70 research outputs found
A complete radio study of SNR G15.4+0.1 from new GMRT observations
No full textAims. The supernova remnant (SNR) G15.4+0.1 is considered to be the possible counterpart of the γ-ray source HESS J1818−154. With the goal of getting a complete view of this remnant and understanding the nature of the gamma-ray flux, we conducted a detailed radio study that includes the search for pulsations and a model of the broadband emission for the SNR G15.4+0.1/HESS J1818−154 system. Methods. Low-frequency imaging at 624 MHz and pulsar observations at 624 and 1404 MHz towards G15.4+0.1 were carried out with the Giant Metrewave Radio Telescope (GMRT). We correlated the new radio data with observations of the source at X-ray and infrared wavelengths from XMM-Newton and Herschel observatories, respectively. To characterize the neutral hydrogen (HI) medium towards G15.4+0.1, we used data from the Southern Galactic Plane Survey. We modelled the spectral energy distribution (SED) using both hadronic and leptonic scenarios. Results. From the combination of the new GMRT observations with existing data, we derived a continuum spectral index alpha = -0.62 +- 0.03 for the whole remnant. The local synchrotron spectra of G15.4+0.1, calculated from the combination of the GMRT data with 330 MHz observations from the Very Large Array, tends to be flatter in the central part of the remnant, accompanying the region where the blast wave is impinging molecular gas. No spectral index trace was found indicating the radio counterpart to the pulsar wind nebula proposed from X-ray observations. In addition, the search for radio pulsations yielded negative results. Emission at far-infrared wavelengths is observed in the region where the SNR shock is interacting with dense molecular clumps. We also identified HI features forming a shell that wraps most of the outer border of G15.4+0.1. Characteristic parameters were estimated for the shocked HI gas. We found that either a purely hadronic or leptonic model is compatible with the broadband emission known so far.Fil: Supán, Jorge Leonardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Castelletti, Gabriela Marta. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Joshi, B. C.. National Centre for Radio Astrophysics; IndiaFil: Surnis, M. P.. National Centre for Radio Astrophysics; IndiaFil: Supanitsky, Alberto Daniel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin
GMRT Galactic Plane Pulsar and Transient Survey and the discovery of PSR J1838+1523
No full textSurnis MP, Joshi BC, McLaughlin MA, et al. GMRT Galactic Plane Pulsar and Transient Survey and the discovery of PSR J1838+1523. Monthly Notices of the Royal Astronomical Society. 2018;478(4):4433-4441.We report the results of a blind pulsar survey carried out with the Giant Metrewave Radio Telescope (GMRT) at 325 MHz. The survey covered about 10 per cent of the region between Galactic longitude 45° < l < 135° and Galactic latitude 1° < |b| < 10° with a dwell time of 1800 s, resulting in the detection of 28 pulsars. One of these, PSR J1838+1523, was previously unknown and has a period of 549 ms and a dispersion measure of 68 pc cm−3. We also present the timing solution of this pulsar obtained from multifrequency timing observations carried out with the GMRT and the Ooty Radio Telescope. The measured flux density of this pulsar is 4.3±1.8 and 1.2±0.7 mJy at 325 and 610 MHz, respectively. This implies a spectral index of −2 ±0.8, thus making the expected flux density at 1.4 GHz to be about 0.2 mJy, which would be just detectable in the high-frequency pulsar surveys like the Northern High Time Resolution Universe pulsar survey. This discovery underlines the importance of low-frequency pulsar surveys in detecting steep spectrum pulsars, thus providing complementary coverage of the pulsar population
Evidence for profile changes in PSR J1713+0747 using the uGMRT
No full textPSR J1713+0747 is one of the most precisely timed pulsars in the international pulsar timing array experiment. This pulsar showed an abrupt profile shape change between 2021 April 16, (MJD 59320) and 2021 April 17 (MJD 59321). In this paper, we report the results from multi-frequency observations of this pulsar carried out with the upgraded Giant Metrewave Radio Telescope (uGMRT) before and after the event. We demonstrate the profile change seen in Band 5 (1260 MHz-1460 MHz) and Band 3 (300 MHz-500 MHz). The timing analysis of this pulsar shows a disturbance accompanying this profile change followed by a recovery with a time-scale of ∼159 days. Our data suggest that a model with chromatic index as a free parameter is preferred over models with combinations of achromaticity with DM bump or scattering bump. We determine the frequency dependence to be ∼ν+1.34. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society
Discovery of an Extremely Intermittent Periodic Radio Source
No full textInternational audienceWe report the serendipitous discovery of an extremely intermittent radio pulsar, PSR J1710-3452, with a relatively long spin period of 10.4 s. The object was discovered through the detection of 97 bright radio pulses in only one out of 66 epochs of observations spanning almost three years. The bright pulses have allowed the source to be localised to a precision of 0.5" through radio imaging. We observed the source location with the Swift X-ray telescope but did not detect any significant X-ray emission. We did not identify any high-energy bursts or multi-frequency counterparts for this object. The solitary epoch of detection hinders the calculation of the surface magnetic field strength, but the long period and the microstructure in the single-pulses resembles the emission of radio-loud magnetars. If this is indeed a magnetar, it is located at a relatively high Galactic latitude (2.9 degree), making it potentially one of the oldest and the most intermittent magnetars known in the Galaxy. The very short activity window of this object is unique and may point towards a yet undetected population of long period, highly transient radio emitting neutron stars
The evolution of nulling in pulsars
No full textNulling is a phenomenon where the emission from a pulsar becomes undetectable (or significantly weaker) for a relatively short period of time, followed by a return to a normal emission state. The time-scale of nulling ranges from a few pulse periods to many hours or even days. The fraction of time a nulling pulsar spends in a null state varies across the population of canonical pulsars, from 0 to 95 per cent. The long-term behaviour of a pulsar’s nulling fraction, however, is currently unknown, as published values have typically been obtained through single observations. Here, we present the first long-term analysis of nulling behaviour in eight pulsars observed in the Parkes Multibeam Pulsar Survey over the course of eight to ten years. We also apply a new Bayesian method for pulse-energy analysis, yielding posterior estimates of the nulling fraction per observation. In several cases, the nulling affects only specific components of the pulse profile, rather than the entirety of the emission. Our analysis reveals that, while most pulsars show no significant trend in their nulling fraction over time, a subset exhibit some evidence for non-zero gradients in nulling fraction. In particular, PSRs J1048–3832, J1745–3040, and J1825–0935 show statistically significant trends over the span of the data. Studying the behaviour of nulling over years and decades is valuable as it can provide insights into the physical emission processes within pulsars. Studying how nulling evolves also provides valuable insights into pulsar evolution and the characterization of the broader pulsar population
A MeerKAT, e-MERLIN, HESS, and Swift search for persistent and transient emission associated with three localized FRBs
No full textWe report on a search for persistent radio emission from the one-off fast radio burst (FRB) 20190714A, as well as from two repeating FRBs, 20190711A and 20171019A, using the MeerKAT radio telescope. For FRB 20171019A, we also conducted simultaneous observations with the High-Energy Stereoscopic System (H.E.S.S.) in very high-energy gamma rays and searched for signals in the ultraviolet, optical, and X-ray bands. For this FRB, we obtain a UV flux upper limit of 1 . 39 ×10 −16 erg cm −2 s −1 Å−1 , X-ray limit of ∼6 . 6 ×10 −14 erg cm −2 s −1 and a limit on the very high energy gamma-ray flux Φ ( E > 120 GeV ) < 1 . 7 ×10 −12 erg cm −2 s −1 . We obtain a radio upper limit of ∼15 μJy beam −1 for persistent emission at the locations of both FRBs 20190711A and 20171019A with MeerKAT. Ho we ver, we detected an almost unresolved (ratio of integrated flux to peak flux is ∼1.7 beam) radio emission, where the synthesized beam size was ∼8 arcsec size with a peak brightness of ∼53 μJy beam −1 at MeerKAT and ∼86 μJy beam −1 at e-MERLIN, possibly associated with FRB 20190714A at z = 0.2365. This represents the first detection of persistent continuum radio emission potentially associated with a (as-yet) non-repeating FRB. If the association is confirmed, one of the strongest remaining distinction between repeaters and non-repeaters would no longer be applicable. A parallel search for repeat bursts from these FRBs revealed no new detections down to a fluence of 0.08 Jy ms for a 1 ms duration burst.J. O. Chibueze, M. Caleb, L. Spitler, H. Ashkar, F. Sch, ussler, B. W. Stappers, C. Venter, I. Heywood, A. M. S. Richards, D. R. A. Williams, M. Kramer, R. Beswick, M. C. Bezuidenhout, R. P. Breton, L. N. Driessen, F. Jankowski, E. F. Keane, M. Malenta, M. Mickaliger, V. Morello, H. Qiu, K. Rajwade, S. Sanidas, M. Surnis, T. W. Scragg, C. R. H. Walker, N. Wrigley, H.E.S.S. Collaboration, F. Aharonian, F. Ait Benkhali, E. O. Ang, uner, M. Backes, V. Baghmanyan, V. Barbosa Martins, R. Batzofin, Y. Becherini, D. Berge, M. B, ottcher, C. Boisson, J. Bolmont, M. de Bony de Lavergne, M. Breuhaus, R. Brose, F. Brun, T. Bulik, F. Cangemi, S. Caroff, S. Casanova, J. Catalano, M. Cerruti, T. Chand, A. Chen, O. U. Chibueze, G. Cotter, P. Cristofari, J. Damascene Mbarubuc ye ye, J. Devin, A. Djannati-Ata, ı, A. Dmytriiev, K. Egberts, J.-P. Ernenwein, A. Fiasson, G. Fichet de Clairfontaine, G. Fontaine, S. Funk, S. Gabici, S. Ghafourizadeh, G. Giavitto, D. Glawion, M.-H. Grondin, M. H, orbe, C. Hoischen, T. L. Holch, Zhiqiu Huang, M. Jamrozy, F. Jankowsky, V. Joshi, I. Jung-Richardt, E. Kasai, K. Katarzy, nski, U. Katz, B. Kh, elifi, W. Klu, zniak, Nu. Komin, K. Kosack, D. Kostunin, A. Lemi, ere, J.-P. Lenain, F. Leuschner, T. Lohse, A. Luashvili, I. Lypova, J. Mackey, D. Malyshev, V. Marandon, P. Marchegiani, A. Marcowith, G. Mart, ı-Devesa, R. Marx, A. Mitchell, R. Moderski, L. Mohrmann, E. Moulin, J. Muller, K. Nakashima, M. de Naurois, A. Nayerhoda, J. Niemiec, A. Priyana Noel, P. O, Brien, S. Ohm, L. Olivera-Nieto, E. de Ona Wilhelmi, M. Ostrowski, S. P ann y, R. D. P arsons, S. Pita, V. Poireau, D. A. Prokhorov, H. Prokoph, G. P, uhlhofer, A. Quirrenbach, P. Reichherzer, A. Reimer, O. Reimer, G. Rowell, B. Rudak, E. Ruiz-Velasco, V. Sahakian, S. Sailer, H. Salzmann, D. A. Sanchez, A. Santangelo, M. Sasaki, H. M. Schutte, U. Schw ank e, J. N. S. Shapopi, A. Specovius, S. Spencer, R. Steenkamp, S. Steinmassl, T . Takahashi, T . Tanaka, C. Thorpe-Morgan, N. Tsuji, C. van Eldik, J. Veh, J. Vink, S. J. Wagner, A. Wierzcholska, Yu Wun Wong, A. Yusafzai, M. Zacharias, D. Zargaryan, A. A. Zdziarski, A. Zech, S. J. Zhu, S. Zouari, and N., Zywuck
A sample of Fast Radio Bursts discovered and localised with MeerTRAP at the MeerKAT telescope
No full textInternational audienceWe present a sample of well-localised Fast Radio Bursts (FRBs) discovered by the MeerTRAP project at the MeerKAT telescope in South Africa. We discovered the three FRBs in single coherent tied-array beams and localised them to an area of ~1 arcmin. We investigate their burst properties, scattering, repetition rates, and localisations in a multi-wavelength context. FRB 20201211A shows hints of scatter broadening but is otherwise consistent with instrumental dispersion smearing. For FRB 20210202D, we discovered a faint post-cursor burst separated by ~200 ms, suggesting a distinct burst component or a repeat pulse. We attempt to associate the FRBs with host galaxy candidates. For FRB 20210408H, we tentatively (0.35 - 0.53 probability) identify a compatible host at a redshift ~0.5. Additionally, we analyse the MeerTRAP survey properties, such as the survey coverage, fluence completeness, and their implications for the FRB population. Based on the entire sample of 11 MeerTRAP FRBs discovered by the end of 2021, we estimate the FRB all-sky rates and their scaling with the fluence threshold. The inferred FRB all-sky rates at 1.28 GHz are and sky d above 0.66 and 3.44 Jy ms for the coherent and incoherent surveys, respectively. The scaling between the MeerTRAP rates is flatter than at higher fluences at the 95 per cent confidence level. There seems to be a deficit of low-fluence FRBs, suggesting a break or turn-over in the rate versus fluence relation below 2 Jy ms. We speculate on cosmological or progenitor-intrinsic origins. The cumulative source counts within our surveys appear consistent with the Euclidean scaling
Radio and X-ray observations of giant pulses from XTE J1810 − 197
No full textInternational audienceWe present the results of two years of radio and X-ray monitoring of the magnetar XTE J1810 − 197 since the radio re-activation in late 2018. Single pulse analysis of radio observations from the Lovell and MkII telescopes at 1564 MHz and the Effelsberg telescope at 6 GHz has resulted in the detection of a total of 91 giant pulses (GPs) between MJDs 58858 and 59117. These GPs appear to be confined to two specific phase ranges (0.473 ≤ ϕ ≤ 0.502 and 0.541 ≤ ϕ ≤ 0.567). We also observe that the first detection of GP emission corresponds to a minimum in the spin-down rate. Simultaneous radio and X-ray observations were performed on MJDs 59009 and 59096. The 0.5–10 keV X-ray spectrum from NICER is well characterized by a two-component blackbody model that can be interpreted as two hot spots on the polar cap of the neutron star. The blackbody temperature decreases with time, consistent with the previous outburst, while the change in the pulsed fraction does not follow the same trend as was seen in the previous outburst. The radio and X-ray flux of XTE J1810 − 197 are correlated during the initial phase of the outburst (MJD 58450 – MJD 58550) and an increase in the radio flux is observed later that may be correlated to the onset of GPs. We argue that the disparity in the evolution of the current outburst compared to the previous one can be attributed to a change in geometry of the neutron star
A complete radio study of SNR G15.4+0.1 from new GMRT observations
No full textAims. The supernova remnant (SNR) G15.4+0.1 is considered to be the possible counterpart of the γ-ray source HESS J1818−154. With the goal of getting a complete view of this remnant and understanding the nature of the γ-ray flux, we conducted a detailed radio study that includes the search for pulsations and a model of the broadband emission for the SNR G15.4+0.1/HESS J1818−154 system.
Methods. Low-frequency imaging at 624 MHz and pulsar observations at 624 and 1404 MHz towards G15.4+0.1 were carried out with the Giant Metrewave Radio Telescope (GMRT). We correlated the new radio data with observations of the source at X-ray and infrared wavelengths from XMM-Newton and Herschel observatories, respectively. To characterize the neutral hydrogen (HI) medium towards G15.4+0.1, we used data from the Southern Galactic Plane Survey. We modelled the spectral energy distribution (SED) using both hadronic and leptonic scenarios.
Results. From the combination of the new GMRT observations with existing data, we derived a continuum spectral index α = −0.62 ± 0.03 for the whole remnant. The local synchrotron spectra of G15.4+0.1, calculated from the combination of the GMRT data with 330 MHz observations from the Very Large Array, tends to be flatter in the central part of the remnant, accompanying the region where the blast wave is impinging molecular gas. No spectral index trace was found indicating the radio counterpart to the pulsar wind nebula proposed from X-ray observations. In addition, the search for radio pulsations yielded negative results. Emission at far-infrared wavelengths is observed in the region where the SNR shock is interacting with dense molecular clumps. We also identified HI features forming a shell that wraps most of the outer border of G15.4+0.1. Characteristic parameters were estimated for the shocked HI gas. We found that either a purely hadronic or leptonic model is compatible with the broadband emission known so far
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