# The Spectral Index Distribution of EGRET Blazars: Prospects for GLAST

## Abstract

The intrinsic distribution of spectral indices in GeV energies of gamma-ray-loud blazars is a critical input in determining the spectral shape of the unresolved blazar contribution to the diffuse extragalactic gamma-ray background, as well as an important test of blazar emission theories. We present a maximum-likelihood method of determining the intrinsic spectral index distribution (ISID) of a population of {gamma}-ray emitters which accounts for error in measurement of individual spectral indices, and we apply it to EGRET blazars. We find that the most likely Gaussian ISID for EGRET blazars has a mean of 2.27 and a standard deviation of 0.20. We additionally find some indication that FSRQs and BL Lacs may have different ISIDs (with BL Lacs being harder). We also test for spectral index hardening associated with blazar variability for which we find no evidence. Finally, we produce simulated GLAST spectral index datasets and perform the same analyses. With improved statistics due to the much larger number of resolvable blazars, GLAST data will help us determine the ISIDs with much improved accuracy. Should any difference exist between the ISIDs of BL Lacs and FSRQs or between the ISIDs of blazars in the quiescent and flaring states, GLAST data willmore »

- Authors:

- Publication Date:

- Research Org.:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)

- Sponsoring Org.:
- USDOE

- OSTI Identifier:
- 1030537

- Report Number(s):
- SLAC-PUB-14794

arXiv:0704.2417; TRN: US201124%%294

- DOE Contract Number:
- AC02-76SF00515

- Resource Type:
- Conference

- Journal Name:
- AIP Conf.Proc.921:163-168,2007

- Additional Journal Information:
- Conference: Prepared for 1st GLAST Symposium, Stanford, Palo Alto, 5-8 Feb 2007

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ACCURACY; DISTRIBUTION; FLARING; GALAXIES; HARDENING; SHAPE; STATISTICS; Astrophysics,ASTRO

### Citation Formats

```
Venters, Tonia M, Pavlidou, Vasiliki, and /SLAC.
```*The Spectral Index Distribution of EGRET Blazars: Prospects for GLAST*. United States: N. p., 2011.
Web.

```
Venters, Tonia M, Pavlidou, Vasiliki, & /SLAC.
```*The Spectral Index Distribution of EGRET Blazars: Prospects for GLAST*. United States.

```
Venters, Tonia M, Pavlidou, Vasiliki, and /SLAC. Tue .
"The Spectral Index Distribution of EGRET Blazars: Prospects for GLAST". United States. https://www.osti.gov/servlets/purl/1030537.
```

```
@article{osti_1030537,
```

title = {The Spectral Index Distribution of EGRET Blazars: Prospects for GLAST},

author = {Venters, Tonia M and Pavlidou, Vasiliki and /SLAC},

abstractNote = {The intrinsic distribution of spectral indices in GeV energies of gamma-ray-loud blazars is a critical input in determining the spectral shape of the unresolved blazar contribution to the diffuse extragalactic gamma-ray background, as well as an important test of blazar emission theories. We present a maximum-likelihood method of determining the intrinsic spectral index distribution (ISID) of a population of {gamma}-ray emitters which accounts for error in measurement of individual spectral indices, and we apply it to EGRET blazars. We find that the most likely Gaussian ISID for EGRET blazars has a mean of 2.27 and a standard deviation of 0.20. We additionally find some indication that FSRQs and BL Lacs may have different ISIDs (with BL Lacs being harder). We also test for spectral index hardening associated with blazar variability for which we find no evidence. Finally, we produce simulated GLAST spectral index datasets and perform the same analyses. With improved statistics due to the much larger number of resolvable blazars, GLAST data will help us determine the ISIDs with much improved accuracy. Should any difference exist between the ISIDs of BL Lacs and FSRQs or between the ISIDs of blazars in the quiescent and flaring states, GLAST data will be adequate to separate these ISIDs at a significance better than 3{sigma}.},

doi = {},

journal = {AIP Conf.Proc.921:163-168,2007},

number = ,

volume = ,

place = {United States},

year = {2011},

month = {11}

}