Aims. We aim to constrain the structural variations within the HST-1 region downstream of the radio jet of M 87, in general as well as in connection to the episodes of activity at very high energy ...(VHE). Methods. We analyzed and compared 26 VLBI observations of the M 87 jet, obtained between 2006 and 2011 with the Very Long Baseline Array (VLBA) at 1.7 GHz and the European VLBI Network (EVN) at 5 GHz. Results. HST-1 is detected at all epochs; we model-fitted its complex structure with two or more components, the two outermost of which display a significant proper motion with a superluminal velocity around ~4 c. The motion of a third feature that is detected upstream is more difficult to characterize. The overall position angle of HST-1 has changed during the time of our observations from −65° to −90°, while the structure has moved by over 80 mas downstream. Our results on the component evolution suggest that structural changes at the upstream edge of HST-1 can be related to the VHE events.
We report our intensive, high angular resolution radio monitoring observations of the jet in M 87 with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from 2011 ...February to 2012 October, together with contemporaneous high-energy (100 MeV < E < 100 GeV) gamma -ray light curves obtained by the Fermi Large Area Telescope. We detected a remarkable (up to ~70%) increase of the radio flux density from the unresolved jetbase (radio core) with VERA at 22 and 43 GHz coincident with the VHE activity. These results in the radio bands strongly suggest that the VHE gamma -ray activity in 2012 originates in the jet base within 0.03 pc or 56 Schwarzschild radii (the VERA spatial resolution of 0.4 mas at 43 GHz) from the central supermassive black hole. This indicates that a new radio-emitting component was created near the black hole in the period of the VHE event, and then propagated outward with progressively decreasing synchrotron opacity.
We present RadioAstron space-based very long baseline interferometry (VLBI) observations of the nearby radio galaxy 3C 84 (NGC 1275) at the centre of the Perseus cluster. The observations were ...carried out during a perigee passage of the Spektr-R spacecraft on September 21–22, 2013 and involved a global array of 24 ground radio telescopes observing at 5 GHz and 22 GHz, together with the Space Radio Telescope (SRT). Furthermore, the Very Long Baseline Array (VLBA) and the phased Very Large Array (VLA) observed the source quasi-simultaneously at 15 GHz and 43 GHz. Fringes between the ground array and the SRT were detected on baseline lengths up to 8.1 times the Earth’s diameter, providing unprecedented resolution for 3C 84 at these wavelengths. We note that the corresponding fringe spacing is 125 μas at 5 GHz and 27 μas at 22 GHz. Our space-VLBI images reveal a previously unseen sub-structure inside the compact ∼1 pc long jet that was ejected about ten years earlier. In the 5 GHz image, we detected, for the first time, low-intensity emission from a cocoon-like structure around the restarted jet. Our results suggest that the increased power of the young jet is inflating a bubble of hot plasma as it carves its way through the ambient medium of the central region of the galaxy. Here, we estimate the minimum energy stored in the mini-cocoon, along with its pressure, volume, expansion speed, and the ratio of heavy particles to relativistic electrons, as well as the density of the ambient medium. About half of the energy delivered by the jet is dumped into the mini-cocoon and the quasi-spherical shape of the bubble suggests that this energy may be transferred to a significantly larger volume of the interstellar medium than what would be accomplished by the well-collimated jet on its own. The pressure of the hot mini-cocoon also provides a natural explanation for the almost cylindrical jet profile seen in the 22 GHz RadioAstron image.
Purpose: Artificial intelligence (AI) is playing an increasingly important role in healthcare and health professions education. This study explored medical students' and interns' knowledge of ...artificial intelligence (AI), perceptions of the role of AI in medicine, and preferences around the teaching of AI competencies. Methods: In this cross-sectional study, the authors used a previously validated Canadian questionnaire and gathered responses from students and interns at KIST Medical College, Nepal. Face validity and reliability of the tool were assessed by administering the questionnaire to 20 alumni as a pilot sample (Cronbach alpha = 0.6). Survey results were analyzed quantitatively (p-value = 0.05). Results: In total 216 students (37% response rate) participated. The median AI knowledge score was 11 (interquartile range 4), and the maximum possible score was 25. The score was higher among final year students (p = 0.006) and among those with additional training in AI (p = 0.040). Over 49% strongly agreed or agreed that AI will reduce the number of jobs for doctors. Many expect AI to impact their specialty choice, felt the Nepalese health-care system is ill-equipped to deal with the challenges of AI, and opined every student of medicine should receive training on AI competencies. Conclusion: The lack of coverage of AI and machine learning in Nepalese medical schools has resulted in students being unaware of AI's impact on individual patients and the healthcare system. A high perceived willingness among respondents to learn about AI is a positive sign and a strong indicator of futuristic successful curricula changes. Systematic implementation of AI in the Nepalese healthcare system can be a potential tool in addressing health-care challenges related to resource and manpower constraints. Incorporating topics related to AI and machine learning in medical curricula can be a useful first step. Keywords: artificial intelligence, healthcare, machine learning, medical students, Nepal
We investigate the radio and γ-ray variability of the flat spectrum radio quasar PKS 1510−089 in the time range between 2010 November and 2012 January. In this period the source showed an intense ...activity, with two major γ-ray flares detected in 2011 July and October. During the latter episode both the γ-ray and the radio flux density reached their historical peak. Multiwavelength analysis shows a rotation of about 380° of the optical polarization angle close in time with the rapid and strong γ-ray flare in 2011 July. An enhancement of the optical emission and an increase of the fractional polarization both in the optical and in radio bands are observed about three weeks later, close in time with another γ-ray outburst. On the other hand, after 2011 September a huge radio outburst has been detected, first in the millimetre regime followed with some time delay at centimetre down to decimetre wavelengths. This radio flare is characterized by a rising and a decaying stage, in agreement with the formation of a shock and its evolution, as a consequence of expansion and radiative cooling. If the γ-ray flare observed in 2011 October is related to this radio outburst, then this strongly indicates that the region responsible for the γ-ray variability is not within the broad line, but a few parsecs downstream along the jet.
We report on the very long baseline interferometry (VLBI) follow-up observations using the Japanese VLBI Network array at 22 GHz for the largest X-ray flare of TeV blazar Mrk 421 that occurred in ...2010 mid-February. The total of five epochs of observations were performed at intervals of about 20 days between 2010 March 7 and May 31. No newborn component associated with the flare was seen directly in the total intensity images obtained by our multi-epoch VLBI observations. However, one jet component located at ~1 mas northwest from the core was able to be identified, and its proper motion can be measured as -1.66 + or - 0.46 mas yr super(-1), which corresponds to an apparent velocity of -3.48 + or - 0.97c. Here, this negative velocity indicates that the jet component was apparently moving toward the core. As the most plausible explanation, we discuss that the apparent negative velocity was possibly caused by the ejection of a new component, which could not be resolved with our observations. In this case, the obtained Doppler factor of the new component is around 10-20, which is consistent with the ones typically estimated by model fittings of spectral energy distribution for this source.
ABSTRACT We investigate the location of the radio jet bases ("radio cores") of blazars in radio images and their stationarity by means of dense very long baseline interferometry (VLBI) observations. ...In order to measure the position of a radio core, we conducted a 12 epoch astrometric observation of the blazar Markarian 421 with the VLBI Exploration of Radio Astrometry at 22 GHz immediately after a large X-ray flare, which occurred in the middle of 2011 September. For the first time,we find that the radio core is not stationary but rather changes its location toward 0.5 mas downstream. This angular scale corresponds to the de-projected length of a scale of 105 Schwarzschild radii (Rs) at the distance of Markarian 421. This radio-core wandering may be a new type of manifestation associated with the phenomena of large X-ray flares.
Aims. We investigate the nature of the compact and possibly variable nuclear radio source in the centre of WISE J0716−19, the proposed host galaxy of the fast radio burst FRB 150418. Methods. We ...observed WISE J0716−19 at 5.0 GHz with the European VLBI Network (EVN) four times between 2016 March 16 and June 2. At three epochs, we simultaneously observed the source with e-MERLIN at the same frequency. Results. We detected a compact source in the EVN data in each epoch with a significance of up to ~8σ. The four epochs yielded consistent results within their uncertainties for the peak surface intensity and positions. The mean values for these quantities are Ipeak = (115 ± 9)μJy beam-1 and RA = 07h16m34.55496(7)s, Dec = −19°00′39.4754(8)′′. The e-MERLIN data provided ~3−5σ detections at a position consistent with those of the EVN data. The emission on angular scales intermediate between the EVN and e-MERLIN is consistent with being null. The brightness temperature of the EVN core is Tb ≳ 108.5 K, close to the value previously required to explain the short-term radio variability properties of WISE J0716−19 in terms of interstellar scintillation. Conclusions. Our observations provide direct and independent evidence of a nuclear compact source in WISE J0716−19, a physical scenario without evident connection with FRB 150418. However, the EVN data do not indicate the variability observed with the VLA.
Context. High-resolution millimeter wave very-long-baseline interferometry (mm-VLBI) is an ideal tool for probing the structure at the base of extragalactic jets in detail. The TeV blazar Mrk 501 is ...one of the best targets among BL Lac objects for studying the nature of off-axis jet structures because it shows different jet position angles at different scales. Aims. The aim of this study is to investigate the properties of the off-axis jet structure through high-resolution mm-VLBI images at the jet base and physical parameters such as kinematics, flux densities, and spectral indices. Methods. We performed Very Long Baseline Array (VLBA) observations over six epochs from 2012 February to 2013 February at 43 GHz. Quasi-simultaneous Global Millimeter VLBI Array (GMVA) observations at 86 GHz were performed in May 2012. Results. We discover a new jet component at the northeast direction from the core in all the images at 43 and 86 GHz. The new component shows the off-axis location from the persistent jet extending to the southeast. The 43 GHz images reveal that the scattering of the positions of the NE component is within ~0.2 mas. The 86 GHz data reveals a jet component located 0.75 mas southeast of the radio core. We also discuss the spectral indices between 43 and 86 GHz, where the northeast component has steeper spectral index and the southeast component has comparable or flatter index than the radio core does.
Aims. We investigate the nature of the compact and possibly variable nuclear radio source in the centre of WISEJ0716-19, the proposed host galaxy of the fast radio burst FRB150418. Methods. We ...observed WISEJ0716-19 at 5.0 GHz with the European VLBI Network (EVN) four times between 2016 March 16 and June 2. At three epochs, we simultaneously observed the source with e-MERLIN at the same frequency. Results. We detected a compact source in the EVN data in each epoch with a significance of up to ~8sigma. The four epochs yielded consistent results within their uncertainties for the peak surface intensity and positions. The mean values for these quantities are I sub(peak)= (115 + or - 9) mu Jy beam super(-1) and RA = 07 super(h) 16 super(m) 34.55496(7) super(s), Dec = -19degrees00'39.4754(8)". The e-MERLIN data provided ~3-5sigma detections at a position consistent with those of the EVN data. The emission on angular scales intermediate between the EVN and e-MERLIN is consistent with being null. The brightness temperature of the EVN core is T sub(b)> or = 10 super(8.5) K, close to the value previously required to explain the short-term radio variability properties of WISEJ0716-19 in terms of interstellar scintillation. Conclusions. Our observations provide direct and independent evidence of a nuclear compact source in WISEJ0716-19, a physical scenario without evident connection with FRB150418. However, the EVN data do not indicate the variability observed with the VLA.
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