diff --git a/ChangeLog b/ChangeLog
index 9585b41..d1ce26d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,7 @@
         * Version 1.1.0 released
         =========================
 
+        Use default GTime in GObservation::deadc() method (#1670)
         The GApplicationPar::filename() methods now take and return GFilename (#1671)
         Add GFilename methods and remove equivalents from GTools (#1666)
         Use column names for CTA response table access (#1656)
diff --git a/NEWS b/NEWS
index 989bddb..c672ea9 100644
--- a/NEWS
+++ b/NEWS
@@ -125,6 +125,11 @@ A non-const GObservation::events() method has been added to allow for
 the manipulation of events within an observation without the need to
 create a local copy.
 
+The argument of GObservation::deadc(GTime) now defaults to GTime() so
+that no argument is needed when calling the method. This reflects the
+fact that the deadtime correction is often computed as an average value
+over the observation, and does in fact not depend on time (#1670).
+
 
 11. Optimization module
 -----------------------
diff --git a/include/GObservation.hpp b/include/GObservation.hpp
index 5c92560..5b9aa5a 100644
--- a/include/GObservation.hpp
+++ b/include/GObservation.hpp
@@ -31,13 +31,17 @@
 #include <string>
 #include "GBase.hpp"
 #include "GEvents.hpp"
-#include "GResponse.hpp"
-#include "GModels.hpp"
 #include "GTime.hpp"
-#include "GEnergy.hpp"
 #include "GFunction.hpp"
-#include "GVector.hpp"
-#include "GMatrixSparse.hpp"
+
+/* __ Forward declarations _______________________________________________ */
+class GVector;
+class GMatrixSparse;
+class GModel;
+class GModels;
+class GModelPar;
+class GResponse;
+class GXmlElement;
 
 
 /***********************************************************************//**
@@ -82,7 +86,7 @@ public:
     virtual std::string      instrument(void) const = 0;
     virtual double           ontime(void) const = 0;
     virtual double           livetime(void) const = 0;
-    virtual double           deadc(const GTime& time) const = 0;
+    virtual double           deadc(const GTime& time = GTime()) const = 0;
     virtual void             read(const GXmlElement& xml) = 0;
     virtual void             write(GXmlElement& xml) const = 0;
     virtual std::string      print(const GChatter& chatter = NORMAL) const = 0;
diff --git a/inst/com/include/GCOMObservation.hpp b/inst/com/include/GCOMObservation.hpp
index f60b100..edccd82 100644
--- a/inst/com/include/GCOMObservation.hpp
+++ b/inst/com/include/GCOMObservation.hpp
@@ -28,12 +28,20 @@
 #define GCOMOBSERVATION_HPP
 
 /* __ Includes ___________________________________________________________ */
+#include <string>
 #include "GObservation.hpp"
 #include "GTime.hpp"
-#include "GModel.hpp"
+#include "GFilename.hpp"
+#include "GSkyDir.hpp"
 #include "GSkyMap.hpp"
 #include "GCOMResponse.hpp"
-#include "GCaldb.hpp"
+//#include "GCaldb.hpp"
+
+/* __ Forward declarations _______________________________________________ */
+class GCaldb;
+class GResponse;
+class GXmlElement;
+class GFitsHDU;
 
 
 /***********************************************************************//**
@@ -52,10 +60,10 @@ class GCOMObservation : public GObservation {
 public:
     // Constructors and destructors
     GCOMObservation(void);
-    GCOMObservation(const std::string& drename,
-                    const std::string& drbname,
-                    const std::string& drgname,
-                    const std::string& drxname);
+    GCOMObservation(const GFilename& drename,
+                    const GFilename& drbname,
+                    const GFilename& drgname,
+                    const GFilename& drxname);
     GCOMObservation(const GCOMObservation& obs);
     virtual ~GCOMObservation(void);
 
@@ -71,16 +79,16 @@ public:
     virtual std::string         instrument(void) const;
     virtual double              ontime(void) const;
     virtual double              livetime(void) const;
-    virtual double              deadc(const GTime& time) const;
+    virtual double              deadc(const GTime& time = GTime()) const;
     virtual void                read(const GXmlElement& xml);
     virtual void                write(GXmlElement& xml) const;
     virtual std::string         print(const GChatter& chatter = NORMAL) const;
 
     // Other methods
-    void           load(const std::string& drename,
-                        const std::string& drbname,
-                        const std::string& drgname,
-                        const std::string& drxname);
+    void           load(const GFilename& drename,
+                        const GFilename& drbname,
+                        const GFilename& drgname,
+                        const GFilename& drxname);
     void           response(const std::string& rspname, const GCaldb& caldb);
     void           obs_id(const double& id);
     void           ontime(const double& ontime);
@@ -98,20 +106,20 @@ protected:
     void init_members(void);
     void copy_members(const GCOMObservation& obs);
     void free_members(void);
-    void load_dre(const std::string& drename);
-    void load_drb(const std::string& drbname);
-    void load_drg(const std::string& drgname);
-    void load_drx(const std::string& drxname);
+    void load_dre(const GFilename& drename);
+    void load_drb(const GFilename& drbname);
+    void load_drg(const GFilename& drgname);
+    void load_drx(const GFilename& drxname);
     bool check_map(const GSkyMap& map) const;
     void read_attributes(const GFitsHDU* hdu);
     void write_attributes(GFitsHDU* hdu) const;
 
     // Protected members
     std::string  m_instrument;  //!< Instrument name
-    std::string  m_drename;     //!< DRE filename
-    std::string  m_drbname;     //!< DRB filename
-    std::string  m_drgname;     //!< DRG filename
-    std::string  m_drxname;     //!< DRX filename
+    GFilename    m_drename;     //!< DRE filename
+    GFilename    m_drbname;     //!< DRB filename
+    GFilename    m_drgname;     //!< DRG filename
+    GFilename    m_drxname;     //!< DRX filename
     GSkyMap      m_drb;         //!< Background model
     GSkyMap      m_drg;         //!< Geometry factors
     GSkyMap      m_drx;         //!< Exposure map
diff --git a/inst/com/pyext/GCOMObservation.i b/inst/com/pyext/GCOMObservation.i
index 3688ce0..0065bc7 100644
--- a/inst/com/pyext/GCOMObservation.i
+++ b/inst/com/pyext/GCOMObservation.i
@@ -1,7 +1,7 @@
 /***************************************************************************
  *             GCOMObservation.i - COMPTEL observation class               *
  * ----------------------------------------------------------------------- *
- *  copyright (C) 2012-2015 by Juergen Knoedlseder                         *
+ *  copyright (C) 2012-2016 by Juergen Knoedlseder                         *
  * ----------------------------------------------------------------------- *
  *                                                                         *
  *  This program is free software: you can redistribute it and/or modify   *
@@ -38,10 +38,10 @@ class GCOMObservation : public GObservation {
 public:
     // Constructors and destructors
     GCOMObservation(void);
-    GCOMObservation(const std::string& drename,
-                    const std::string& drbname,
-                    const std::string& drgname,
-                    const std::string& drxname);
+    GCOMObservation(const GFilename& drename,
+                    const GFilename& drbname,
+                    const GFilename& drgname,
+                    const GFilename& drxname);
     GCOMObservation(const GCOMObservation& obs);
     virtual ~GCOMObservation(void);
 
@@ -54,15 +54,15 @@ public:
     virtual std::string         instrument(void) const;
     virtual double              ontime(void) const;
     virtual double              livetime(void) const;
-    virtual double              deadc(const GTime& time) const;
+    virtual double              deadc(const GTime& time = GTime()) const;
     virtual void                read(const GXmlElement& xml);
     virtual void                write(GXmlElement& xml) const;
 
     // Other methods
-    void           load(const std::string& drename,
-                        const std::string& drbname,
-                        const std::string& drgname,
-                        const std::string& drxname);
+    void           load(const GFilename& drename,
+                        const GFilename& drbname,
+                        const GFilename& drgname,
+                        const GFilename& drxname);
     void           response(const std::string& rspname, const GCaldb& caldb);
     void           obs_id(const double& id);
     void           ontime(const double& ontime);
diff --git a/inst/com/src/GCOMObservation.cpp b/inst/com/src/GCOMObservation.cpp
index a74ef70..a399bc0 100644
--- a/inst/com/src/GCOMObservation.cpp
+++ b/inst/com/src/GCOMObservation.cpp
@@ -30,9 +30,10 @@
 #endif
 #include <typeinfo> 
 #include "GObservationRegistry.hpp"
+#include "GTools.hpp"
 #include "GException.hpp"
 #include "GFits.hpp"
-#include "GTools.hpp"
+#include "GCaldb.hpp"
 #include "GCOMObservation.hpp"
 #include "GCOMEventCube.hpp"
 #include "GCOMSupport.hpp"
@@ -45,8 +46,8 @@ const GObservationRegistry g_obs_com_registry(&g_obs_com_seed);
 #define G_RESPONSE                    "GCOMObservation::response(GResponse&)"
 #define G_READ                          "GCOMObservation::read(GXmlElement&)"
 #define G_WRITE                        "GCOMObservation::write(GXmlElement&)"
-#define G_LOAD_DRB                  "GCOMObservation::load_drb(std::string&)"
-#define G_LOAD_DRG                  "GCOMObservation::load_drg(std::string&)"
+#define G_LOAD_DRB                    "GCOMObservation::load_drb(GFilename&)"
+#define G_LOAD_DRG                    "GCOMObservation::load_drg(GFilename&)"
 
 /* __ Macros _____________________________________________________________ */
 
@@ -93,10 +94,10 @@ GCOMObservation::GCOMObservation(void) : GObservation()
  *
  * Each of the four files is mandatory.
  ***************************************************************************/
-GCOMObservation::GCOMObservation(const std::string& drename,
-                                 const std::string& drbname,
-                                 const std::string& drgname,
-                                 const std::string& drxname) : GObservation()
+GCOMObservation::GCOMObservation(const GFilename& drename,
+                                 const GFilename& drbname,
+                                 const GFilename& drgname,
+                                 const GFilename& drxname) : GObservation()
 {
     // Initialise members
     init_members();
@@ -374,10 +375,10 @@ void GCOMObservation::write(GXmlElement& xml) const
  * factors from DRG file and the exposure map from the DRX file. All files
  * are mandatory.
  ***************************************************************************/
-void GCOMObservation::load(const std::string& drename,
-                           const std::string& drbname,
-                           const std::string& drgname,
-                           const std::string& drxname)
+void GCOMObservation::load(const GFilename& drename,
+                           const GFilename& drbname,
+                           const GFilename& drgname,
+                           const GFilename& drxname)
 {
     // Load DRE
     load_dre(drename);
@@ -529,8 +530,10 @@ void GCOMObservation::free_members(void)
  * @brief Load event cube data from DRE file
  *
  * @param[in] drename DRE filename.
+ *
+ * Loads the event cube from a DRE file.
  ***************************************************************************/
-void GCOMObservation::load_dre(const std::string& drename)
+void GCOMObservation::load_dre(const GFilename& drename)
 {
     // Delete any existing event container (do not call clear() as we do not
     // want to delete the response function)
@@ -541,17 +544,17 @@ void GCOMObservation::load_dre(const std::string& drename)
     m_events = new GCOMEventCube;
 
     // Open FITS file
-    GFits file(drename);
+    GFits fits(drename);
 
     // Read event cube
-    m_events->read(file);
+    m_events->read(fits);
 
     // Read observation attributes from primary extension
-    GFitsHDU* hdu = file[0];
+    GFitsHDU* hdu = fits[0];
     read_attributes(hdu);
 
     // Close FITS file
-    file.close();
+    fits.close();
 
     // Store event filename
     m_drename = drename;
@@ -572,13 +575,13 @@ void GCOMObservation::load_dre(const std::string& drename)
  * Load the background model from the primary image of the specified FITS
  * file.
  ***************************************************************************/
-void GCOMObservation::load_drb(const std::string& drbname)
+void GCOMObservation::load_drb(const GFilename& drbname)
 {
     // Open FITS file
-    GFits file(drbname);
+    GFits fits(drbname);
 
     // Get image
-    const GFitsImage& image = *file.image("Primary");
+    const GFitsImage& image = *fits.image("Primary");
 
     // Load background model as sky map
     m_drb.read(image);
@@ -587,7 +590,7 @@ void GCOMObservation::load_drb(const std::string& drbname)
     com_wcs_mer2car(m_drb);
 
     // Close FITS file
-    file.close();
+    fits.close();
 
     // Check map dimensions
     if (!check_map(m_drb)) {
@@ -615,13 +618,13 @@ void GCOMObservation::load_drb(const std::string& drbname)
  * Load the geometry factors from the primary image of the specified FITS
  * file.
  ***************************************************************************/
-void GCOMObservation::load_drg(const std::string& drgname)
+void GCOMObservation::load_drg(const GFilename& drgname)
 {
     // Open FITS file
-    GFits file(drgname);
+    GFits fits(drgname);
 
     // Get image
-    const GFitsImage& image = *file.image("Primary");
+    const GFitsImage& image = *fits.image("Primary");
 
     // Load geometry factors as sky map
     m_drg.read(image);
@@ -630,7 +633,7 @@ void GCOMObservation::load_drg(const std::string& drgname)
     com_wcs_mer2car(m_drg);
 
     // Close FITS file
-    file.close();
+    fits.close();
 
     // Check map dimensions
     if (!check_map(m_drg)) {
@@ -654,13 +657,13 @@ void GCOMObservation::load_drg(const std::string& drgname)
  *
  * Load the exposure map from the primary image of the specified FITS file.
  ***************************************************************************/
-void GCOMObservation::load_drx(const std::string& drxname)
+void GCOMObservation::load_drx(const GFilename& drxname)
 {
     // Open FITS file
-    GFits file(drxname);
+    GFits fits(drxname);
 
     // Get HDU
-    const GFitsImage& image = *file.image("Primary");
+    const GFitsImage& image = *fits.image("Primary");
 
     // Load exposure map as sky map
     m_drx.read(image);
@@ -669,7 +672,7 @@ void GCOMObservation::load_drx(const std::string& drxname)
     com_wcs_mer2car(m_drx);
 
     // Close FITS file
-    file.close();
+    fits.close();
 
     // Store DRX filename
     m_drxname = drxname;
diff --git a/inst/lat/include/GLATObservation.hpp b/inst/lat/include/GLATObservation.hpp
index 05899c4..9d59916 100644
--- a/inst/lat/include/GLATObservation.hpp
+++ b/inst/lat/include/GLATObservation.hpp
@@ -1,7 +1,7 @@
 /***************************************************************************
  *             GLATObservation.hpp - Fermi/LAT observation class           *
  * ----------------------------------------------------------------------- *
- *  copyright (C) 2008-2014 by Juergen Knoedlseder                         *
+ *  copyright (C) 2008-2016 by Juergen Knoedlseder                         *
  * ----------------------------------------------------------------------- *
  *                                                                         *
  *  This program is free software: you can redistribute it and/or modify   *
@@ -29,12 +29,14 @@
 
 /* __ Includes ___________________________________________________________ */
 #include <string>
+#include "GTime.hpp"
 #include "GObservation.hpp"
 #include "GLATResponse.hpp"
 #include "GLATLtCube.hpp"
-#include "GTime.hpp"
-#include "GModel.hpp"
-#include "GModels.hpp"
+
+/* __ Forward declarations _______________________________________________ */
+class GResponse;
+class GXmlElement;
 
 
 /***********************************************************************//**
@@ -64,7 +66,7 @@ public:
     virtual std::string         instrument(void) const;
     virtual double              ontime(void) const;
     virtual double              livetime(void) const;
-    virtual double              deadc(const GTime& time) const;
+    virtual double              deadc(const GTime& time = GTime()) const;
     virtual void                read(const GXmlElement& xml);
     virtual void                write(GXmlElement& xml) const;
     virtual std::string         print(const GChatter& chatter = NORMAL) const;
diff --git a/inst/lat/pyext/GLATObservation.i b/inst/lat/pyext/GLATObservation.i
index 4fd3eb1..bba0028 100644
--- a/inst/lat/pyext/GLATObservation.i
+++ b/inst/lat/pyext/GLATObservation.i
@@ -1,7 +1,7 @@
 /***************************************************************************
  *              GLATObservation.i - Fermi/LAT observation class            *
  * ----------------------------------------------------------------------- *
- *  copyright (C) 2008-2014 by Juergen Knoedlseder                         *
+ *  copyright (C) 2008-2016 by Juergen Knoedlseder                         *
  * ----------------------------------------------------------------------- *
  *                                                                         *
  *  This program is free software: you can redistribute it and/or modify   *
@@ -50,7 +50,7 @@ public:
     virtual std::string         instrument(void) const;
     virtual double              ontime(void) const;
     virtual double              livetime(void) const;
-    virtual double              deadc(const GTime& time) const;
+    virtual double              deadc(const GTime& time = GTime()) const;
     virtual void                read(const GXmlElement& xml);
     virtual void                write(GXmlElement& xml) const;
 
diff --git a/inst/mwl/include/GMWLObservation.hpp b/inst/mwl/include/GMWLObservation.hpp
index 418ae6d..759270c 100644
--- a/inst/mwl/include/GMWLObservation.hpp
+++ b/inst/mwl/include/GMWLObservation.hpp
@@ -28,12 +28,15 @@
 #define GMWLOBSERVATION_HPP
 
 /* __ Includes ___________________________________________________________ */
+#include <string>
+#include "GTime.hpp"
 #include "GFilename.hpp"
 #include "GObservation.hpp"
 #include "GMWLResponse.hpp"
 
 /* __ Forward declarations _______________________________________________ */
-class GTime;
+class GResponse;
+class GXmlElement;
 
 
 /***********************************************************************//**
@@ -66,7 +69,7 @@ public:
     virtual std::string         instrument(void) const;
     virtual double              ontime(void) const;
     virtual double              livetime(void) const;
-    virtual double              deadc(const GTime& time) const;
+    virtual double              deadc(const GTime& time = GTime()) const;
     virtual void                read(const GXmlElement& xml);
     virtual void                write(GXmlElement& xml) const;
     virtual std::string         print(const GChatter& chatter = NORMAL) const;
diff --git a/inst/mwl/pyext/GMWLObservation.i b/inst/mwl/pyext/GMWLObservation.i
index 8f0184c..cebd642 100644
--- a/inst/mwl/pyext/GMWLObservation.i
+++ b/inst/mwl/pyext/GMWLObservation.i
@@ -56,7 +56,7 @@ public:
     virtual std::string         instrument(void) const;
     virtual double              ontime(void) const;
     virtual double              livetime(void) const;
-    virtual double              deadc(const GTime& time) const;
+    virtual double              deadc(const GTime& time = GTime()) const;
     virtual void                read(const GXmlElement& xml);
     virtual void                write(GXmlElement& xml) const;
 
diff --git a/src/obs/GObservation.cpp b/src/obs/GObservation.cpp
index d6fd374..87144ca 100644
--- a/src/obs/GObservation.cpp
+++ b/src/obs/GObservation.cpp
@@ -28,16 +28,22 @@
 #ifdef HAVE_CONFIG_H
 #include <config.h>
 #endif
+#include "GTools.hpp"
 #include "GException.hpp"
-#include "GObservation.hpp"
-#include "GModelSky.hpp"
-#include "GModelData.hpp"
 #include "GIntegral.hpp"
 #include "GDerivative.hpp"
-#include "GTools.hpp"
+#include "GVector.hpp"
+#include "GMatrixSparse.hpp"
+#include "GObservation.hpp"
+#include "GResponse.hpp"
 #include "GEventCube.hpp"
 #include "GEventList.hpp"
 #include "GEventBin.hpp"
+#include "GModel.hpp"
+#include "GModels.hpp"
+#include "GModelPar.hpp"
+#include "GModelSky.hpp"
+#include "GModelData.hpp"
 
 /* __ Method name definitions ____________________________________________ */
 #define G_LIKELIHOOD           "GObservation::likelihood(GModels&, GVector*,"\