Multiwavelength observations of Mrk 501 in 2008
Multiwavelength observations of Mrk 501 in 2008
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DOI：
10.1051/0004-6361/201322906
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发表时间：
2015-01-01
影响因子：
6.5
通讯作者：
Kovalev, Y. Y.
中科院分区：
文献类型：
--
作者：
Aleksic, J.;Ansoldi, S.;Kovalev, Y. Y.
上下文。耀变体是各种时间尺度上的可变源，其能量范围从射电到非常高能量（bbb100 GeV，以下简称VHE）。Mrk 501是TeV能量下最亮的耀变体之一，自1996年首次探测到它以来，人们对它进行了广泛的研究。然而，在过去的几年中，在Mrk 501上进行的大多数伽马射线研究都与耀斑活动有关，当时可用的伽马射线仪器更容易进行源探测和表征。我们的目标是详细描述源伽玛射线发射，以及射电到x射线发射，在非耀斑（低）活动期间，这比偶尔的耀斑（高）活动研究得少。我们于2008年3月至5月在Mrk 501上组织了多波长（MW）运动。这项多仪器工作包括北半球最敏感的VHE伽马射线仪器，即成像大气切伦科夫望远镜MAGIC和VERITAS，以及Swift、RXTE、F-GAMMA、gaspwebt和其他合作和仪器。这为Mrk 501在整个活动中提供了广泛的能量和时间覆盖。Mrk 501在活动期间被发现处于低活动状态，其VHE通量在蟹状星云通量的10%-20%范围内。然而，用各种仪器检测到明显的通量变化，随能量变化的趋势越来越大，x射线和甚高能辐射通量之间初步存在相关性。在均匀的单区同步加速器自康普顿模型中，两种不同发射状态下的宽带光谱能量分布可以得到充分的描述，电子数密度的增加可以描述（稍）高的状态。单区域SSC模型可以充分描述在MW运动覆盖的两个月期间源的宽带频谱能量分布。这与先前对该源在燃烧和非燃烧状态下的宽带发射的研究一致。我们首次报道了在如此低的VHE活动期间x射线与VHE的初步相关性。尽管在燃烧活动期间，x射线和VHE之间的这种正相关性已经被多次报道，但这一正相关性表明，在非燃烧活动期间主导x射线/VHE发射的机制与在燃烧活动期间负责发射的机制并没有本质上的不同。
Context. Blazars are variable sources on various timescales over a broad energy range spanning from radio to very high energy (>100 GeV, hereafter VHE). Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. However, most of the gamma-ray studies performed on Mrk 501 during the past years relate to flaring activity, when the source detection and characterization with the available gamma-ray instrumentation was easier to perform.Aims. Our goal is to characterize the source gamma-ray emission in detail, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity.Methods. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE gamma-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. This provided extensive energy and temporal coverage of Mrk 501 throughout the entire campaign.Results. Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy and a tentative correlation between the X-ray and VHE fluxes. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density.Conclusions. The one-zone SSC model can adequately describe the broadband spectral energy distribution of the source during the two months covered by the MW campaign. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during such a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity.