Highly Ionized Warm Absorbers in AGNs: Simulations with the IXO Calorimeter (2009)
Tombesi, F., Cappi, M., Yaqoob, T., Reeves, J., Palumbo, G. G. C.
We have performed several simulations in order to test the scientific capabilities of the IXO calorimeter, with particular emphasis on the detection of absorption lines in the 3-11keV band. We...
On the efficiency of production of the Fe Kalpha emission line in neutral matter (2009)
Yaqoob, T., Murphy, K. D., Miller, L., Turner, T. J.
The absolute luminosity of the Fe Kalpha emission line from matter illuminated by X-rays in astrophysical sources is nontrivial to calculate except when the line-emitting medium is optically-thin to...
On the Prospect of Constraining Black-Hole Spin Through X-ray Spectroscopy of Hotspots (2009)
Murphy, K. D., Yaqoob, T., Dovčiak, M., Karas, V.
Future X-ray instrumentation is expected to allow us to significantly improve the constraints derivedfrom the Fe K lines in AGN, such as the black-hole angular momentum (spin) and the inclination...
Cappi, M., Tombesi, F., Bianchi, S., Dadina, M., Giustini, M., Malaguti, G., ...
There is growing evidence for the presence of blueshifted Fe K absorption lines in a number of radio-quiet AGNs and QSOs. These may be fundamental to probe flow dynamics near supermassive black...
An X-ray Spectral Model for Compton-Thick Toroidal Reprocessors (2009)
The central engines of both type 1 and type 2 AGNs are thought to harbor a toroidal structure that absorbs and reprocesses high-energy photons from the central X-ray source. If the reprocessor is...
A Suzaku observation of the ULIRG IRAS19254-7245: disclosing the AGN component (2009)
Braito, V., Reeves, J. N., Della Ceca, R., Ptak, A., Risaliti, G., Yaqoob, T.
We discuss here a long Suzaku observation of IRAS 19254-7245 (also known as the Superantennae), one of the brightest and well studied Ultra Luminous Infrared Galaxies in the local Universe. This long...
The Suzaku Observation of NGC 3516: Complex Absorption and the Broad and Narrow Fe K Lines (2007)
Markowitz, A., Reeves, J. N., Miniutti, G., Serlemitsos, P., Kunieda, H., Yaqoob, T., ...
We present results from a 150 ksec Suzaku observation of the Seyfert 1.5 NGC 3516 in October 2005. The source was in a relatively highly absorbed state. Our best-fit model is consistent with the...
Relativistic Iron K Emission and absorption in the Seyfert 1.9 galaxy MCG-5-23-16 (2007)
Braito, V., Reeves, J. N., Dewangan, G. C., George, I., Griffiths, R. E., Markowitz, A., ...
We present the results of the simultaneous deep XMM and Chandra observations of the bright Seyfert 1.9 galaxy MCG-5-23-16, which is thought to have one of the best known examples of a...
Markowitz, A., Takahashi, T., Watanabe, S., Nakazawa, K., Fukazawa, Y., Kokubun, M., ...
A Suzaku observation of the nucleus of the radio-loud AGN Centaurus A in 2005 has yielded a broadband spectrum spanning 0.3 to 250 keV. The net exposure times after screening were: 70 ks per X-ray...
Gliozzi, M., Sambruna, R. M., Eracleous, M., Yaqoob, T.
We present the results from simultaneous chandra and rxte observations of the X-ray bright Broad-Line Radio Galaxy (BLRG) 3C 382. The long (120 ks) exposure with chandra HETG allows a detailed study...
Suzaku Observations of Iron Lines and Reflection in AGN (2006)
Reeves, J. N., Fabian, A. C., Kataoka, J., Kunieda, H., Markowitz, A., Miniutti, G., ...
Initial results on the iron K-shell line and reflection component in several AGN observed as part of the Suzaku Guaranteed time program are reviewed. This paper discusses a small sample of...
Suzaku observation of NGC 3516: complex absorption and the broad and narrow Fe K lines (2006)
Markowitz, A., Reeves, J. N., Serlemitsos, P., Yaqoob, T., Awaki, H., Fabian, A., ...
The iron emission line complex of MCG-5-23-16: the long XMM-Newton look (2006)
Braito, V., Reeves, J. N., Dewangan, G., George, I., Griffiths, R., Markowitz, A., ...
Reeves, J.N., Pounds, Kenneth A., Uttley, P., Kraemer, S., Mushotzky, R., Yaqoob, T., ...
The definitive version of this paper, with enhancements, is available from http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v633n2/19868/19868.html
Ionization structure of the warm wind in NGC 5548 (2005)
Steenbrugge, K. C., Kaastra, J. S., Crenshaw, D. M., Kraemer, S. B., Arav, N., George, I. M., ...
We present the results from our 140 ks XMM-Newton and 500 ks Chandra observation of NGC 5548. The velocity structure of the X-ray absorber is consistent with the velocity structure measured in the...
The Spectral Energy Distribution of the Seyfert galaxy Ton S180 (2005)
Turner, T. J., Romano, P., Kraemer, S. B., George, I. M., Yaqoob, T., Crenshaw, D. M., ...
We present spectral results from a multi-satellite, broad-band campaign on the Narrow-line Seyfert 1 galaxy Ton S180 performed at the end of 1999. We discuss the spectral-energy distribution of the...
Reeves, J. N., Pounds, K., Uttley, P., Kraemer, S., Mushotzky, R, Yaqoob, T., ...
We report the detection of redshifted iron K-alpha absorption lines in the Chandra LETG spectrum of the narrow-line quasar, PG 1211+143. The absorption lines are observed at 4.22 keV and 4.93 keV in...
Relativistic outflow in CXO CDFS J033260.0-274748 (2005)
Wang, J. X., Wang, T. G., Tozzi, P., Giacconi, R., Hasinger, G., Kewley, L., ...
In this letter we report the detection of a strong and extremely blueshifted X-ray absorption feature in the 1 Ms Chandra spectrum of CXO CDFS J033260.0-274748, a quasar at z = 2.579 with L_2-10keV ~...
Constraints on hot metals in the Vicinity of the Galaxy (2005)
McKernan, B., Yaqoob, T., Reynolds, C. S.
We have searched for evidence of soft X-ray absorption by hot metals in the vicinity of the Galaxy in the spectra of a small sample of fifteen Type I AGN observed with the high resolution X-ray...
Chandra High-Resolution X-ray Spectroscopy of the Fe K Line in the Seyfert 1 Galaxy NGC 3783 (2005)
Yaqoob, T., Reeves, J. N., Markowitz, A., Serlemitsos, P. J., Padmanabhan, U.
We report on the results of detailed X-ray spectroscopy of the Fe K region in the Seyfert 1 galaxy NGC 3783 from five ~170 ks observations with the Chandra high energy gratings. Monitoring was...
Iron K Features in the Quasar E 1821+643: Evidence for Gravitationally Redshifted Absorption? (2005)
Yaqoob, T., Serlemitsos, P. J.
We report a Chandra high-energy grating detection of a narrow, redshifted absorption line superimposed on the red wing of a broad Fe K line in the $z=0.297$ quasar E1821+643. The absorption line is...
Steenbrugge, K. C., Kaastra, J. S., Crenshaw, D. M., Kraemer, S. B., Arav, N., George, I. M., ...
We present the results from a 500 ks Chandra observation of the Seyfert 1 galaxy NGC 5548. We detect broadened emission lines of O VII and C VI in the spectra, similar to those observed in the...
Relativistic outflow in CXOCDFS J033260.0-274748 (2005)
Wang, J. X., Wang, T. G., Tozzi, P., Giacconi, R., Hasinger, G., Kewley, L., ...
X-ray Evidence for Multiple Absorbing Structures in Seyfert Galaxies (2004)
Gelbord, Jonathan, Weaver, K. A., Yaqoob, T.
We have used X-ray spectra to measure attenuating columns in a large sample of Seyfert galaxies. Over 30 of these sources have resolved radio jets, allowing the relative orientation of the nucleus...
O VII and O VIII absorption by hot gas in the vicinity of the Galaxy (2004)
McKernan, B., Yaqoob, T., Reynolds, C. S.
(abridged) We searched for evidence of soft X-ray absorption by hot gas in the vicinity of the Galaxy in a small sample of fifteen type I AGN observed with the high resolution X-ray gratings on board...
An XSPEC model to explore spectral features from black-hole sources (2004)
Dovciak, M., Karas, V., Martocchia, A., Matt, G., Yaqoob, T.
We report on a new general relativistic computational model enhancing, in various respects, the capability of presently available tools for fitting spectra of X-ray sources. The new model is intended...
Kaastra, J. S., Steenbrugge, K. C., Crenshaw, D. M., Kraemer, S. B., Arav, N., George, I. M., ...
The Seyfert 1 galaxy NGC 5548 was observed for a week by Chandra using both the HETGS and LETGS spectrometers. In this paper we study the time variability of the continuum radiation. During our...
Dovciak, M., Karas, V., Yaqoob, T.
Accreting black holes are believed to emit X-rays which then mediate information about strong gravity in the vicinity of the emission region. We report on a set of new routines for the Xspec package...
The XMM-Newton iron line profile of NGC 3783 (2004)
Reeves, J.N., Nandra, K., George, I.M., Pounds, Kenneth A., Turner, T.J., Yaqoob, T.
The definitive version of this paper is that available at http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v602n2/58961/58961.html
High Resolution X-ray Spectroscopy of the Fe K complex in IC 4329A (2004)
We report the detection of complex Fe K line emission from a Chandra High Energy Transmission Grating Spectrometer observation of the Seyfert 1 galaxy IC 4329A. The line emission is double-peaked,...
The XMM-Newton Iron Line Profile of NGC 3783 (2003)
Reeves, J. N, Nandra, K., George, I. M., Pounds, K. A., Turner, T. J., Yaqoob, T.
We report on observations of the iron K line in the nearby Seyfert 1 galaxy, NGC 3783, obtained in a long, 2 orbit (240 ks) XMM-Newton observation. The line profile obtained exhibits two strong...
A warm hot intergalactic medium towards 3C 120? (2003)
McKernan, B., Yaqoob, T., Mushotzky, R., George, I. M., Turner, T. J.
We observed the Seyfert I active galaxy/broad line radio galaxy 3C120 with the Chandra high energy transmission gratings and present an analysis of the soft X-ray spectrum. We identify the strongest...
Yaqoob, T., George, I. M., Kallman, T. R., Padmanabhan, U., Weaver, K. A., Turner, T. J.
We report the detection of Fe XXV and Fe XXVI $K\alpha$ emission lines from a Chandra HETGS observation of the Seyfert~1 galaxy NGC 7314, made simultaneously with RXTE. The lines are redshifted (cz ~...
A Puzzling X-Ray Source Found in the chandra Deep Field South (2003)
Wang, J., Yaqoob, T., Szokoly, G., Gilli, R., Kewley, L., Mainieri, V., ...
In this letter we report the detection of an extremely strong X-ray emission line in the 940ks chandra ACIS-I spectrum of CXO CDFS J033225.3-274219. The source was identified as a Type1 AGN at...
Crenshaw, D. M., Kraemer, S. B., Gabel, J. R., Kaastra, J. S., Steenbrugge, K. C., Brinkman, A. C., ...
We present new UV spectra of the nucleus of the Seyfert 1 galaxy NGC 5548, which we obtained with the Space Telescope Imaging Spectrograph at high spectral resolution, in conjunction with...
McKernan, B., Yaqoob, T., George, I. M., Turner, T. J.
We observed the Seyfert 1 galaxy NGC 4593 with the Chandra high energy transmission gratings and present a detailed analysis of the soft X-ray spectrum. We measure strong absorption lines from...
A puzzling X-ray source found in the Chandra Deep Field-South (2003)
Wang, J., Yaqoob, T., Szokoly, G., Gilli, R., Kewley, L., Mainieri, V., ...
New Chandra/HST-STIS results on Seyfert I AGN: Photoionized Outflows (2002)
We present soft X-ray results from observations with the Chandra HETGS of the Seyfert I AGN NGC 4593 and Mrk 509. We discuss the photoionized outflows associated with Seyfert I AGN in terms of their...
New {\it Chandra} Results on Seyfert I galaxies: Fe-K lines (2002)
We present measurements of the Fe-K line for nine Seyfert I galaxies using Chandra High Energy Transmission Grating Spectrometer (HETGS) data. The centroid energies are narrowly dispersed (6.403 +/-...
Chandra Grating Observations of AGN (2002)
The highest spectral resolution data for the Fe-K lines in type I AGN, as observed with the Chandra High Energy Grating (HEG), reveal a variety of line shapes. However, the energies of the most...
Yaqoob, T., McKernan, B., Kraemer, S. B., Crenshaw, M., Gable, J., George, I. M., ...
We observed the Seyfert 1 galaxy Mrk 509 simultaneously with Chandra/HETG, HST/STIS and RXTE. We measure strong absorption lines from He-like Ne and Mg, and from H-like N, O, and Ne. The lines are...
Kraemer, S. B., Crenshaw, D. M., Yaqoob, T., McKernan, B., Gabel, J. R., George, I. M., ...
We present observations of the UV absorption lines in the luminous Seyfert 1 galaxy Mrk 509, obtained with the medium resolution (lambda/Delta-lambda ~ 40,000) echelle gratings of the Space Telescope...
Turner, T. J., Mushotzky, R. F., Yaqoob, T., George, I. M., Snowden, S. L., Netzer, H., ...
We present results from a simultaneous Chandra HETG and XMM-Newton observation of NGC 3516. We find evidence for several narrow components of Fe Kalpha along with a broad line. We consider the...
The Effect of Changes in the ASCA Calibration on the Fe-Kalpha Lines in Active Galaxies (2001)
Yaqoob, T., Padmanabhan, U., Dotani, T., Nandra, K.
The ASCA calibration has evolved considerably since launch and indeed, is still evolving. There have been concerns in the literature that changes in the ASCA calibration have resulted in the...
The Detection of Circumnuclear X-ray Emission from the Seyfert Galaxy NGC 3516 (2001)
George, I. M., Turner, T. J., Netzer, H., Kraemer, S. B., Ruiz, J., Chelouche, D., ...
We present the first high-resolution, X-ray image of the circumnuclear regions of the Seyfert 1 galaxy NGC 3516, using the Chandra X-ray Observatory (CXO). All three of the CXO observations reported...
The Spectral Energy Distribution of the Seyfert galaxy Ton S180 (2001)
Turner, T. J., Romano, P., Kraemer, S. B., George, I. M., Yaqoob, T., Crenshaw, D. M., ...
We present spectral results from a multi-satellite, broad-band campaign on the Narrow-line Seyfert 1 galaxy Ton S180 performed at the end of 1999. We discuss the spectral-energy distribution of the...
Subtleties in Measuring Iron K Lines in AGN (2001)
Yaqoob, T., Padmanabhan, U., Dotani, T., George, I. M., Turner, T. J., Nandra, K.
Chandra and XMM observations are showing that the Fe-K emission lines in type 1 AGN are composite, in general consisting of a narrow and a broad component. We review the latest Chandra HETG results...
Chandra Grating Observations of Seyfert 1 Galaxies (2001)
Yaqoob, T., George, I. M., Turner, T. J.
We present new results from a Chandra HETG observation of NGC 5548 and give a comparison of absorption and emission features found in other Seyfert 1 galaxies using Chandra grating observations. Deep...
Quasi-Periodic Oscillation in Seyfert galaxies: Significance levels. The Case of Mrk 766 (2001)
Benlloch, S., Wilms, J., Edelson, R., Yaqoob, T., Staubert, R.
We discuss methods to compute significance levels for the existence of quasi-periodic oscillations (QPOs) in Active Galactic Nuclei (AGN) which take the red-noise character of the X-ray lightcurves...
The Future of Fe-K Line Diagnostics for Probing Strong Gravity (2001)
We review what we have learnt with ASCA from studying the Fe-K lines in AGN and describe a program to deconvolve the narrow, non-disk components of the lines with Chandra. This is necessary to derive...
The X-ray Emission from the Nucleus of the Dwarf Elliptical Galaxy NGC 3226 (2001)
George, I. M., Mushotzky, R. F., Yaqoob, T., Turner, T. J., Kraemer, S., Ptak, A. F., ...
We present the first high resolution X-ray image of the dwarf elliptical galaxy NGC 3226. The data were obtained during an observation of the nearby Seyfert Galaxy NGC 3227 using the Chandra X-ray...
The Spectral Energy Distribution of the Seyfert galaxy Ton S180 (2001)
Turner, T. J., Romano, P., Kraemer, S. B., George, I. M., Yaqoob, T., Crenshaw, D. M., ...
We present spectral results from a multi-satellite, broad-band campaign on the Narrow-line Seyfert 1 galaxy Ton S180 performed at the end of 1999. We discuss the spectral-energy distribution of the...
The Spectral Energy Distribution of the Seyfert galaxy Ton S180 (2001)
Turner, T. J., Romano, P., Kraemer, S. B., George, I. M., Yaqoob, T., Crenshaw, D. M., ...
We present spectral results from a multi-satellite, broad-band campaign on the Narrow-line Seyfert 1 galaxy Ton S180 performed at the end of 1999. We discuss the spectral-energy distribution of the...
Chandra Grating Spectroscopy of the Seyfert Galaxy Ton S180 (2000)
Turner, T. J., George, I. M., Yaqoob, T., Kriss, G., Crenshaw, D. M., Kraemer, S., ...
This paper presents results from spectral observations of Ton S180 using Chandra and ASCA. The data confirm the presence of the soft excess but the Chandra LETG spectrum reveals it to be broad and...
A Broad Fe-Kalpha Emission Line in the X-Ray Spectrum of the Quasar 3C 273 (2000)
Yaqoob, T., Serlemitsos, P. J.
The Fe-K line, an important physical diagnostic in the X-ray spectra of AGN, has been notoriously difficult to measure in the high-luminosity, radio-loud quasar 3C 273 (z=0.158). On the few occasions...
Variable Iron K-alpha Lines in Seyfert 1 Galaxies (2000)
Weaver, K. A., Gelbord, J., Yaqoob, T.
We find that variability of the iron K-alpha line is common in Seyfert 1 galaxies. Using data from the ASCA archive for objects that have been observed more than once during the mission, we study the...
Yaqoob, T., George, I. M., Nandra, K., Turner, T. J., Serlemitsos, P. J., Mushotzky, R. F.
We report the detection of a narrow Fe-K emission line in the Seyfert 1 galaxy NGC 5548 with the Chandra High-Energy Transmission Gratings. In the galaxy frame we measure a center energy of 6.40 \pm...
What Kind of Obscured AGN Make the Cosmic X-ray Background? (2000)
While it is understood that the origin of the Cosmic X-ray Background (CXRB) can be explained in terms of a combination of obscured and unobscured AGN, the identity of these obscured AGN showing up...
Iron K line Variability in the Low-Luminosity AGN NGC 4579 (2000)
Terashima, Y., Ho, L. C., Ptak, A. F., Yaqoob, T., Kunieda, H., Misaki, K., ...
We present results of new ASCA observations of the low-luminosity AGN (LLAGN) NGC 4579 obtained on 1998 December 18 and 28, and we report on detection of variability of an iron K emission line. The...
ASCA Observations of "Type 2" LINERs: Evidence for a Stellar Source of Ionization (1999)
Terashima, Y., Ho, L. C., Ptak, A. F., Mushotzky, R. F., Serlemitsos, P. J., Yaqoob, T., ...
We present ASCA observations of LINERs without broad H$\alpha$ emission in their optical spectra. The sample of "type 2" LINERs consists of NGC 404, 4111, 4192, 4457, and 4569. We have detected X-ray...
X-ray Observations of Optically-Selected, Radio-Quiet Quasars I: The ASCA results (1999)
George, I. M., Turner, T. J., Yaqoob, T., Netzer, H., Laor, A., Mushotzky, R. F., ...
We present the result of 27 ASCA observations of 26 radio-quiet quasars (RQQs) from the PG survey. All the RQQs were detected except 2 BALQSOs. We find the variability characteristics of the sources...
A Highly Doppler Blueshifted Fe-K Emission Line in the High-Redshift QSO PKS 2149-306 (1999)
Yaqoob, T., George, I. M., Nandra, K., Turner, T. J., Zobair, S., Serlemitsos, P. J.
We report the results from an \asca observation of the QSO PKS 2149-306 (z=2.345). We detect an emission line centered at $\sim 17$ keV in the quasar frame. Line emission at this energy has not been...
The properties of the relativistic iron K-line in NGC 3516 (1999)
Nandra, K., George, I. M., Mushotzky, R. F., Turner, T. J., Yaqoob, T.
We present an analysis of the relativistic iron K-alpha line in the Seyfert 1 galaxy NGC 3516, based on a continuous, five-day ASCA observation. The broad profile which has been found in several...
Short-timescale Variability in the Broadband Emission of the Blazars Mkn421 and Mkn501 (1999)
Carson, M. J., McKernan, B., Yaqoob, T., Fegan, D. J.
We analyse ASCA x-ray data and Whipple \gamma-ray data from the blazars Mkn421 and Mkn501 for short-timescale variability. We find no evidence for statistically significant (>3\sigma) variability in...
X-ray Constraints on Accretion and Starburst Processes in Galactic Nuclei I. Spectral Results (1998)
Ptak, A., Serlemitsos, P., Yaqoob, T., Mushotzky, R.
The results of a 0.4-10.0 keV ASCA spectral analysis of a sample of low-luminosity AGN (LLAGN; M51, NGC 3147, NGC 4258), low-ionization nuclear emission line regions (LINERs; NGC 3079, NGC 3310, NGC...
A Peculiar Emission Line Feature in the X-ray Spectrum of the Quasar PKS 0637-752 (1998)
Yaqoob, T., George, I. M., Turner, T. J., Nandra, K., Ptak, A., Serlemitsos, P. J.
We report the results from an ASCA observation of the high-luminosity, radio-loud quasar PKS 0637-752 (redshift 0.654), covering the 0.8-15 keV band in the quasar-frame. We find the source to have a...
The X-ray Spectral Variability of the Seyfert Galaxy NGC 3227 (1998)
George, I. M., Mushotzky, R. F., Turner, T. J., Yaqoob, T., Ptak, A., Nandra, K., ...
(Abridged) We present the results from {\it ASCA} observations of NGC 3227 along with those from a {\it ROSAT} observation. The 0.6--10 keV continuum is consistent with a powerlaw with $\Gamma \sim...
Quasi-simultaneous observations of 3C 273 by BeppoSAX and ASCA (1998)
Orr, Astrid, Yaqoob, T., Parmar, A. N., Piro, L., White, N. E., Grandi, P.
We report the results of quasi-simultaneous observations of the bright quasar 3C 273 using the BeppoSAX Low-Energy Concentrator Spectrometer (LECS) and the ASCA Solid-State Imaging Spectrometer...
X-ray Variability as a Probe of Advection-Dominated Accretion in Low-Luminosity AGN (1998)
Ptak, A., Yaqoob, T., Mushotzky, R., Serlemitsos, P., Griffiths, R.
As a class, LINERs and Low-Luminosity AGN tend to show little or no significant short-term variability (i.e., with time-scales less than a day). This is a marked break for the trend of increased...
Occultation Mapping of the Central Engine in the Active Galaxy MCG -6-30-15 (1998)
The colossal power output of active galactic nuclei (AGN) is believed to be fueled by the accretion of matter onto a supermassive black hole. This central accreting region of AGN has hitherto been...
Parameter Estimation In X-ray Astronomy Revisited (1998)
The method of obtaining confidence intervals on a subset of the total number of parameters (p) of a model used for fitting X-ray spectra is to perturb the best-fitting model until, for each...
BeppoSAX observations of low-energy spectral features in AGN (1997)
Orr, Astrid, Parmar, A. N., Yaqoob, T., Guainazzi, M.
The combination of the broad band coverage and moderate spectral resolution of the LECS and MECS instruments on-board BeppoSAX allow the spectra of AGN to be studied in unprecedented detail down to...
Yaqoob, T., McKernan, B., Ptak, A., Nandra, K., Serlemitsos, P. J.
We present a new, simple method for analysing gapped time-series which is particularly suited to probe the X-ray power spectra of active galactic nuclei (AGN).The method is applied to a four-day...
George, I. M., Turner, T. J., Netzer, Hagai, Nandra, K., Mushotzky, R. F., Yaqoob, T.
(Abridged) We present the results from a detailed analysis of the 0.6 - 10 keV spectra of 23 ASCA observations of 18 objects. We find that in most cases the underlying continuum can be...
On the dependence of the iron K-line profiles with luminosity in Active Galactic Nuclei (1997)
Nandra, K., George, I. M., Mushotzky, R. F., Turner, T. J., Yaqoob, T.
We present evidence for changes in the strength and profile of the iron K-alpha line in Active Galactic Nuclei (AGN), based on X-ray observations with ASCA. There is a clear decrease in the strength...
The Complex X-ray Spectra of M82 and NGC 253 (1997)
Ptak, A., Serlemitsos, P., Yaqoob, T., Mushotzky, R., Tsuru, T.
We present the results of the first imaging X-ray observations in the 0.4-10.0 keV bandpass of the nearby starburst galaxies M82 and NGC 253. The ASCA spectra of both M82 and NGC 253 are complex with...
X-ray Observations of LINER and Starburst Galaxies (1997)
Serlemitsos, P., Ptak, A., Yaqoob, T.
We present the results of ASCA observations of a heterogenous sample of 15 spiral galaxies. 8 are LINERs or low-luminosity AGN (LLAGN), 5 are starburst galaxies and 2 are normal spiral galaxies. We...
ASCA observations of Seyfert 1 galaxies: I. Data Analysis, Imaging and Timing (1996)
Nandra, K., George, I. M., Mushotzky, R. F., Turner, T. J., Yaqoob, T.
We present the first in a series of papers describing the X-ray properties of a sample of 18 Seyfert 1 galaxies, using data obtained by \asca. The imaging data reveal a number of serendipitous hard...
Variability of the iron K-emission line in the Seyfert 1 galaxy NGC 3516 (1996)
Nandra, K., Mushotzky, R. F., Yaqoob, T., George, I. M., Turner, T. J.
We present strong evidence for variability of the flux of the iron K$\alpha$ emission line in the Seyfert 1 galaxy, NGC 3516. Two ASCA observations, separated by $\sim 1$~yr, showed a marked decrease...
ASCA observations of Seyfert 1 galaxies: II. Relativistic Iron K-alpha emission (1996)
Nandra, K., George, I. M., Mushotzky, R. F., Turner, T. J., Yaqoob, T.
We present evidence for widespread relativistic effects in the central regions of active galactic nuclei. In a sample of 18 Seyfert 1 galaxies observed by \asca, 14 show an iron K$\alpha$ line which...
X-ray observations of liner and starburst galaxies (1996)
Serlemitsos, P J, Ptak, A, Yaqoob, T
We present the results of ASCA observations of a heterogenous sample of 15 spiral galaxies. 8 are LINERs or low-luminosity AGN (LLAGN), 5 are starburst galaxies and 2 are normal spiral galaxies. We...
The X-Ray Spectral Variability of Mrk 766 (1996)
Leighly, K. M., Mushotzky, R. F., Yaqoob, T., Kunieda, H., Edelson, R.
Analysis results from ASCA and ROSAT observations of the narrow-line Seyfert 1 galaxy Mrk 766 are reported. In the ASCA observation we observed rapid variability with a doubling time scale of 1000...
The nature of the low-luminosity AGN in NGC 3147 (1995)
Ptak, A, Yaqoob, T, Serlemitsos, P J, Kunieda, H, Terashima, Y
The iron K$_{\alpha}$ line profile in NGC 4151 (1995)
Yaqoob, T, Edelson, R, Weaver, K A, Warwick, R S, Mushotzky, R F, Serlemitsos, P J, ...
X-ray spectrum and variability of the quasar PG1211+143 (1994)
Yaqoob, T, Serlemitsos, P J, Mushotzky, R F, Madejski, G M, Turner, T J, Kunieda, H