اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA Chandra Look at Five of the Broadest Double-Peaked Balmer-Line Emitters
62
0
0.0
(
0
)
تأليف
Iskra V. Strateva
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We study the 0.5-10keV emission of a sample of five of the broadest double-peaked Balmer-line emitters with Chandra. The Balmer lines of these objects originate close (within a few hundred gravitational radii) to the central black holes of the Active Galactic Nuclei (AGNs), and their double-peaked profiles suggest an origin in the AGN accretion disk. We find that four of the five targets can be modeled by simple power-law continua with photon indices (1.6-1.8) typical of similar luminosity AGNs. One object, SDSS J0132-0952, shows evidence of ionized intrinsic absorption. The most-luminous SDSS double-peaked emitter, SDSS J2125-0813, has either an unusual flat spectrum (~1) or is also highly absorbed. It is the only double-peaked emitter for which no external illumination is necessary to account for the Balmer line emission. The strength of the Balmer-line emission in the remaining four objects suggests that the total line flux likely exceeds the viscous energy that can be extracted locally from the accretion disk and external illumination is necessary. All five double-peaked emitters have unusually strong X-ray emission relative to their UV/optical emission, which is the likely source of the external illumination necessary for the production of the observed strong broad lines. On average about 30% of their bolometric luminosities are emitted between 0.5-10keV. The spectral energy distributions of the five double-peaked emitters show the big blue bumps characteristic of radiatively efficient accretion flows. The Balmer line profiles, as well as the optical and X-ray fluxes of the double-peaked emitters, are highly variable on timescales of months to years in the AGN rest frame.
قيم البحث
اقرأ أيضاً
Double-peaked Balmer lines have been observed in about 150 AGNs and were interpreted preferably as emission from relativistic accretion disks. In this paper, we report the discovery of extreme double-peaked lines in SDSS J0942+0900 and SDSS J1417+614
1. The FWHM of the Halpha line ~40,600 km/s in the first object is almost twice as large as the broadest one previously known. By comparing the line profile with accretion disk models, we find that most of the line flux is emitted from a narrow annulus around 100Rg in SDSS J0942+0900, and from a disk of radii between 100 and 400Rg in SDSS J1417+6141. This is the first time that an accretion disk at radii below 100Rg can be directly probed through optical emission lines. A certain asymmetry in the disk is required for both objects. Another much weaker broad Halpha component (EW~20A, and FWHM 4000km/s) is also detected in both objects. Both objects show weak radio emission and strong high-ionization narrow lines.
We summarize the optical, UV, and X-ray properties of double-peaked emitters -- AGN with double-peaked Balmer emission lines believed to originate in the AGN accretion disk. We focus on the X-ray spectroscopic results obtained from a new sample of th
e 16 broadest Balmer line AGN observed with Chandra and Swift.
We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the ASAS-SN survey at an absolute magnitude of $M_Vsim -20.2$ mag, in the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows
a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. High cadence follow-up spectra show broad Balmer lines and He I in early spectra, with He II making an appearance after $sim70-100$ days. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disc emission, and back to smooth at late times. The Balmer lines are unlike typical AGN in that they show a flat Balmer decrement (H$alpha$/H$betasim1.5$), suggesting the lines are collisionally excited rather than being produced via photo-ionisation. The flat Balmer decrement together with the complex profiles suggest that the emission lines originate in a disc chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material due to a possible partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He II may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.
We detected a very strong X-ray decline in the galaxy IRAS23226-3843 within the XMM-Newton slew survey in 2017. Subsequently, we carried out multi-band follow-up studies to investigate this fading galaxy in more detail. We took deep follow-up Swift,
XMM-Newton, and NuSTAR observations in combination with optical SALT spectra of IRAS23226-3843 in 2017. In addition, we reinspected optical, UV, and X-ray data that were taken in the past. IRAS23226-3843 decreased in X-rays by a factor of more than 30 with respect to ROSAT and Swift data taken 10 to 27 years before. The broadband XMM-Newton/NuSTAR spectrum is power-law dominated, with a contribution from photoionized emission from cold gas, likely the outer accretion disk or torus. The optical continuum decreased by 60 percent and the Balmer line intensities decreased by 50 percent between 1999 and 2017. The optical Seyfert spectral type changed simultaneously with the X-ray flux from a clear broad-line Seyfert 1 type in 1999 to a Seyfert 1.9 type in 2017. The Balmer line profiles in IRAS23226-3843 are extremely broad. The profiles during the minimum state indicate that they originate in an accretion disk. The unusual flat Balmer decrement Ha/Hb with a value of 2 indicates a very high hydrogen density of n_(H) > 10 exp(11) cm^(-3) at the center of the accretion disk. IRAS23226-3843 shows unusually strong FeII blends with respect to the broad line widths, in contrast to what is known from Eigenvector 1 studies.
Double-peaked Balmer-line profiles originate in the accretion disks of a few percent of optically selected AGN. The reasons behind the strong low-ionization line emission from the accretion disks of these objects is still uncertain. In this paper, we
characterize the X-ray properties of 39 double-peaked Balmer line AGN, 29 from the Sloan Digital Sky Survey and 10 low optical-luminosity double-peaked emitters from earlier radio-selected samples. We find that the UV-to-X-ray slope of radio-quiet (RQ) double-peaked emitters as a class does not differ substantially from that of normal RQ AGN with similar UV monochromatic luminosity. The radio-loud (RL) double-peaked emitters, with the exception of LINER galaxies, are more luminous in the X-rays than RQ AGN, as has been observed for other RL AGN with single-peaked profiles. The X-ray spectral shapes of double-peaked emitters, measured by their hardness ratios or power-law photon indices, are also largely consistent with those of normal AGN of similar radio-loudness. In practically all cases studied here, external illumination of the accretion disk is necessary to produce the Balmer-line emission, as the gravitational energy released locally in the disk by viscous stresses is insufficient to produce lines of the observed strength. In the Appendix we study the variability of Mrk 926, a double-peaked emitter with several observations in the optical and X-ray bands.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
