level accretion onto the neutron star during the X-ray high mode that are interrupted by rapid ejections of plasma by the active rotation-powered pulsar, possibly initiated by a reconfiguration of the pulsar magnetosphere, that cause a transition to a less X-ray luminous mode. The observed anti-correlation between radio and X-ray luminosity has an additional consequence: transitional MSPs can make excursions into a region of the radio/X-ray luminosity plane previously thought to be occupied solely by black hole X-ray binary sources. This complicates the use of this luminosity relation for identifying candidate black holes, suggesting the need for additional discriminants when attempting to establish the true nature of the accretor
Recommended from our members
An ASKAP Search for a Radio Counterpart to the First High-significance Neutron Star-Black Hole Merger LIGO/Virgo S190814bv
We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star-black hole (NSBH) merger, with the Australian Square Kilometre Array Pathfinder. We imaged a 30 deg2 field at ΔT = 2, 9, and 33 days post-merger at a frequency of 944 MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers 89% of the LIGO/Virgo localization region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates. For one of these, AT2019osy, we performed multiwavelength follow-up and ultimately ruled out the association with S190814bv. All other candidates are likely unrelated variables, but we cannot conclusively rule them out. We discuss our results in the context of model predictions for radio emission from NSBH mergers and place constrains on the circum-merger density and inclination angle of the merger. This survey is simultaneously the first large-scale radio follow-up of an NSBH merger, and the most sensitive widefield radio transients search to-date
Quasi-simultaneous Radio/X-Ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 during its Low-luminosity Accretion-disk State
3FGL J1544.6-1125 is a candidate transitional millisecond pulsar (tMSP).
Similar to the well-established tMSPs - PSR J1023+0038, IGR J18245-2452, and
XSS J12270-4859 -- 3FGL J1544.6-1125 shows -ray emission and discrete
X-ray "low" and "high" modes during its low-luminosity accretion-disk state.
Coordinated radio/X-ray observations of PSR J1023+0038 in its current
low-luminosity accretion-disk state showed rapidly variable radio continuum
emission-possibly originating from a compact, self-absorbed jet, the
"propellering" of accretion material, and/or pulsar moding. 3FGL J1544.6-1125
is currently the only other (candidate) tMSP system in this state, and can be
studied to see whether tMSPs are typically radio-loud compared to other neutron
star binaries. In this work, we present a quasi-simultaneous Very Large Array
and Swift radio/X-ray campaign on 3FGL J1544.6-1125. We detect 10 GHz radio
emission varying in flux density from Jy down to 15
Jy (3 upper limit) at four epochs spanning three weeks. At the
brightest epoch, the radio luminosity is erg s for a quasi-simultaneous X-ray luminosity
erg s (for an assumed distance of 3.8
kpc). These luminosities are close to those of PSR J1023+0038, and the results
strengthen the case that 3FGL J1544.6-1125 is a tMSP showing similar
phenomenology to PSR J1023+0038.Comment: Accepted for publication in the Astrophysical Journa
Black holes, gravitational waves and fundamental physics: a roadmap
The grand challenges of contemporary fundamental physics—dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem—all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'
SN2019wxt: An ultrastripped supernova candidate discovered in the electromagnetic follow-up of a gravitational wave trigger
We present optical, radio, and X-ray observations of a rapidly evolving transient SN2019wxt (PS19hgw), discovered during the search for an electromagnetic counterpart to the gravitational-wave (GW) trigger S191213g. Although S191213g was not confirmed as a significant GW event in the off-line analysis of LIGO-Virgo data, SN2019wxt remained an interesting transient due to its peculiar nature. The optical/near-infrared (NIR) light curve of SN2019wxt displayed a double-peaked structure evolving rapidly in a manner analogous to currently known ultrastripped supernovae (USSNe) candidates. This double-peaked structure suggests the presence of an extended envelope around the progenitor, best modeled with two components: (i) early-time shock-cooling emission and (ii) late-time radioactive 56Ni decay. We constrain the ejecta mass of SN2019wxt at Mej ≈ 0.20M⊙, which indicates a significantly stripped progenitor that was possibly in a binary system. We also followed up SN2019wxt with long-term Chandra and Jansky Very Large Array observations spanning ∼260 days. We detected no definitive counterparts at the location of SN2019wxt in these long-term X-ray and radio observational campaigns. We establish the X-ray upper limit at 9.93 × 10−17 erg cm−2 s−1 and detect an excess radio emission from the region of SN2019wxt. However, there is little evidence for SN1993J- or GW170817-like variability of the radio flux over the course of our observations. A substantial host-galaxy contribution to the measured radio flux is likely. The discovery and early-time peak capture of SN2019wxt in optical/NIR observations during EMGW follow-up observations highlight the need for dedicated early, multiband photometric observations to identify USSNe
Simultaneous NICER and NuSTAR observations of the Ultracompact X-ray Binary 4U 0614+091
We present the first joint NuSTAR and NICER observations of the ultracompact X-ray binary 4U 0614+091. This source shows quasiperiodic flux variations on the timescale of ∼days. We use reflection modeling techniques to study various components of the accretion system as the flux varies. We find that the flux of the reflected emission and the thermal components representing the disk and the compact object trend closely with the overall flux. However, the flux of the power-law component representing the illuminating X-ray corona scales in the opposite direction, increasing as the total flux decreases. During the lowest flux observation, we see evidence of accretion disk truncation from roughly 6 gravitational radii to 11.5 gravitational radii. This is potentially analogous to the truncation seen in black hole low-mass X-ray binaries, which tends to occur during the low/hard state at sufficiently low Eddington ratios
Accretion spin-up and a strong magnetic field in the slow-spinning Be X-ray binary MAXI J0655-013
We present MAXI and NuSTAR observations of the Be X-ray binary, MAXI
J0655-013, in outburst. NuSTAR observed the source once early in the outburst,
when spectral analysis yields a bolometric (0.1--100 keV), unabsorbed source
luminosity of , and a
second time 54 days later, by which time the luminosity dropped to
after first undergoing
a dramatic increase. Timing analysis of the NuSTAR data reveals a neutron star
spin period of s during the first observation, which decreased
to s by the time of the second observation, indicating spin-up due
to accretion throughout the outburst. Furthermore, during the first NuSTAR
observation, we observed quasiperiodic oscillations with centroid frequency
mHz, which exhibited a second harmonic feature. By combining the
MAXI and NuSTAR data with pulse period measurements reported by Fermi/GBM, we
are able to show that apparent flaring behavior in the MAXI light-curve is an
artifact introduced by uneven sampling of the pulse profile, which has a large
pulsed fraction. Finally, we estimate the magnetic field strength at the
neutron star surface via three independent methods, invoking a tentative
cyclotron resonance scattering feature at keV, QPO production at the inner
edge of the accretion disk, and spin-up via interaction of the neutron star
magnetic field with accreting material. Each of these result in a significantly
different value. We discuss the strengths and weaknesses of each method and
infer that MAXI J0655-013 is likely to have a high surface magnetic field
strength, G.Comment: 19 pages, 10 figure, 4 tables; submitted to ApJ on May 24, 202
Quasi-simultaneous Radio/X-Ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 during its Low-luminosity Accretion-disk State
3FGL J1544.6-1125 is a candidate transitional millisecond pulsar (tMSP). Similar to the well-established tMSPs - PSR J1023+0038, IGR J18245-2452, and XSS J12270-4859 - 3FGL J1544.6-1125 shows γ-ray emission and discrete X-ray "low"and "high"modes during its low-luminosity accretion-disk state. Coordinated radio/X-ray observations of PSR J1023+0038 in its current low-luminosity accretion-disk state showed rapidly variable radio continuum emission - possibly originating from a compact, self-absorbed jet, the "propellering"of accretion material, and/or pulsar moding. 3FGL J1544.6-1125 is currently the only other (candidate) tMSP system in this state, and can be studied to see whether tMSPs are typically radio-loud compared to other neutron star binaries. In this work, we present a quasi-simultaneous Very Large Array and Swift radio/X-ray campaign on 3FGL J1544.6-1125. We detect 10 GHz radio emission varying in flux density from 47.7 ± 6.0 μJy down to ≲15 μJy (3σ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is L 5 GHz = (2.17 ± 0.17) × 1027 erg s-1 for a quasi-simultaneous X-ray luminosity L 2-10 keV = (4.32 ± 0.23) × 1033 erg s-1 (for an assumed distance of 3.8 kpc). These luminosities are close to those of PSR J1023+0038, and the results strengthen the case that 3FGL J1544.6-1125 is a tMSP showing similar phenomenology to PSR J1023+0038.A.J. and J.W.T.H. acknowledge funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement nr. 337062 (DRAGNET). A.J. also acknowledges support from the NuSTAR mission. A.P. acknowledges support from an NWO Vidi Fellowship. J.C.A.M.-J. is the recipient of an Australian Research Council Future Fellowship (FT 140101082). S.B. was supported in part by NASA Swift Guest Investigator Cycle 12 program grant NNX16AN79G awarded through Columbia University
- …