In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supe... more In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of ∼15%. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data r...
The integration time calculator (ITC) for POL2 has as input for the calculation the requested noi... more The integration time calculator (ITC) for POL2 has as input for the calculation the requested noise level in the Q and U maps. However, the Q and U maps are not the normal end products of the data reduction. The end product is typically a polarization vector map in percentage of the total intensity. To covert the Q and U maps to a fractional polarization map, a total intensity map is required. The total intensity map is also needed for removing the instrumental polarization (IP) from the Q and U maps. Currently the total intensity map is not obtained during a POL2 map it needs to be obtained separately. The computation of the polarized intensity, vector directions and the removal of the IP effects the noise level in the final result and rises questions like: What is the implication for the required noise level in the Q and U maps? What is the required noise level in the total intensity map? Should the total intensity map be obtained close in time to the polarization map as a part of...
We present 850 μm imaging polarimetry data of the ρ Oph-A core taken with the Submillimeter Commo... more We present 850 μm imaging polarimetry data of the ρ Oph-A core taken with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its polarimeter (POL-2), as part of our ongoing survey project, BISTRO (Bfields In STar forming RegiOns). The polarization vectors are used to identify the orientation of the magnetic field projected on the plane of the sky at a resolution of 0.01 pc. We identify 10 subregions with distinct polarization fractions and angles in the 0.2 pc ρ Oph A core; some of them can be part of a coherent magnetic field structure in the ρ Oph region. The results are consistent with previous observations of the brightest regions of ρ Oph-A, where the degrees of polarization are at a level of a few percents, but our data reveal for the first time the magnetic field structures in the fainter regions surrounding the core where the degree of polarization is much higher (> 5%). A comparison with previous near-infrared polarimetric data shows that there are several mag...
arXiv: Instrumentation and Methods for Astrophysics, 2020
Namakanui is an instrument containing three inserts in an ALMA type Dewar. The three inserts are ... more Namakanui is an instrument containing three inserts in an ALMA type Dewar. The three inserts are Alaihi, Uu and Aweoweo operating around 86, 230 and 345GHz. The receiver is being commissioned on the JCMT. It will be used for both Single dish and VLBI observations. We will present commissioning results and the system.
Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wav... more Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg ≡ GM/c2) scales in nearby sources1. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find...
Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around t... more Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density n e ∼ 104–7 cm−3, magnetic field strength B ∼ 1–30 G, and electron temperature T e ∼ (1–12) × 1010 K of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloid...
3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variab... more 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift of z = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmos...
Observatory Operations: Strategies, Processes, and Systems VI, 2016
The newly formed East Asian Observatory assumed operations of the James Clerk Maxwell Telescope i... more The newly formed East Asian Observatory assumed operations of the James Clerk Maxwell Telescope in March of 2015. In just three weeks, the facility needed to run up completely mothballed observatory operations, introduce the telescope to a vast new scientist base with no familiarity with the facility, and create a non-existent science program. The handover to the EAO has since been a succession of challenging time-lines, and nearly unique problems requiring novel solutions. The results, however, have been spectacular, with subscription rates at unprecedented levels, a new series of Large Programs underway, as well as an exciting Future Instrumentation Project that together promises to keep JCMT at the forefront of wide-field submillimeter astronomy for the next decade.
... transitions used by Pickett and Davis according to our value of the rotational temperature an... more ... transitions used by Pickett and Davis according to our value of the rotational temperature and the optical depth implied for the 817 -~ 808 transition, and we find that many of the Pickett and Davis ... e 2.5 a. I Plateau present; see published spectrum in Irvine and Hjalmarson 1983. ...
We present the first results from the B-fields In STar-forming Region Observations (BISTRO) surve... more We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array 2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey{\rsquo}s aims and objectives. We describe the rationale behind the survey, and the questions that the survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC 1 region. We see that the magnetic field lies approximately perpendicular to the famous {\ldquo}integral filament{\rdquo} in the densest regions of that filament. Furthermore, we see an {\ldquo}hourglass{\rdquo} mag...
In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supe... more In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of ∼15%. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data r...
The integration time calculator (ITC) for POL2 has as input for the calculation the requested noi... more The integration time calculator (ITC) for POL2 has as input for the calculation the requested noise level in the Q and U maps. However, the Q and U maps are not the normal end products of the data reduction. The end product is typically a polarization vector map in percentage of the total intensity. To covert the Q and U maps to a fractional polarization map, a total intensity map is required. The total intensity map is also needed for removing the instrumental polarization (IP) from the Q and U maps. Currently the total intensity map is not obtained during a POL2 map it needs to be obtained separately. The computation of the polarized intensity, vector directions and the removal of the IP effects the noise level in the final result and rises questions like: What is the implication for the required noise level in the Q and U maps? What is the required noise level in the total intensity map? Should the total intensity map be obtained close in time to the polarization map as a part of...
We present 850 μm imaging polarimetry data of the ρ Oph-A core taken with the Submillimeter Commo... more We present 850 μm imaging polarimetry data of the ρ Oph-A core taken with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its polarimeter (POL-2), as part of our ongoing survey project, BISTRO (Bfields In STar forming RegiOns). The polarization vectors are used to identify the orientation of the magnetic field projected on the plane of the sky at a resolution of 0.01 pc. We identify 10 subregions with distinct polarization fractions and angles in the 0.2 pc ρ Oph A core; some of them can be part of a coherent magnetic field structure in the ρ Oph region. The results are consistent with previous observations of the brightest regions of ρ Oph-A, where the degrees of polarization are at a level of a few percents, but our data reveal for the first time the magnetic field structures in the fainter regions surrounding the core where the degree of polarization is much higher (> 5%). A comparison with previous near-infrared polarimetric data shows that there are several mag...
arXiv: Instrumentation and Methods for Astrophysics, 2020
Namakanui is an instrument containing three inserts in an ALMA type Dewar. The three inserts are ... more Namakanui is an instrument containing three inserts in an ALMA type Dewar. The three inserts are Alaihi, Uu and Aweoweo operating around 86, 230 and 345GHz. The receiver is being commissioned on the JCMT. It will be used for both Single dish and VLBI observations. We will present commissioning results and the system.
Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wav... more Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg ≡ GM/c2) scales in nearby sources1. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find...
Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around t... more Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density n e ∼ 104–7 cm−3, magnetic field strength B ∼ 1–30 G, and electron temperature T e ∼ (1–12) × 1010 K of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloid...
3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variab... more 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique – global Very Long Baseline Interferometry (VLBI) at 1.3 mm (230 GHz) – to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable γ-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ∼20 μas (at a redshift of z = 0.536 this corresponds to ∼0.13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation. We find a multicomponent inner jet morphology with the northernmos...
Observatory Operations: Strategies, Processes, and Systems VI, 2016
The newly formed East Asian Observatory assumed operations of the James Clerk Maxwell Telescope i... more The newly formed East Asian Observatory assumed operations of the James Clerk Maxwell Telescope in March of 2015. In just three weeks, the facility needed to run up completely mothballed observatory operations, introduce the telescope to a vast new scientist base with no familiarity with the facility, and create a non-existent science program. The handover to the EAO has since been a succession of challenging time-lines, and nearly unique problems requiring novel solutions. The results, however, have been spectacular, with subscription rates at unprecedented levels, a new series of Large Programs underway, as well as an exciting Future Instrumentation Project that together promises to keep JCMT at the forefront of wide-field submillimeter astronomy for the next decade.
... transitions used by Pickett and Davis according to our value of the rotational temperature an... more ... transitions used by Pickett and Davis according to our value of the rotational temperature and the optical depth implied for the 817 -~ 808 transition, and we find that many of the Pickett and Davis ... e 2.5 a. I Plateau present; see published spectrum in Irvine and Hjalmarson 1983. ...
We present the first results from the B-fields In STar-forming Region Observations (BISTRO) surve... more We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array 2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey{\rsquo}s aims and objectives. We describe the rationale behind the survey, and the questions that the survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC 1 region. We see that the magnetic field lies approximately perpendicular to the famous {\ldquo}integral filament{\rdquo} in the densest regions of that filament. Furthermore, we see an {\ldquo}hourglass{\rdquo} mag...
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Papers by Per Friberg