Extragalactic Gamma-Ray Absorption and the Intrinsic Spectrum of Markarian 501 during the 1997 Flare

Using the recent models of Malkan & Stecker for the infrared background radiation and extrapolating them into the optical and UV range using recent galaxy count data, we rederive the optical depth of the universe to high-energy ?-rays as a function of energy and redshift for energies between 50 GeV and 100 TeV and redshifts between 0.03 and 0.3. We then use these results to derive the intrinsic ?-ray spectrum of Mrk 501 during its 1997 high state. We find that the time-averaged spectral energy distribution of Mrk 501 while flaring had a broad, flat peak in the ~5-10 TeV range that corresponds to the broad, flat, time-averaged X-ray peak in the ~50-100 keV range observed during the flare. The spectral index of our derived intrinsic differential photon spectrum for Mrk 501 at energies below ~2 TeV was found to be ~1.6-1.7. This corresponds to a time-averaged spectral index of 1.76 found in soft X-rays at energies below the X-ray (synchrotron) peak. These results apparently favor a synchrotron self-Compton (SSC) origin for the TeV emission, together with jet parameters that are consistent with time variability constraints within the context of a simple SSC model.

[1]  T. Weekes,et al.  Measurement of the Multi-TeV Gamma-Ray Flare Spectra of Markarian 421 and Markarian 501 , 1998, astro-ph/9808333.

[2]  David J. Schlegel,et al.  Detection of a Far-Infrared Excess with DIRBE at 60 and 100 Microns , 2000, astro-ph/0004175.

[3]  M. Rowan-Robinson,et al.  The Star Formation History of the Universe: An Infrared Perspective , 2001 .

[4]  Sky confusion noise in the far-infrared: Cirrus, galaxies and the cosmic far{infrared background ? , 2001, astro-ph/0110143.

[5]  Greenbelt,et al.  On the Absorption of High-Energy Gamma-Rays by Intergalactic Infrared Radiation , 1997 .

[6]  J. Weiland,et al.  Comparison of the COBE FIRAS and DIRBE Calibrations , 1997, astro-ph/9707192.

[7]  Jonathan C. Tan,et al.  A Semiempirical Model of the Infrared Universe , 1999, astro-ph/9904004.

[8]  Lucia Pozzetti,et al.  Deep galaxy counts, extragalactic background light and the stellar baryon budget , 1999, astro-ph/9907315.

[9]  E. L. Wright,et al.  The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background. IV. Cosmological Implications , 1997, astro-ph/9806129.

[10]  M. Malkan,et al.  An Empirically Based Model for Predicting Infrared Luminosity Functions, Deep Infrared Galaxy Counts, and the Diffuse Infrared Background , 2000, astro-ph/0009500.

[11]  H. Ferguson,et al.  Ultraviolet Galaxy Counts from Space Telescope Imaging Spectrograph Observations of the Hubble Deep Fields , 2000 .

[12]  Michael G. Hauser,et al.  THE COSMIC INFRARED BACKGROUND: Measurements and Implications ⁄ , 2001 .

[13]  Cong Xu,et al.  Local Luminosity Function at 15 Microns and Galaxy Evolution Seen by ISOCAM 15 Micron Surveys , 2000, astro-ph/0004216.

[14]  E. L. Wright,et al.  Detection of the Cosmic Infrared Background at 2.2 and 3.5 Microns Using DIRBE Observations , 1999, astro-ph/9912523.

[15]  T. Stanev,et al.  Constraints on the Extragalactic Infrared Background from Gamma-Ray Observations of Markarian 501 , 1997, astro-ph/9708162.

[16]  E. Dwek.  Unveiling the cosmic infrared background : College Park, MD April 1995 , 1996 .

[17]  F. W. Stecker,et al.  New tests of Lorentz invariance following from observations of the highest energy cosmic γ-rays , 2001 .

[18]  Michael Hauser,et al.  The Extragalactic Infrared Background and Its Cosmological Implications: IAU Symposium 204 , 2001 .

[19]  E. L. Wright,et al.  The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background. I. Limits and Detections , 1998, astro-ph/9806167.

[20]  F. Stecker.  The cosmic gamma-ray spectrum from secondary- particle production in the metagalaxy. , 1969 .

[21]  O. C. de Jager,et al.  TeV gamma rays from 3C 279 - A possible probe of origin and intergalactic infrared radiation fields , 1992 .

[22]  Absorption of High-Energy Gamma Rays by Interactions with Extragalactic Starlight Photons at High Redshifts and the High-Energy Gamma-Ray Background , 1997, astro-ph/9704166.

[23]  Milano,et al.  Constraints on the Physical Parameters of TeV Blazars , 1998, astro-ph/9809051.

[24]  R. Schlickeiser,et al.  On the location of the acceleration and emission sites in gamma-ray blazars , 1994 .

[25]  E. Wright,et al.  The Extragalactic Infrared Background and Its Cosmological Implications: IAU Symposium 204 , 2001 .

[26]  Matthew A. Bershady,et al.  Near-Infrared Galaxy Counts to J and K ~ 24 as a Function of Image Size* , 1998 .

[27]  et al,et al.  Reanalysis of the high energy cutoff of the 1997 Mkn 501 TeV energy spectrum , 2000, astro-ph/0011483.

[28]  C. Bennett,et al.  The Spectrum of the Extragalactic Far-Infrared Background from the COBE FIRAS Observations , 1998, astro-ph/9803021.

[29]  G. Lagache,et al.  New constraints on the cosmic mid-infrared background using TeV gamma-ray astronomy , 2000, astro-ph/0012094.

[30]  Italy Universita dell'Insubria,et al.  X-Ray Emission of Markarian 421: New Clues from Its Spectral Evolution. II. Spectral Analysis and Physical Constraints , 2000, astro-ph/0005067.

[31]  Extragalactic background light absorption signal in the TeV γ-ray spectra of blazars , 1999, astro-ph/9908088.