Revisit Short Term X-ray Spectral Variability of NGC 4151 with Chandra

Abstract

We present new X-ray spectral data for the Seyfert 1 nucleus in NGC 4151 observed with Chandra for 200 ks. A significant ACIS pileup is present, resulting in a non-linear count rate variation during the observation. With pileup corrected spectral fitting, we are able to recover the spectral parameters and find consistency with those derived from unpiled events in the ACIS readout streak and outer region from the bright nucleus. The absorption corrected 2-10 keV flux of the nucleus varied between 6E-11 and 1E-10 erg s^{-1} cm^{-2}. Similar to earlier Chandra studies of NGC 4151 at a historical low state, the photon indices derived from the same absorbed power-law model are Γ~0.7-0.9. However, we show that Γis highly dependent on the adopted spectral models. Fitting the power-law continuum with a Compton reflection component gives Γ~1.1. By including passage of non-uniform X-ray obscuring clouds, we can reproduce the apparent flat spectral states with Γ~1.7, typical for Seyfert 1 AGNs. The same model also fits the hard spectra from previous ASCA "long look" observation of NGC 4151 in the lowest flux state. The spectral variability during our observation can be interpreted as variations in intrinsic soft continuum flux relative to a Compton reflection component that is from distant cold material and constant on short time scale, or variations of partially covering absorber in the line of sight towards the nucleus. An ionized absorber model with ionization parameter \logξ~ 0.8-1.1 can also fit the low-resolution ACIS spectra. If the partial covering model is correct, adopting a black hole mass M_{BH} ~ 4.6E+7 Msun we constrain the distance of the obscuring cloud from the central black hole to be r<~9 light-days, consistent with the size of broad emission line region of NGC 4151 from optical reverberation mapping.

Accepted to ApJ. 41 pages, 11 figures, and 4 tables.

References in corpus (13)

• Occultation measurement of the size of the X-ray emitting region in the Active Galactic Nucleus of NGC 1365
• A Reverberation-Based Mass for the Central Black Hole in NGC 4151
• X-ray Absorption and Reflection in Active Galactic Nuclei
• Feeding versus Feedback in NGC 4151 probed with Gemini NIFS. I. Excitation
• Rapid N_H changes in NGC 4151
• The variable X-ray spectrum of Markarian 766 - I. Principal components analysis
• Suzaku observations of Markarian 335: evidence for a distributed reflector
• The broad band spectrum and variability of NGC 4151 observed by BeppoSAX
• A Photoionization Model For The Soft X-Ray Spectrum Of NGC 4151
• XMM-Newton View of the Multi-Phase Warm Absorber in Seyfert 1 Galaxy NGC985
• The Highest Resolution Chandra View of Photoionization and Jet-Cloud Interaction in the Nuclear Region of NGC 4151
• Suzaku Monitoring of the Iron K Emission Line in the Type 1 AGN NGC 5548
• A Chandra Look at Five of the Broadest Double-Peaked Balmer-Line Emitters

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