Follow-up of 27 radio-quiet gamma-ray pulsars at 110-190 MHz using the international LOFAR station FR606
Follow-up of 27 radio-quiet gamma-ray pulsars at 110-190 MHz using the international LOFAR station FR606
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使用国际 LOFAR 站 FR606 对 110-190 MHz 的 27 颗无线电静伽马射线脉冲星进行跟踪
DOI：
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发表时间：
2021
影响因子：
6.5
通讯作者：
M. Serylak
中科院分区：
文献类型：
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作者：
J. Grießmeier;D. Smith;G. Theureau;T. Johnson;M. Kerr;L. Bondonneau;I. Cognard;M. Serylak
上下文费米大面积望远镜已经探测到超过260个伽马射线天体。其中约四分之一被标记为无线电安静，即它们在1400 MHz下的无线电频率密度< 30 μ Jy，或者它们在无线电域中根本没有被检测到。在非循环伽马射线源中，无线电宁静源的比例更高，约为一半。目标。大多数伽玛射线暴的射电观测都是在300 MHz到2GHz之间进行的。然而，脉冲星的射电超声波随着频率的降低而迅速增加，它们的射电波束往往在低频处变宽。因此，即使在300 MHz以上没有检测到无线电流，其中一些脉冲星也可能在低无线电频率下被检测到。我们的目标是用低频射电观测来检验这一假设。方法.我们用国际低频阵射线（LOFAR）站FR 606在单站模式下观测了27个费米发现的γ射线源。我们使用了LOFAR高频段天线（110 − 190 MHz），每个目标的平均观测时间为13小时。由于无线电频率干扰，部分数据不得不被丢弃。平均而言，我们在删除一个被检测的数据集后，对每个目标保持了9小时的观察，从而使脉冲平均的X射线的灵敏度达到1 - 10 mJy的量级。结果我们没有检测到来自27个来源中任何一个的无线电脉动，并且我们对它们的低频无线电脉动设定了严格的上限。这些未检测到的是兼容的上限来自无线电观测在其他频率。我们还从伽马射线分布图中确定了恒星的几何形状，以确定低频无线电波束预计将穿过地球的恒星。结论.这组观测结果提供了27个无线电安静伽马射线天体在150 MHz下的最具约束力的伽马射线密度上限。尽管在低无线电频率下预期会有波束展宽，但我们的大多数未探测到可以用不利的观测几何来解释;对于其余的观测，特别是那些在较高频率下探测到的双星，未探测到与灵敏度不足是相容的。
Context. The Fermi Large Area Telescope has detected over 260 gamma-ray pulsars. About one quarter of these are labeled as radio- quiet, that is they either have radio flux densities < 30 µ Jy at 1400MHz, or they are not detected at all in the radio domain. In the population of nonrecycled gamma-ray pulsars, the fraction of radio-quiet pulsars is higher, about one half. Aims. Most radio observations of gamma-ray pulsars have been performed at frequencies between 300MHz and 2GHz. However, pulsar radio fluxes increase rapidly with decreasing frequency, and their radio beams often broaden at low frequencies. As a conse- quence, some of these pulsars might be detectable at low radio frequencies even when no radio flux is detected above 300MHz. Our aim is to test this hypothesis with low-frequency radio observations. Methods. We have observed 27 Fermi -discovered gamma-ray pulsars with the international LOw Frequency ARray (LOFAR) station FR606 in single-station mode. We used the LOFAR high band antenna band (110 − 190MHz), with an average observing time of 13h per target. Part of the data had to be discarded due to radio frequency interference. On average, we kept 9h of observation per target after the removal of a ff ected datasets, resulting in a sensitivity for pulse-averaged flux on the order of 1 − 10mJy. Results. We do not detect radio pulsations from any of the 27 sources, and we establish stringent upper limits on their low-frequency radio fluxes. These nondetections are compatible with the upper limits derived from radio observations at other frequencies. We also determine the pulsars’ geometry from the gamma-ray profiles to see for which pulsars the low-frequency radio beam is expected to cross Earth. Conclusions. This set of observations provides the most constraining upper limits on the flux density at 150MHz for 27 radio-quiet gamma-ray pulsars. In spite of the beam-widening expected at low radio frequencies, most of our nondetections can be explained by an unfavorable viewing geometry; for the remaining observations, especially those of pulsars detected at higher frequencies, the nondetection is compatible with insu ffi cient sensitivity.