type-II Bursts Research Articles

The variable radio jet of the accreting neutron star the Rapid Burster

ABSTRACT The Rapid Burster is a unique neutron star low-mass X-ray binary system, showing both thermonuclear v-I and accretion-driven Type-II X-ray bursts. Recent studies have demonstrated how coordinated observations of X-ray and radio variability can constrain jet properties of accreting neutron stars – particularly when the X-ray variability is dominated by discrete changes. We present a simultaneous very large array, Swift, and INTErnational Gamma-Ray Astrophysics Laboratory observing campaign of the Rapid Burster to investigate whether its jet responds to Type-II bursts. We observe the radio counterpart of the X-ray binary at its faintest-detected radio luminosity, while the X-ray observations reveal prolific, fast X-ray bursting. A time-resolved analysis reveals that the radio counterpart varies significantly between observing scans, displaying a fractional variability of $38 \pm 5$ per cent. The radio faintness of the system prevents the robust identification of a causal relation between individual Type-II bursts and the evolution of the radio jet. However, based on a comparison of its low-radio luminosity with archival Rapid Burster observations and other accreting neutron stars, and on a qualitative assessment of the X-ray and radio light curves, we explore the presence of a tentative connection between bursts and jet: i.e. the Type-II bursts may weaken or strengthen the jet. The former of those two scenarios would fit with magnetorotational jet models; we discuss three lines of future research to establish this potential relation between Type-II bursts and jets more confidently.

Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations

Radio bursts provide important diagnostics of energetic phenomena of the Sun. In particular, bursts in decimetric and metric wavelengths probe the physical conditions and the energy release processes in the low corona as well as their association with heliospheric phenomena. The advent of spectral radio data with high time and high frequency resolution has provided a wealth of information on phenomena of short duration and narrow bandwidth. Of particular value are spectral data combined with imaging observations at specific frequencies. In this work we briefly review the results of a series of observations comprised from high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-IV/JLS solar radiospectrograph, in conjunction with high time-resolution images from the Nançay Radioheliograph (NRH). Our studies include fine structures embedded in type-IV burst continua (mostly narrow-band “spikes” and intermediate drift “fiber” bursts) and spike-like structures detected near the front of type-II bursts. The implications of the observational results to theoretical models are discussed.

High-resolution observations with ARTEMIS/JLS and the NRH

Context.Narrowband bursts (spikes) are very small duration and bandwidth bursts which appear on dynamic spectra from microwave to decametric frequencies. They are believed to be manifestations of small-scale energy release through magnetic reconnection.Aims.We study the position of the spike-like structures relative to the front of type-II bursts and their role in the burst emission.Methods.We used high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-JLS solar radiospectrograph, in conjunction with high-time-resolution images from the Nançay Radioheliograph (NRH) in order to study spike-like bursts near the front of a type-II radio burst recorded at the west limb during the November 3, 2003 extreme solar event. The spike-like emission in the dynamic spectrum was enhanced by means of high-pass-time filtering.Results.We identified a number of spikes in the NRH images. Due to the lower temporal resolution of the NRH, multiple spikes detected in the dynamic spectrum appeared as single structures in the images. These spikes had an average size of ≈200″ and their observed brightness temperature was 1.4 to 5.6 × 109K, providing a significant contribution to the emission of the type-II burst front. At variance with a previous study on the type-IV associated spikes, we found no systematic displacement between the spike emission and the emission between spikes. At 327.0 MHz, the type II emission was located about 0.3R⊙above the pre-existing continuum emission, which, in turn, was located 0.1R⊙above the western limb.Conclusions.This study, combined with our previous results, indicates that the spike-like chains aligned along the type II burst MHD shock front are not a perturbation of the type II emission, as in the case of type IV spikes, but a manifestation of the type II emission itself. The preponderance of these chains, together with the lack of isolated structures or irregular clusters, points towards some form of small-scale magnetic reconnection, organized along the type-II propagating front.

Multiwavelength observations of a metric type-II event

We have studied a complex metric radio event that originated in a compact flare, observed with the ARTEMIS-JLS radiospectrograph on February 12, 2010. The event was associated with a surge observed at 195 and 304 Å and with a coronal mass ejection observed by instruments on board STEREO A and B near the eastern and western limbs respectively. On the disk the event was observed at ten frequencies by the Nançay Radioheliograph (NRH), in Hαby the Catania observatory, in soft X-rays by GOES SXI and Hinode XRT, and in hard X-rays by RHESSI. We combined these data, together with MDI longitudinal magnetograms, to get as complete a picture of the event as possible. Our emphasis is on two type-II bursts that occurred near respective maxima in the GOES light curves. The first, associated with the main peak of the event, showed an impressive fundamental-harmonic structure, while the emission of the second consisted of three well-separated bands with superposed pulsations. Using positional information for the type-IIs from the NRH and triangulation from STEREO A and B, we found that the type-IIs were associated neither with the surge nor with the disruption of a nearby streamer, but rather with an extreme ultraviolet (EUV) wave probably initiated by the surge. The fundamental-harmonic structure of the first type-II showed a band split corresponding to a magnetic field strength of 18 G, a frequency ratio of 1.95 and a delay of 0.23−0.65 s of the fundamental with respect to the harmonic; moreover it became stationary shortly after its start and then drifted again. The pulsations superposed on the second type-II were broadband and had started before the burst. In addition, we detected another pulsating source, also before the second type-II, polarized in the opposite sense; the pulsations in the two sources were out of phase and hence hardly detectable in the dynamic spectrum. The pulsations had a measurable reverse frequency drift of about 2 s−1.

New Insight into the Rapid Burster by Insight-HXMT

Abstract We report the timing and spectral analyses of the type-II X-ray bursts from the rapid burster (MXB 1730–335) observed by the Hard X-ray Modulation Telescope (Insight-HXMT) and Swift/X-Ray Telescope (XRT). By stacking the long-duration bursts, we find for the first time that the hard X-rays are lagging behind the soft X-rays by 3 s. However, such a lag is not visible for the short-duration bursts, probably because of the poor statistics. For all bursts the energy spectrum is found to be nonthermal, thanks to the broadband coverage of Insight-HXMT. These findings provide new insights into the type-II bursts and require a temporally visible corona for possible interpretation.

Temporal and Spatial Association Between a Solar Flare, CME, and Radio Burst on 19 November 2013

We present multi-wavelength and multi-instrument observations and analysis of a major X 1.0 class flare, radio burst, halo coronal mass ejection (CME), and loop eruption from the solar active region NOAA 11893 on 19 November 2013 (SOL2013-11-19T10:26). The aim of this work is twofold: The first aim to study the evolution of the loop eruption and the second is to find the link between this eruption and radio emissions. Initial signatures of eruption from the solar source region are confirmed using observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot channel at 94 A wavelength. These observations confirm that the source of the CME was associated with a magnetic-loop eruption, which was visible before the flare initiation. The photospheric magnetic configuration displayed a complex network of $\upbeta \updelta $ sunspots. After the eruption, a CME was observed by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph with linear speed and acceleration of $740~\text{km}\,\text{s}^{-1}$ and $-2~\text{m}\,\text{s}^{-2}$ , respectively. Dynamic radio-spectrum observation from the Learmonth Observatory in the metric frequency range shows Type-III and Type-II radio emissions that reveal the field-line opening and coronal-shock formation closely associated with the CME. From the metric Type-II radio observation and assuming Newkirk’s density model, we estimate the shock formation height range of $1.14\,\text{--}\,1.54~\text{R}_{\odot }$ with the corresponding shock speed ( $\approx650~\text{km}\,\text{s}^{-1}$ ). With the heliographic observations from the Nancay heliograph at different frequencies we could disentangle Type-II bursts from Type-III bursts. Likely, the Type-III burst would correspond to the loop eruption while the Type-II comes from the northern flank of the CME.

Imaging and Spectral Observations of a Type-II Radio Burst Revealing the Section of the CME-Driven Shock That Accelerates Electrons

We report on a multi-wavelength analysis of the 26 January 2014 solar eruption involving a coronal mass ejection (CME) and a Type-II radio burst, performed by combining data from various space-and ground-based instruments. An increasing standoff distance with height shows the presence of a strong shock, which further manifests itself in the continuation of the metric Type-II burst into the decameter-hectometric (DH) domain. A plot of speed versus position angle (PA) shows different points on the CME leading edge travelled with different speeds. From the starting frequency of the Type-II burst and white-light data, we find that the shock signature producing the Type-II burst might be coming from the flanks of the CME. Measuring the speeds of the CME flanks, we find the southern flank to be at a higher speed than the northern flank; further the radio contours from Type-II imaging data showed that the burst source was coming from the southern flank of the CME. From the standoff distance at the CME nose, we find that the local Alfven speed is close to the white-light shock speed, thus causing the Mach number to be small there. Also, the presence of a streamer near the southern flank appears to have provided additional favorable conditions for the generation of shock-associated radio emission. These results provide conclusive evidence that the Type-II emission could originate from the flanks of the CME, which in our study is from the the southern flank of the CME.

Solar Radio Bursts Associated with Standing Shock Waves

A number of phenomena with radio bursts in the decimeter and centimeter wavelength ranges similar to type-II bursts in the meter range have been considered. In all phenomena, the radio bursts are characterized by the cessation of frequency drift and its reversal. Analysis of all of the available data on relevant bursts provides evidence of termination shocks with particle accelerations in their fronts. This is confirmed by the generation of new sources of hard X-ray radiation and the radio emission of fast bursts (spikes), fibers, and zebra structures. The sources of drift stripes with a drift turn are located either between the burst loop and the lower shock wave or between the lower and upper shock waves. Estimates of the critical Mach number for common parameters of the burst plasma indicated that the values (Mcr = 1.1–1.3) can easily be observed in the given phenomena and that the radiation can be associated with the Buneman instability. The conditions necessary for the generation of observed electromagnetic radiation bursts can be provided in helmet-shaped magnetic structures in the solar corona.

A modified direct demodulation method applied to Insight-HXMT Galactic plane scanning survey

We present a modified direct demodulation (DD) method for the detection of fast variable objects with the Insight-HXMT Galactic plane survey, which is dedicated to hunting for new transients and monitoring known variable sources. The novelty of the improved DD method is the reconstruction of the modified response matrix, in which the variability of a source is properly handled. Monte Carlo (MC) simulation results demonstrate its power for the detection of variable sources with different time scales, resulting in more accurate location and precise flux monitoring. The application of the method to the Insight-HXMT Galactic plane survey data reveals that the type-II bursts can be well detected for the Rapid Burster MXB 1730–335, with an average rate of 2 bursts min−1 in a manner of the well-known relaxation oscillation.

Predicting the arrival time of CME associated with type-II radio burst using neural networks technique

Type-II radio bursts have been extensively studied as it is considered as a means of inspecting the coronal shock speeds effectively. In this paper, we study the type-II radio burst that occurred on 2 May 2013 through combined observations from the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO), in parallel with the ground-based observation from the DARO-CALLISTO station in Germany. We calculate the shock parameters by employing the clear band-splitting of the type-II burst. By using the Newkirk electron density model, we trace the height at which the emission has been produced. Then we trace the shock speed, the Alfven speed, and the coronal magnetic field strength at heights ranging from 1.96–1.99 Rs. We trace the evolution of the accompanied partial-halo Coronal Mass Ejection (CME) event in the inner corona through combined observations from STEREO-A and SOHO. Finally, we establish a prediction model based on artificial Neural Networks (NN) to estimate the arrival time of the CME (May 4th, 20:18), which is close to the actual arrival time (May 5th, ∼ 08:00).

Detection of spike-like structures near the front of type-II bursts

Aims. We examine high time resolution dynamic spectra for fine structures in type II solar radio bursts Methods. We used data obtained with the acousto-optic spectrograph receiver of the Artemis-JLS (ARTEMIS-IV) solar radio spectrograph in the 450–270 MHz range at 10 ms cadence and identified more than 600 short, narrowband features. Their characteristics, such as instantaneous relative bandwidth and total duration were measured and compared with those of spikes embedded in type IV emissions. Results. Type II associated spikes occur mostly in chains inside or close to the slowly drifting type II emission. These spikes coexist with herringbone and pulsating structures. Their average duration is 96 ms and their average relative bandwidth 1.7%. These properties are not different from those of type IV embedded spikes. It is therefore possible that they are signatures of small-scale reconnection along the type II shock front.

Interplanetary type II radio bursts and their association with CMEs and flares

We study the characteristics of the CMEs and their association with the end-frequency of interplanetary (IP)-type-II bursts by analyzing a set of 138 events (IP-type-II bursts–flares–CMEs) observed during the period 1997–2012. The present analysis consider only the type II bursts having starting frequency $< 14~\mbox{MHz}$ to avoid the extension of coronal type IIs. The selected events are classified into three groups depending on the end-frequency of type IIs as follows, (A) Higher, (B) Intermediate and (C) Lower end-frequency. We compare characteristics of CMEs, flares and type II burst for the three selected groups of events and report some of the important differences. The observed height of CMEs is compared with the height of IP type IIs estimated using the electron density models. By applying a density multiplier ( $m$ ) to this model, the density has been constrained both in the upper corona and in the interplanetary medium, respectively as $m= 1 \mbox{ to } 10$ and $m = 1 \mbox{ to } 3$ . This study indicates that there is a correlation between the observed CME height and estimated type II height for groups B and C events whereas this correlation is absent in group A. In all the groups (A, B & C), the different heights of CMEs and type II reveal that the type IIs are not only observed at the nose but also at the flank of the CMEs.

Heights of Coronal Mass Ejections and Shocks Inferred from Metric and DH Type II Radio Bursts

A set of 27 continuous events that showed extension of metric Type-II radio bursts (m-Type IIs) into the deca–hectometric (DH) domain is considered. The coronal mass ejections (CMEs) associated with this type of continuous event supply more energy to produce space-weather effects than the CMEs that produce Type-II bursts in any one region. Since the heights of shock formation at the start of m-Type IIs were not available from observations, they were estimated using kinematic modeling in previous studies. In the present study, the heights of shock formation during metric and DH Type-II bursts are determined using two methods: i) the CME leading-edge method and ii) a method employing known electron-density models and start/end frequencies. In the first method, assuming that the shocks are generated by the associated CMEs at the leading edge, the height of the CME leading edge (LE) is calculated at the onset and end of m-Type IIs using the kinematic equation with constant acceleration or constant speed. The LE heights of CMEs that are assumed to be the heights of shock formation/end of nearly 79% of m-Type IIs are found to be within the acceptable range of \(1\,\mbox{--}\,3~\mbox{R}_{\odot}\). For other events, the heights are beyond this range, for which the shocks might either have been generated at the CME flanks/flare-blast waves, or the initial CME height might have been different. The CME/shock height at the onset and end of 17 DH Type IIs are found to be in the range of \(2\,\mbox{--}\,6~\mbox{R}_{\odot}\) and within \(30~\mbox{R}_{\odot}\), respectively. In addition, the CME LE heights from observations at the onset and end of metric/DH Type IIs are compared with the heights corresponding to the observed frequency that is determined using the known electron-density models, and they are in agreement with the model results. The heights are also estimated using the space speed available for 15 halo CMEs, and it is found that the difference is smaller at the m-Type II start/end (0.02 to \(0.66~\mbox{R}_{\odot}\)) and slightly greater at the DH Type II end (0.19 to \(1.94~\mbox{R}_{\odot}\)). Finally, the possibility of CME–streamer interactions at the start of DH Type IIs is checked, and it is found that many of the events with streamers have lower start frequencies. In addition, these results are discussed in comparison with the values reported in the literature. This study will be useful to find the source region of metric and DH Type IIs and to understand the CME-shock propagation.

A strongly truncated inner accretion disc in the Rapid Burster

Abstract The neutron star (NS) low-mass X-ray binary (LMXB) the Rapid Burster (RB; MXB 1730-335) uniquely shows both Type I and Type II X-ray bursts. The origin of the latter is ill-understood but has been linked to magnetospheric gating of the accretion flow. We present a spectral analysis of simultaneous Swift, NuSTAR and XMM–Newton observations of the RB during its 2015 outburst. Although a broad Fe K line has been observed before, the high quality of our observations allows us to model this line using relativistic reflection models for the first time. We find that the disc is strongly truncated at $41.8^{+6.7}_{-5.3}$ gravitational radii (∼87 km), which supports magnetospheric Type II burst models and strongly disfavours models involving instabilities at the innermost stable circular orbit. Assuming that the RB magnetic field indeed truncates the disc, we find B = (6.2 ± 1.5) × 108 G, larger than typically inferred for NS LMXBs. In addition, we find a low inclination ($i = 29^{\circ } \pm 2^{\circ }$). Finally, we comment on the origin of the Comptonized and thermal components in the RB spectrum.

Relationship of decametric-hectometric type II radio burst, coronal mass ejections and solar flare observed during 1997–2014

In the present study we have investigated 426 DH Type II radio burst and associated CMEs events observed during the time period of 1997–2014. The starting frequency of most of associated DH type-II bursts (85%) lies in the range of 1–14MHz (364 out of 426) with mean value of starting frequency is ∼11MHz. The study of starting frequency (1–16MHz) of DH type II bursts and heliocentric distance in solar radii indicate that DH type II radio bursts originate from 2.2–4.5 (RS) heliocentric distance in solar radii. We also found that the ∼ 48% DH Type II radio bursts associated CMEs are located between ±40° of solar central disc and we also found that duration of DH type II radio bursts located at solar disc center are more than the duration of DH type II radio bursts located at solar limb. It is found that mean value for linear and initial speed of DH Type II associated CMEs are 1157km/s and 1200km/s, respectively. The CMEs speed are not correlated with duration of DH Type II radio bursts indicate that the durations of DH Type II radio bursts does not depend on speed of CMEs. The study also show that 426 DH type II radio bursts associated CMEs/flares occurred when there is coronal holes(CH) in nearby area and the mean distance between DH type II burst associated CMEs/ flares and boundary of coronal hole (CH) is 26°. The study also shows that there is no relation between drift velocity of DH type II radio bursts and speed of CMEs. The study also indicate that about 45% flares those associated DH Type II radio bursts have duration about 60 minutes and long duration DH Type II radio bursts are associated with X-class flares. We have also discussed that the results obtained in the present investigation in view of latest heliophysics interpretations.

PHYSICAL CONDITIONS OF CORONAL PLASMA AT THE TRANSIT OF A SHOCK DRIVEN BY A CORONAL MASS EJECTION

We report here on the determination of plasma physical parameters across a shock driven by a Coronal Mass Ejection using White Light (WL) coronagraphic images and Radio Dynamic Spectra (RDS). The event analyzed here is the spectacular eruption that occurred on June 7th 2011, a fast CME followed by the ejection of columns of chromospheric plasma, part of them falling back to the solar surface, associated with a M2.5 flare and a type-II radio burst. Images acquired by the SOHO/LASCO coronagraphs (C2 and C3) were employed to track the CME-driven shock in the corona between 2-12 R$_\odot$ in an angular interval of about 110$^\circ$. In these intervals we derived 2-Dimensional (2D) maps of electron density, shock velocity and shock compression ratio, and we measured the shock inclination angle with respect to the radial direction. Under plausible assumptions, these quantities were used to infer 2D maps of shock Mach number $M_\text{A}$ and strength of coronal magnetic fields at the shock's heights. We found that in the early phases (2-4 R$_\odot$) the whole shock surface is super-Alfv\'enic, while later on (i.e. higher up) it becomes super-Alfvenic only at the nose. This is in agreement with the location for the source of the observed type-II burst, as inferred from RDS combined with the shock kinematic and coronal densities derived from WL. For the first time, a coronal shock is used to derive a 2D map of the coronal magnetic field strength over a 10 R$_\odot$ altitude and $\sim 110^\circ$ latitude intervals.

Observations of Near-Simultaneous Split-Band Solar Type-II Radio Bursts at Low Frequencies

We report ground-based radio spectral and polarimeter observations of two successive split-band Type-II bursts that occurred on 20 February 2014 at low frequencies ( ${<}\,100~\mbox{MHz}$ ) in association with a solar coronal mass ejection (CME). The temporal interval between the onset of the two bursts was very small, ≈ one minute. Both of the bursts exhibited fundamental–harmonic structure. The coronal magnetic-field strength [ $B$ ] in the upstream region of the associated magnetohydrodynamic (MHD) shock, estimated from the split-band observations, is in the range $B \approx1.3\,\mbox{--}\,1.1~\mbox{G}$ over the radial distance [ $r$ ] interval $r \approx1.49\,\mbox{--}\,1.58~\mbox{R}_{\odot}$ for the first Type-II burst, and $B \approx1.3\,\mbox{--}\,1.0~\mbox{G}$ over $r \approx1.49\,\mbox{--}\,1.64~\mbox{R}_{\odot}$ for the second Type-II burst. Based on the results obtained, we show that the first and the second Type-II bursts in the present case were likely due to MHD shocks generated by the near-simultaneous interaction of two different regions of the aforementioned CME with a preceding CME and a pre-existing coronal streamer.

Solar type II radio bursts associated with CME expansions as shown by EUV waves

We investigate the physical conditions of the sources of two metric Type-II bursts associated with CME expansions with the aim of verifying the relationship between the shocks and the CMEs, comparing the heights of the radio sources and the heights of the EUV waves associated with the CMEs. The heights of the EUV waves associated with the events were determined in relation to the wave fronts. The heights of the shocks were estimated by applying two different density models to the frequencies of the Type-II emissions and compared with the heights of the EUV waves. For the 13 June 2010 event, with band-splitting, the shock speed was estimated from the frequency drifts of the upper and lower branches of the harmonic lane, taking into account the H/F frequency ratio fH/fF = 2. Exponential fits on the intensity maxima of the branches revealed to be more consistent with the morphology of the spectrum of this event. For the 6 June 2012 event, with no band-splitting and with a clear fundamental lane on the spectrum, the shock speed was estimated directly from the frequency drift of the fundamental emission, determined by linear fit on the intensity maxima of the lane. For each event, the most appropriate density model was adopted to estimate the physical parameters of the radio source. The 13 June 2010 event presented a shock speed of 664-719 km/s, consistent with the average speed of the EUV wave fronts of 609 km/s. The 6 June 2012 event was related to a shock of speed of 211-461 km/s, also consistent with the average speed of the EUV wave fronts of 418 km/s. For both events, the heights of the EUV wave revealed to be compatible with the heights of the radio source, assuming a radial propagation of the shock.

An Interpretation of a Possible Mechanism for the First Ground-Level Enhancement of Solar Cycle 24

It is well known that solar flares and shocks driven by coronal mass ejections (CMEs) are high-energy particle acceleration processes that might cause a high-energy particle event known as a ground-level enhancement (GLE). In this context, we have attempted to understand the processes responsible for the first GLE event (GLE71 17 May 2012 01:50 UT) of Solar Cycle 24. We studied the spatial and spectral data from the Solar Dynamics Observatory (SDO) the Culgoora radio-heliograph, and Wind/WAVES instrument, and analyzed the temporal data of the solar-flare components, the solar radio-flux density, and the electron fluxes from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the Geostationary Operational Environmental Satellite (GOES), the Radio Solar Telescope Network (RSTN), and Wind spacecraft. The flare had two ribbons separated by the neutral line between negative and positive magnetic polarity. Their structure was also almost consistent with the contours of some flare components, which were almost saturated during the flare-peak time. As indicated by the metric–kilometric Type-II burst, and because it extended over a wide heliolongitude (> ≈ 41∘) range, the CME-driven shock was fast enough to cause high-energy particle acceleration at a high altitude in the solar corona. Moreover, the CME and flare-flash phases were aligned along the same direction, which implies that if the CME-driven shock played the leading role in causing the GLE, preceding flare components may have contributed to the shock.

Solar Type II Radio Bursts Recorded by the Compound Astronomical Low-Frequency Low-Cost Instrument for Spectroscopy in Transportable Observatories in Brazil

It is well established that solar Type-II radio bursts are signatures of magnetohydrodynamical (MHD) shock waves propagating outward through the solar corona. Nevertheless, there are long-standing controversies about how these shocks are formed; solar flares and the coronal mass ejections (CMEs) are considered to be the most likely drivers. We present the results of the analysis of four solar Type-II bursts recorded between 20 January 2010 and 17 November 2011 by the Compound Astronomical Low-frequency Low-cost Instrument for Spectroscopy in Transportable Observatories (CALLISTO-BR) (in Brazil), which operates in the frequency range of 45 – 870 MHz. For all four solar Type-II radio bursts, which consisted of one event without band splitting and three split-band variants, the outcomes are consistent with those reported in the literature. All four Type-II radio bursts were accompanied by both solar flares and CMEs, which are associated with the impulsive phase of the flares and, very likely, with the acceleration phase of the CMEs.