Peter Michelson, Postdoctoral Faculty Sponsor
X-ray polarization evidence for a 200-year-old flare of Sgr A.
The centre of the Milky Way Galaxy hosts a black hole with a solar mass of about 4 million (Sagittarius A* (Sgr A)) that is very quiescent at present with a luminosity many orders of magnitude below those of active galactic nuclei1. Reflection of X-rays from Sgr A* by dense gas in the Galactic Centre region offers a means to study its past flaring activity on timescales of hundreds and thousands of years2. The shape of the X-ray continuum and the strong fluorescent iron line observed from giant molecular clouds in the vicinity of Sgr A* are consistent with the reflection scenario3-5. If this interpretation is correct, the reflected continuum emission should be polarized6. Here we report observations of polarized X-ray emission in the direction of the molecular clouds in the Galactic Centre using the Imaging X-ray Polarimetry Explorer. We measure a polarization degree of 31% ± 11%, and a polarization angle of -48° ± 11°. The polarization angle is consistent with Sgr A* being the primary source of the emission, and the polarization degree implies that some 200 years ago, the X-ray luminosity of Sgr A* was briefly comparable to that of a Seyfert galaxy.
View details for DOI 10.1038/s41586-023-06064-x
View details for PubMedID 37344593
- Equalizing the Pixel Response of the Imaging Photoelectric Polarimeter Onboard the IXPE Mission ASTRONOMICAL JOURNAL 2023; 165 (5)
- Simultaneous space and phase resolved X-ray polarimetry of the Crab pulsar and nebula NATURE ASTRONOMY 2023
- The Fermi-LAT Lightcurve Repository ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 2023; 265 (2)
- IXPE Observations of the Quintessential Wind-accreting X-Ray Pulsar Vela X-1 ASTROPHYSICAL JOURNAL LETTERS 2023; 947 (2)
- Polarisation leakage due to errors in track reconstruction in gas pixel detectors ASTRONOMY & ASTROPHYSICS 2023; 672
- X-Ray Polarimetry Reveals the Magnetic-field Topology on Sub-parsec Scales in Tycho's Supernova Remnant ASTROPHYSICAL JOURNAL 2023; 945 (1)
- The IXPE View of GRB 221009A ASTROPHYSICAL JOURNAL LETTERS 2023; 946 (1)
- Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826-238 in the High Soft State ASTROPHYSICAL JOURNAL 2023; 943 (2)
- A Strong X-Ray Polarization Signal from the Magnetar 1RXS J170849.0-400910 ASTROPHYSICAL JOURNAL LETTERS 2023; 944 (2)
- X-Ray Polarization Observations of BL Lacertae ASTROPHYSICAL JOURNAL LETTERS 2023; 942 (1)
- Low-energy Electron-track Imaging for a Liquid Argon Time-projection-chamber Telescope Concept Using Probabilistic Deep Learning ASTROPHYSICAL JOURNAL 2023; 942 (2)
Vela pulsar wind nebula X-rays are polarized to near the synchrotron limit.
2022; 612 (7941): 658-660
Pulsar wind nebulae are formed when outflows of relativistic electrons and positrons hit the surrounding supernova remnant or interstellar medium at a shock front. The Vela pulsar wind nebula is powered by a young pulsar (B0833-45, aged 11,000 years)1 and located inside an extended structure called Vela X, which is itself inside the supernova remnant2. Previous X-ray observations revealed two prominent arcs that are bisected by a jet and counter jet3,4. Radio maps have shown high linear polarization of 60% in the outer regions of the nebula5. Here we report an X-ray observation of the inner part of the nebula, where polarization can exceed 60% at the leading edge-approaching the theoretical limit of what can be produced by synchrotron emission. We infer that, in contrast with the case of the supernova remnant, the electrons in the pulsar wind nebula are accelerated with little or no turbulence in a highly uniform magnetic field.
View details for DOI 10.1038/s41586-022-05476-5
View details for PubMedID 36543953
- The X-Ray Polarimetry View of the Accreting Pulsar Cen X-3 ASTROPHYSICAL JOURNAL LETTERS 2022; 941 (1)
Polarized x-rays from a magnetar.
Science (New York, N.Y.)
2022; 378 (6620): 646-650
Magnetars are neutron stars with ultrastrong magnetic fields, which can be observed in x-rays. Polarization measurements could provide information on their magnetic fields and surface properties. We observed polarized x-rays from the magnetar 4U 0142+61 using the Imaging X-ray Polarimetry Explorer and found a linear polarization degree of 13.5 ± 0.8% averaged over the 2- to 8-kilo-electron volt band. The polarization changes with energy: The degree is 15.0 ± 1.0% at 2 to 4 kilo-electron volts, drops below the instrumental sensitivity ~4 to 5 kilo-electron volts, and rises to 35.2 ± 7.1% at 5.5 to 8 kilo-electron volts. The polarization angle also changes by 90° at ~4 to 5 kilo-electron volts. These results are consistent with a model in which thermal radiation from the magnetar surface is reprocessed by scattering off charged particles in the magnetosphere.
View details for DOI 10.1126/science.add0080
View details for PubMedID 36356124
Polarized x-rays constrain the disk-jet geometry in the black hole x-ray binary Cygnus X-1.
Science (New York, N.Y.)
2022; 378 (6620): 650-654
A black hole x-ray binary (XRB) system forms when gas is stripped from a normal star and accretes onto a black hole, which heats the gas sufficiently to emit x-rays. We report a polarimetric observation of the XRB Cygnus X-1 using the Imaging X-ray Polarimetry Explorer. The electric field position angle aligns with the outflowing jet, indicating that the jet is launched from the inner x-ray-emitting region. The polarization degree is 4.01 ± 0.20% at 2 to 8 kiloelectronvolts, implying that the accretion disk is viewed closer to edge-on than the binary orbit. These observations reveal that hot x-ray-emitting plasma is spatially extended in a plane perpendicular to, not parallel to, the jet axis.
View details for DOI 10.1126/science.add5399
View details for PubMedID 36356134
Polarized blazar X-rays imply particle acceleration in shocks.
2022; 611 (7937): 677-681
Most of the light from blazars, active galactic nuclei with jets of magnetized plasma that point nearly along the line of sight, is produced by high-energy particles, up to around 1TeV. Although the jets are known to be ultimately powered by a supermassive black hole, how the particles are accelerated to such high energies has been an unanswered question. The process must be related to the magnetic field, which can be probed by observations of the polarization of light from the jets. Measurements of the radio to optical polarization-the only range available until now-probe extended regions of the jet containing particles that left the acceleration site days to years earlier1-3, and hence do not directly explore the acceleration mechanism, as could X-ray measurements. Here we report the detection of X-ray polarization from the blazar Markarian 501 (Mrk 501). We measure an X-ray linear polarization degree PiX of around 10%, which is a factor of around 2 higher than the value at optical wavelengths, with a polarization angle parallel to the radio jet. This points to a shock front as the source of particle acceleration and also implies that the plasma becomes increasingly turbulent with distance from the shock.
View details for DOI 10.1038/s41586-022-05338-0
View details for PubMedID 36418451
- Observations of 4U 1626-67 with the Imaging X-Ray Polarimetry Explorer ASTROPHYSICAL JOURNAL 2022; 940 (1)
- Determination of X-ray pulsar geometry with IXPE polarimetry NATURE ASTRONOMY 2022
- X-Ray Polarization Detection of Cassiopeia A with IXPE ASTROPHYSICAL JOURNAL 2022; 938 (1)
- The X-Ray Polarization View of Mrk 421 in an Average Flux State as Observed by the Imaging X-Ray Polarimetry Explorer ASTROPHYSICAL JOURNAL LETTERS 2022; 938 (1)
- Calibration of the IXPE Focal Plane X-Ray Polarimeters to Polarized Radiation ASTRONOMICAL JOURNAL 2022; 164 (3)
- Limits on X-Ray Polarization at the Core of Centaurus A as Observed with the Imaging X-Ray Polarimetry Explorer ASTROPHYSICAL JOURNAL 2022; 935 (2)
- ixpeobssim: A simulation and analysis framework for the imaging X-ray polarimetry explorer SOFTWAREX 2022; 19
- BASS. XXV. DR2 Broad-line-based Black Hole Mass Estimates and Biases from Obscuration ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 2022; 261 (1)
- Search for New Cosmic-Ray Acceleration Sites within the 4FGL Catalog Galactic Plane Sources ASTROPHYSICAL JOURNAL 2022; 933 (2)
- The Coupling of an EUV Coronal Wave and Ion Acceleration in a Fermi-LAT Behind-the-Limb Solar Flare ASTROPHYSICAL JOURNAL 2022; 929 (2)
- A Weighted Analysis to Improve the X-Ray Polarization Sensitivity of the Imaging X-ray Polarimetry Explorer ASTRONOMICAL JOURNAL 2022; 163 (4)
- Imaging X-ray Polarimetry Explorer: prelaunch JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS 2022; 8 (2)
- An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE ASTRONOMICAL JOURNAL 2022; 163 (2)
- The Instrument of the Imaging X-Ray Polarimetry Explorer ASTRONOMICAL JOURNAL 2021; 162 (5)
- The Imaging X-ray Polarimetry Explorer (IXPE): technical overview III SPIE-INT SOC OPTICAL ENGINEERING. 2021
- The Imaging X-Ray Polarimetry Explorer (IXPE): Technical Overview IV SPIE-INT SOC OPTICAL ENGINEERING. 2021
- An observation-simulation and analysis framework for the Imaging X-ray Polarimetry Explorer (IXPE) NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 2019; 936: 224–26
- The Imaging X-ray Polarimetry Explorer (IXPE): technical overview II SPIE-INT SOC OPTICAL ENGINEERING. 2019
Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A
2018; 361 (6398): 146-+
Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera-electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray-emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.
View details for DOI 10.1126/science.aat1378
View details for Web of Science ID 000438449200037
View details for PubMedID 30002226
- Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar SCIENCE ADVANCES 2018; 4 (2)
Einstein@Home discovers a radio-quiet gamma-ray millisecond pulsar.
2018; 4 (2): eaao7228
Millisecond pulsars (MSPs) are old neutron stars that spin hundreds of times per second and appear to pulsate as their emission beams cross our line of sight. To date, radio pulsations have been detected from all rotation-powered MSPs. In an attempt to discover radio-quiet gamma-ray MSPs, we used the aggregated power from the computers of tens of thousands of volunteers participating in the Einstein@Home distributed computing project to search for pulsations from unidentified gamma-ray sources in Fermi Large Area Telescope data. This survey discovered two isolated MSPs, one of which is the only known rotation-powered MSP to remain undetected in radio observations. These gamma-ray MSPs were discovered in completely blind searches without prior constraints from other observations, raising hopes for detecting MSPs from a predicted Galactic bulge population.
View details for DOI 10.1126/sciadv.aao7228
View details for PubMedID 29503868
View details for PubMedCentralID PMC5829974
- The Imaging X-ray Polarimetry Explorer (IXPE): technical overview SPIE-INT SOC OPTICAL ENGINEERING. 2018
- XIMPOL: a new x-ray polarimetry observation-simulation and analysis framework. SPIE-INT SOC OPTICAL ENGINEERING. 2017