GCRT J1742-3001: A New Radio Transient Toward the Galactic Center (original) (raw)
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A Faint, Steep Spectum Burst from the Radio Transient GCRT J1745-3009
2007
GCRT J1745-3009 is a transient bursting radio source located in the direction of the Galactic center. It was discovered in a 330 MHz VLA observation from 2002 September 30--October 1 and subsequently rediscovered in a 330 MHz GMRT observation from 2003 September 28 by Hyman et al. Here we report a new radio detection of the source in 330 MHz GMRT data taken on 2004 March 20. The observed properties of the single burst detected differ significantly from those measured previously, suggesting that GCRT J1745-3009 was detected in a new physical state. The 2004 flux density was ~0.05 Jy, ~10x weaker than the single 2003 burst and ~30x weaker than the five bursts detected in 2002. We derive a very steep spectral index, alpha = -13.5 +/- 3.0, across the bandpass, a new result previously not detectable due to limitations in the analysis of the 2002 and 2003 observations. Also, the burst was detected for only ~2 min., in contrast to the 10 min. duration observed in the earlier bursts. Due to sparse sampling, only the single burst was detected in 2004, as in the 2003 epoch, and we cannot rule out additional undetected bursts that may have occurred with the same ~77 min. periodicity observed in 2002 or with a different periodicity. Considering our total time on source throughout both our archival and active monitoring campaigns, we estimate the source exhibits detectable bursting activity ~7% of the time.
The Astrophysical Journal
The origin of the high-frequency radio emission detected from several magnetars is poorly understood. In this paper, we report the 40 GHz properties of SGR J1745−29 measured using Jansky Very Large Array (JVLA) and Robert C. Byrd Green Bank Telescope (GBT) observations between 2013 October 26 and 2014 May 31. Our analysis of a Q-band (45 GHz) GBT observation on 2014 April 10 resulted in the earliest detection of pulsed radio emission at high frequencies (20 GHz ); we found that the average pulse has a singly peaked profile with width 75 ms (∼2% of the 3.764 s pulse period) and an average pulsed flux density of ∼100 mJy. We also detected very bright, short 10 ms < () single pulses during ∼70% of this neutron star's rotations, and the peak flux densities of these bright pulses follow the same log-normal distribution as measured at 8.5 GHz. Additionally, our analysis of contemporaneous JVLA observations suggest that its 41/44 GHz flux density varied between ∼1-4 mJy during this period, with a 2ć hange observed on ∼20minute timescales during a JVLA observation on 2014 May 10. Such a drastic change over short timescales is inconsistent with the radio emission resulting from a shock powered by the magnetar's supersonic motion through the surrounding medium, but consistent with pulsed emission generated in its magnetosphere.
New Results on Emission from the GCRT
Proceedings of Bursts, Pulses and Flickering: wide-field monitoring of the dynamic radio sky — PoS(Dynamic2007), 2008
is a transient bursting radio source located ∼1 • away from the Galactic center with a brightness temperature possibly in excess of 10 12 Kelvin. It was discovered from a 330 MHz VLA archival observation in 2002 and was rediscovered in a 330 MHz GMRT observation in 2003 by Hyman et al. Here we report a new radio detection of the source in 330 MHz GMRT data taken on 2004 March 20. The properties of this single burst differ significantly from those observed previously. The 2004 flux density was 0.05 Jy, about an order of magnitude lower than the single 2003 burst and the five bursts detected in 2002. We derive a very steep spectral index, α = −13.5 ± 3.0, across a bandwidth of 32 MHz, a new result not obtained from earlier 2 detections. This burst was detected for only 2 minutes in the middle of a scan, in contrast to the 10 minute duration observed in the earlier bursts.
The Astrophysical Journal, 2011
We present new Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz of 18 X-ray bright galaxy groups. These observations are part of an extended project, presented here and in future papers, which combines low-frequency radio and X-ray data to investigate the interaction between central active galactic nuclei (AGN) and the intra-group medium (IGM). The radio images show a very diverse population of group-central radio sources, varying widely in size, power, morphology and spectral index. Comparison of the radio images with Chandra and XMM-Newton X-ray images shows that groups with significant substructure in the X-ray band and marginal radio emission at > ∼ 1 GHz host low-frequency radio structures that correlate with substructures in IGM. Radio-filled X-ray cavities, the most evident form of AGN/IGM interaction in our sample, are found in half of the systems, and are typically associated with small, low-or mid-power double radio sources. Two systems, NGC5044 and NGC4636, possess multiple cavities, which are isotropically distributed around the group center, possibly due to group weather. In other systems the radio/X-ray correlations are less evident. However, the AGN/IGM interaction can manifest itself through the effects of the high-pressure medium on the morphology, spectral properties and evolution of the radio-emitting plasma. In particular, the IGM can confine fading radio lobes in old/dying radio galaxies and prevent them from dissipating quickly. Evidence for radio emission produced by former outbursts that coexist with current activity is found in six groups of the sample.
Recurrent Radio Outbursts at the Center of the NGC 1407 Galaxy Group
The Astrophysical Journal, 2012
We present deep Giant Metrewave Radio Telescope (GMRT) radio observations at 240, 330 and 610 MHz of the complex radio source at the center of the NGC1407 galaxy group. Previous GMRT observations at 240 MHz revealed faint, diffuse emission enclosing the central twin-jet radio galaxy. This has been interpreted as an indication of two possible radio outbursts occurring at different times. Both the inner double and diffuse component are detected in the new GMRT images at high levels of significance. Combining the GMRT observations with archival Very Large Array data at 1.4 and 4.9 GHz, we derive the total spectrum of both components. The inner double has a spectral index α = 0.7, typical for active, extended radio galaxies, whereas the spectrum of the large-scale emission is very steep, with α = 1.8 between 240 MHz and 1.4 GHz. The radiative age of the large-scale component is very long, ∼ 300 Myr, compared to ∼30 Myr estimated for the central double, confirming that the diffuse component was generated during a former cycle of activity of the central galaxy. The current activity have so far released an energy which is nearly one order of magnitude lower than that associated with the former outburst. The group X-ray emission in the Chandra and XMM-Newton images and extended radio emission show a similar swept-back morphology. We speculate that the two structures are both affected by the motion of the group core, perhaps due to the core sloshing in response to a recent encounter with the nearby elliptical galaxy NGC 1400.
J021659-044920: a relic giant radio galaxy atz ∼ 1.3
Monthly Notices of the Royal Astronomical Society, 2015
We report the discovery of a relic Giant Radio Galaxy (GRG) J021659-044920 at redshift z ∼ 1.3 that exhibits large-scale extended, nearly co-spatial, radio and X-ray emission from radio lobes, but no detection of Active Galactic Nuclei core, jets and hotspots. The total angular extent of the GRG at the observed frame 0.325 GHz, using Giant Metrewave Radio Telescope observations is found to be ∼2.4 arcmin, that corresponds to a total projected linear size of ∼1.2 Mpc. The integrated radio spectrum between 0.240 and 1.4 GHz shows high spectral curvature (α 1.4 GHz 0.610 GHz-α 0.325 GHz 0.240 GHz > 1.19) with sharp steepening above 0.325 GHz, consistent with relic radio emission that is ∼8 × 10 6 yr old. The radio spectral index map between observed frame 0.325 and 1.4 GHz for the two lobes varies from 1.4 to 2.5 with the steepening trend from outer-end to inner-end, indicating backflow of plasma in the lobes. The extended X-ray emission characterized by an absorbed power law with photon index ∼1.86 favours inverse-Compton scattering of the Cosmic Microwave Background (ICCMB) photons as the plausible origin. Using both X-ray and radio fluxes under the assumption of ICCMB we estimate the magnetic field in the lobes to be 3.3 µG. The magnetic field estimate based on energy equipartition is ∼3.5 µG. Our work presents a case study of a rare example of a GRG caught in dying phase in the distant Universe.
J021659-044920: a relic giant radio galaxy at z ∼ 1.3
2015
We report the discovery of a relic Giant Radio Galaxy (GRG) J021659-044920 at redshift z∼1.3 that exhibits large-scale extended, nearly co-spatial, radio and X-ray emission from radio lobes, but no detection of Active Galactic Nuclei core, jets and hotspots. The total angular extent of the GRG at the observed frame 0.325 GHz, using Giant Metrewave Radio Telescope observations is found to be ∼ 2.4 arcmin, that corresponds to a total projected linear size of ∼ 1.2 Mpc. The integrated radio spectrum between 0.240 and 1.4 GHz shows high spectral curvature (α1.4 GHz0.610 GHz−α0.325 GHz0.240 GHz > 1.19) with sharp steepening above 0.325 GHz, consistent with relic radio emission that is ∼ 8 × 106 yr old. The radio spectral index map between observed frame 0.325 and 1.4~GHz for the two lobes varies from 1.4 to 2.5 with the steepening trend from outer-end to inner-end, indicating backflow of plasma in the lobes. The extended X-ray emission characterized by an absorbed power-law with photon index ∼ 1.86 favours inverse-Compton scattering of the Cosmic Microwave Background (ICCMB) photons as the plausible origin. Using both X-ray and radio fluxes under the assumption of ICCMB we estimate the magnetic field in the lobes to be 3.3 μG. The magnetic field estimate based on energy equipartition is ∼ 3.5 μG. Our work presents a case study of a rare example of a GRG caught in dying phase in the distant Universe.
Two new X-ray transients near the Galactic Centre
Advances in Space Research, 1991
Analysis of data obtained in 1989 with the X-ray widefield camera TTM of the ROENTGEN-KVANT-M~observatory revealed the existence of two new X-ray transients: KS1732-273 and KS1741-293, the latter of which is situated in the error boxes of MXB1742-29 as well as MXB1743-29. Significant detections of KS].741-293 were made on 3 consecutive days during which it exhibited 2 bursts.
A Radio Transient 0.1 Parsecs from Sagittarius A*
The Astrophysical Journal, 2005
We report the discovery of a transient radio source 2.7 arcsec (0.1 pc projected distance) South of the Galactic Center massive black hole, Sagittarius A*. The source flared with a peak of at least 80 mJy in March 2004. The source was resolved by the Very Large Array into two components with a separation of ∼ 0.7 arcsec and characteristic sizes of ∼ 0.2 arcsec. The two components of the source faded with a power-law index of 1.1 ± 0.1. We detect an upper limit to the proper motion of the Eastern component of ∼ 3 × 10 3 km s −1 relative to Sgr A*. We detect a proper motion of ∼ 10 4 km s −1 for the Western component relative to Sgr A*. The transient was also detected at X-ray wavelengths with the Chandra X-ray Observatory and the XMM-Newton telescope and given the designation CXOGC J174540.0-290031. The X-ray source falls in between the two radio components. The maximum luminosity of the X-ray source is ∼ 10 36 erg s −1 , significantly sub-Eddington. The radio jet flux density predicted by the X-ray/radio correlation for X-ray binaries is orders of magnitude less than the measured flux density. We conclude that the radio transient is the result of a bipolar jet originating in a single impulsive event from the X-ray source and interacting with the dense interstellar medium of the Galactic Center.