分类： 天文学 >> 天文学 提交时间： 2023-02-19
Shivani Bhandari
Alexa C. Gordon
Danica R. Scott
Lachlan Marnoch
Navin Sridhar
Pravir Kumar
Clancy W. James
Hao Qiu
Keith W. Bannister
Adam T. Deller
Tarraneh Eftekhari
Wen-fai Fong
Marcin Glowacki
J. Xavier Prochaska
Stuart D. Ryder
Ryan M. Shannon
Sunil Simha
摘要： We present the discovery of as-of-yet non-repeating Fast Radio Burst (FRB) with the Australian Square Kilometer Array Pathfinder (ASKAP) as a part of the Commensal Real-time ASKAP Fast Transients (CRAFT) Survey. FRB 20210117A was detected at the center frequency of 1271.5 MHz with a dispersion measure (DM) of $728.95\pm 0.01$ pc cm$^{-3}$. The sub-arcsecond localization of the burst led to the identification of its host galaxy at a $z=0.214(1)$. Optical observations reveal the host to be a dwarf galaxy with little on-going star formation, very different to the dwarf host galaxies of known repeating FRBs 20121102A, and 20190520B. We find an excess DM contribution from the host and attribute it to the FRB's local environment. We do not find any radio emission from the FRB site or host galaxy. The low magnetized environment and lack of a persistent radio source (PRS) indicate that the FRB source is older than those found in other dwarf host galaxies and establish the diversity of FRB sources in dwarf galaxy environments. We find our observations to be best described by the hypernebula model, where FRB is powered by accretion-jet from a hyper-accreting black hole. Finally, our high-time resolution analysis reveal burst characteristics similar to those seen in repeating FRBs. We encourage follow-up observations of FRB 20210117A to establish any repeating nature.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Małgorzata Curyło
Timothy T. Pennucci
Matthew Bailes
N. D. Ramesh Bhat
Andrew D. Cameron
Shi Dai
George Hobbs
Agastya Kapur
Richard N. Manchester
Rami Mandow
Matthew T. Miles
Christopher J. Russell
Daniel J. Reardon
Ryan M. Shannon
Renée Spiewak
Andrew Zic
Xing-Jiang Zhu
摘要： In 2018 an ultra-wide-bandwidth low-frequency (UWL) receiver was installed on the 64-m Parkes Radio Telescope enabling observations with an instantaneous frequency coverage from 704 to 4032 MHz. Here, we present the analysis of a three-year data set of 35 millisecond pulsars observed with the UWL by the Parkes Pulsar Timing Array (PPTA), using wideband timing methods. The two key differences compared to typical narrow-band methods are, firstly, generation of two-dimensional templates accounting for pulse shape evolution with frequency and, secondly, simultaneous measurements of the pulse time-of-arrival (ToA) and dispersion measure (DM). This is the first time that wideband timing has been applied to a uniform data set collected with a single large-fractional bandwidth receiver, for which such techniques were originally developed. As a result of our study, we present a set of profile evolution models and new timing solutions including initial noise analysis. Precision of our ToA and DM measurements is in the range of 0.005 $-$ 2.08 $\mu$s and (0.043$-$14.24)$\times10^{-4}$ cm$^{-3}$ pc, respectively, with 94% of the pulsars achieving a median ToA uncertainty of less than 1 $\mu$s.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Alexa C. Gordon
Wen-fai Fong
Charles D. Kilpatrick
Tarraneh Eftekhari
Joel Leja
J. Xavier Prochaska
Anya E. Nugent
Shivani Bhandari
Peter K. Blanchard
Manisha Caleb
Cherie K. Day
Adam T. Deller
Yuxin Dong
Marcin Glowacki
Kelly Gourdji
Alexandra G. Mannings
Elizabeth K. Mahoney
Lachlan Marnoch
Adam A. Miller
Kerry Paterson
摘要： We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our sample comprises six repeating FRBs and 17 apparent non-repeaters. We present 82 new photometric and eight new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing non-parametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of $\approx 10^{9.8}\,M_{\odot}$, mass-weighted age of $\approx 5.1$~Gyr, and ongoing star formation rate $\approx 1.2\,M_{\odot}$~yr$^{-1}$ but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 91\% (21/23 hosts) are star-forming, one is transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least two FRBs originate in less active environments, both of which are apparent non-repeaters. Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and non-repeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of non-repeaters arise in more optically luminous galaxies. While four of the galaxies with the most clear and prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last $\lesssim 100$~Myr, one non-repeating host shows this SFH. Our results support the young magnetar model for most FRBs in which their progenitors formed through core-collapse supernovae, but the presence of some FRBs in less active environments suggests a fraction form through more delayed channels.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiao Xue
Zi-Qing Xia
Xingjiang Zhu
Yue Zhao
Jing Shu
Qiang Yuan
N. D. Ramesh Bhat
Andrew D. Cameron
Shi Dai
Yi Feng
Boris Goncharov
George Hobbs
Eric Howard
Richard N. Manchester
Aditya Parthasarathy
Daniel J. Reardon
Christopher J. Russell
Ryan M. Shannon
Renée Spiewak
Nithyanandan Thyagarajan
摘要： The nature of dark matter remains obscure in spite of decades of experimental efforts. The mass of dark matter candidates can span a wide range, and its coupling with the Standard Model sector remains uncertain. All these unknowns make the etection of dark matter extremely challenging. Ultralight dark matter, with $m \sim10^{-22}$ eV, is proposed to reconcile the disagreements between observations and predictions from simulations of small-scale structures in the cold dark matter paradigm, while remaining consistent with other observations. Because of its large de Broglie wavelength and large local occupation number within galaxies, ultralight dark matter behaves like a coherently oscillating background field with an oscillating frequency dependent on its mass. If the dark matter particle is a spin-1 dark photon, such as the $U(1)_B$ or $U(1)_{B-L}$ gauge boson, it can induce an external oscillating force and lead to displacements of test masses. Such an effect would be observable in the form of periodic variations in the arrival times of radio pulses from highly stable millisecond pulsars. In this study, we search for evidence of ultralight dark photon dark matter (DPDM) using 14-year high-precision observations of 26 pulsars collected with the Parkes Pulsar Timing Array. While no statistically significant signal is found, we place constraints on coupling constants for the $U(1)_B$ and $U(1)_{B-L}$ DPDM. Compared with other experiments, the limits on the dimensionless coupling constant $\epsilon$ achieved in our study are improved by up to two orders of magnitude when the dark photon mass is smaller than $3\times10^{-22}$~eV ($10^{-22}$~eV) for the $U(1)_{B}$ ($U(1)_{B-L}$) scenario.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiao Xue
Ligong Bian
Jing Shu
Qiang Yuan
Xingjiang Zhu
N. D. Ramesh Bhat
Shi Dai
Yi Feng
Boris Goncharov
George Hobbs
Eric Howard
Richard N. Manchester
Christopher J. Russell
Daniel J. Reardon
Ryan M. Shannon
Renée Spiewak
Nithyanandan Thyagarajan
Jingbo Wang
摘要： A cosmological first-order phase transition is expected to produce a stochastic gravitational wave background. If the phase transition temperature is on the MeV scale, the power spectrum of the induced stochastic gravitational waves peaks around nanohertz frequencies, and can thus be probed with high-precision pulsar timing observations. We search for such a stochastic gravitational wave background with the latest data set of the Parkes Pulsar Timing Array. We find no evidence for a Hellings-Downs spatial correlation as expected for a stochastic gravitational wave background. Therefore, we present constraints on first-order phase transition model parameters. Our analysis shows that pulsar timing is particularly sensitive to the low-temperature ($T \sim 1 - 100$ MeV) phase transition with a duration $(\beta/H_*)^{-1}\sim 10^{-2}-10^{-1}$ and therefore can be used to constrain the dark and QCD phase transitions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiao Xue
Ligong Bian
Jing Shu
Qiang Yuan
Xingjiang Zhu
N. D. Ramesh Bhat
Shi Dai
Yi Feng
Boris Goncharov
George Hobbs
Eric Howard
Richard N. Manchester
Christopher J. Russell
Daniel J. Reardon
Ryan M. Shannon
Renée Spiewak
Nithyanandan Thyagarajan
Jingbo Wang
摘要： A cosmological first-order phase transition is expected to produce a stochastic gravitational wave background. If the phase transition temperature is on the MeV scale, the power spectrum of the induced stochastic gravitational waves peaks around nanohertz frequencies, and can thus be probed with high-precision pulsar timing observations. We search for such a stochastic gravitational wave background with the latest data set of the Parkes Pulsar Timing Array. We find no evidence for a Hellings-Downs spatial correlation as expected for a stochastic gravitational wave background. Therefore, we present constraints on first-order phase transition model parameters. Our analysis shows that pulsar timing is particularly sensitive to the low-temperature ($T \sim 1 - 100$ MeV) phase transition with a duration $(\beta/H_*)^{-1}\sim 10^{-2}-10^{-1}$ and therefore can be used to constrain the dark and QCD phase transitions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Wen-fai Fong
Yuxin Dong
Joel Leja
Shivani Bhandari
Cherie K. Day
Adam T. Deller
Pravir Kumar
J. Xavier Prochaska
Danica R. Scott
Keith W. Bannister
Tarraneh Eftekhari
Alexa C. Gordon
Kasper E. Heintz
Clancy W. James
Charles D. Kilpatrick
Elizabeth K. Mahony
Alicia Rouco Escorial
Stuart D. Ryder
Ryan M. Shannon
Nicolas Tejos
摘要： We present the Australian Square Kilometre Array Pathfinder (ASKAP) localization and follow-up observations of the host galaxy of the repeating fast radio burst (FRB) source, FRB20201124A, the fifth such extragalactic repeating FRB with an identified host. From spectroscopic observations using the 6.5-m MMT Observatory, we derive a redshift of $z=0.0979 \pm 0.0001$, a star formation rate inferred from H$\alpha$ emission of SFR(H$\alpha$) $\approx 2.1 M_{\odot}$ yr$^{-1}$, and a gas-phase metallicity of 12+log(O/H)$\approx 9.0$. By jointly modeling the 12-filter optical-mid-infrared (MIR) photometry and spectroscopy of the host, we infer a median stellar mass of $\approx 2 \times 10^{10} M_{\odot}$, internal dust extinction of $A_V\approx 1-1.5$ mag, and a mass-weighted stellar population age of $\approx 5-6$ Gyr. Connecting these data to the radio and X-ray observations, we cannot reconcile the broad-band behavior with strong AGN activity and instead attribute the dominant source of persistent radio emission to star formation, likely originating from the circumnuclear region of the host. The modeling also indicates a hot dust component contributing to the MIR luminosity at a level of $\approx 10-30\%$. We model the host galaxy's star formation and mass assembly histories, finding that the host assembled $>90\%$ of its mass by 1 Gyr ago and exhibited a fairly constant SFR for most of its existence, with no clear evidence of past star-burst activity.
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